Thread: A weight on my mind

Multiply the waterline length, by waterline beam, then multiply by hull depth.

For example, lets say you have a 16' (4.87 m) waterline, times a 5.5' (1.67 m) waterline beam. Times this by a depth of say 9" (.2 m). This gives you 66 cu. ft. (1.78 cu. meters). The midship coefficient for a boat like this will be about .6 (an educated guess) so multiply by this, which offers 39.6 cu ft. (1.06 cu. m). This is the volume of the immersed portion of the boat, so multiply by the weight of water, which is 2,455 pounds (1113 kg) for the above hypothetical figures.

Thanks Par
I had to play around with the tape measure and calculator a bit and do some creative guessing about the waterline length and depth but I eventually kept coming up with a calculated weight of about 300kgs. Given that I had about 440kgs as a maximum I can confidently buy the trailer.
I won't tell the friends I have coming over to help turn the boat and put it on the trailer how much it weighs !
Cheers
bagman

The calculations I mentioned will get you close enough, but remember all the stuff you might stow on the boat. In other words, if you have to be wrong, be so on the heavy side. Seeing as you're looking at a half ton trailer, you'll probably be okay, especially given the usual safety margin built into the trailer's rating system. Simply put, I've carried 2 1/2 ton boats, on 1 ton trailers, with some spring rate left over.

Thanks again PAR
I only used the calculation to confirm my research of similar boat plans with known weights (for example Hartley Flareline 15 @ 226.8kg hull weight) and then added a generous allowance for my over-engineered repairs and boat contents. I have plenty of tolerance for any under estimation errors.
I have purchased the trailer and when the boat is loaded (without motor) and is being moved I will put it through a weigh station to satisfy my initial concern and current curiousity about the real weight.
I don't presently own braces but in my dear old Dad's words - it's good to be a belt and braces man.
Bagman

When you do get her weighed, let us know how close the weight estimates were. Also, I often weigh stock and items, before I install them, so I can get a good handle on what's being added to the boat. I also make a note of where I've install this weight (particularly important in the ends of the boat), so I can consider its trim moment (more easy math calculations), so she'll settle on her lines properly, come launch day and not be bow down or up (read embarrassing). There's absolutely nothing more enjoyable, then painting a boot stripe or waterline and having her sit dead bang on it, when you slide her in for the first time. This is especially true of remodels, renovations or highly modified setups. It makes you look like you knew what you where doing, even if you know better.