TP 15392E - Guidelines for fishing vessel major modification or a change in activity

From: Transport Canada

The fishing vessel safety regulations came into force on July 13, 2017. The regulations contain new stability requirements. A vessel constructed on any date that has a hull length of more than 9 m, that has undergone a major modification or a change in activity that is likely to adversely affect its stability after July 13, 2017 or is fitted with an anti-roll tank, will be required to undergo a stability assessment by a competent person. The guidelines will help fishing vessel owners and operators understand how a major modification or change in activity can impact the stability of their vessel.

If you wish to receive a copy of the guidelines, please submit your request to the marine safety general email inbox at marinesafety-securitemaritime@tc.gc.ca.

Acknowledgements

These guidelines have been produced and developed jointly and under contract with the Canadian Independent Fish Harvesters Federation (CIFHF) and Transport Canada and in consultation with the Canadian Marine Advisory Council (CMAC).

Information in this document is written for personal and public non-commercial use. Transport Canada allows the reproduction in whole or in part, with appropriate credit, provided no changes have been made to the content and it is intended for non-commercial use only.

A written permission from Transport Canada is necessary to reproduce multiple copies of this material, in whole or in part, for the purposes of commercial redistribution. Contact TCcopyright-droitdauteurTC@tc.gc.ca for more information.

Instructions on the use of this guide

The Regulations Amending the Small Fishing Vessel Inspection Regulations (herein referred to as the Fishing Vessel Safety Regulations), came into force on July 13, 2017. The regulations contain new stability requirements for small fishing vessels in Canada. For example, section 3.48(1)(a)(ii) of the regulations states that, “No person shall operate, or permit another person to operate, a fishing vessel in the following cases unless the vessel has successfully undergone a stability assessment conducted by a competent person: (a) the vessel has a hull length of more than 9 m and (i) it is new, or (ii) it has undergone a major modification or change in activity that is likely to adversely affect its stability.”

Please note that some fishing vessels are required to have a stability assessment. Reference can be made to Ship Safety Bulletin 03/2017 “Coming into force of phase 1 of the new Fishing Vessel Safety Regulations.” which outlines which fishing vessels are required to have a stability assessment and which fishing vessels are required to have adequate stability. The regulations define major modification as, “a modification or repair, or a series of modifications or repairs that substantially changes the capacity or size of a fishing vessel or the nature of a system on board a fishing vessel that affects its watertight integrity or its stability.”

It is important to be stability safety conscious at all times. No vessel is immune from capsizing no matter how stable it is and irrelevant of the fact that it may have operated without incident for years. It is also important to note that each vessel’s configuration and particular operations are different and therefore the use of these guidelines is vessel specific.

These guidelines have two main sections.

Section 1 is the Potential Fishing Vessel Modification and Potential Change in Activity checklist. Put a check in the box for each checklist item which you have verified for your vessel and use the N/A check-box for any checklist item that is not relevant or applicable. An item not checked N/A should meet the intent of the supporting guidelines located in section 2. Please ensure that you review each checklist item.

Section 2 is the Supporting Stability Information which provides some technical supporting documentation for each checklist item.

While these guidelines are voluntary, fishing vessel owners and operators are encouraged to use and review them periodically. The use of these guidelines should help you understand the stability of your fishing vessel and whether it is likely to have adequate stability or not. If you are unsure about how your vessel may be impacted by a major modification or change in activity or you have concerns about the stability of your fishing vessel, you should contact a marine consultant or regional Transport Canada Marine Safety office, for further assistance.

Note: Adherence to these guidelines and completing the checklist does not guarantee that a stability assessment would not be required for your fishing vessel. These guidelines are not a stability assessment nor are they a tool to measure your vessel’s stability.

Brief rationale for the stability principles or criteria used in this guide:

Impact on the vessel’s stability due to changes in the center of gravity:

Many modification projects result in raising the overall center of gravity of a vessel. The height of the vessel’s center of gravity determines both the initial stability as well as the overall large angle stability of the vessel. The higher the center of gravity, the smaller the righting levers and subsequently, the less overall reserves of stability that a vessel has.
Impact on the vessel’s stability due to increased free surface effect:

Free surface effect (FSE) refers to the loss of stability due to the transverse (side-to-side) movement of liquids or liquid-like cargo (i.e. fish) in a vessel. The amount of FSE is highly dependent on the breadth of a tank or space. If any on-board fluids, or fish with fluid-like characteristics are allowed to shift uncontrolled, they can seriously diminish a vessel’s reserves of stability.
Impact on the vessel’s stability due to change in freeboard:

The amount of freeboard that a vessel has, at any given time, contributes to its reserve buoyancy and determines its range of stability. As a vessel is heeled, for any reason, including the forces of the sea, it is this reserve buoyancy that provides the required righting energy. Having adequate freeboard provides the necessary buoyancy on the low side, which creates levers (forces) to return the vessel back upright. A vessel with low or no freeboard will submerge its deck edge at smaller angles of heel. This will then result in an overall net loss of buoyancy and righting energy.
Impact on the vessel’s watertight integrity (potential downflooding points):

Downflooding refers to the entry of water into spaces of a vessel which form part of its watertight structure and are either providing buoyancy initially or are reserved for when the vessel is inclined, for whatever reason. The prevention of downflooding is essential to preserving a vessel’s stability. Downflooding can occur at varying degrees, from slow leaks to the catastrophic entry of water into the vessel.
Changes to initial stability (at lower angles of heel):

