Fabricating a new Spade Rudder

[Secondshift]

Originally Posted by Jim Cate

Are you sure that the old stock was monel? That's a fairly expensive material and not so often seen in that application.

For the new one, you might consider 2205 duplex s/s. A lot stronger than 316 (the most commonly used alloy) and far less susceptible to various forms of corrosion.

Jim

2205 duplex stainless is a good suggestion but only if it's welded correctly Have it done at a trustworthy shop familiar with the specific alloy. The techniques are dissimilar to welding 304 and 316.
Plate stock requires preheating and interpass control. Additional info can be found on the Rolled Alloys website under
"Welding duplex stainless"

Best Regards,
Ed W

[Emouchet]

3rd vote for Foss Foam.
I shipped them my old broken rudder and they used it as a model to rebuild a new one.


The only issue is that those guys works in imperial, and original part were metric, since it came from Dufour. The shaft final diameter on the new one ended up 59mm versus original 60mm. I had to replace the rudder bearings with a custom made one.

[heron237]

Thanks for that info Raggedy, that steel "pintle" at the bottom of the keel to strengthen the post looks like it was original, I could do that....currently there is none, the two post bushings are at each end of the post mounting as it passes through the hull, that would put a third support down lower-- a good thing! I will have a qualified welder fabricate the post with the plates and fabricate the rest myself. No way am I paying the kind of money the others mention.

[heron237]

Wow what a brain trust! Thank you all for your comments suggestions. Ahun that looks like a good plan for a one off rudder, build up the profile with marine ply and epoxy, then use the power planer to get close to the final profile. Weight is not an issue as a rudder should be of neutral buoyancy, of course the weight of the shaft is helpful. At one point I had to drill and drain a couple of years ago, mine will be better than anything a production shop could do in a case like mine. One other consideration is that the shaft should bend/break before a strike would pull out the transom! Thank you all, now I have the information I need.

[chris95040]

When I was working with a large marine fabrication shop in glocester mass, they claimed 2205 wasn’t available in 1.25”, and machining down would be extremely expensive and had sone metallurgical side effects too. That was several years ago.

Edit: oops, that was a 1 5/8” shaft. nevermind....

[Bill O]

Heron,
We just replaced our rudder since a PO replaced the original rudder with a flat board (no lift). It wasn't that hard and once you get your new shaft manufactured with the rudder post extensions, the rudder blade will be somewhat easy.

We made a NACA 0010 profile rudder for our boat and you can print out the profile you want at airfoiltools.com. We then transferred the template to FRP.

Based on our research we didn't make the rudder out of wood as eventually it will absorb water. Instead we laminated sheets of 26# Coosa Blue Water to obtain the chord thickness, then used the router to remove excess material. We chose the Coosa BW due to the limited water absorption and strength of the internal f/g sheets. A little over kill for strength but what the heck, only want to do this once.

The router did leave small "steps" that needed to be removed later, but also left helpful contour lines on the surface that were good depth indicators for sanding. I've seen others make a fancy router jig to cut out the whole profile, but that seemed like too much work.

We made and installed our rudder in ~2 weeks. The new rudder has much better lift and the relatively small amount of leading edge helped add some "power steering" for easier steering.

The biggest decision you'll have to make is to stay w/your old rudder shape or change it for better performance/helm feel.

Bill O.