Thread: Weighing boats

Originally Posted by woodeneye

In the next week I want to weigh my GIS and was wondering about what methods to use. I think digital bathroom scales are accurate enough for these purposes, but some might disagree. For instance, even 1 kilogram either way is not really an issue.

Probably the easiest method for weighing a Goat is to simply turn the hull onto its side and balance it on a digital bathroom scale while it rests on the gunwale. Sounds simple enough.

However, I’m thinking that weighing each end and adding the two weights together would also work? For instance, weigh yourself first, then pick up each end of the boat subtracting your weight, and adding them together. Seems logical to me, but does it give a fair reflection? Also, does it matter that you lift each end by the same amount?

I’m interested to see how much weight is added by the coatings, although I have already coated the inside of the sides and the tanks, but largely it remains uncoated at present.

I'm interested in any ideas that forum members have.

I would find a friend with a strong back and a second bathroom scale. Then one person on each end of the boat could pick up an end and stand on a scale. Record the amounts. Then without the boat, weigh yourselves again, record the number and subtract the second number from the first. That should be as accurate as you can get using this method.

Rick.

Originally Posted by pdr311

I would find a friend with a strong back and a second bathroom scale. Then one person on each end of the boat could pick up an end and stand on a scale. Record the amounts. Then without the boat, weigh yourselves again, record the number and subtract the second number from the first. That should be as accurate as you can get using this method.

Rick.

Hi Rick, yours seems to be the identical method just made more complicated by needing another person, another scale, more maths and differences between 2 scales. What advantages do you see here?

Originally Posted by woodeneye

Hi Rick, yours seems to be the identical method just made more complicated by needing another person, another scale, more maths and differences between 2 scales. What advantages do you see here?

The advantage is accuracy. I have run into similar issues when weighing travel trailers, or caravans, or whatever you call a camping trailer in Oz. When weighing the ends independantly, there are discrepencies that creep in that have to do with the fulcrum point, leverages etc. I do not exactly know the math, but when measuring trailers that weigh 2000+kgs, there can be differences of up to 20%! That is significant when the local establishment pulls you over for being overweight for the tow car.
I see the same issues creep in when weighing your boat. I know you don't mind being a kilogram or two out, but 20% would really give you an inaccurate reading.
Rick.

You can weigh it with one set of scales but you need to be sure the boat doesn't change orientation when you move the scales from one end to the other i.e. sit the boat on pieces of wood the same height as the scales and then substitute the scales for the wood to get an accurate measurement.

Using 2 sets of scales might seem more complicated but is easier as you just add them up.

Originally Posted by murray44

You can weigh it with one set of scales but you need to be sure the boat doesn't change orientation when you move the scales from one end to the other i.e. sit the boat on pieces of wood the same height as the scales and then substitute the scales for the wood to get an accurate measurement.

Using 2 sets of scales might seem more complicated but is easier as you just add them up.

If the weight at one end of the boat is considerably more or less than the other end, that method will still be inaccurate. It will be close, but maybe not close enough. If the ends of the boat are similar weight, you will be pretty much exact.

Rick.

OK, so my first method of standing it on a scale while balanced on the gunwale might be the way to go then.

Thanks guys.

Hi Everyone,

Weighing your boat on a single set of digital bathroom scales is probably the simplest, most accurate method.

Digital scales should not be subject to the accuracy limitations of lower weights that analogue scales are known for ( analogue bathroom scales are most accurate in the upper third of their weight measuring capacity, with increasing inaccuracy as the weight gets lower than this ! ), but I have not seen any proof of this.

If its easy enough and not to much trouble to put on the roof racks, take a trip to your local tip (without the boat) have your car weighed, then take a second trip with the boat on top. subtract the first from the second. they do that here with your trailer to work out how much to charge you for dumping stuff at the tip. prob a bit too much work though...

Originally Posted by MiLKey

If its easy enough and not to much trouble to put on the roof racks, take a trip to your local tip (without the boat) have your car weighed, then take a second trip with the boat on top. subtract the first from the second. they do that here with your trailer to work out how much to charge you for dumping stuff at the tip. prob a bit too much work though...

Mmm, and it costs $30 to do it at my local tip

ah really!? that sucks! any truck weighing stations nearby?

if not the only other thing i can think of are them suspended scales they use to weigh massive fish. could hang one from your ceiling and lash the boat to it?

A block and tackle from the ceiling, with the boat in a sling, using a fish scale, multiply the weight by falls for the actual weight. A 300 pound (136.3 k) boat with 4:1 tackle will produce a 75 pound (34 k) pull on the fish scale. You'll pick up some frictional lose with a big tackle and lousy pulleys, so use good tackle or subtract 1 or 2 percent from the total.

Originally Posted by MiLKey

If its easy enough and not to much trouble to put on the roof racks, take a trip to your local tip (without the boat) have your car weighed, then take a second trip with the boat on top. subtract the first from the second. they do that here with your trailer to work out how much to charge you for dumping stuff at the tip. prob a bit too much work though...

Hi MilKey,

The other obvious drawback with this method is the difference in the weight of the fuel in the car after the second trip !!!.

Originally Posted by dhgomm

Hi MilKey,

The other obvious drawback with this method is the difference in the weight of the fuel in the car after the second trip !!!.

Originally Posted by woodeneye

Mmm, and it costs $30 to do it at my local tip

Originally Posted by MiLKey

If its easy enough and not to much trouble to put on the roof racks, take a trip to your local tip (without the boat) have your car weighed, then take a second trip with the boat on top. subtract the first from the second. they do that here with your trailer to work out how much to charge you for dumping stuff at the tip. prob a bit too much work though...

You blokes are over thinking the situation.

Pick a time when the weighbridge of choice is empty and the operators are bored enough to enjoy something different.
Drive on.
Explain the situation.
Take the first reading.
Lift the boat off the roof.
Take the second reading.
Get off the ramp quick smart, THEN restrap the boat down.
Have a yarn with the bloke in the booth while you add up the numbers.

Any operator too grouchy to let you do this for free (provided nothing's happening at the time), won't give you a reading in the first place. The secret is in the timing, the presentation, your attitude and the fact that humans are curious critters who enjoy the unusual

Richard

Yes, we're talking about a circa 50-55kg GIS here, not a big trailer sailor. All the methods mentioned here so far will work, so they can go into the bank.

I weighed my GIS late last night balanced on the gunwale on a single bathroom scale. I got roughly the same reading (47.6kg) as I got lifting each end while standing on the scale, so that's good enough for me! By the way, it's not complete, just an interim weight as there are a few things to be done yet, including coating. I'm very interested in how much weight the coatings will add, hence wanting to get an interim weight recorded.