The initial stability of a vessel is determined by the relative positions of the centers of buoyancy and gravity. Initial stability is often referred to as that which is ‘felt’, at the low angles of heel. A vessel with large initial stability may often be referred to as being ‘stiff’, whereas one with lower initial stability might be referred to as being ‘tender’. It is very important to understand that a vessel can have good initial stability and feel fine, but still have poor larger angle stability.
Changes to large angle reserves of stability:

Large angle stability characteristics allow a vessel to upright itself when inclined by an external force. It is determined by the amount of reserve buoyancy that is available as a vessel is inclined, as well as the relative height of the center of gravity. Reserve buoyancy is provided by freeboard, as well as other watertight spaces that may provide buoyancy if the vessel were to be inclined to a large angle, for any reason, such as the force of the sea. To preserve reserve buoyancy, it is imperative that all potential downflooding points be maintained watertight.
Changes to longitudinal trim:

Longitudinal trim refers to the difference between a vessel’s drafts aft and forward. A typical small fishing vessel may have normal operating trim of 2 to 4 feet by the stern. A vessel that is trimmed poorly by the stern for example, will have reduced freeboard aft and if inclined for any reason, including the forces of nature, it will subsequently have less reserves of stability.

Fishing vessel modifications

Before undertaking any modification to a fishing vessel, consideration should be given to the potential impact that it could have on its stability characteristics. This section of the guidelines has been developed to provide general information to vessel owners of the potential impact that typical modification projects could have on the stability of a fishing vessel. The information in these guidelines is directed at vessel owners and operators so that more informed decisions can be made when considering a modification or change in activity to their vessel.

It is important to point out that nothing precludes a vessel owner from contacting a marine consultant for the purpose of obtaining a stability assessment. The stability assessment, conducted by a competent person, whether simplified or full, needs to conform to either the recommended practices and standards such as ISO 12217, or in the case of a full stability assessment, the IS Code 2008.

Typical fishing vessel repair and modification projects

1.0 Hull Related

	CHECKED	N/A
a. Lengthening the hull of a vessel by adding a stern appendage (buoyancy tank) with no change in the vessel’s fish hold capacity and no additional tanks added.
b. Lengthening the hull of a vessel by adding a stern appendage (buoyancy tank) with no change in the vessel’s fish hold capacity but additional tanks added aft.
c. Lengthening the hull of a vessel by adding a stern appendage (buoyancy tank) and changing the vessel’s fish hold capacity, by moving the aftermost bulkhead further aft.
d. Widening the hull of a vessel by adding a new centerline section extension.
e. Adding additional permanent ballast low in the vessel or to the underside of the keel.
f. Increasing the physical height of the bulwarks on the main deck or forward deck.
g. Replacement of the main deck with no increase in height and/or structural weight.
h. Replacement of the main deck with an increase in height and/or structural weight.
i. Addition of a bulbous bow appendage.
j. Lengthening a vessel by cutting and adding a new amidships area section.
k. Moving a bulkhead further forward to increase carrying capacity.
l. Moving a bulkhead further aft to increase carrying capacity.
m. The hull is completely covered with several layers of fiberglass reinforced plastic (FRP).
n. Installation of a shrouded propeller such as a Kort or Rice Brand Nozzle.
o. Installation of a bow or stern thruster arrangement.
p. Adding a permanent stern ramp extension.
q. The hull is completely rebuilt but with no changes in weight or dimensions.
r. A set of bilge keels (anti-roll shocks) are installed.
s. Adding hull mounted hinged fin anti-roll devices.
t. A set of hull mounted buoyancy sponsors are added.
u. The height of the main fish hold hatch coaming is permanently increased.

2.0 Superstructure and/or deckhouse

	CHECKED	N/A
a. Complete or partial replacement of the wheelhouse and/or deckhouse with no changes in position or dimensions, weight.
b. Complete or partial replacement of the wheelhouse and/or deckhouse with changes in the physical dimensions and/or structural weight.
c. Replacing fixtures and/or hardware such as railings and riggings, above the deck level with that of similar weights.
d. The heights of the door sills for the exterior doors to the wheelhouse are raised.

3.0 Below deck equipment and machinery

	CHECKED	N/A
a. Replacement of below deck machinery in the same location with that of similar weight.
b. Replacement of below deck machinery in the same location with that of greater weight.
c. Replacement of below deck machinery in the same location with that of less weight.
d. Replacement of below deck machinery in a different location.
e. Replacing a below deck tank with one of same capacity, material and configuration.
f. Increasing below deck tank capacity by replacing or adding additional tank(s).

4.0 Above deck equipment and machinery

	CHECKED	N/A
a. Replacement of above deck equipment and machinery in the same location with that of similar weight.
b. Replacement of above deck equipment and machinery in the same location with that of greater weight and/or capacity.
c. Replacement of above deck equipment and machinery in the same location with that less weight.
d. Moving or replacement of above deck equipment and machinery to a different location.
e. Permanent removal of above deck equipment and/or machinery.
f. The addition of a set of outrigger booms (stabilizers) or replacement of an existing set with larger ones.
g. Installation of an anti-roll tank.

