In the process I have seen a couple of boats with a board marked as above.

Some one said this is how much coal the boat can carry ?. On the River Thames.

Another told me it was the Registerd Tonage?.

Can anyone confirm which is correct please?.

I don't think adding coal to the boat is a normal these days.

Ray

I would imagine it is referring to Gross Tonnage, the definition of GT is given here .

Mike

I think this refers to Part 1 registry. O.N. is the Official Number and R.T. is the Registered Tonnage. The ON is issued and the RT is measured as part of the application, both are to be “marked on the main beam or on a readily accessible visible permanent part of the boat”. If I recall you are also supposed to have the vessel name and Port of Choice “marked conspicuously on the stern”.

As mentioned RT is an old concept relating to the internal volume of the vessel and is calculated in units of 100 cubic feet, this is why I think the fraction is expressed in 100’s. For yachts I think you could estimate this from (0.45 x LOA x B x D)/100, All in feet and where D is the height from the deckhead to the inside of the hull at midships (other estimation formula are available), but for registration I believe you have to get a qualified measurer.

Jon

SS26/96