# Could someone explain the kindergarten method of calculating CLP for me?

Discussion in 'Sailboats' started by choppy, Oct 28, 2011.

1. Joined: Oct 2011
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### choppyJunior Member

I am sorry but I can't picture in my mind what the original poster is saying below. Can someone explain this differently so that I can understand exactly what to do?

Thanks in advance for any help,
choppy

2. Joined: Jan 2006
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Location: Lakeland Fl USA

Look at the profile view of the boat. You are interested only in the underwater part of the profile. Make a cardboard cutout of the underwater shape. Now balance it on a triangular or cylindrical object, like a round pencil or dowel rod. Make a mark at the balance point. That is usually all you are interested in. Balancing with the pivot in the diagonal directions is not necessary. If you do all three of the balance exercises, the intersection of the three lines establish the center of gravity of the whole bit of cardboard. That method will find the vertical center of area but we are not usually interested in the top to bottom center of the the test piece.

All this is well and good but it is strictly a ball park estimate of the exact center of lateral resistance. Differences in hull forms will modify the actual location of the effective CLR. Round chines, square chines, bevel chines, vee bottoms all play into the variables for finding the real CLR. The boat may pitch roll or dive and when it does the center that you are looking for will move. We have to be satisfied that we'll only sail in flat water. You have to start somewhere.

After you are satisfied that you have found the center of lateral resistance with the carboard cutout, you can proceed to the next set of decisions. You wanted to know the position of the CLR so that you could make a reasonable assesment of where to locate the mast. I presume the purpose here is to figure out where to place the mast if it is to be a sailboat. Now you need to know the location of the center of effort of the sails. This is a case where the CE moves fore or aft depending on what course you are sailing. After that you can make a wild guess about how much lead to give the sailplan with respect to the CLR.

Last edited: Oct 28, 2011
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### choppyJunior Member

Thank you for taking the time to reply. I think I have it now. Also, thanks for providing the extra information. This will be very helpful.

Thanks,
choppy

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### PARYacht Designer/Builder

It's much easier to fold your cardboard cutout (stiff paper works well too). Fold just below the LWL and parallel to it. Place this on a pin and adjust the location until it balances level, which you can eyeball against a shelf or window sill. This is because, just as Messabout has mentioned, we only want to look at the longitudinal center of the "plane".

If the cut out is pre-divided into segments, then you can accurately determine where the CLP is (CLR is much more difficult to define). Divide the LWL on the cut out into 10 equal length segments (before printing of course) with the area between 40% and 60% of it's length, also subdivided into 10th's. This will permit you to place the pin within a 1/2 a percent or so in accuracy. This is close enough for preliminary balance work.

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### choppyJunior Member

Thank you for taking the time to help. This will give me a good starting point for my design.

Kind regards,
choppy

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