Change in activity

A change to a new or different fishing activity may have a negative impact on your fishing vessel’s stability. The forces acting on your fishing vessel may change as a result of a change in activity. This section of the guidelines has been developed to assist fish harvesters make more informed decisions prior to undertaking a change in activity. Before undertaking any change in fishing activity, consideration should be given to the potential effects that it could have on the vessel’s stability characteristics. It is important to mention again that this is general information only and is intended to assist in guiding owners to make more informed decisions during the initial stages, when contemplating a change in activity.

A list of potential changes in activity, along with supporting stability related information is provided. One or more of these identified changes may be applicable to your proposal and therefore you should understand what the stability impact may be to your fishing vessel.

5.0 Changes to a different type of fishing operation

	CHECKED	N/A
a. Conversion from fixed gear to trawling or dragging. (Addition of equipment such as, an A frame and/or winch(s) and/or net drum(s)).
b. Conversion to purse seining. (Addition of equipment such as, a power block, boom, winch and associated fishing gear such as a seine and purse line).
c. The vessel is operating in an area where more adverse sea conditions exist.

6.0 Changes in the amount or type of fishing gear to be carried

	CHECKED	N/A
a. Carriage of more fishing gear on or above the deck.
b. Carriage of fishing gear below deck, in addition to the usual amount on the deck.
c. Change to fishing gear that is more difficult to secure and/or restricts good drainage.

7.0 Changes in the species to be harvested and/or on-board storage arrangement

	CHECKED	N/A
a. Changing from dry to wet storage (RSW or live-well tanks).
b. Change in activity to harvesting and/or carrying fish in bulk that exhibit free surface effect.

8.0 Addition of temporary equipment

	CHECKED	N/A
a. Changes due to the placement of a temporary deck that is not watertight and/or does not add to the watertightness of the hull.
b. Adding any temporary appendage at or above the deck level.
c. Changes due to temporary on-board carriage of a tow skiff or other supplementary boat.
d. Changes due to temporary addition of any above deck equipment or machinery.

Supporting stability information

1.0 Hull related modifications

Lengthening the hull of a vessel by adding a stern appendage (buoyancy tank), with no change in the vessel’s fish hold capacity and no additional tanks or equipment added.

A typical fishing vessel with a wheelhouse and engine room situated forward of amidships which is lengthened by adding a stern appendage, without changing the fish hold dimensions, will usually result in a reduced stern trim when operating in a loaded or partially loaded condition. The added stern section will provide additional buoyancy aft and as such, increase the vessel’s freeboard. To be effective and achieve these benefits, no additional weight storage, such as fuel or fishing gear, would be added. All opening appliances, such as manhole covers, must be watertight to protect against downflooding. It is likely that by lengthening a vessel in this manner it may slightly reduce its initial stability at lower angles of heel, but with the increase in freeboard it will likely improve its stability reserves at larger angles of heel.

While many small fishing vessels are relatively wide as compared to their overall length (i.e. they have a relatively low length to beam ratio), it is noteworthy that to lengthen a relatively narrow vessel (with a high length to beam ratio) could have a negative effect on its overall stability and sea keeping characteristics.

If this type of modification is properly designed and constructed, it could improve the overall stability characteristics of most vessels.
Lengthening the hull of a vessel by adding a stern appendage (buoyancy tank) with no change in the vessel’s fish hold capacity, but with additional tanks, (such as fuel tanks), added aft.

A typical fishing vessel with a wheelhouse and engine room situated forward of amidships which is lengthened, and the aftermost bulkhead is not moved, will usually result in a decreased stern trim and increase freeboard, when operating in a loaded or partially loaded condition. The added stern section will provide additional buoyancy aft but, the added weight of fluid in the added tanks along with the increased free surface effect would diminish and possibly cancel out this gain. In addition, since stern extensions typically narrow-in somewhat, the gained buoyancy, diminishes per foot of hull extension aft. Additional weight storage, if added, would make stability matters worse. It is also likely that this modification may reduce the vessel’s initial stability at lower angles of heel.

While many small fishing vessels are relatively wide as compared to their overall length (i.e. they have a relatively low length to beam ratio), it is important to mention that lengthening a relatively narrow vessel (with a high length to beam ratio), could have a serious negative effect on its overall stability and sea keeping characteristics. It is of vital importance with all modifications, to ensure that all opening appliances, such as manhole covers, are watertight, to protect against downflooding.

If properly designed and constructed, this type of modification could improve the overall stability characteristics of most vessels, however the addition of added weight such as tanks, may result in a negative impact on the vessel’s stability.

A marine consultant should be consulted prior to undertaking this project, to determine the stability characteristics of the vessel and what changes can be made within normal fishing vessel stability safety limits.
Lengthening the hull of a vessel by adding a stern appendage (buoyancy tank) and changing the vessel’s fish hold capacity, by moving the aftermost bulkhead further aft.

A typical fishing vessel with its wheelhouse and engine room situated forward of amidships which is lengthened and the aftermost bulkhead is shifted aft proportionally, will usually result in an increase to stern trim and reduce freeboard aft when operating in a loaded or partially loaded condition. The added stern section will provide additional buoyancy near the stern, but the added weight of catch, when loaded, combined with the potential free surface effect could cancel out this gain. In addition, since stern extensions typically narrow-in somewhat, the additional buoyancy diminishes per foot of hull extension aft. In comparison to the extra weight being carried, there would likely be a net loss of buoyancy.

