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Old 06-01-2009
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How to template a keel

This is installment 1 of the ongoing saga of the Ranger 22 keel. The boat belongs to a friend of mine, and I crew on this boat for the club races. I couldn't find much info about how to template a keel, so this is what we did. I'm sure there's a better way, but for lack of any info we were winging it. If you have a j-boat or something like that, call the manufacturer or Computer Keel to get correct templates.

Step 1. Gather info. Since there is very little info available for the Ranger 22, we did the best we could. We did find a class regulations manual from the Brazilian Ranger club. It's written in Portuguese, so we had to read the pictures and guess. It had some keel specs in the back, but not enough to make templates.

Step 2. Figure out which profile you should be using. With very little info to go off of, we selected a couple of different profiles and checked them against the keel to see which one fit best. We assumed that the designer was making an attempt as some sort of foil shape, it was just hard to tell what. After hours of making temporary templates we finally landed on a NACA 63-009 with an actual section thickness of 9.786% at 30% chord. This shape closely matched the thickness specs the keel, and the shape was closest for the top of the keel. The bottom of the keel was a wreck no matter what pattern we tried. Here's a few of the designs we looked at:



The differences are initial drag and stall angles. The 63 series foils are great low drag foils the 0010 foil has higher initial drag, but is harder to stall which makes it better for rudders.

Step 3. Create the foil. To get the accurate foil thickness to match the specs we had, we had to use a non-standard thickness. Standard thicknesses are 9%, 10% or 12%. We needed something between 9 and 10%. Good thing Bill is an engineer. We ended up at 9.786%. The foil shape was created using JavaFoil. We doubled the number of coordinate points so the leading edge is smooth when the foil is plotted. Then save the foil shape as a .dat file. Next we used CompuFoil to loft and print the foil. The program is purchased in modules, but since Bill is an engineer, we only bought the basic version. You may need to purchase the modification module and the lofting module as well.

Step 4. Templates. The CompuFoil program will print the foil on multiple sheets of paper with alignment targets. We cut out the foil pattern and transferred it to a piece of Mat Board for picture framing. Then the templates were stapled onto pieces of wood for stability.




CompuFoil will also print templates for the leading edge section, which was very useful in getting the initial shape down.


Step 5. Marking the keel. We marked the keel for the proper template positions. We made ours fit every 12 inches starting 3 inches from the bottom. I also marked the centerline on the leading edge of the keel, and after I could actually fit the templates on I marked the point of maximum thickness.


Step 6. Initial shaping. I used a power planer and a Surform file to match the leading edge shape. Be careful with the power planer. They're not made for use on lead. They're really not made to follow a foil contour. The combination of lead and too deep cutting due to trying to follow a curve caused a brand new planer to come apart. Fortunately the parts flew away from me, so I only had to dig half a blade out of the keel. Wear your eye protection and run the planer up and down on the keel, not front to back.


Once you get it close, use the Surform file until the high spots are gone. The templates should now fit the keel with gaps in the low spots.

And yes, the black marker line is the center of the keel.


Step 7. Between the templates. Now level off the high areas between the templates using a straight edge and the planer and/or a surform file.
Bill hard at work.



More to come later.
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Last edited by US27inKS; 12-17-2011 at 04:27 PM.
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Old 12-16-2011
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R22 templates

Hi,
do you still have the photos and/or template data?? I have a Ranger 22 and getting ready to undertake the same task.

I see by your signature that it looks like you no longer have the boat. I am unable to pm due to not enough posts yet. I would love to hear and see more about this project.

Will Anderson
South Lake Tahoe
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Old 12-17-2011
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I fixed the pictures. There are more pictures at keel fairing pictures by US27inKS - Photobucket

I never did upload the rest of the pictures, and they're long gone by now. The basics are that you then need to fill the low areas with epoxy mixed with a low density fairing filler. Keep filling and sanding until your templates fit perfectly, and you can run a straight edge between your template positions with no high spots or gaps.

The boat actually belongs to my friend Bill, who is the guy you see in a few pictures. He didn't race last year, so I got recruited over onto another boat. We'll see if Bill races the R22 next year, and if I can be persuaded to leave the Tartan 27 I got on last year.

I'll fire up my old computer Monday to see if I still have the lofting info we used. I can't guarantee we used the correct shape, but given the lack of data, it was the best we could come up with. Honestly the boat didn't get much faster, but it did sail the same on both tacks. The lack of improved performance likely has more to do with sailing skills of the driver and crew than keel shape. At least now it looks fast. It's on the hard at the lake. If I get up there in the next few weeks I'll snap a pic of the finished product.
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Old 01-05-2012
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Thank you for fixing the photos. I'm not going to remove that much lead. I will try to make it fair and symmetric in cross section top to bottom. I'm also changing to VC17 for paint after the epoxy barrier and filler.

Glad to see another R22 out there still racing strong!!
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