J/30 Class Association

Weight and waterline

Posted By: nathankt79

Weight and waterline - 03/21/19 12:30 PM

Does anyone have a handle on how much weight (on or off) will move the waterline on a J/30 a given distance...For instance, something like 300lbs=1"?


Posted By: Russ Atkinson

Re: Weight and waterline - 03/23/19 10:17 PM

How good is your math? I don't think there is a simple straight line ratio for pounds to inches since the hull gets wider and longer as it sits deeper in the water. That said lets do some simple math. 1 cubic foot of water weighs 62.43 pound. At the water line the boat is about 25' long and 8 ft wide. Figure the area of an eclipse that is 25' X 8' wide. Multiply it by 1/12' (1"). You will then have a rough idea of cubic feet of 1" of water at the water line
If your boat is out of the water - measure how much longer and wider it is 1" higher than the water line, 2" higher than the water line,etc.
Multiply each of those calc by the wight of 1cubic ft of water. It won't be exact but it will get you in the ball park.
Posted By: nathankt79

Re: Weight and waterline - 03/25/19 03:16 PM

Thanks for the input. I can probably riddle that out. I was really hoping someone already figured out a chart or something, lol. I'm trying to figure out how much the weight savings of switching to lithium batteries would have on freeboard. I also read something that said if one can reduce weight forward and aft of the center 1/3 of the hull, she'll cut through waves a bit better without "slapping".
Posted By: Johnny Blizzard

Re: Weight and waterline - 07/22/19 04:36 PM

nathankt79, Did you get your weight-to-freeboard question figured out?
Posted By: nathankt79

Re: Weight and waterline - 08/17/19 06:27 PM

No...I kinda gave up on that one.
© 2020 J/30 Class Association