Additional weight storage, such as fuel or fishing gear, if incorporated, could make matters even worse. It is also likely that it may reduce the vessel’s initial stability at lower angles of heel. While many small fishing vessels are relatively wide as compared to their overall length (i.e. they have a relatively low length to beam ratio), it is noteworthy that to lengthen a relatively narrow vessel (with a high length to beam ratio) could have a serious negative effect on its overall stability and sea keeping characteristics.

It is of vital importance with all modifications to ensure that all opening appliances such as manhole covers are watertight in order to protect against downflooding.

This type of modification would likely have a negative impact on the overall stability characteristics of most vessels in a loaded condition.

You should contact a marine consultant if you are considering this type of vessel modification. A modification of this nature will have to be verified by Transport Canada.
Widening the hull of a vessel by adding a new centerline section extension.

This type of major modification essentially creates a completely different vessel. A professional analysis of how this could affect the stability, as well as the sea-keeping characteristics and impact on the structural strength of the vessel would be an important first step. Widening a vessel in this manner, changes both the position of the center of gravity and the position of the center of buoyancy, both of which have a direct impact on the vessel’s stability characteristics. In most cases, it will improve the vessel’s initial stability, making it stiffer (it will roll quicker) however it will also have an effect on its larger angle stability characteristics.

Widening a vessel will usually improve its initial stability, but it will also allow it to submerge its deck edge at smaller angles of heel and as such it may not meet regulatory stability standards.

This type of modification may also reduce the range of positive stability as well as the angle at which the forces of stability will be greatest and it possibly could reduce the vessel’s angle of vanishing stability. This may result in a vessel that will capsize at smaller angles than the original vessel.

Widening and raising the deck simultaneously may solve this problem, but it will also reduce stability due to the rise of the center of gravity as the deck and everything on, or above it, also rises.

This modification also requires careful consideration to ensure that the structural strength of the vessel is adequate, for its intended purpose. It is of vital importance with all modifications, to ensure that all fixtures, such as manhole covers, are watertight, in order to protect against downflooding. This project will essentially create a completely different vessel with unknown stability characteristics; therefore a careful analysis should be undertaken before considering such a modification.

You should contact a marine consultant if you are considering this type of vessel modification.

Figure 1.0 (d)(i)
Widening of a fishing vessel by adding a new centerline area section.
(Source: Unknown)
Adding additional permanent ballast low in the vessel or to the underside of the keel.

Permanent ballast should only be added to a fishing vessel on the advice of a naval architect. If other conditions remain unchanged, permanent ballast can improve some aspects of stability and diminish others. Adding extra weight in a low position in the vessel, such as in the shaft tunnel or on the fish hold floor, will invariably lower the center of gravity and improve its initial, small angle stability. However, it will also reduce the vessel’s freeboard and subsequently it will usually reduce the large angle stability of the vessel because it will now submerge its deck edge at a smaller angle of heel.

Adding the correct amount of permanent ballast is dependent on several factors surrounding the design and construction of the vessel and can only be determined through calculations. Based on this, many fishing vessels do require permanent ballast, but only in the correct amount and position to find that optimal balance between all aspects of stability.

If ballast is added to your vessel, make sure that it is permanently secured to avoid shifting.

Permanent ballast can sometimes improve a vessel’s initial stability but it is not something that should be done without professional advice.
Figure 1.0 (e)(i)
Permanent lead ballast in the lazarette of a fishing vessel. Note that ballast must be permanently secured to prevent shifting. (Courtesy of J.G. Personal collection)

Increasing the physical height of the bulwarks on the main deck or forward deck.

Adding any weight above the deck of a fishing vessel will generally raise its center of gravity. In all likelihood raising the height of the bulwarks will add some weight, but to what degree that it will negatively affect the stability, is dependent on the specific project specifications. Similarly the added weight will reduce freeboard, which negatively affects stability and it may have an effect on the vessel’s longitudinal trim. These changes may or may not be negligible. It is important however, to be mindful of the cumulative effect that a series of small modifications could have on the stability of a fishing vessel.

The added safety, resulting from the protection provided by the higher rail, may justify the added weight. This modification will not impact free surface effect as long as the freeing ports (scuppers) are of adequate size to permit rapid drainage from the deck of the larger volume of water that may otherwise be trapped. If done properly, this modification should not affect the watertightness of the hull.

This modification will have some impact on the stability of the vessel, the extent of which is dependent upon its pre-project stability status.
Replacement of the main deck with no increase in height and/or structural weight.

This type of modification could probably best be described as a major repair. If the weight of the new deck is the same as that being replaced and it’s going back in the same position, then it will have no effect on the vessel’s stability characteristics. If, by undertaking this project, issues such as water leaking into the vessel either though the deck structure itself or fixtures such as man hole covers are addressed, then this modification could improve the vessel’s stability.

This modification should very little or no impact on the stability of the vessel.
Replacement of the main deck with an increase in height and/or structural weight.

Increasing the height of the main deck and/or increasing the structural weight, will raise the center of gravity of the vessel and, depending on its initial stability characteristics, could have a significant negative impact. Additionally, by raising the deck, all permanent weights on the deck, such as a winch or hauler, as well as temporary weights like fishing gear or fish, will also be raised- further contributing to the rise of the center of gravity of the vessel. Raising the deck height of a fishing vessel will also increase its volume and gross tonnage.

Compounding this, negative heeling forces due to fishing operations from high points of suspension will be increased because of the increased deck height.

