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boatingcruising 07-26-2012 03:13 PM

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?

Tim R. 07-26-2012 03:21 PM

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?

boatingcruising 07-26-2012 03:31 PM

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

chuck53 07-26-2012 03:42 PM

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.

sea_hunter 07-26-2012 05:00 PM

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.

boatingcruising 07-26-2012 06:03 PM

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.

WDS123 07-26-2012 06:51 PM

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

boatingcruising 07-26-2012 08:27 PM

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

rbrasi 07-27-2012 07:25 AM

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.

zedboy 07-27-2012 12:46 PM

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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