Properly locating the waterline

Figment · Post by **Figment** » Tue Jul 19, 2005 7:17 pm

My boaty magazine addiction rears its ugly head once more. I just read this, and had to pass it along:

A proper (painted) waterline should be raised (above the actual waterline) 1" for every 10' of the boat's length... this makes the topsides look narrower, which makes the boat appear sleeker.

I'm not even sure that "sleeker" is a word, but once I got beyond that, the 1"/10' rule stuck in my craw a bit. I read on.

...the line should curve upward. This compensates for the waterline receding inward toward the stem... To find the waterline's high point at the stem, divide the waterline length in inches by 160..... In addition a proper waterline is always crowned with a boot topping.... As with the waterline, the boot topping should curve upward. To find the boot topping's high point on the stem, divide the waterline length in inches by 220...

I'd never seen these principles applied to actual mathematical ratios before. Interesting. In application, a Triton's painted waterline should be 2.8 inches above the actual waterline, the upward swoop at the ends should add about an inch and a half to that height, and the boot top should swoop about an inch.

Anyone ever seen or used such ratios before?

Tim, doesn't it make you feel silly for all of that taping and squinting you recently endured on the Daysailor?? You could've just ticked-off a few measurements and been done!!! (joking. easy, killer)

....

Post by **Tim** » Tue Jul 19, 2005 9:07 pm

The 1" for every 10 or so feet of length is a fairly reasonable approximation, actually. I think 2" above the actual waterline is about right on a Triton; 2.8 or 3" might be getting a bit high, but not too bad.

As to the other figures and calculations...I don't think that one can generalize so cleanly about such a thing, given the variety of boat shapes out there. Personally, I'm not a big fan of boottops that swoop too much; that said, some sheer is required at the bow for the right look. I don't believe that it's possible to reduce the right look to a mathematical formula. Aesthetics are far too subjective for that.

In the end, what looks right is right, no matter how you get there.

Figment · Post by **Figment** » Wed Jul 20, 2005 2:13 pm

What looks right is right... you said it, brother.
Case in point: my bootstripe ain't right. too heavy by about an inch.

I just love finding (and occasionally testing) these cute little mathematical guidelines. Can't get enough of them.

1hp per 1000lbs displacement
combined engine bed thickness (in inches) should be half of beam (in feet)
Ideal beam at WL < 1/3 LWL
Cruising boat carrying capacity should be min. 500lbs per crew member (not sure about that one)
Oar length = beam x1.5 plus 7 inches.
and on and on and on..... such a nerd.

Post by **dasein668** » Wed Jul 20, 2005 3:05 pm

Tim wrote:The 1" for every 10 or so feet of length is a fairly reasonable approximation, actually. I think 2" above the actual waterline is about right on a Triton; 2.8 or 3" might be getting a bit high, but not too bad.

2 inches on a Triton is about 1 inch per 10 feet of LWL, FWIW...

Post by **Tim** » Wed Jul 20, 2005 3:32 pm

Well, it said...

...1" for every 10' of the boat's length...

...which I read as the overall length rather than the waterline (since it didn't specify), so I was thinking 2.8", which seems too much. Probably using the DWL length as the "length" is a better approximation, as you so aptly pointed out.

Post by **dasein668** » Wed Jul 20, 2005 9:55 pm

Yeah, I just thought of that (L/DWL vs LOA) today riding back in from the boat... not sure why I was even thinking about it....

Post by **Tim** » Thu Jul 21, 2005 6:18 am

dasein668 wrote:Yeah, I just thought of that (L/DWL vs LOA) today riding back in from the boat...not sure why I was even thinking about it....

I'm sorry to be the bearer of bad news, but I'm afraid that such ridiculous random thoughts are one of the signs of a terrible case of terminal boat obsession.

I offer my sincere condolences! All you can do now is make yourself as comfortable as possible while you suffer the inevitable consequences of this rare, but vigorous, disease.

Figment · Post by **Figment** » Thu Jul 21, 2005 7:51 am

oh yeah. Using waterline length as the basis for the math does make more sense. hmph.

That's what I get for reading a powerboat magazine.

Allen · Post by **Allen** » Tue Jul 26, 2005 10:56 pm

With regard to a Triton (or any boat actually), wouldn't it really depend on what the Triton was being used for? For example a stripped racing boat, which would always sit about the same, would not need the same waterline as a cruising Triton which was going to be carrying a substantial load that would vary over time.