Raising the deck will however, increase freeboard, with a resultant change in the large angle stability characteristics of the vessel, as well as an increased height of downflooding points. This aspect may have a positive impact on its large angle stability characteristics. It is possible however and likely with most projects of this nature, that the losses will outweigh the gains. As the center of gravity rises due to the factors outlined, the vessel’s initial small angle stability will be negatively impacted. In addition, its large angle reserves of stability will diminish, as will its angle of vanishing stability.

In terms of downflooding considerations, if properly constructed, this project should not negatively affect the watertightness of the vessel and could be an improvement.

This modification could have a negative impact on the reserves of stability, the extent of which is dependent on the pre-project stability status of the vessel. If carried out, the vessel’s stability should be reassessed afterwards. Raising the deck should only be done with the advice of a naval architect.

You should contact a marine consultant if you are considering this type of vessel modification. A proposed modification of this nature will have to be verified by Transport Canada.

Figure 1.0 (h)(i)
Before Modification

Figure 1.0 (h)(ii)
After Modifications

The preceding two figures show a vessel before and after a modification that has increased its working deck height and modified the wheelhouse structure.
Addition of a bulbous bow appendage.

A bulbous bow appendage (which is added to the vessel after it is originally built) will increase the vessel’s buoyancy. The structural strength of this section is of critical importance, due to the potential forces in which the vessel could be exposed to in this area and the risk of flooding, should it be compromised. Flooding due to damage of the bulbous bow could be catastrophic.

From a stability perspective, assuming that it is structurally sound, the added buoyancy forward will change the longitudinal trim of the vessel. It will usually decrease forward trim and increase stern trim, unless ballasting arrangements are incorporated to compensate for the added buoyancy. Depending on the configuration, some designs will incorporate a ballast tank to permit trimming in different conditions of load while others may require the addition of permanent ballast or a combination of the both. The effect on the vessel’s center of gravity is difficult to determine, but in many cases it will be minimal. The proper design of a bulbous bow appendage along with appropriate ballasting considerations can only be determined through calculations carried out by a naval architect using the pre-project stability data of the vessel.

If properly designed and constructed, this type of modification could improve the overall stability characteristics of most vessels but its effect on longitudinal trim may negatively impact stability in a loaded condition.

You should contact a marine consultant if you are considering this type of vessel modification.

Figure 1.0 (I)(i)

Figure 1.0 (I)(ii)

Figure 1.0 (I)(iii)

Figure 1.0 (I)(iv)

Figures 1.0 (l)(i to iv) The existing fishing vessel, ‘Newfoundland Spirit’ fitted with a bulbous bow. (Courtesy of J.G. Personal collection)

Figure 1.0 (I)(v)

Figure 1.0 (I)(vi)

Figures 1.0 (l)(v & vi): Typical fishing vessels with bulbous bows. (Courtesy of J.G. Personal collection)
Lengthening a vessel by cutting and adding a new amidships area section.

This type of major modification essentially creates a completely different vessel. A professional analysis of how this could affect both the stability, as well as the sea-keeping characteristics of the vessel, would be an important first step.

Lengthening a vessel in this manner, changes both the position of the center of gravity as well as the position of the center of buoyancy, both of which have a direct impact on the stability characteristics. Depending on the design involved, this project could improve the overall stability of the vessel or negatively impact it. It will also impact the longitudinal trim and the sea keeping characteristics of the vessel.

If the fish hold capacity is increased, it will impact the potential free surface effect that the vessel could be exposed to in partially loaded conditions. This modification also requires careful consideration to ensure that the structural strength of the vessel is adequately maintained for its intended purpose. It is of vital importance, with all modifications, to maintain watertightness as protection against downflooding.

This project will essentially create a completely different vessel with unknown stability characteristics. Therefore, a careful analysis should be undertaken before considering such a modification. A marine consultant should be consulted prior to undertaking this project. A modification of this nature will have to be verified by Transport Canada.

Figure 1.0 (j)(i)

Figure 1.0 (j)(ii)

Figure 1.0 (j)(i & ii)
The fiberglass fishing vessel ‘Andrew and Nicholas’ was cut amidships and
had an additional 10 feet added. It was then renamed ‘Northern Navigator II’. A
full stability reassessment was completed after the modification was completed.
(Courtesy of J.G. Personal collection)
Moving a bulkhead further forward to increase carrying capacity.

Most small fishing vessels have at least three transverse bulkheads. They provide structural strength to the hull and, if properly constructed, they serve to isolate a compartment in the case of flooding or fire. They are positioned to provide appropriate space for each functional area, such as engine and machinery, accommodation, fish hold and steering gear. The potential consequences of changing the position of either of a vessel’s main bulkheads, to increase capacity, should be fully considered prior to doing so.

The new transverse bulkhead should meet the regulatory requirements of the Fishing Vessel Safety Regulations and provide at least equivalent strength and watertightness as the original transverse bulkhead.

Shifting the bulkhead between the engine room and the fish hold further ahead in a typical fishing vessel with the engine room and wheelhouse forward of amidships, will cause it to load deeper in fully loaded conditions. In partially loaded conditions however, it may provide the option to carry the load further ahead, improving longitudinal trim -possibly providing remedy to a trim problem. Depending on the pre-existing stability and loading characteristics of the vessel, increasing capacity primarily to carry larger loads, will diminish the large angle reserves of stability and cause the vessel to downflood at smaller angles of heel in those conditions. It will also cause the vessel to ship water onto the deck more readily, reducing stability due to added weight and free surface effect if it is unable to rapidly clear itself. In partially loaded conditions, a larger fish hold will expose the vessel to more free surface effect if carrying fluid-like fish such as capelin and herring.

