Want to weigh my boat

[W+T]

Morning all, i read some time ago about a way to weigh my boat by the way of balancing it and using small bathroom type small , and and little mathematics, It heard it ok fo a rough guide but not accurate, now i wrote it down but its gone AWOL, like most thinsg in this house that written down, i need a filing cabinet that say `BOAT info dont touch` lol.

 

So if anyone can help who knows that way please tell.

 

Now a better way if anyone has any lying around in there bilges is industrial scales, cattle scales even to take 3000kg, I am sure some folk need them at times Is there anywhere that hires out industrial scales, if i get three i can sit he boat on them and then do the math, which i am unsure what that would be yet.

 

 

Oh its not a NB but a twenty foot GRP cruiser and at a guess no more than 3 ton, i know but some say it will weigh that much but my guess is around 1750kg. I would like to know also to get a suitable trailer sorted for it.

 

Have a good day all

 

Wolly:)

[boat fan]

I think you could do it this way , if you can get eveerything to stay put , and not shift around all over the place.

 

May be easier said than done though ........ .......be safe please.

 

http://www.engineersedge.com/calculators/trailer-weight-balance.htm

 

Your estimate of 1750 KG sounds reasonable to me.

[koukouvagia]

Morning all, i read some time ago about a way to weigh my boat by the way of balancing it and using small bathroom type small , and and little mathematics, It heard it ok fo a rough guide but not accurate, now i wrote it down but its gone AWOL, like most thinsg in this house that written down, i need a filing cabinet that say `BOAT info dont touch` lol.

 

 

This method uses, inter alia, bathroom scales.

 

http://www.canalworld.net/forums/index.php?showtopic=18541&p=298506

 

I've never met anyone else who has used this method, though.

 

eta: I seem to have mis-remembered. We used a spring balance, not bathroom scales!

Edited May 5, 2016 by koukouvagia

[Sea Dog]

Someone placed a copy of the manufacturer's advertising blurb for your boat on one of your previous threads. Did it mention displacement and would that be accurate enough for what you need?

[Giant]

This method uses, inter alia, bathroom scales.

 

http://www.canalworld.net/forums/index.php?showtopic=18541&p=298506

 

I've never met anyone else who has used this method, though.

 

eta: I seem to have mis-remembered. We used a spring balance, not bathroom scales!

 

Very interesting method, but that would need the boat to be in the water and running, which W+T's isn't yet.

 

I know a method used to weigh gliders, which sit on three points - the main wheel, the tail wheel or skid, and one wingtip. You just put the scale under each point in turn, and then add the results. It's not perfect, because lifting any of these points by the height of the scale changes the weight distribution, but only very slightly, because the points are far apart and the centre of gravity is low. Might be more of an issue with weighing a boat.

 

W+T, I suspect the method you have been told is something similar. You would need to get the weight of the boat spread over enough points that each one is within the capability of your scale. I suspect the "balancing" part of the instructions you have lost is an attempt to reduce the number of measurements you need to take, by balancing the boat so the measurements should be similar and can just be multiplied. Balancing will also help ensure there is not too much weight at any one point.

Edited May 5, 2016 by Giant

[bizzard]

A beam placed across the apex of your house perfectly balanced, attach the boat with a rope to one end of the beam in the front garden and place 56lb weights on the other end of the beam in the back garden until you find the balance. 2lb bags of sugar could be used as an alternative.

[boat fan]

Below is an email from Tom Lathrop, designer and builder of "Liz", explaining how to weigh a boat while on the trailer using only a bathroom scale.

 

 

https://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwju84LozcLMAhVX_WMKHU99BdEQFggcMAA&url=http%3A%2F%2Fwww.egyptian.net%2F~raymacke%2FWeigh.html&usg=AFQjCNGf58M6IHjMLHmoWxvu4hcw5-Q-Cw

[Neil Smith]

If you can borrow a trailer take it to a public weigh bridge and get the total then take boat off and re weigh and deduct from first figure and you will have it.

 

Neil

[RLWP]

I know how to weigh a whale

 

Richard

[Giant]

Below is an email from Tom Lathrop, designer and builder of "Liz", explaining how to weigh a boat while on the trailer using only a bathroom scale.

