As mentioned above, Chapter II-1, "Construction - Structure, subdivision and stability, machinery and electrical installations" of the SOLAS Convention defines the specific regulations for ship construction related to the hull and installation of machinery.
Below we will take a look at some elements related to the machinery installation.
Requirements for steering gear
The Convention states that all ships must be equipped with steering gear and that tests done on this gear must meet specific criteria.
The requirements are very specific and precise. For example, when a ship is at its deepest draft and running ahead at maximum ahead service speed, the main steering gear shall be able to turn from 35 degrees on one side to 30 degrees on the other side in no more than 28 seconds. As for the auxiliary steering gear, it shall be able to go from 15 degrees on one side to 15 degrees on the other side in the same conditions as the main steering gear in not more than 60 seconds.
Requirements for emergency generating sets
Requirements for emergency generating sets involve starting in cold condition and starting energy-storing devices.
The Convention contains the following in the regulations:
- Emergency generating sets shall be capable of being readily started at a temperature of 0°C. If this is impracticable, or if lower temperatures are likely to be encountered, provision shall be made for the maintenance of heating arrangements.
- Each emergency generating set arranged to be automatically started shall be equipped with starting devices approved by the Administration with a stored energy capability of at least three consecutive starts. A second source of energy shall be provided for an additional three starts within 30 min unless manual starting can be demonstrated to be effective.
Ships constructed on or after 1 October 1994, in lieu of the provision of the second paragraph of the section above, shall comply with the following requirements:
- The source of stored energy shall be protected to preclude critical depletion by the automatic starting system, unless a second independent means of starting is provided. In addition, a second source of energy shall be provided for an additional three starts within 30 min unless manual starting can be demonstrated to be effective.
The stored energy shall be maintained at all times, as follows:
- electrical and hydraulic starting systems shall be maintained from the emergency switchboard;
- compressed air starting systems may be maintained by the main or auxiliary compressed air receivers through a suitable non-return valve or by an emergency air compressor which, if electrically driven, is supplied from the emergency switchboard;
- all of these starting, charging and energy-storing devices shall be located in the emergency generator space; […]. This does not preclude the supply to the air receiver of the emergency generating set from the main or auxiliary compressed air system through the non-return valve fitted in the emergency generator space.
Where automatic starting is not required, manual starting is permissible, such as manual cranking, inertia starters, manually charged hydraulic accumulators, or powder charge cartridges, where they can be demonstrated as being effective.
- When manual starting is not practicable, the requirements of paragraphs 2 and 3 shall be complied with except that starting may be manually initiated.
The section on electrical installations sets out all the requirements concerning a ship's power supply. Clearly, Regulation 44 provides requirements for the starting systems of emergency generating sets.
Pressure requirements for fire mains
The fire-fighting system is also a central element of the SOLAS Convention, so it contains many requirements.
Chapter II-2, Regulation 4 of the SOLAS Convention, "Fire pumps, fire mains, hydrants and hoses" contains the details of the regulations governing this aspect.
The maximum pressure calculation must be done with standard nozzle sizes. The fire hose nozzle specifications are set out in point 8: Nozzles. It states that for machinery spaces and exposed locations, the nozzle size shall be such as to obtain the maximum discharge possible from two jets at the pressure mentioned in paragraph 4 from the smallest pump, provided that a nozzle size greater than 19 mm need not be used.
All nozzles shall be of an approved dual-purpose type (i.e., spray/jet type) incorporating a shutoff.
The maximum pressure is the pressure that the system can support. This means that it shall not exceed that at which the effective control of a fire hose can be demonstrated.
The minimum pressure required varies based on the type of ship (passenger ship or cargo ship) and its tonnage according to the table below:
A ship's propeller is the last piece of equipment in the propulsion system. Propeller efficiency depends on many factors, the main ones being:
Propeller and hub diameters
The difference between the two is the effective surface. In general, a greater effective surface means higher efficiency.
Propeller rotation speed
Generally, slower propeller rotation speed means better efficiency.
Number of blades
In theory, fewer blades mean greater efficiency (3 or 4 blades). However, a higher number of blades (up to 8) greatly reduces vibration, which can be useful on passenger ships and naval ships.
This is the most difficult criteria to evaluate when designing a propeller. This angle depends on all the factors listed above. In addition, it is preferable for the angle to change on a blade. For instance, the blade angle is more pronounced close to the hub and less pronounced near the blade tip.
Propeller pitch is defined as the linear distance covered by the propeller in one complete revolution, if the propeller were operating in a solid. The actual linear distance covered will be less because water is not a solid.
If propeller blades could operate in a solid, travel per rotation would be equal to the pitch. But since water is not solid, the propeller action is weaker and the thruster "slips" in the substance in which it is operating. Actual travel per rotation is thus less than the pitch. Slip is expressed as a percentage.
Slip = (Pitch − Actual traven per rotation) ÷ Pitch