This modification could have a negative impact on the stability characteristics of the vessel, the extent of which is dependent on the intended operational requirements and the pre-project stability status of the vessel. A careful analysis should be undertaken before considering this type of modification.

Figure 1.0 (k)(i)
The vertical red lines show the typical placement of bulkheads in a 13.7 m (45 ft.) fishing vessel.
Moving a bulkhead further aft to increase carrying capacity.

Most small fishing vessels have at least three transverse bulkheads. They provide structural strength to the hull, and if properly constructed, they serve to isolate a compartment in the case of flooding or fire. They are positioned to provide appropriate space for each functional area, such as engine and machinery, accommodation, fish hold and steering gear. The potential consequences of changing the position of either of a vessel’s main bulkheads, to increase capacity, should be fully considered prior to doing so. The new transverse bulkhead should meet the regulatory requirements of the Fishing Vessel Safety Regulations and provide at least equivalent strength and watertightness as the original transverse bulkhead.

Shifting the bulkhead between the fish hold and the lazarette further aft, in a typical vessel with the engine room and wheelhouse forward of amidships, will cause it to load deeper and trim more by the stern, in fully loaded conditions. It will also reduce freeboard in those conditions, especially near the stern. The cumulative effect of reduced freeboard and increased stern trim may have a significant negative impact on the vessel’s large angle reserves of stability. It will also cause the vessel to ship water onto the deck more readily, reducing stability due to added weight and free surface effect, if it is unable to rapidly clear itself.

Depending on the pre-existing stability and loading characteristics of the vessel, increasing capacity primarily to carry larger loads, will diminish the large angle reserves of stability and cause the vessel to downflood at smaller angles of heel, in those conditions. In partially loaded conditions, a larger fish hold will expose the vessel to more free surface effect, if carrying fluid-like fish such as capelin and herring. Moving or, probably more accurately, reconstructing a bulkhead a small distance from its previous position and of similar construction, will however have minimum effect on the lightship (empty) stability characteristics of the vessel.

This modification could have a negative impact on the stability characteristics of the vessel, the extent of which is dependent on the intended operational requirements and the pre-project stability status of the vessel. A careful analysis should be undertaken before considering this type of modification.
The hull is completely covered with several layers of fiberglass reinforced plastic (FRP).

To extend their service life, many wooden fishing vessels undergo a glass-over modification/repair project. Assuming that there are no changes made to the hull of the vessel, at the end of this process, the same vessel will emerge, with only very slightly increased dimensions, possibly in the order of less than one inch (@2.5 cm) in overall length and hull breadth. The changes in the position of the center of buoyancy as a result, will subsequently be negligible. It has been observed in some cases however, that possibly due to the removal of hull sheathing as well as the drying-out process, necessary in preparation for adding the fiberglass, the weight of the wooden hull itself sometimes diminishes somewhat, raising the vessel’s center of gravity. In addition to this, in some cases, wooding planking that is replaced prior to fiber glassing is much heavier than the new material going back. This could also amount to a net reduction in hull weight, raising the center of gravity.

However, in some cases, the weight of the glass may exceed the benefits of the weight reduction of the hull when dried out. In some cases, the vessel may become heavier than before.

These changes in stability are usually, but not always, minimal- although vessel owners have sometimes reported a slightly noticeable change in the ‘feel of the vessel’ when at sea. If properly done, this type of project will usually strengthen the hull of the vessel and add protection against flooding. However, due to the preparation work outlined as well as the addition of the fiberglass materials, the stability of the vessel may change somewhat. This should be carefully monitored.

A careful analysis carried out by a marine consultant or naval architect should be undertaken before considering this type of modification.
Installation of a shrouded propeller such as a Kort or Rice Nozzle.

To increase thrust and efficiency, some fishing vessels are fitted with a shrouded propeller system. Common types are the ‘Kort’ or ‘Rice’ brands. Attributes of shrouded propellers include more thrust due to reduced propeller slip, reduced transverse thrust and reduced cavitation.

From a stability perspective, the addition of weight in the propeller area will slightly lower the vessel’s center of gravity and its freeboard as well as cause a slight increase in stern trim. Depending on the situation, these changes may or may not be negligible.

Another consideration with this type of project is centered on the physical attachment of the shroud or nozzle to the vessel’s hull. Given both the axial and transverse forces in this region, as well as other potential shock loads that may be exerted on this unit during operation, its attachment to the hull must be very robust to protect against failure and subsequent flooding. Navigating in ice is but one example where additional forces may be exerted upon a propeller shroud or nozzle. As with any hull attachment, adequate measures to protect against potential flooding are of paramount importance.

A careful analysis should be undertaken before considering this type of modification.

Figure 1.0 (n)(i)
Typical shrouded propeller on a fishing vessel. (Courtesy of http://www.propellerpages.com/?c=nozzles&f=Speed_Nozzle_Tests

Figure 1.0 (n)(ii)
Typical shrouded propeller.
(Courtesy of J.G. Personal collection)
Installation of a bow or stern thruster arrangement.

Bow thruster units are commonly installed on a small fishing vessel to help with maneuvering the vessel in confined spaces, such as around docks. Stern thrusters are not as common on small fishing vessels.

