A remark about the texture of Olympic speed skaters' suits led me to the following paragraph in the Encyclopedia Brittanica:
"It is turbulence in the boundary layer that is responsible for the dramatic drop in the drag coefficient for both spheres and cylinders that occurs, as can be seen from Figure 16. Variation of drag coefficient with Reynolds number for spheres, cylinders, and disks when the Reynolds number is about 3 105. This drop enables golf balls to travel farther than they would do otherwise, and the dimples on the surface of golf balls are meant to encourage turbulence in the boundary layer. If swimsuits with rough surfaces help swimmers to move faster, as has been claimed, the same explanation may apply".
Is there anyone out there who knows enough about fluid mechanics to comment on the ideal texture of a boat bottom?
edwardr@optonline.net
Rough bottoms?
Moderator: Jim Walsh
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Ed Haley
Re: Rough bottoms?
I redid the bottom of both my O'Day DaySailer and my Sunfish last spring with a 2-part epoxy bottom paint called VC Performance Epoxy Bottom Finish I purchased from West Marine. It only comes in white and is ideal for trailered or shelf stored boats. The finish is very hard and can be smoothed by burnishing. When I saw the finish after I sprayed it on, I remembered the effect the rough surface has on golf balls and deliberately left it alone. The finish was matted but not as rough as a golf ball.
Did it make a difference while sailing? There is no way for me to quantify a difference but I can say there is a distinct difference in the way both boats sail! Spritely would be the word. The only thing I can say for sure is that the response time at the tiller is a lot faster and the spray over the bow is greater than before. Plus the enjoyability was cranked up a notch to 11 out of 10.
It was after I finished painting it that I read where the surface on my Daysailer is illegal. They only allow a smooth bottom. The rough surface gives an edge in racing, according to the association. But, hey, I'm in no hurry to take away any of the performance. Besides, it was also illegal to change to a loose-footed main and probably some of the other improvements I made. I'll let my son get caught (hahaha).
Ed Haley
Captain Mokita
CD330 #1
eghaley@twcny.rr.com
Did it make a difference while sailing? There is no way for me to quantify a difference but I can say there is a distinct difference in the way both boats sail! Spritely would be the word. The only thing I can say for sure is that the response time at the tiller is a lot faster and the spray over the bow is greater than before. Plus the enjoyability was cranked up a notch to 11 out of 10.
It was after I finished painting it that I read where the surface on my Daysailer is illegal. They only allow a smooth bottom. The rough surface gives an edge in racing, according to the association. But, hey, I'm in no hurry to take away any of the performance. Besides, it was also illegal to change to a loose-footed main and probably some of the other improvements I made. I'll let my son get caught (hahaha).
Ed Haley
Captain Mokita
CD330 #1
eghaley@twcny.rr.com
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Prof. Lam N. R. Flow,
I refer you to the noteworthy thread.....
......that occurred on this board, about a fortnight ago. While others were involved in a less scholarly pursuit......
Read the entire progression of the thread if you please. Then take the online "course" on Fluid Dynamics.
Since you are late to the "lecture" and missed that class, your term paper will be double the number of pages as the rest of the class.
Cap'n Stump has been excused from the assignment as he is just auditing the course....everybody knows Pirates don't earn their credits...they steal them.... ;-}
Just kidding...........but the material is interesting....
Good Luck,
John Nuttall
s/v Aimless
CD31 #28
Hmpt: Oriental, NC
Read the entire progression of the thread if you please. Then take the online "course" on Fluid Dynamics.
Since you are late to the "lecture" and missed that class, your term paper will be double the number of pages as the rest of the class.
Cap'n Stump has been excused from the assignment as he is just auditing the course....everybody knows Pirates don't earn their credits...they steal them.... ;-}
Just kidding...........but the material is interesting....
Good Luck,
John Nuttall
s/v Aimless
CD31 #28
Hmpt: Oriental, NC