On Sat, 16 Apr 2005 09:32:25 GMT, "Roger Long"
wrote:

Comments below.

Most of my career has been spent on metal vessels. If I were going
around the world, I'd want to go in a steel or aluminum boat. I'd
favor aluminum because of a more reliable compass and because you can
patch it with a hand drill and sheet metal screws. Aluminum tends to
bend flat and intact where steel fractures even though it is stronger
in the stiffness sense.

Interesting. I work with aluminum on the mast and I've fabbed up 1/4
in. backing plates for most of the deck gear, so I know simple hand
tools will suffice, but usually the knock AGAINST aluminum is that it
requires special welding gear and skills. I didn't think of it in
terms of making a through bolted patch and running a bead of sealant
around...but why not as a "get you home" metallic fothering?

I once saw an aluminum yacht that went ashore on Nomans Land Island.
The keel was torn off and one side was pounded in about five feet for
three quarters of the length of the vessel. There were only about
three six inch cracks that would have let water in. If she had been
worth saving, she could have been made watertight and floated off with
a roll of duct tape. A steel boat would have been in pieces all over
the beach.

I would think it would be worth saving for the aluminum alone...isn't
"marine" aluminum a fairly expensive alloy?

The key thing I would look for is a full length skeg along the leading
edge of the rudder all the way to the bottom. The directional
stability comes from that fixed foil. Turning the rudder makes it a
lifting surface in the direction you want to move the stern. A lot of
the turning force then is created by something fixed to the hull
instead of on a hinge where you have to resist it with your hands.

I'm a big fan of skegs for safety and directional reasons. If you
ground by the stern with a spade rudder, usually it's game over. A
skeg can help...maybe...to save it.


The typical semi skeg with a bit of balance forward (as on the
Endeavors) is a silly arrangement usually. There isn't enough balance
on 90% of the rudders you see to effect the helm forces, the
directional stability is reduced, and a line catcher created. The
only rational for this kind of rudder is to look techie like an
airplane.

So you're no fan of the "Brewer Bite"?

snip
For directional stability, you want lots of leading edge back there.
I think my beef with a lot of Brewer/Wallstrom boats was that the
cutout ahead of the rudder is often kind of a token so that there is
very little leading edge.

I am not sure of the logic either, except that it makes otherwise
traditional boats more "modern" looking on the undersides.

R.

I'm a big fan of skegs for safety and directional reasons. If you
ground by the stern with a spade rudder, usually it's game over. A
skeg can help...maybe...to save it.


Just to clarify: That is a fixed skeg shown on my proposed
modification.

On spade rudders: On power boats, I favor spade rudders. If the
rudder has good clearance from the hull at the top, it will often
remain functional after a grounding. The shaft may bend and the boat
steer funny but it will still be steerable. With a bottom bearing, a
little bit of bending will usually bind the whole thing up so if is
useless. In a glass boat, it will be hard to make the skeg stiff
enough to support the rudder. The whole thing can flex enough that
the shaft will bend and the skeg will then bind the rudder. Even in
metal, the sailboat type skeg will be hard to make sufficiently stiff.

It doesn't take a lot of extra metal to make a rudder stock strong to
be self supporting. If I were designing a boat that was not a weight
critical racer, I would make the stock large enough to be a spade
rudder. The skeg would then be structurally separate with just a line
guard at the bottom. Grounding damage, which usually will bend the
stock aft, would then leave the boat steerable in most cases.

--

Roger Long