There are many different types of thruster units on the market, but the most common type of installation found on small fishing vessels are tunnel thrusters. From a stability perspective, there are two primary considerations. Firstly, the installation of a bow thruster unit will necessitate some loss of buoyancy in a vessel due to the installation of the thruster tunnel, as well as a slight change in the vessel’s center of gravity as some weight is removed while more is added. The extent that these changes will affect its stability characteristics is dependent upon the pre-project stability status of the vessel, although in most vessels the stability changes are minimal. Secondly, the installation of the tunnel, as well as its associated thruster guards, must be done properly to ensure that the watertightness of the hull is maintained under all operating conditions. In addition to the dynamical forces of the sea, other navigational hazards that may exert shock loads on the unit or its guards must be considered. The fairing of the outer edges of the thruster tunnel in wooden and fiberglass vessels presents special challenges in terms of ensuring proper attachment to the hull, while at the same time not impeding the functionality of the unit or creating a protuberance that could lead to potential hull damage and flooding.

Outer hull fairing is not usually as much of a problem with steel or aluminum hull vessels. As with any hull attachment or penetration, adequate measures to protect against potential leakage or downflooding are of paramount importance.

A careful analysis should be undertaken before considering this type of modification.

Figure 1.0 (o)(i)
Typical bow thruster unit found on small fishing vessels.
(Courtesy of http://www.marinelink.com/maritime/prop)

Figure 1.0 (o)(ii, iii & iv)
Installation of the bow thruster tunnel during the construction of the fishing vessel ‘Newfoundland Spirit’.
Adding a permanent stern ramp extension.

Unless a vessel is inclined, the position of the center of gravity is unknown. But it is generally safe to assume that it is usually below the level of the main deck in the majority of small fishing vessels. The addition of any weight above the deck of a vessel will cause the center of gravity to shift upwards and as such, negatively affect its initial stability. Subsequently, the permanent addition of a stern ramp will cause a shift of the center of gravity upwards as well as further aft- affecting both the stability and trim of the vessel. Furthermore, if the extra deck space is to be used to carry additional weights, such as fishing gear or catch, this will further impact stability and trim.

These factors, along with the normal operational factors, such as heeling moments from handling fishing gear and the pre-project stability status of the vessel must be considered.

This modification will have some negative impact on the stability of the vessel, the extent of which is dependent upon its operational requirements and its pre-project stability status. Ensure that the vessel has sufficient reserves of stability prior to adding a stern ramp.
The hull is completely rebuilt but with no changes in weight or dimensions.

This project will essentially replace the old construction material with new, extending the service life of the vessel. If there is no change in the weight of the structure of the vessel, as is indicated in this checklist item, then its stability characteristic will obviously be unchanged. While this is a realistic expectation with regard to steel, aluminum or even fiberglass hulls, it is noteworthy that with wooden hull vessels, structural members such as hull planking, framing, and decking, may have retained considerable moisture over time. As all of this material is removed and replaced with new wood, of the same dimensions, but with lower moisture content, it may result in a considerably lighter hull, upon completion. This would cause a rise of the center of gravity of the vessel. Its stability characteristics may not necessarily be the same as when it was newly built because many other changes or additions may have occurred since then.

During the process of rebuilding a wooden vessel, it is advisable to monitor the weight of material being replaced as compared to the new structural members. If there is a significant difference, the stability of the vessel after reconstruction should be assessed.

This project should have very little impact on the stability of the vessel as long as the replacement materials are not of a different weight.

A careful analysis should be undertaken before considering this type of modification.
A set of bilge keels (anti-roll shocks) are installed.

Bilge keels are sometimes referred to as anti-roll shocks. They are relatively small ‘fins’ projecting outward from the hull, near the turn of the bilge and extending over the amidships region of the hull, for about half of the vessel’s length. Of the various anti-roll devices installed on fishing vessels, their installation probably has the least effect on the stability.

From a stability perspective it is important to have bilge keels properly installed. The installation should ensure that if the vessel were to hit an obstruction, such as ice or a shoal, the bilge keel will separate from the hull without impacting the watertightness of the vessel. They must be installed to be torn away from the hull without stripping the outer shell of the vessel. Other than this consideration, the added weight of the bilge keels will have some effect on the stability by lowering the center of gravity slightly and reducing freeboard, but this will likely be minimal.

It is notable also that bilge keels need to be properly profiled and positioned to effectively match the water flow along the hull so as not to apply a drag on the vessel while steaming.

Lastly, some observed disadvantages with bilge keels on fishing vessels include the fouling of fishing gear, such as pots, during retrieval. Moreover, when the vessel is navigating in ice the bilge keels might be susceptible to damage. In general though, bilge keels are effective roll dampening devices which have minimal impact on the stability or efficiency of the vessel- as long as they are properly installed.

A careful analysis should be undertaken before considering this type of modification.

Figure 1.0 (r)(i)
Typical bilge keel on a steel fishing vessel.
(Courtesy of J.G personal collection)
Adding hull mounted hinged fin anti-roll devices

Most anti-roll devices, such as hull mounted hinged fins, may provide a more comfortable working platform by reducing the rolling motion- but they do not improve a vessel’s stability characteristics. These particular types of anti-roll device are essentially flat plates of steel that are hinged to the hull of a vessel, below the waterline, and held in place while in use by a hinged and/or hydraulically operated arm.

