Stainless rudder stock needs replacing in foam core rudder?

Thanks guys.

I already have a new boat. A Crowther 43 catamaran. This boat needs to be finished and sold ASAP. So the emphasis is on ease and speed of construction and a low price rather than building a rudder better than the old one (the new one will already be stronger). So CNC routering is out. But the product needs to be decent. If I did not care about the new owner I would have left them with a corroded shaft.

Thanks for the suggestions everyone

 

Don't panic DennisRB, the profile guage method will get you within a few tenths of a millimeter. Saves having to 'draw' it and is just as quick and accurate. I've never had a foil I've built hum, twist or misbehave so go ahead. If it is fair and straight it will be fine.

I do try different foil sections and have worked through moving the chord around a bit to establish any difference on small dinghies. As they say, only experience leads you along a journey of discovery!. I have learnt quite a bit about foils on a limited range of boats but it has been interesting and instructive. I have the tools to 3D model and 2D draw but these are used in conjunction with 'hands on' build and experience. BTW these boats are also in your speed range, so far from useless info.

You will be fine, the only other tip I will pass on is watch for the chord centre moving either aft or forward as it progresses down the foil IF the foil tapers in length front to stern. A good foil (if not parallel) should have chord centre taper to keep a consistent percentage (chord thickness max) - quite a few do not...

 

CNC router costs should not be more than $150 FYI. ..

 

Anyway its done. Just put the last coat of epoxy over the microballons. I used the original half, and I made a template of the foil from it to work off before I cut it up. The rudder itself is also full of layers of glass over the tabbing and shaft like how you build with a composite shaft. I keyed up the metal well with a grinder, but the primary torque resistor is the metal tabbing.

Of course I should have listened and just made a whole new rudder, would have been much quicker and probably saved me a lot of money in epoxy. But which other amateurs listen to the pros around here

Thanks to everyone that helped.

 

Looks like a good job, well done. At least you know the thing is sound and have confidence in it.