The long skinny fins on RG65s were outside my experience as somebody who mainly makes wooden boats. The first thing I tried was a helicopter blade. Too floppy. Then I made a fin with a balsa core reinforced with a 3 mm carbon fiber tube at the point of maximum thickness and wrapped with carbon fiber felt. Better, but still too floppy. Then I read a posting on a full-size boating forum about fins made with carbon fiber over cedar. Bingo!
Materials:
4mm or so cedar strip
3mm carbon fiber tube
.002 unidirectional carbon fiber from Aerospace Composite Products
3M MP200 tape-based adhesive from tapecase.com
4 oz glass cloth
epoxy
Glue up a core of cedar with the carbon tube at the point of maximum thickness. Fill the gaps and plane to airfoil of choice. Laminate the unidirectional CF to this using the tape-based adhesive, sticking to the carbon fiber first (making, in effect, self-stick carbon fiber tape) and then to the fin. The 200 MP turns what would otherwise be a messy job requiring molds, vacuum bagging, etc. a walk in the park. Use plenty of pressure with a wallpaper roller and let the 200MP set up for 24 hours. Epoxy on a layer of glass cloth, fill and paint. A 3mm thick airfoil shape, 26 cm long with chord 4cm tapering to 3 cm holding a 450 g weight deflects 4-5mm when held horizontally, which is good enough for me.
Earl
Have you ever been concerned that doing this by eye/hand might leave you with a slightly assymetrical foil that would increase drag? I’ve wondered if I might be a little anal about this.
Don
Oh, I’m sure it’s not as good as a foil made from a mold CNC milled to a proper NACA profile, but given my indifferent sailing skills I doubt I’ll see the difference The main thing is the process yields a “reasonable” fin without time/money investment in tooling.
The success of the class all over the world comes exactly from the KISS principle and the fact that you can build and desing every component of your boat. Of course that twisted rudders or fins or assimetrical fins meand a poor efficiency of the entire boat, as well as low quality sails, but this does not mean i have to order a special rig from Black Magic Sails.
All comments and tips relay on the fact that a person will build straight and correct shaped pieces, otherwise, bantock plans for the IOMS will be useless.
Lets encourage people to build their own boats and components, I am sure that after they achive that, they will notice the weak points of their boats and start to improve.
I am making my own rudders in 3 mm balsa with one layer of 5oz fiberglass and epoxy resin. Stiff enought. The rod is stainless steel, wich is may be heavy enought in comparison with carbone tubes.
The keel is made in hard wood sticks 4mm square, epoxy laminated and the final foil of 3mm thick.
I’ve seen wooden propellers being made by hand, and I can tell you they come out pretty well; even the ones made by new people. The trick they used was the right airfoil templates, and painfully slow shaping ( sanding) . I don’t see why you couldn’t do the same thing with fins and rudders.
Hi
I have made my fin from Alum sheet 2.5mm thick which means I can tap the top 2mm for the securing bolt. It works very well I have made an effort to give it an aerofoil profile but I am not sure at the speeds my 65 move,s that it is necessary.
This is a very simple method and I would be surprised if you can measure the additional speed the a correctly formed areofoil would give.
I just made one for a footy…the fin part is 20cm long, and the bulb is 500g. It’s 55mm at the top, tapering to 35mm at the bulb. Simply carved it to a foil shape from 1/4 inch basswood. About 2mm deflection.
I’m thinking it would probably still work fine if it were 6 cm longer.
Probably more likely to be an anchor than a secret weapon, Frank…but I’ve been wanting to explore the heavy end of the Footy spectrum for some time now. Decided to do it for the Nats. It will be about 700 grams all up.
Don’t worry about the sharp bow that’s reinforced with sheet aluminum…if you can’t beat 'em - sink 'em!
The main thing is the process yields a “reasonable” fin without time/money investment in tooling.