Weight vs. Displacement

GrandadPig said:
Could I please check I have this correct?

Boat data says my boat displaces 2000lbs (907kgms)

Am I correct in thinking this is the same as its weight? Trying to calculate, roughly, if the wife’s car will tow it legally. Displacement (weight) plus weight of the braked trailer equals the tow weight. I need to check but her car will tow 1500kgms braked. It will be close but will it be legal?

Thanks guys

Steve
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Yes - Archimedes etc. Weight is displacement. As for your question plod will drag you off to a weighbridge so whats on a data base is irrelevant. You can easily find some factory with a weighbridge at the gate who will weigh your set up for free of a tenner to the gate man.
 
The weighbridge suggestion was exactly to take the guesswork out of the equation.
The weight of the trailer, laden with the boat & that-ever you carry in it, is what count when selecting the vehicle to pull it.

Hence, if you find the actual weight under, at or above the desired 1500 kg, you know what to do. Simply moving things from the boat to the car will allow you to reduce the trailer weight and still bring it all with you..
 
I've seen police / the driving agency stopping everything with a trailer, HGV, lorry or car, at a point designed for that on the A17, and also at a similar point on the M74. Also the police recently had a crackdown on the A11 on trailers... From the accounts in the papers it's a very thorough vehicle / trailer examination.
 
The Q said:
I've seen police / the driving agency stopping everything with a trailer, HGV, lorry or car, at a point designed for that on the A17, and also at a similar point on the M74. Also the police recently had a crackdown on the A11 on trailers... From the accounts in the papers it's a very thorough vehicle / trailer examination.
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Christmas is coming after all..........
 
Another example of stuff not included in the manufacturer's "Total weight":

I'm carrying:

Diesel (600 liters)
Water (250 liters)
Tools and spares (50 kg)
Anchor and chain (50 kg at least)
More batteries
Two heaters
Pots and pans and then some in the pantry
2 gas bottles, full
Food and bevs. Enough to be on the safe side.
Electronics
Safety gear, fire extinguishers
Lines and fenders

+all sorts of bits and bobs


Crew

Obviously, this boat is not trailerable, but when discussing fuel consumption, speed, handling etc. weight is a thing. Boats referred to in tests normally also are lighter than your Ready-to-Go boat of same make and model.
 
ChromeDome said:
The weighbridge suggestion was exactly to take the guesswork out of the equation.
The weight of the trailer, laden with the boat & that-ever you carry in it, is what count when selecting the vehicle to pull it.

Hence, if you find the actual weight under, at or above the desired 1500 kg, you know what to do. Simply moving things from the boat to the car will allow you to reduce the trailer weight and still bring it all with you..
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Take care ..... every car has a total Overall Gross Weight towing figure. I have seen caravanners fail not because of the caravan and whats inside the van - but because of the gear in the car ...

On the subject of Weigh Bridges ..... When I was Baltic Boss of Intertek - one of my jobs was to visit Weigh Bridges to issue check weigh certificates. You'd be surprised at the allowed range when check weighing. As you go up the size of WB ... it gets worse !!
 
As said before, nose weigh is critical....get out your bathroom scales, put a block of wood on the scales that the tow hitch can rest on and look up the limitations in your car’s handbook. Nothing worse than snaking down the road (well, jack knifing is worse)
 
vyv_cox said:
My 35 ft boat weighs more than a ton more than its official weight. I understand that not only are fluids not included but also sails, anchor gear and of course all the other cruising gear like warps, fenders etc.
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The theoretical design weight of my boat was published as 14.5 metric tonnes. It has never weighed less than 18.3 tonnes when we have lifted out. Fuel and water tanks full compared to empty is 1.3 tonnes. The boat has 7 sails and none of those are spare sails. I suspect the 4t difference is about right
 
geem said:
The theoretical design weight of my boat was published as 14.5 metric tonnes. It has never weighed less than 18.3 tonnes when we have lifted out. Fuel and water tanks full compared to empty is 1.3 tonnes. The boat has 7 sails and none of those are spare sails. I suspect the 4t difference is about right
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That’s a lot to tow!
 
I’ve had a bit of experience at towing near the limits. Though as the boat was a lightweight trimaran, we’d already cut the handles off our toothbrushes, so to speak. Our cruising kit was about 150kg inc anchors, inflatable canoe, bedding, galley gear and the like. We used to empty the water tank, the primary reason for electric fresh water pump! It’s bloody tedious emptying 30 litres of left over water otherwise. With that load, a boat with a manufacturers quote of 1340kg dry, on it's trailer, squeezed in at 2500kg. We were able to leave it loaded ready to launch. That was a steel twin axle trailer.
 
The current standard for Principal data for small craft is ISO 8666 in which there are 8 different loading conditions for displacement.

Prior to the RCD coming in most quoted displacements were educated guesses and usually lower than even a newly completed boat (never mind varying from boat to boat to the same design) even before owners added their gear.
 
Many cranes (not boat lifters) have weight gauging on the boom base .. so operator can know limits he can swing / extend etc.

Its how I found out my boat was near 1mt more than design ....

xYdImDIl.jpg


and then I bit my lip ..... clenched buttocks !! >

P89NGCDl.jpg
 
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