Strictly from a stability perspective, and depending on the particular installation, when in the deployed position, their addition to the hull may slightly lower the vessel’s center of gravity. When they are in their stored position however, they may raise the vessel’s center of gravity. The added weight will also reduce the freeboard of the vessel.

Hull mounted hinged-fins also introduces a potential risk to flooding. As with bilge keels, a system of hinged fins should be mounted such that they will tear away from the hull, without compromising the outer shell of the vessel and causing it to flood. Given the forces acting on the fins when steaming, in the event of a shock load from striking an obstruction, significant stress will be applied to the hinge and hull mounting structure, elevating the risk of hull damage, with subsequent flooding.

Downward forces due to fishing gear entanglement into a fin or hinge and hull mounting apparatus could also cause the vessel to heel to one side, submerging the entanglement, making it difficult and dangerous to remedy. With a severe entanglement, especially in unfavorable sea conditions, it could contribute to capsizing.

In icing conditions, ice buildup could occur, reducing overall stability and contributing to a heavy list. In the event that one hull mounted fin is lost or damaged and rendered inoperable, the handling characteristics of the vessel could change significantly, especially in heavy seas.

When docked or docking, hinged fins as well as their mounting fixtures and the hull itself, can be susceptible to damage because they extend out a past the body of the hull. Appropriate fenders must be available and used at all times.

The fins and all associated mounting fixtures as well as the hull in the area where they are mounted, should be checked regularly for signs of fatigue or damage. Further information on the risk associated with the installation and use of hinged fin type anti-roll devices on fishing vessels can be obtained from Transport Canada Ship Safety Bulletin #04/2010, “Fishing Vessel Safety: Hinged Fins as Anti-Roll Devices".

The hull structure and watertight integrity must not be compromised.

Note: Hinged fins are not approved by Transport Canada. However the interaction of the hinged fin to the vessel’s hull structure is subject to TC approval.

A careful analysis should be undertaken before considering this type of modification.

Figure 1.0 (s)(i)
Typical hinged fin configuration on a small fishing vessel. (Courtesy of http://www.chantier-naval.com/en/portfolio/fc-mercator-2008-2)

Figure 1.0 (s)(ii)

Figure 1.0 (s)(iii)

Figure 1.0(s)(i & ii): Hinged fin, hull mounted anti-roll devices on fishing vessels.
(Retrieved from the FVSS. Courtesy of the CCPFH)
A set of hull mounted buoyancy sponsons are added.

Sponsons are added to the exterior hull of a vessel, usually along the sides, to provide added buoyancy and to improve its stability. Stern sponsons can also sometimes be added, in varying shapes, to provide added buoyancy aft, often done to diminish stern trim and improve freeboard in a loaded condition, assuming that larger weights are not loaded.

Adding sponsons along the sides changes the entire stability characteristics of a vessel and should only be done under the guidance of a naval architect. If properly designed, sponsons will increase the beam of a vessel and if properly faired into the hull, can improve its profile, both functionally and aesthetically.

In terms of the post-project stability characteristics, given that the vessel will be wider, the initial stability will likely be improved considerably. Improvements in the large angle stability are also likely but are dependent on the amount of freeboard that the vessel has. A vessel with low freeboard will submerge its deck edge at smaller angles of heel, when its width is increased, and may not meet stability standards.

With the added buoyancy from side sponsons, the vessel will not load as deep, provided that there is no changes in the fish hold capacity or other weights added such as fuel tanks or equipment. In the case of stern mounted sponsons, with the added buoyancy not being used for anything other than increased flotation, the increased buoyancy aft should improve trim and freeboard of the vessel in most cases.

This type of modification will produce a completely different vessel and as such should only be undertaken on the advice of a marine consultant or naval architect.
The height of the main fish hold hatch coaming is permanently increased.

Increasing the height of the hatch coaming on a fishing vessel is a relatively minor modification, but it is one which could have either positive or negative effects on its overall stability characteristics. It is noteworthy that under current regulations, there are minimum height requirements for fish hold hatch coamings as well as a requirement to have a means to secure them watertight.

Raising the height of a potential downflooding point, such as the hatch coaming, will increase the angle at which the vessel could downflood in that location. In addition it will minimize the risk of leakage and subsequent downflooding through the hatch, from water shipped on deck, during adverse conditions. A third advantage, from a workplace health and safety perspective, is that a higher coaming may reduce the risk of injuries from someone accidentally falling into the fish hold.

From the vessel’s stability perspective, the addition of the extra materials to make the coaming higher, will add some weight, slightly raising the vessel’s center of gravity and lowering freeboard, both of which reduce the vessel’s reserves of stability.

The added height of the hatch coaming will provide the means to fill spaces that previously remained void in the upper areas of the fish hold, during fully loaded conditions. Extra hydrostatic pressure, from fish in the higher coaming, during loading operations, will force some types of fish, such as capelin and herring into all available spaces in the upper regions of the hold. This additional weight will reduce the vessel’s reserves of stability. Harvesters that have undertaken this type of modification sometimes attest to a small but noticeable increase in accessible fish hold capacity as a result, in addition to the added hatch coaming space. Subsequent negative consequences from this would include a decrease in freeboard and reserves of stability, due to the increased weight on board.

Depending on the pre-project stability characteristics of the vessel as well as the intended operational requirements, this project could provide positive outcomes, if the potential negative impacts on stability, such as not overloading the vessel are carefully considered.