carbon fibre rudder stock shaft bearings

[MikeJohns]

In this neck of the woods there have recently been two sinkings of large expensive boats that snapped their CF rudder shafts both vessels were lost so no root casue failure analysis is possible. Snapping a shaft can be from poor fatigue related design, layup faults, collision with an animal or debris, and you cannot design for that in your FOS.

The catch it that you use a light material but need a large diameter tube with a material that exhibits catastrophic brittle failure.
The shaft breaks at the maximum bending moment inside the vessel and you are left with a hole the size of the shaft. The boat can be lost in seconds

I think it should be mandatory that With brittle rudder shafts there should be some compartmentalization of the vessel in the stern.

[Karl Wittnebel]

There are much less risky places to save weight. And unless the class has no minimum weight, it seems penny wise/pound foolish to trust such an important part to a process which fails commonly even in highly engineered applications.

I have a carbon rudder shaft on my sailing canoe, engineered for the application. I worry all the time about a bit of sand getting into the bearing and eating the carbon away, even though I put brass bushings on it. I have also had similar shafts fail, fortunately in racing situations where help was close at hand.

When you have seen how fast even thick carbon laminate disappears when subjected to an abrasive sanding disk on a die grinder, it seems truly foolhardy to trust anything other than stainless for a rudder, again unless every ounce truly counts.

Good luck either way, and good sailing.

[ramminjammin]

update

the rudder build is underway
I have chosen old school , and will be using stainless 316 solid two inch steel

cost of the stock = $275
labor to build the rudder, epoxy and pine , machine the stock and weld $800
materials estimate : wood, fiberglass, bearings = $325

total cost around $1400

thanks again for the discussion

[CatBuilder]

Originally Posted by ramminjammin

update

the rudder build is underway
I have chosen old school , and will be using stainless 316 solid two inch steel

cost of the stock = $275
labor to build the rudder, epoxy and pine , machine the stock and weld $800
materials estimate : wood, fiberglass, bearings = $325

total cost around $1400

thanks again for the discussion

Could you name the sources you found for the 316SS and bearings?