Anyone know what this number means? Thames tons?

[Mudhook]

Hi all. My 1970 boat has a number engraved into a hard plastic placard in the saloon. It says 'ON 340057' and '5 23/100' (that's five and twenty-three hundredths). I have always assumed this is some original British Register of Ships number and the second one is the Thames tonnage.

My SSR number is different to this. Does this sound right? Could it be a manufacturer's number? Does anyone know what 'ON' means? Five and a bit Thames tons would probably be about right I think: a 27-footer grossing about 3,258kg displacement when built.

Any light shed on this would be welcome.

Regards, Mudhook

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[sailorman]

the "Official Number " was issued by the registrational port ie> dover , ipswich, portsmouth ect.
the "Thames Tonnage" weight is a function of measuring "volume" of the hull (dont know how its worked-out though) BUT give it a couple of hrs & all our more informed forumites will respond.
as the ship was originally registered (blue book) u should be able to trace her previous owners
as for thr ssr thats just another tax

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[celandine]

Mudhook

You can calculate Thames Tonnage by the following formula:-

(L-B) X B X 1/2B all over 94

Wher B= max beam, L= stem to after side of stern post, measured at deck level.

It is an ancient system and has very little to do with actual displacement, especially modern-shaped yachts.

The Imperial Russian Navy built a ship with six propellors, 2400 horse-power and a completely round hull. Her Thames tonnage was zero.


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[celandine]

Mudhook

You can calculate Thames Tonnage by the following formula:-

(L-B) X B X 1/2B all over 94

Where B = max beam, L = stem to after-side of stern post, measured at deck level.

It is an ancient system and has very little to do with actual displacement, especially modern-shaped yachts.

The Imperial Russian Navy built a ship with six propellors, 2400 horse-power and a completely round hull. Her Thames tonnage was zero.


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[halcyon]

Does it not go back to the days of tuns, and was the number of barrels you can carry, not displacement.

Brian

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[Mudhook]

Re: Anyone know what this number means? Thames ton

Well thanks so far - I hadn't anticipated there's be so many people active at this time of the afternoon. Isn't there any footie on? I can't get near my boat until next weekend!

I have to drop the length substantially to get the formula to work, but it's clearly a pretty arbitrary system. Any idea where I can track this number down and find some history? Original British Registry now lapsed - at least I don't have any docs.

Regards, Mudhook

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[sailorman]

Re: Anyone know what this number means? Thames ton

wots footballs
been to the boat to-day
u may need to multiply the penultimate answer with your age to get it to work?.

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[Mirelle]

A stab at an answer

The first number is your boat's Official Number. The second is her Net Register Tonnage, which is NOT the same as her Thames tonnage OR her displacement. It is there because it was the tonnage on which yachts paid Light Dues when yachts did pay Light Dues, and it was the tonnage on which a foreign port, if it were so minded, might charge port dues (these are usually waived for yachts, but not always).

The Net Register Tonnage is in essence the volume below the weather deck in cubic feet, divided by 100, less allowances for propelling machinery, crew accomodation and navigation spaces, plus the volume of any weathertight deck erections. The formula for working it out is settled by an international treaty, and has changed since your boat was built. Don't bother trying to work it out, just accept that the Board of Trade (now DoTp) surveyor did his job.

Thames Tonnage which as stated is

(L-B) X B X 1/2B all over 94

is quite another matter. This was developed from Builders Old Measurement by the Royal Thames Yacht Club in 1847 as the basis of a rating rule for yacht racing.

Builder's Old Measurement was the length that the keel treads the ground, x beam, x depth in hold, all over 100 and was the formula for tonnage measurement of ships used until the nineteenth century. One of Patrick O'Brian's occasional schoolboy howlers has Aubrey and Maturin discussing a ship's Thames tonnage - it would have been Builder's Old Measurement.

The RTYC changed the measurements because the length of straight keel was not easy to measure (impossible with the yacht afloat!) and the depth in hold was also tricky. For a yacht of old fashioned shape, length from stem to rudder post less half the beam is a fair stab at the length of keel and half the beam is a fair stab at the depth in hold (which is the depth from sailing beam to keelson in way of the mast, in a yacht).

You will notice that the formula uses beam as a multiplier twice, i.e. beam is very heavily penalised. This resulted in very narrow racing yachts - the so called "plank on edge" types - deep, heavily ballasted and very narrow indeed. These were taken to extremes and became unsafe and the Length and Sail Area Rule (length on waterline, times sail area, over 6,000) was developed instead in the late 1880's.