 

https://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwju84LozcLMAhVX_WMKHU99BdEQFggcMAA&url=http%3A%2F%2Fwww.egyptian.net%2F~raymacke%2FWeigh.html&usg=AFQjCNGf58M6IHjMLHmoWxvu4hcw5-Q-Cw

 

Ooh that is clever. Here's the text, lest someone find this thread in the future when it's disappeared from the internet:

 

Ray,

 

Here is the method I use to weigh boats on a trailer without hauling the boat to a commercial scale, which requires two trips for boat and trailer.

 

It's simple, accurate and will cause bystanders to marvel at your engineering whiz.

 

The boat stays on the trailer the entire time. Put the scale under the tongue near the end. You can even put a block on the scale to lift the tongue so you can see the dial. Record the weight. Now, slide the boat aft on the trailer 12" to 18". You must measure exactly how many inches you moved it, and record that. With the scale in the same location under the tongue, record the new scale reading. Finally, measure the distance in inches between the trailer axle (wheel centerline) and the point on the tongue where it touches the scale. You have then four measurements:

 

W1 = first (heavier) scale reading in lbs, W2 = second scale reading in lbs, X = the distance you shifted the boat in inches, C = distance between trailer axle and scale point in inches.

 

The formula is Boat Weight = C (W1-W2)/X

 

A couple of notes. The result, like any measurement, is sensitive to the accuracy of the input data. In this case, the most critical is the distance you slide the boat. One inch error out of 12 inches will really make a difference in the result. Slide the boat as far as you can and still have a readable load on the scales. Notice, too, that by subtracting the two scale readings, any constant error in the scale is canceled out.

 

Note to techies: The formula was derived by taking the sum of the moments around the trailer axle for each case and (since the sum of moments about a stationary object is zero) set the two equations equal to each other and solve for the trailer weight. Things that you don't know, like the trailer's weight and the location of the boat's center of gravity cancel out, leaving just the variables that you can measure, and the boat weight.

 

I also use another version of this formula for weighing a boat while it is under construction so I don't get a bad surprise when it's finished. You can use two bridged scales and/or a trailer extension to increase the range of weights you can measure. I usually shoot for measurements of about 30-40lbs

for a low end and 250lbs or so for the high end.

 

In your case I would reverse the order of moving the boat and do it when you next go to the launch ramp so you can move the boat in a partial launch.

 

Tom Lathrop

[Paul C]

If you can borrow a trailer take it to a public weigh bridge and get the total then take boat off and re weigh and deduct from first figure and you will have it.

 

Neil

 

This would be my preferred method, but of course if you need to know the weight before buying a trailer/towing it, its not feasible. However I'd say you can use a rough first estimate based on its being GRP and its length, to "size" the trailer and tow vehicle. For example, I imagine manufacturers of boat trailers suitable for a 20' boat will know more or less the weight of a 20' boat and specify the trailer suspension and hitch accordingly.

 

 

 

Ooh that is clever. Here's the text, lest someone find this thread in the future when it's disappeared from the internet:

 

Ray,

 

Here is the method I use to weigh boats on a trailer without hauling the boat to a commercial scale, which requires two trips for boat and trailer.

 

It's simple, accurate and will cause bystanders to marvel at your engineering whiz.

 

The boat stays on the trailer the entire time. Put the scale under the tongue near the end. You can even put a block on the scale to lift the tongue so you can see the dial. Record the weight. Now, slide the boat aft on the trailer 12" to 18". You must measure exactly how many inches you moved it, and record that. With the scale in the same location under the tongue, record the new scale reading. Finally, measure the distance in inches between the trailer axle (wheel centerline) and the point on the tongue where it touches the scale. You have then four measurements:

 

W1 = first (heavier) scale reading in lbs, W2 = second scale reading in lbs, X = the distance you shifted the boat in inches, C = distance between trailer axle and scale point in inches.

 

The formula is Boat Weight = C (W1-W2)/X

 

A couple of notes. The result, like any measurement, is sensitive to the accuracy of the input data. In this case, the most critical is the distance you slide the boat. One inch error out of 12 inches will really make a difference in the result. Slide the boat as far as you can and still have a readable load on the scales. Notice, too, that by subtracting the two scale readings, any constant error in the scale is canceled out.

 

Note to techies: The formula was derived by taking the sum of the moments around the trailer axle for each case and (since the sum of moments about a stationary object is zero) set the two equations equal to each other and solve for the trailer weight. Things that you don't know, like the trailer's weight and the location of the boat's center of gravity cancel out, leaving just the variables that you can measure, and the boat weight.

