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Go Back   SailNet Community > On Board > Boat Review and Purchase Forum > Design Weight vs. Actual Weight..
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Thread: Design Weight vs. Actual Weight.. Reply to Thread
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Topic Review (Newest First)
11-08-2007 01:19 AM
Valiente I was told that my 41 foot steel cutter weighed about 26,000 lbs. or 13 short tons, "half-load" (full diesel tanks, empty water tanks). I thought this was a little light, as a friend with a similarly sized steel ketch weighs 36,000 lbs.

The "official weight" on the mandatory federal registry plaque is "18.18 tonnes", which is just shy of 40,000 lbs. Yikes! But I believe this is an arcane number relating to displacement, not actual mass. Look up "Thames measurement"...it's crazy and arbitrary.

http://en.wikipedia.org/wiki/Thames_measurement

So are more general measures of "tonnage":
http://en.wikipedia.org/wiki/Tonnage

So I had a word with the crane operator, saying that while I estimated the weight as 30,000 lbs., would he be so kind as to give me the "crane estimate"?

His figure was 29,500 lbs. This may not be super-accurate, but it conforms closely with what I expect is the "real weight". That is what a truck driver will care about, and only accurate sling or crane scales can give that figure, unless you want to drive into a tight lock and, using Archimedes' principle, figure out how much water of a given volume you are displacing.

Strangely, there are fibreglass boats in my yard considerably heavier than mine. For a steel hulk, it's just a middleweight.
11-07-2007 11:44 PM
Sailormann
Quote:
Sorry to disagree
It's okay - it doesn't make you a bad person.

The reason I had mentioned it was that there was a thread on the CS owner's group a little while ago about designed vs actual weight. People were noting that their boats all seemed a bit heavier than their designed weight. So, when we hauled for the winter we asked for the weight of the boat on the lift. We found that we're about 1600 pounds over what the boat's spec weight is, according to the Travelift at our marina. We have a fairly light disp. 30 footer.

Granted, this is a big difference from the OP's weight difference of 10K, but it may be a contributing factor.
11-07-2007 11:32 PM
Insails If it were CD's boat ,the difference would be in grill weight?)
11-07-2007 11:28 PM
Giulietta
Quote:
Originally Posted by Sailormann View Post
Very few builders were careful or consistent enough to turn out boats with the perfect mix of glass to resin, keels that weigh exactly what they're supposed to or even build two units of the same boat in exactly the same manner.
Sorry to interrupt, but I never heard of this...I agree a difference of one drum of resin (that's 200 liters), may happen, but I believe that even the most careless builder controls resin wastage and usage...

Also if that was the case, they woud have problems fiiting internals, and would notice it in the water tank tests...

I am not saying its not possible, but never heard of this, not to the point of having such a great weight differnce...200Kg I believe, not more...

As to the different sailing characteristics...well from the guy driving to sail trim to rig tension...you name it...

Sorry to disagree
11-07-2007 11:21 PM
paul77 Sailormann - Yeah I was wondering that, a little thicker layup could explain the few thousand extra pounds. Am tempted to strip all the gear before we splash her so I can see how skinny she could be but that would be just too much work.
11-07-2007 10:54 PM
Sailormann I believe you'll find most of the cruising boats out there ended up built well over their designed weight. The weight is usually calculated by the designer/architect on the drawing board. Very few builders were careful or consistent enough to turn out boats with the perfect mix of glass to resin, keels that weigh exactly what they're supposed to or even build two units of the same boat in exactly the same manner.

The serious racers are usually pretty close, but a 20 year old production cruiser is anyone's bet. This is why you'll find that there can be two boats from the same builder, of the same design, that have differing performance levels or characteristics.
11-07-2007 07:55 PM
paul77 I left the bilge pump on for the trip, as there are leaks in hatches so figured I wanted a dry bilge.. So the bilge is dry.. Maybe I missed a water tank. I'll have to check when I go back tonight.

100 gal diesel tank, so that's 800lbs at most.

The hull sounded fine, no blisters, though we didn't do a moisture reading as it was raining at the survey. the boat is only 10 years old, and was in CT for anumber of years where it was put on the hard in winters.. Amazing though.

This number really makes my SA/D look pretty bad now I Haven't even got the BBQ grille mounted yet!
11-07-2007 07:39 PM
Giulietta
Quote:
Originally Posted by max-on View Post

I cannot resist, Giu, during its life, do American designed boats gain more weight than European designed boats??
Hey you edited it, so I missed it..

Actually since we don't haul our boats in winter (except the Nordics), our boats spend more time in the water, absorbing more.

Also, judging by the time some members are here, their boats might be pretty dry...
11-07-2007 07:21 PM
GeorgeB It wouldn’t be the first time a builder used a stripped down boat to determine their weight measurement. No builder wants their vessel to appear as a “lead sled” in the specs no matter how true it really is. My last two boats both came in at a couple thousand pounds over their design weight. A fellow sailor who owned the same 28’ knew the true weight of the boat and was able to successfully appeal his PHRF rating (his was the first of it’s class to get rated here in Nor Cal). I believe that the C30’s also have a more accurate weight in their PHRF measurement which gives them their (sandbagged) rating of 180 here in San Francisco.
11-07-2007 07:19 PM
sailingdog The displacement often neglects the equipment and gear necessary for cruising. As donradclife points out, there's a lot on a fully fitted out cruising boat that will boost the numbers quite a bit.
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