tonnage

[rtchina]

Can anybody tell me what the tonnage measures? Is it the weight of water displaced by the yacht? I have an epoxy version of a production yacht which floats pretty high and is over 500kgs lighter than the polyester version. So is my tonnage the same as the others (which the documents indicate).

 

[Bilgediver]

Can anybody tell me what the tonnage measures? Is it the weight of water displaced by the yacht? I have an epoxy version of a production yacht which floats pretty high and is over 500kgs lighter than the polyester version. So is my tonnage the same as the others (which the documents indicate).

The tonnage measurement may well be the same if the designs are identical as the tonnage measurement is a volumetric measurement.

You boat however may have a lighter displacement.

 

[Tranona]

As already noted, Tonnage is a measure of the carrying capacity of the boat, not its weight (or displacement). The calculation is used for registration purposes because it is the measure used to calculate such things as light dues and harbour dues. For most yachts completely irrelevant. So yes, if the hull of your boat (and therefore probably displacement) is lighter than a different construction method it will still have the same registered tonnage.

 

[RestlessL]

I think it is related to the internal volume. Basically, it is the number of tuns (barrels) of wine that could be fitted in that volume.

J

 

[magdalena]

Can't remember where I got this from, but here it is anyway.

If you have ships papers that refer to the depth then it is nothing to do with draught - see below. Marina staff don't seem to realise this at all.

Regards,

Robin

snip....

Where the gross tonnage of a ship has not been calculated under the Merchant Shipping Acts it is to be determined for the purposes of VAT only by the following formula:

For vessels 24 metres or greater in length:
L(m) x B(m) x D(m) x 0.235

For vessels less than 24 metres in length:
L(m) x B(m) x D(m) x 0.16

Where:

L = Length measured from foreside of the foremost fixed permanent structure to the afterside of the aftermost permanent structure. This measurement must not include appendages that do not contribute to the volume of the vessel.

B = Beam – breadth of vessel at widest part to the outside of outer planking. This measurement must not include the thickness of any moulding or rubbing strake which may be fitted, in way of such measurement.

D = Depth measured vertically from the midpoint overall.
The upper calculation point will be:
 for a decked vessel - the underside of the deck on the middle line, or (if there is no deck on the middle line) the underside of the deck at the side of the vessel.
 for an open decked vessel – the top of the upper strake or gunwale.
The lower calculation point will be:
 for a wooden vessel – the upper side of the plank at the side of the keel.
 for a metal vessel – the top of the plating at the side of the keelson.
 for a moulded vessel (for example one made of glass-reinforced plastic) – the inside of the hull. Where no keel member is fitted and the keel is of open trough construction, the calculation point shall be the top of the keel filling, if fitted, or the level at which the inside breadth of the trough is 10 centimetres – whichever gives the greater depth.