How to weigh a boat?

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

Wow, i feel like the nun smacking everyone on the hand with a ruler. Ya'll got in line very nicely. For the record I think that witches sink. thanks for the feedback but its obviously still a challenge to weigh a boat isn't it?

No if they float they are a Witch that's WHY YOU BURN THEM.

Agree, NIST for commercial use is 0.1%, 5 lb per 5,000 lb. I bought a 5,000 lb load cell to weigh multihulls on a crane for ratings. The load cell was certified again last year at Acme Scale / San Leandro. Fortunately, a local IRC measurer gave me a hint on what to ask for.

Acme Scale explained it to me. The commercial certification is to 0.1% with offsets or corrections at 1,000 lb (+2lb) 2000 lb (+1lb) ... 5,000 lb -3 lb.

An automobile (or small truck) scale is ~OK for larger multihulls ( > 24 feet).
10,000 * 0.001 = 10 ~ok
300,000*0.001 = 300 not ok

The ISAF ERS gives some guidance on weighing boats. The F18 fellows weigh more boats than most, hats off. The texel/schrs outputs are sensitive to the sailing weight inputs. Weighing a boat consumes time many sailors prefer to spend on the water.

Ooo..that's right. Witches do float. People sink...er...well - I guess that's why there was a little uncertainty in that test.

I'm a little surprised there isn't an app for this.

Also small rocks, and churches float.

I think they also used to weigh boats with hanging scales.
You put some straps under the hulls and hoist it up with a mainsheet.

Yes, that was the second option I was referring to (hang that thing from a winch/mainsheet block, attached to a swingset, being sure to tare/zero out the straps).

Mike

In 20 years we have only weighed once and that was nationals. The set up was two scales and a set of beach trac wheels. Pull your boat up on the trailer mast up and pull it on to the

tare

beach wheels. Up the ramp on to a pair of scales. They had one guy hold the boat and make sure it was balance and he called when to weigh. They added the weights. No one complained and those that had weighed before had very very close to the same numbers. They then put the boat back on the trailer and off you went. All in all a non issue. JMHO, YMMV, Ricardo.

For those of you at OSYC working on the O 20 Class development today and all other N 20 owners hoping to form a fresh approach to your Class and DPN Racing...

A NEMA 4 Enclosure rated at 2000 +/- 2% from Mc Master, part number 1820T11 will cost $1,264. 91 plus shipping. The load cell could be stored at Schurr Sails (three blocks from the hoist at Pensacola Yacht Club).

Set a minimal fee for the weight declaration and sail plan declarations to be certified with a formal O 20 measurement certificate (an ISAF future will be sooner yours).

Listen to Steve Green and include the Texel system in your research.

These scales can be rented for use by other Classes for measurement as well for their major USA Championships to cover costs down the road.

Charge for the measurement certificate (minimal) and incorporate modest Class dues in order to sustain Class growth and networking (web site etc). I just spent eight days with the Thistle Class, and they are going into their fourth generation of family sailing. Study the Class by - laws and constitution of the Thistle Class. You just might achieve ISAF Formula status sooner than you think.