Surfski rudder plug for moulding/casting from.

240mm deep, volume of 165mm. Skinnier than the carbon fibre think rudders. Aluminium has a density of 2.7 x that of water so an aluminium rudder of these dimensions will be approx 280grams when submersed. To protect the surface you can wire brush, annodise and dye....google it. The rudder has a tapered shaft entry, 8mm tapering to 4mm diameter over a length of 60mm. There's also an indentation for drilling and tapping a grub screw but it's better to cut some gripping notches into the SS rudder shaft and cast the aluminium around it. Look up sand casting and get hold of silica sand and bentonite clay, make a moulding box of greater inside dimensions than the fin outside dimensions. Alternatively you can make a mould around it and then cast carbon fibre etc with some low viscosity epoxy resin. Try to find a supplier of infusion moulding resins for best wetting out characteristics. You can also scale the rudder in your slicing program to use in a plane for tail, wing or rudder sections. As a wing, it will provide neutral lift so it's best in an acrobatic plane needing to fly well either side up.