put it on a scale right? I've heard of a few methods (bathroom scales, truck scales). What is a reliable, reproducible method for getting an accurate weight?
thanks

cc

Balance the boat on a pair of bathroom scales
Take the mast down or wait for a windless day

I have also driven onto a truck scale (at a dump that my friend had a garage at) and then removed the cat from the trailer. i found out my cat was fat... very very very

The most accurate way is to get someone with class scales i.e. Dave Ingram (sorry Dave) and ply him with rum and cash and have him weigh it for you at his convenience, where he chooses.
There are a couple of folks on here with race car scales (same thing) that may do it also.

What level of precision are you looking for? It all comes down to the the accuracy and precision of the scales (load cells) you're using.

A high quality scale might have an accuracy of +/- .1%. If it's intended for a 5000lb race car, that would be +/- 5lb. Maybe that's good enough for you, maybe it isn't. I suspect a truck scale would not provide a sufficiently accurate reading for a 400lb catamaran. Same goes with using a couple bathroom scales. They may get you in the ballpark, but if you're looking to get within say +/- a pound, they're probably not going to cut it.

McMaster Carr has 1000lb capacity dial scales good to +/- 5lb for $1k, or a digital version good to +/- 1lb for $1800 just to put things in perspective.

Sailors love to talk about weighing boats, but without an understanding of the accuracy of the measuring equipment, the data is basically useless.

sm

They are no longer in my care (hurray!)

pulley, rope and a few weights? How about a barrel of water (known volume)?

Otherwise know as the Fred Flintstone method.

That one made me laugh... just in time too!

"What else floats in water?"

very small rocks no wait a duck?

Witches? No...wait, they sink.

turds?

testes?

"They all float down here." Pennywise

Witches!!!!

yep, that's what i thought. I expected a serious discussion of how to accurately weigh a catamaran. We have a responsibility to have a proper measurement to maintain consistency in our sport and you make jokes.
Ha! This is funny. This just adds so much to the argument that no matter what you set a weight for a class it doesn't matter. the ability to measure the weight is too variable. The weight is dependent on the manufacturer and their reputation to weigh and report it accurately.
note: i only responded with the hurt feelings routine to get your attention. I just want to know how much my boat weighs. I have no plan to weigh boats before races. in the Open 20 class i want to know how big your sails are and how long your boat is. lets race!!!!!!

At our YC we have two hoists .... the best would be to borrow/aquire/purchase a "loadcell" of a suitable range & accuracy (Mr SRM is quite correct in his analysis/comments) ...hang it on the hoist ... make up a bridle/harness ... and pick the boat up. (This is basically the set-up they had at the 2007 Hobie TheMightyHobie18/17/Youth/Womans North Americans in Geneva NY ... worked nice!!!)

Harry
H18Mag/P19MX

The F18 scales with four measurement pads wired back to a main processing unit is very accurate. If I recall, it's well within 1/10 of a lb.

To echo the others above, I've seen two basic types:

Four load cells, placed under the fore and aft of each hull, connected back to a central display.

One load cell, hanging from a winch on a frame (an old steel swing set works well).

As mentioned, weigh the boat with the mast down. Be sure to include all boat equipment (sails, blocks, tiller), empty the hulls of water or other gear, and remove all removable gear (tramp bags, etc.).

Putting this weighing gear together is somewhat of a PITA, so I would not suggest bothering unless you have reason to suspect the weight is WAY off, and you intend to race at a major regatta where the boat will be weighed, and you need to make corrections in advance. Otherwise, just sail it and get it weighed at a major regatta when the time comes.

Hope this helps.

Mike