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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