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Old 07-26-2012
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How do you measure the waterline

How do you measure the waterline on a sailboat? I want to calculate the approximate best speed of my sailboat.
Do I measure the curve of the boat or just a straight line from the bow to the stern on the waterline?
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Old 07-26-2012
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Re: How do you measure the waterline

Unless this is a custom one-off build you should be able to find the LWL easily online. What kind of boat specifically?
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Re: How do you measure the waterline

Hello Tim,
it is a Hunter 29' I am not sure of the model name
Domenic
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Re: How do you measure the waterline

Go to sailboatdata.com.
Theres a Hunter 290 listed with a 26.92 waterline.
One foot one way or the other is maybe one tenth of a knot so unless you are into serious racing, it really doesn't matter much.
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Old 07-26-2012
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Quote:
Originally Posted by boatingcruising:901643
How do you measure the waterline on a sailboat? I want to calculate the approximate best speed of my sailboat.
Do I measure the curve of the boat or just a straight line from the bow to the stern on the waterline?
Straight line through center at water line, overall inside toe rail bow to inside toe rail stern through center.
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Re: How do you measure the waterline

Tks everyone
My goal is to simply have some idea of what the optimum performance of the sailboat would be so I can have a goal to shoot for. I am not into racing, at least not yet!

so if the waterline is 26.92 than the sq root is about 5.18 ( i used the calculator) so the optimum speed should be about 6.95 say 7kn. I hope I can learn to get at least 5.5 - 6 out of the boat.
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Re: How do you measure the waterline

If you ever get to hull speed , please tell us the conditions
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Re: How do you measure the waterline

I am new to sailing but based on conversations with other sailors I get the feeling that reaching optimum hull speed is like getting the advertised gas millage in your car or obtaining the published speed of small aircraft at a set RPMs.

FORMUL: Optimum Hull Speed = Incredible Accomplishment
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Old 07-27-2012
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Re: How do you measure the waterline

So, if at 25' LWL, my hull speed calculates to 6.7 Kt. What is the best measure? I currently use a Garmin GPS to get my speed readings, but that is speed over land. How does that translate? I routinely exceed 6.7 with current and a decent wind, according to my Garmin.
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Old 07-27-2012
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Quote:
Originally Posted by boatingcruising:901784
I get the feeling that reaching optimum hull speed is like getting the advertised gas millage in your car or obtaining the published speed of small aircraft at a set RPMs.
Apples to oranges - hull speed is an approximation of how a displacement hull will move. In flat water it shouldn't be hard to reach (I can even get close in my boat, which has horrific hydrodynamics - motor in well below w/l, ballast bolted to side of keel...

What builders/designers advertise is not hull speed, but polars - which ought to be based on their real world measurements (tho designers may post calculated polars on a design before it's built)

Ability to maintain hull soeed in varying conditions and over a sustained period of time is much trickier than hitting it for a few minutes 135 off the wind on a nice day
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