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  #1  
Old 08-20-2003, 05:41 PM
max max is offline
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16 M performance sailboat

Hi there,

I will do some towing tank test with a 16m sailing boat for my exames at the univerisity in Hamburg.
The main thing is to compare 3 different keel designs, as I posted some weeks ago in the boat forum ( Tandem/"racing"/cruising )
Now I developed a first lines plan for the boat and I must say Im not very experianced with it. Its my first one. So I have several questions about it and would be very pleased if someone could give me a hint.

L: 16.00m
Displ: 15.00 t
B: 4.20 m

1. I tried to keep the curve at the CL (under water) going to the transom as flat as possible. So at the end of the boat I have only 100 mm space between the transom and water surface. Would this be enough, where are the limits at this point.

2. I tried to save volume in the front of the boat and to make a sharp bow, to get the boat easier through the waves etc.
If I heel the boat for example 30 to one side (free trim) it moves down with its bow with an angle of 1.8
Is this a normal behaviour or will I get problems steering it in upwind situations, or could I even get it more skinny at the front area ?

Im also pleased if you give me somefeedback about other aspekts of the linesplan that maybe will not work.

PS: Rudder and keel are very preliminary !!!

Thanxx

Max
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  #2  
Old 08-21-2003, 11:22 AM
dionysis dionysis is offline
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just a couple of general comments...

Hi max,

This design is really good for a first effort. A couple of points:

The reverse curve at the stem does not look right: you need bouyancy forward to stop the boat from burying into waves. There may be a problem here with anchoring as well. The rope will chaff on the hull around the water line. Better to draw it plumb.

Keel foil depth look tiny, you need area to resist leeway, and depth to resist healing moment.

The center of bouyancy seems too far back. The general requirement is about 5% aft of midcenter. This far aft gives you no lever arm to counter downtrim at the nose.

I'm not sure but 1.8 degrees downtrim at the stem, is not a good sign. Your sail thrust will dig the stem in even deeper.

Displacement is about right, and the plan view looks really good. Transom height is Ok.

You will need to run some numbers to compare your design with similar and successfull boats:

displacement to length ratio
sail area to wetted surface ratio
etc.


Hope this helps, cheers dionysis.
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  #3  
Old 08-21-2003, 11:27 AM
dionysis dionysis is offline
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think about prismatic coefficient too.
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Old 08-21-2003, 12:42 PM
max max is offline
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Thanks a lot for your feedback dionysis !!!

I think you are right with the curve at the stem.

The keel is not really shown at the drawing ( sorry for that) .
The keel wich can be hardly seen with the bulb at the end, contains a metal centerboard, wich can be moved down to a total depth of 3.5 m.
I think that should be enough resist leeway. The area of the keel will be then 4% of the sail area. I want to try to reduce it as far as possible during the tank tests.

I will also get the center of bouyancy to 5% of WL backwards from midship, as you suggested.
Maybe then the bow is also not to going down that much during heeling. I will see.

The idea of comparing the boat to others is good, I did so and was able to find sail areas, L, LWL,, Displ. and so on. But for example wetted surfaces and prismatic coefficients are hard to find. In my case it is:

waterplane = 0,677
prismatic = 0,547
Displ/L = 116,55
W.S. area = 42,24 m^2

If you know any possibility to get these or even more datas from similar boats I would be glad to see them !

Thanx for all,

Max

PS.: More comments are always welcome.
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  #5  
Old 08-21-2003, 02:48 PM
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gonzo gonzo is offline
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The hull looks a bit like the old IOR's without the knuckles in the aft sections. The narrow vee sections forward will make the boat go bow down when heeled. Also, it will make the boat point down, therefore counteracting the weather helm. This effect depends also on the position of the mast and keel. The further forward they are the more accentuated the effect will be.
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  #6  
Old 08-21-2003, 10:52 PM
dionysis dionysis is offline
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comparisons

Do a seach with google for "yacht designers", and have a look through each of their sites for comparable designs. It is surprising how much information you can get from them.

good luck.
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