{Stus-List} Fw: Keel tuning?

Ross MacLennan rmaclennan at accesscomm.ca
Mon Mar 5 10:24:43 EST 2007

Buried in here is some of Greg's note's about the keel but it relates to the bottom as well >
IMHO Cary went way beyond the necessary with 12 coats of Interprotect etc. from what I know putting on more than one coat of some of the bottom paints doesn't do that much either .
Sanding to a very fine level ( 600) and then Greg "burnishes it yet may be where you might need to spend some time.

The question that always comes to my mind is when have you reached the level of bottom preparation that equates with your level of racing and also how much more can I gain by doing the next step.

Don't get me wrong I'm a big fan of smooth bottoms because it is one thing you can control before a race & then don't have to worry about it .

IMHO 4 coats of Interprotect plus one or 2 coats of a good anti-fouling paint should be sufficient .

BUT ...I don't have experience maintaining a boat in salt water so what do I know???

Ross MacLennan
C&C 24, Tobermory
----- Original Message ----- 
From: Dennis C. 
To: cnc-list at cnc-list.com 
Sent: Saturday, January 06, 2007 8:37 PM
Subject: Re: {Stus-List} Keel tuning?

  Gregory Cutter <gcutter at odu.edu> wrote:

  Ross - You don't recall my replies to a similar post late last year? Yes,
  go ahead and flatten it (1/8" for your 24 sounds about right), but if
  you've got the shed, I'd "template" the keel - fait it to a good,
  symmetrical shape. Someone should have saved my instructions on this
  (where's Beth when you need her?), but I probably have it written down on
  one of my computers.

Here's some of Greg's posts:

I use the assumption that the keel was cast close to what 
designer wanted, and that its use and abuse that has made is less 
fair...bumps and hollows. So, I look for the side with the smoothest, 
symmetrical shape to select the templating side (e.g., it should look 
the top of an airplane wing). It's very subjective, but your eye and 
are very good at detecting symmetry and shape.

Microballons get wet, so no. I use the 3M Marine Premium 
(vinylester) that I've found sands really nicely and cures pretty 
fast (as
fairing is very time consuming and waiting 12h for a cure is a 
If there is bare lead, I sand it (wear respirator!) to bring metal, 
it, then immediately apply Interprotect 2000 (or whatever # it is 
This sticks well to lead (don't need all those basecoats they 
Then I fair. When I'm all done, then 4 coats of Interprotect over the 
thing, sand, and paint.
One trick with the interprotect for saving $$: mix up the whole can, 
parts, to avoid mistakes in mixtures (and I'm speaking as a 
chemist!). Pour
out what you need for that coat, then immediately put the rest (in 
the can)
in a very cold refrigerator, or in an ice chest with plenty of ice in 
yard). This slows the cure rate to almost zip. For the next coat 
(8-10 h),
mix it up again, pour out what you need (back on ice with the rest) 
and let
it come back to room (ambient) temperature BEFORE applying.
OK, someone save this and load it on the DIY part of the web site!
Cheers, Greg

Then there was this post from Don Wagner:

According to C A Marchaj, the Polish ( no Polish jokes please) aerodynamicist who published books on SailingTheory and Practice, and the Aero-hydronamics of Sailing, he suggests that the overall chord length of the theoretical foil may be cut off and squared. He suggests that the  chord can be reduced by 5% and perhaps as much as 10%. Note he does not suggest a particular square dimension, but to consider the overall chord length of the design, and then reduce that chord length by 5% with a squared off end.

If you are interested, you can check out his book "Aero-hydronamics of Sailing" , on pages 223 - 226.I have the 1979 edition, but I suspect that there are newer editions available He has published curve illustrating the higher lift coefficient that is achievable with the cut of section on page 223.

I am planning on shaping my keel soon.  I have "commandeered" some long pieces of foam board from a friend with a framing gallery and a 40" flexible curve.  I intend to follow Greg's advice.

Hope this helps.

Dennis C.
Touche' 35-1 #83
Mandeville, LA

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