DSI centerboard profile

[Dick Andrews]

What governs the centerboard thickness? If I understood, correctly it would be the inside width of the centerboard trunk opening. Is this correct? Does anyone have the equation for plotting a 30% max cord profile?

[Phill]

Hi,

You are correct. The slot width will dictate CB Thickness up to a point.
If you go to the "Day Sailer Association" tab on the home page and then select "part 3" you can find the exact spec for the CB. There is no min/max thickness measurement for the Board. The oldest DS 1's have only a 7/8" slot, and some of the newest boats Have on that is nearly 2". There is a minimum 1 3/8" slot width that the newer boats can narrow their slots to. The older narrower slots can not be modified.
To your question. I would suggest making your CB as thick as your trunk will allow, up to about 1 1/2". The DS has a tendancy to stall the CB rather easily if the board is too narrow. A high point of 30% to 40% seems to work best. At the front of the racing fleets you will find narrow boards and thicker ones. If you sail in a high wind area thinner will work ok. But in light to medium stuff, the thicker the better.

Try doing a search of the NACA 0009 section. I found one site www.desktopaero.com/appliedaero/airfoil ... metry.html that has a graphic where you can put in the NACA foil name and it will draw the section. Use
' 0 0 09 ' and you will see the section at 9% thickness to cord. Use ' 0 0 10 ' for 10% or '0 0 12' for 12% and so on until you have the foil you want. I did not try to print anything from this site, but it could be a good starting point.

phill

[Dick Andrews]

Thanks for the help; I am trying to restore an older boat to race condition.
I had planned to sail it in Shreveport two years ago. The further I looked into the boat the more problems there were. I had two boxes of Harken blocks and new sails ready to use. I just ran out of time and had to give up ship so to speak.

As far as the centerboard, do you think I could any better than the board Cape Cod uses?

[Phill]

The Cape Cod is a good board, but a little too thin in my opinion. I sailed with one in a charter boat for the '98 NACR, and did ok. Once up to speed the boat was fine, but, I could definatlely tell that when tacking and coming out of mark roundings, the boat felt sick until I put the bow down and got my speed up before trying to point. The price is very good for the Cape Cod. Unless they have fixed their mold, you will have to do a little modification to the tip or trailing edge to get it to measure in.

phill