 

I also use another version of this formula for weighing a boat while it is under construction so I don't get a bad surprise when it's finished. You can use two bridged scales and/or a trailer extension to increase the range of weights you can measure. I usually shoot for measurements of about 30-40lbs

for a low end and 250lbs or so for the high end.

 

In your case I would reverse the order of moving the boat and do it when you next go to the launch ramp so you can move the boat in a partial launch.

 

Tom Lathrop

 

This is logical and would work.

[TheBiscuits]

I know how to weigh a whale

 

Richard

 

 

Yes, indeed.

 

I know WHERE to weigh a pie.

[RLWP]

 

 

Yes, indeed.

 

I know WHERE to weigh a pie.

 

You are well informed, have a garland

 

Richard

[W+T]

I think you could do it this way , if you can get eveerything to stay put , and not shift around all over the place.

 

May be easier said than done though ........ .......be safe please.

 

http://www.engineersedge.com/calculators/trailer-weight-balance.htm

 

Your estimate of 1750 KG sounds reasonable to me.

 

 

That is very simliar to what i had written down, but it didnt mention using a aier which got me thinking how i would do it without.

 

Thank for that.

 

 

If you can borrow a trailer take it to a public weigh bridge and get the total then take boat off and re weigh and deduct from first figure and you will have it.

 

Neil

 

 

Now that would make life to easy lol.

 

 

 

Very interesting method, but that would need the boat to be in the water and running, which W+T's isn't yet.

 

I know a method used to weigh gliders, which sit on three points - the main wheel, the tail wheel or skid, and one wingtip. You just put the scale under each point in turn, and then add the results. It's not perfect, because lifting any of these points by the height of the scale changes the weight distribution, but only very slightly, because the points are far apart and the centre of gravity is low. Might be more of an issue with weighing a boat.

 

W+T, I suspect the method you have been told is something similar. You would need to get the weight of the boat spread over enough points that each one is within the capability of your scale. I suspect the "balancing" part of the instructions you have lost is an attempt to reduce the number of measurements you need to take, by balancing the boat so the measurements should be similar and can just be multiplied. Balancing will also help ensure there is not too much weight at any one point.

 

 

Ye s,i have been trying to find 3 scales to total the 3 ton, i think more than i need but soem folk think it will weigh that much

 

 

Below is an email from Tom Lathrop, designer and builder of "Liz", explaining how to weigh a boat while on the trailer using only a bathroom scale.

 

 

https://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwju84LozcLMAhVX_WMKHU99BdEQFggcMAA&url=http%3A%2F%2Fwww.egyptian.net%2F~raymacke%2FWeigh.html&usg=AFQjCNGf58M6IHjMLHmoWxvu4hcw5-Q-Cw

 

 

i will read that now thanks

Below is an email from Tom Lathrop, designer and builder of "Liz", explaining how to weigh a boat while on the trailer using only a bathroom scale.

 

 

https://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwju84LozcLMAhVX_WMKHU99BdEQFggcMAA&url=http%3A%2F%2Fwww.egyptian.net%2F~raymacke%2FWeigh.html&usg=AFQjCNGf58M6IHjMLHmoWxvu4hcw5-Q-Cw

 

 

So with this idea as i have no trailer i use a central cross beam under the boat

[Murflynn]

A beam placed across the apex of your house perfectly balanced, attach the boat with a rope to one end of the beam in the front garden and place 56lb weights on the other end of the beam in the back garden until you find the balance. 2lb bags of sugar could be used as an alternative.

Dear Prof. Bizz,

 

Please can you clarify what cross-section of beam would be necessary, and how you would ensure the ridge board does not collapse.

I am seriously concerned that there may shortly be a rash of house collapses, particularly those lightly built constructions from the 1970's.

Please can you provide a template for the Risk Assessment which would assist the foolhardy to avoid catastrophic results.

 

If I may be so bold, I suggest sky hooks and a row of spring balances roped in parallel might be safer.

 

respectfully yours,

 

a concerned potential boat weigher.

[W+T]

Dear Prof. Bizz,

 

Please can you clarify what cross-section of beam would be necessary, and how you would ensure the ridge board does not collapse.

I am seriously concerned that there may shortly be a rash of house collapses, particularly those lightly built constructions from the 1970's.

Please can you provide a template for the Risk Assessment which would assist the foolhardy to avoid catastrophic results.

 

If I may be so bold, I suggest sky hooks and a row of spring balances roped in parallel might be safer.

 

respectfully yours,

 

a concerned potential boat weigher.

