Scale to weigh boat

[R Schofield USA 463]

Anyone want to recommend a scale to weigh a boat, keel or rig with? I am looking to get a scale in the next month or so to weight my boat. Ryan

[Lester]

In my experience, the real issue isn't the scales -- almost anything with a 1 gram resolution will work, particularly for keeping track of other IOM weight budget items such as batteries, and 2 grams is OK, though 5 grams resolution is only good for the whole boat's 4 kg.

No, the real issue accuracy and repeatability. The real issue is obtaining and using a set of calibrated and certified check weights, which will probably cost way more than the scales did. Ideally you'll need a set of three, say, 200 g, 1000 g, and 4000 g, certified to within 0.25 g... Even though your scales may resolve to 1 g, they'll almost certainly be inaccurate out the box and may well report a 4000 g certified weight as 4017 or 3992 or even 4056 (I've seen that!) or similar... Unless you pay some (very!) serious money for scales which allow you to adjust their calibration, you'll always need to pop on the calibrated weight just before a weighing session to figure out what % to adjust your readings... Good luck!

[Hiljoball]

Harbor freight sell a nice digital scale that weighs up to 5kg, suitable for IOMs. It is accurate and repeatable. Sells for under $20. It is easy to calibrate to increase accuracy.

I could not find it in the web site today. It is similar to this one, which looks like its big brother.

http://www.harborfreight.com/70-lb-32-k ... 95069.html

John

[Lester]

I think this is the item John referenced:

http://www.harborfreight.com/digital-scale-95364.html

To calibrate it, the manual says to use two 2500 g weights. A very nice touch for a $20 scale. Of course, a 2500 g weight certified to M1 standard would probably cost around $40. (I couldn't find a supplier who advertised M2 or M3 which, curiously, are significantly less accurate.)

In all other respects, there is no information nor claim as to accuracy, repeatability, precision, readability, drift, (hysteresis if you want to get technical), etc.

These pages might help with these technical terms:

http://balances.net/applications/glossary.html
http://www.labnetwork.org/en/metrology- ... -metrology

If you are really enthusiastic, you need the GUM (Guide to Uncertainty in Measurement), downloadable from the BIPM website:

http://www.bipm.org/en/publications/guides/gum.html