However, Thames Tonnage has another use - it is a very accurate way of expressing the size of a cruising yacht. It was therefore used by anyone who went cruising to describe their boat. For this reason the various models of Hillyards, for instance, were marketed on the basis of their Thames tonnage.

This lasted until GRP, when the practice of describing a boat by her overall length, which the Americans had used, became universal. Which is a pity, as Thames tonnage gives a much better idea of the relative sizes of boats and what accomodation they are likely to have.

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[chrishewett]

How do I trace my boats previous owners. She was originally registered but the last owner cant find the papers.
Chris

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[Samphire]

As Sailorman correctly points out it is a measurement of volume (carrying capacity)
and is interesting in so far as it tells you the hull size of lets say three 27ft yachts
which can have big differences in Thames Tonnage measurement.
It was common up to the 60s when yacht sizes were always referred to in Thames tonnage primarily rather than length.
Samphire.


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[sailorman]

find someone with a "Lloyds Register"
there is bound to be a forumite with that info

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[Joe_Cole]

You could try this:

<A target="_blank" HREF=http://www.lr.org/services_overview/shipping_information/history_service.htm>http://www.lr.org/services_overview/shipping_information/history_service.htm</A>

Joe


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[bob_tyler]

Lloyds Register of Yachts might help, up to 1980, when it ceased publication.

More likely try the Registry of Shipping and Seamen at:

Anchor Court
Ocean Way
Cardiff
CF24 5JW

Tel: 029 2044 8800

They will have complete records of previous registered ownership of your boat - 340057.

As to the tonnage - this is worked to a Formula which gives three different figures, Gross, Registered and Net.

My Invicta 26 is Gross 4 6/100; Registered 3 72/100 and Net 0 0/100. These figures are shown on the Registration Certificate in decimals but carved on the main beam in 1/100ths. Net I don't understand.

I have always understood that the difference between Gross and Registered is accounted for by deducting the volume of the engine and steering compartments from the total volume of the vessel.

None of the figures have any relationship to the displacement (weight) of the vessel, (Eureka! - Archimedes Principle if I remember my schooldays of very many moons ago correctly)


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[charles_fhw@yahoo.co.uk]

How do I trace my boats previous owners. She was originally registered but the last owner cant find the papers.
Chris

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Dear Chris I have only just seen your posts re SEA CYGNET. I used to own this yacht many years ago I think 1970/6. Please reply for further info. Charles Waters

 

[macd]

Dear Chris I have only just seen your posts re SEA CYGNET. I used to own this yacht many years ago I think 1970/6. Please reply for further info. Charles Waters

Doubt you'll get a response, Charles. Chris last posted 14 years ago.

 

[RichardS]

Dear Chris I have only just seen your posts re SEA CYGNET. I used to own this yacht many years ago I think 1970/6. Please reply for further info. Charles Waters

Doubt you'll get a response, Charles. Chris last posted 14 years ago.

Although using an email address as a user name will probably elicit a lot of responses ..... most of which will be unwelcome. :ambivalence:

But I'm intrigued as to where the boat name "SEA CYGNET" came from as I can't see any reference to it.

Richard

 

[macd]

But I'm intrigued as to where the boat name "SEA CYGNET" came from as I can't see any reference to it.

As you've evidently discovered, from this equally elderly thread: http://www.ybw.com/forums/showthread.php?33096-Sea-Cygnet&p=298319&highlight=#post298319
The paramedics have been busy

 

[Norman_E]

Re: A stab at an answer

This formula: (L-B) X B X 1/2B all over 94 gives me a Thames tonnage of 34.53 for my boat, assuming all measurements are feet. Is that likely to be correct as I am told that the Jeanneau 45.2 which has a light displacement of 9.8 tons has a measured tonnage of 18.9 tons for Part 1 registration purposes.

EDIT: I understand that the measurement tonnage is based on tun barrels. If anyone can provide me with enough barrels of good Bordeaux wine I am willing to test the theory.

 

[macd]

Re: A stab at an answer

EDIT: I understand that the measurement tonnage is based on tun barrels. If anyone can provide me with enough barrels of good Bordeaux wine I am willing to test the theory.

It once did. Then the filled weight of such barrels became the original ton. (A bit lighter than the present one.) Evidently 'tun' originally came from the Greek for tuna, so for olfactory (and other) reasons, you're probably wise to prefer Bordeaux. Or brandy: wasn't Nelson pickled in once such tun for his the return from Trafalgar?