# heeling hull waterlines

Discussion in 'Sailboats' started by kvsgkvng, Apr 6, 2012.

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### kvsgkvngSenior Member

In my learning of the boat building theory, I am at the point when I start to think about heeling angles. It is very interesting and as an exercise, I am posting a hull, which has various heeling angle waterlines. Could anyone please comment on these waterlines as the derivative of the hull shape? Am I guessing right that there are two mode behaviors: one is planning and the other is similar to a V-shaped hull slicing through the water?
Thank you for any help, respectfully -- kvsgkvng

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Any boat that is designed, must begin with an SOR (Statement of Requirements). This defines what the boat must achieve, in other words, what you're aiming at. IF the SOR states you must be no more than 20m long and do 40knots....then the design reflects this. Thus you wouldn't make the boat out of steel and be just 10m long and 5m wide, as an example.

Therefore you must first start with an SOR and then the design must satisfy this requirement. So what does all this mean for you? If you are focusing upon one aspect, underwater lines/shape, you're missing the bigger picture. In designing a boat, it is multi disciplined. There are many design features that are all wanting your attention and to say ME, ME, ME...so your job, as the designer, is to balance all the requirements to ensure you satisfy the SOR.

Since if you focus solely upon underwater shape, what must be compromised to achieve your "optimum"? These compromises generally render the final design unable to satisfy the SOR if you focus upon just one to the detriment of the others.

So, understanding about the influences of underwater shape/geometry is important, but it is NOT your sole driver when designing a boat. You must balance them all, no matter how conflicting they are with each other.

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### kvsgkvngSenior Member

I keep on forgetting to state SOR !!!

Sorry, I keep on forgetting about SOR. I already know what it means. This boat what I showed is a basic dinghy, about 12.5' long and 5' wide. The purpose of this boat is to just cruise at normal sailing speed, I would speculate just about 3~4 kt Occasionally this boat would be powered under oars. This hull would be traversing rivers, lakes, canals, shallow coastal calm water. Could you please advise me with these SOR parameters?
Thank you, kvsgkvng.

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Well, first of all, you need to draw out the boats layout intoo a GA, and then perform a weight and centres check. Simple as it sounds, but many fail to do so. Since once you work out the weight of the structure and outfit items, then you'll know will the boat float and float upright and float on the draft you expect.

Until you do that, the rest is a waste of time.

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### gonzoSenior Member

A common failure is to draw the heeled waterlines as static. When the boat heels it is normally moving which creates a bow and stern wave and a hollow somewhere in between.

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### kvsgkvngSenior Member

Do you mean that usual rules of sailboat propulsion should also apply for a heeled footprint? If so, in this case the heeled waterlines may be more important than the level ones, as the boat moves fastest with some heeling under wind (in most cases). Is this what you meant?

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