 

 

I am sure a 8x2 joist will do fine, short as possible though, so say sticking out 7 foot out the side of the house with my fishing scale hanging from a shackle will do, i have a 7t shackle int shed aswell, i have caught some big fish in my time

[TheBiscuits]

 

 

I am sure a 8x2 joist will do fine, short as possible though, so say sticking out 7 foot out the side of the house with my fishing scale hanging from a shackle will do, i have a 7t shackle int shed aswell, i have caught some big fish in my time

7 tonnes! How big were the ones that got away?

[bizzard]

Wotcha cock, Mrs Chrysanthemum Dithermore here, professor bizzards chroniclar and tea maker. Unfortunately Professor bizzard is resting in his egg box at present and rudely waved me away and made me tremble something rotten he did, but I have found a note of his about the boat weighing thing which he had filed away in the teapot. It strongly recommends the following to meet H & S regulations.

It says, a long beam made of balsa wood will be quite strong and light enough if reinforced with an extra long knitting needle.

The roof apex ridge beam can be propped up within the loft with a broomstick but great care must be taken to ensure that its placed precisely beneath the beam on the roof.

Also to meet safety regs its imperative that the correct and appropriate togs should be worn for the weighing operation.

These include a bobble hat, non synthetic under ware, long Johns, swimming trunks, hazard jacket, football boots and marigold gloves.

Hope this helps. Mrs C. Dithermore.

Edited May 5, 2016 by bizzard

[Murflynn]

that'll be all right then.

I'll put my sky hooks back ion the loft.

[bizzard]

that'll be all right then.

I'll put my sky hooks back ion the loft.

No! professor bizzard has just croaked out ''bring em on'', they can be held in reserve, just in case.

Regards, Chrysanthemum.

[RLWP]

So with this idea as i have no trailer i use a central cross beam under the boat

 

Yes

 

Richard

[W+T]

 

Ooh that is clever. Here's the text, lest someone find this thread in the future when it's disappeared from the internet:

 

Ray,

 

Here is the method I use to weigh boats on a trailer without hauling the boat to a commercial scale, which requires two trips for boat and trailer.

 

It's simple, accurate and will cause bystanders to marvel at your engineering whiz.

 

The boat stays on the trailer the entire time. Put the scale under the tongue near the end. You can even put a block on the scale to lift the tongue so you can see the dial. Record the weight. Now, slide the boat aft on the trailer 12" to 18". You must measure exactly how many inches you moved it, and record that. With the scale in the same location under the tongue, record the new scale reading. Finally, measure the distance in inches between the trailer axle (wheel centerline) and the point on the tongue where it touches the scale. You have then four measurements:

 

W1 = first (heavier) scale reading in lbs, W2 = second scale reading in lbs, X = the distance you shifted the boat in inches, C = distance between trailer axle and scale point in inches.

 

The formula is Boat Weight = C (W1-W2)/X

 

A couple of notes. The result, like any measurement, is sensitive to the accuracy of the input data. In this case, the most critical is the distance you slide the boat. One inch error out of 12 inches will really make a difference in the result. Slide the boat as far as you can and still have a readable load on the scales. Notice, too, that by subtracting the two scale readings, any constant error in the scale is canceled out.

 

Note to techies: The formula was derived by taking the sum of the moments around the trailer axle for each case and (since the sum of moments about a stationary object is zero) set the two equations equal to each other and solve for the trailer weight. Things that you don't know, like the trailer's weight and the location of the boat's center of gravity cancel out, leaving just the variables that you can measure, and the boat weight.

 

I also use another version of this formula for weighing a boat while it is under construction so I don't get a bad surprise when it's finished. You can use two bridged scales and/or a trailer extension to increase the range of weights you can measure. I usually shoot for measurements of about 30-40lbs

for a low end and 250lbs or so for the high end.

 

In your case I would reverse the order of moving the boat and do it when you next go to the launch ramp so you can move the boat in a partial launch.

 

Tom Lathrop

 

 

I guess the tongue is the keel?

 

Mite have a goo this weekend, see how far i get with the prep work.

[RLWP]

I think the tongue is the part of the trailer where you connect it to a car

 

Richard

[Neil Smith]

If you know the maker you might find some info on Google on spec.

 

Neil

[W+T]

If you know the maker you might find some info on Google on spec.

 

Neil

 

 

for the life i have me i have looked for info on these boats and i cant find anything,, but for info earlier in this thread.