Since the same gage number will give different thicknesses for different alloys, consideration of the alloy used must be take into account. In general steels will be thicker than aluminums by different amounts according to the gage number. Alloys of the same type can be stronger, but will not be stiffer. Stiffness will be a function of the thickness, not alloy type.

Aluminum turn fins can be made much more rigid by supporting the upper part of the fin that is not in the water at speed with a 1/8" thick, 90* weave, carbon fiber plate. Also, the .060" thick flat aluminum support seen in the photo, gives no drag & greatly reduces the load placed on the sponson boom tube, on that side of the hull. Bend the support close to the needed dimension & add whatever thickness shim is necessary. Notice the 3/16", G-10 fiber glass support, added inside the hull. Simple, but very effective stuff on any oval or straight away boat if you want to use a turn fin. Notice how both turn fins on two different hulls are supported above the water line. Both carbon fiber turn fin supports have a taper on the front & bottom edges.

Jim Allen

Jim. I like the little CF support piece you use. I do the same with aluminum. Surprising how stiffer it makes the fin.

I agree Randy, but I have found hardened & tempered steel to be the best. Of course the turn fin would be slightly heavier (.062" thick) & much more difficult to machine when making a full wedge front to rear. Hardened & tempered steel works very well for a very short type straightaway turn fin used on an angled mount. Some people have suggested Titanium, but this alloy would not be stiff enough. Looks like model boats will have to stick with aluminum until something better comes along.

JA

You really are a metalsmith Jim, thanks for sharing...I am getting ready to mount the turn fin on my rigger and trying to find a metal rod like you have to bolt the sponson to the tub

Here's something else you might want to try. I use a solid carbon fiber, .3750" OD rod, that is secured in the hull body with two 1.000" long carbon fiber tubes that are epoxied in place. No screws, mounting blocks or bolts are necessary to hold the solid carbon rod in place. Notice the machined metal washer epoxied in the reinforced hull sides. The solid rod passes into tubes epoxied into the sponsons. Reinforced, 2.000" wide Scotch tape secures the sponson's tubes to the epoxied 1.000" pieces.

Jim Allen