Keel template

Please see the post RE new 7.9 masts

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Mookie
Posts: 32
Joined: Thu Sep 05, 2013 4:07 pm

Keel template

Post by Mookie »

Does anyone have a source for a printed keel template? I made one from the specifications in this website, but I would very much like to verify its accuracy. Something on paper I could lay my template on would be great.
DougH
Posts: 15
Joined: Sat Sep 05, 2020 6:03 pm

Re: Keel template

Post by DougH »

There is popular software that the model airplane guys use. http://www.compufoil.com/tour.shtml It will also print "large" airfoils on multiple sheets of paper that you tape together, like for the 7.9 keel. Though I would think that if you were careful when laying out the points when you made your template you should have been able to achieve something plenty accurate enough for hand filling and sanding. Avoiding "bumps", "dips", and "waves" in your keel surface is probably more important than ultra precise fidelity to the target curve. Good luck.
Jameso
Posts: 33
Joined: Tue Sep 04, 2012 6:04 pm

Re: Keel template

Post by Jameso »

You can buy the template kit for $95 or buy the completed template $145.

http://www.computerkeels.com/
Mookie
Posts: 32
Joined: Thu Sep 05, 2013 4:07 pm

Re: Keel template

Post by Mookie »

I was VERY careful laying out the points for the keel template, but it was not an exact match for the existing keel. So, I rechecked it and redid it about a thousand times, and finally went with it. The keel is certainly beautiful, smooth, straight and not bumpy because I’m particular about that stuff, but the small difference has always nagged me. I’ll be pulling the boat for a bottom job, and would like to verify the keel first and plan accordingly.

FWIW, the boat had been grounded by me and by the previous owner(s). Pretty standard, I’d guess. When this boat grounds, the keel rocks back, crushes the trailing edge, and splits the fiberglass skin from the foam core - think of blowing open an envelope. There was evidence of previous drilling and filling of the keel, which is a useless effort.

I cut the skins off mine with a roto zip where they were delaminated, cleaned everything up, epoxied them back on, and filled and faired. The good news is that the keel is originally very well built. The glass is thick, and the foam is closed cell and had zero deterioration. These are good keels.

The bad news is that about 50% of the skin was delaminated. It deforms and does not return to the original shape when delaminated from grounding. Mine had also twisted about 1/2” out of true vertically. Fixed that also.

The leading edge radius was thicker than the template leading edge radius. Why, I don’t know. This is what has always bugged me, and what I’d like to double check. I went with the template.

The boat always sailed higher on one tack than the other, and now I know why! It sails the same on both tacks now. I can’t say if it’s higher or faster because we haven’t tried the good sails yet.
Mookie
Posts: 32
Joined: Thu Sep 05, 2013 4:07 pm

Re: Keel template

Post by Mookie »

I forgot to mention computerkeels. I tried to get a template from them originally, but was told they didn’t have any and would have to do a run of them to make it worth their while, or something to that effect iirc. The price was much higher. I did not get a template from them.
DougH
Posts: 15
Joined: Sat Sep 05, 2020 6:03 pm

Re: Keel template

Post by DougH »

Mookie wrote: Sun Aug 01, 2021 5:56 pm I was VERY careful laying out the points for the keel template,
Good. All Compufoil would do is take the data points you punch in and draw a best fit bezier curve through them. That will likely just match what you did by hand. So Compufoil may not be what you want. Not sure. Price is $38 and the time to learn the software.
but it was not an exact match for the existing keel.
I've no experience in comparing a factory built 7.9 keel to the class-published profile data. Maybe someone else has done this?
The keel is certainly beautiful, smooth, straight and not bumpy because I’m particular about that stuff,
Nice. If you did your best with your template, and it looks good to the eye and a stroke of your fingers, chances are good you are going to get best performance.

I should do the same to my keel and rudder. :)
wkwtucson
Posts: 40
Joined: Fri Nov 02, 2007 12:20 pm

Re: Keel template

Post by wkwtucson »

I have made S2 7.9 rudders and repaired the keel using autocad templates that I drafted up based on section drawings available from the Class documents for the boat. Let me know if you are interested in any of this. I drilled and inserted small diameter pins (skinny finish nails) around the center line of the forward and rear edges at the top and bottom and at key intermediate distances between the top and bottom. The pins were installed so you could pull them out when working an area and put them back afterwards. These were used for reference and measurements. I treated each side separately to make any repairs of cracks and dings using West Systems epoxy. I made a reverse template from sheet metal that worked well while fairing down the sides with a long board. When I was done, I pulled the pins and filled with epoxy. Don't forget to over sand to account for the paint thickness if you are painting it.
Kevin in Tucson
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