In article , Donals Dilemma
wrote:

On Thu, 04 Dec 2003 09:35:47 +1100, Peter Wiley
wrote:


Balanced spade rudders with only one support for the shaft - at the top
- are far more prone to failure than rudders with top & bottom support
as provided by a full keel.

Thought that was obvious.

You'd think so eh?
However, the engineering of a spade rudder is quite good, working on
the cantilevered beam concept.

Agreed or the failure rate would be even worse. They *need* to be a lot
stiffer/stronger to work at all.

Unfortunately they are not quite as well protected as a full keeled
rudder but nonethe less are covered pretty well by the keel.

True but I wasn't going there - this thread started out on
seaworthiness and if we bring into it the ability to survive a
collision with a hard object, all boats are going to fail - just
depends on how big an object and at what speed the collision.

I'd content that most rudder failures are during racing where streese
are high, full keelers don't race anywhere near as much making the
incidence of spade rudder failure appear much higher.

Maybe. Seems obvious as full keel boats aren't these days much use for
racing and I'd agree that failures of almost anything are going to be
higher when people are building to minimum engineering specs and
maximum stress. I say min engineering specs because each kilo extra
weight over what's needed is a penalty you're hauling around. That's
fine for the intended purpose too.

PDW