Measuring tonnage measurement depth (TMD) of Canadian vessels less than 24 m in length (L) - SSB No.: 17/2025

Scope

This bulletin applies to Canadian vessels that are less than 24m long.

Purpose

This bulletin explains how to measure tonnage measurement depth (TMD) when there’s a notch or any other discontinuity in the keel at the middle of the tonnage measurement length (TML).

Background

“Tonnage measurement depth (TMD)” is defined in paragraph 3.2.7.1 of TP 13430 (Standard for the Tonnage Measurement of Vessels) as the depth of a vessel measured at the middle of the tonnage measurement length (TML) from the top edge of the upper deck at the side of the vessel to the bottom of the keel.

What you need to know

Transport Canada has learned that some shipowners have tried to minimize their vessels’ tonnage by making a notch in a keel, because they think this affects the tonnage measurement depth (TMD).

To resolve this issue, we want to clarify how Transport Canada measures tonnage measurement depth (TMD).

If there is a notch or any other discontinuity in the keel at the middle of the tonnage measurement length (TML), measure the tonnage measurement depth (TMD) to the continuation of the line representing the bottom of the keel (projected line corresponding to the line of keel).

We will add this clarification to:

• TP 13533 A Guide for Tonnage Measurers, Part 14 – Interpretations and Rulings, and
• Form 4A - Simplified method of tonnage measurement (Form 85-0405)

If you’re planning to modify your vessel, talk to an appointed tonnage measurer or Transport Canada to understand how it might affect how you use your vessel.

Keywords:

1. Tonnage measurement
2. Tonnage Measurement Depth
3. Small vessel

Questions concerning this Bulletin should be addressed to:

Contact us at: Email: marinesafety-securitemaritime@tc.gc.ca or Telephone: 1-855-859-3123 (Toll Free).