Getting a boat weighed

[Tim M]

I've just bought a boat and want to know what it weighs for transport purposes. Can anyone suggest how I can get this done (in the Southampton area)? Do the majority of cranes have the facility to weigh their loads? Towing the boat to a weigh bridge isn't an option.

[Poly]

Tim,

If you search the forum far enough back there is a method using some bathroom scales and some maths. Its in a post I made about 5 yrs ago, and came from an article in PBO so probably refers to that.

[Tim M]

Not sure how that's going to work! This boat weighs around 4.5 tonnes (we think!)

[yam man]

Drivers wharf dry berthing on the itchen can via there Crain. I know this we re engined a vessel and weighed her before and after .

[Tim M]

Thanks for the tip. Can most cranes do this?

[Searider]

If you hire a load cell for the day you place this as a link between the crane hook and the slings.

[Erin]

Originally Posted by Tim M

Not sure how that's going to work! This boat weighs around 4.5 tonnes (we think!)

It's actually not that mad!

You need to be able to weigh the noseweight of the hitch on the scales then roll the boat back a short distance and re-weigh. Based on a bit of maths comparing the weights and distance you rolled the boat back by you can estimate the mass. I did this on my setup and came to 1700kg. I then went to a weighbridge and it measured 1610kg, so not too far off.

[Poly]

Originally Posted by Erin

It's actually not that mad!

You need to be able to weigh the noseweight of the hitch on the scales then roll the boat back a short distance and re-weigh. Based on a bit of maths comparing the weights and distance you rolled the boat back by you can estimate the mass. I did this on my setup and came to 1700kg. I then went to a weighbridge and it measured 1610kg, so not too far off.

Indeed, although its probably more complex with a twin or triple axle trailer(?), and manhandling 4.5 tonnes back on the trailer might be fun especially if its not got rollers.

However it does provide a possibility without the need to transport it anywhere, which given the boat is 4.5 tonnes is not going to be cheap/legal*. *delete as applicable!

[Tim M]

Boat is currently on the water with no trailer hence I'm hoping we can just take it somewhere with a crane, get it weighed, job done! Previous owner reckons it weighs 4.5 tonnes, I think less. I'm hoping it will be significantly less so it can be transported on a tri axle trailer. Wishful thinking perhaps!

[Searider]

What boat is it Tim?

[Poly]

Originally Posted by Tim M

Boat is currently on the water with no trailer hence I'm hoping we can just take it somewhere with a crane, get it weighed, job done! Previous owner reckons it weighs 4.5 tonnes, I think less. I'm hoping it will be significantly less so it can be transported on a tri axle trailer. Wishful thinking perhaps!

Ah, ok that makes sense.

[Tim M]

Originally Posted by Searider

What boat is it Tim?

1930's wooden motor launch!

[jumpinjack]

Any modern crane will be able to weigh it.
Not sure about marina straddle carriers though??

[Mbryant]

Tim, try the guys at Trafalgar wharf, I'm pretty sure their forklift weighs everything it lifts. You'll have to get the boat to Pompey though

[HughN]

Very approximate method but...

If I slide four pieces of paper under my car tyre (two front/back, two on the sides) they are 100 mm and 165 mm apart respectively, giving an approximate contact area of 0.1 x 0.165 = 0.0165 sq.m

A gauge tells me that the air pressure is 33 psi, or 227535 Pa, so the load on that tyre (Area x Pressure) is approx 0.0165 * 227535 = 3754 N. Divide this by 9.81 gives a load of approx 382 kg for that wheel - probably not far out for a car with 1610 kg curb weight.

Only a ball-park figure but no weighbridge necessary.

[EnglishLes]

Originally Posted by HughN

Very approximate method but...

If I slide four pieces of paper under my car tyre (two front/back, two on the sides) they are 100 mm and 165 mm apart respectively, giving an approximate contact area of 0.1 x 0.165 = 0.0165 sq.m

A gauge tells me that the air pressure is 33 psi, or 227535 Pa, so the load on that tyre (Area x Pressure) is approx 0.0165 * 227535 = 3754 N. Divide this by 9.81 gives a load of approx 382 kg for that wheel - probably not far out for a car with 1610 kg curb weight.

Only a ball-park figure but no weighbridge necessary.

But he doesn't have a trailer!

[9D280]

If it's a 1930s wooden sportsboat, do you have slinging kit for it?

Simply because you might be able to clip a 4 point harness to a rib on the side of a ferry, but without suitable slinging, you presumably know the best place to sling it and / or have a spreader frame to stop the straps crushing the deck or breaking it's back with the deadweight of the engine as it clears the water?

The straps on the travel hoists in marinas are secured to the lifting gear outboard of the gunwhales, so it's never usually a problem. A crane will be lifting from above the CoG, and by definition the straps will be trying to compress the hull.


Easy enough to weigh the lifting gear / spreader bar separately & subtract.

[Searider]

Load cell and Gosport Boat Yard will be your best bet. They have suitable spreaders on their crane.

[Leapy]

Originally Posted by HughN

Very approximate method but...

If I slide four pieces of paper under my car tyre (two front/back, two on the sides) they are 100 mm and 165 mm apart respectively, giving an approximate contact area of 0.1 x 0.165 = 0.0165 sq.m

A gauge tells me that the air pressure is 33 psi, or 227535 Pa, so the load on that tyre (Area x Pressure) is approx 0.0165 * 227535 = 3754 N. Divide this by 9.81 gives a load of approx 382 kg for that wheel - probably not far out for a car with 1610 kg curb weight.

Only a ball-park figure but no weighbridge necessary.

Can't get me 'ed round that one, son, but I daren't ask for further explanation

[kerny]

Originally Posted by Leapy

Can't get me 'ed round that one, son, but I daren't ask for further explanation

I was sh*te at maths at school as well