SailNet Community - View Single Post - Interesting Sailboats
View Single Post
  #4212  
Old 04-17-2013
Anders B Anders B is offline
Junior Member
 
Join Date: Apr 2013
Location: South Sweden
Posts: 25
Thanks: 1
Thanked 0 Times in 0 Posts
Rep Power: 0
Anders B is on a distinguished road
Unhappy Re: Advanced keels

Quote:
Originally Posted by PCP View Post

I saw the keels on that study you mention and then went to the conclusions to see if there were some surprises, but no. What he found confirms what is common knowledge regarding keel performance and shape.
My conclusions from the three Chalmers investigations are:
The first conclusion is that maximum thickness of the bulb must be placed well back from maximum thickness of the fin. Otherwise an extended lowpressure area is generated on the suction side (with contributions from both the bulb and the fin) that causes flow separation. Loss of lift is obtained and a really bad keel from the hydrodynamic point of view is obtained. Two T-keel designs were investigated, one with coinciding maximum thicknesses of the bulb and fin and one with maximum bulb thickness behind the rear end of the fin. The results clearly showed that the second one was best.

The second conclusion is the a flat bottom with sharp edges (chines) of the bulb is not a competitive design. A optimization was peformed where the shape of the bulb was allowed to vary from flat bottom (with sharp edges) to rounded. Rounded showed higher performance.

The Chalmers investigations were performed about 2 years ago, the results are public and should be known by serious designers (especially as Lars Larsson was the supervisor). Fixed keel design for recent custom yachts do not show an impact of this and my personal conclusion is that keel design is an ad hoc thing.
Reply With Quote Share with Facebook