On Wed, 31 Mar 2004 11:56:00 -0800, "Rod McInnis"
wrote:


"Rodney Myrvaagnes" wrote in message
.. .

Our boat exhibits no prop walk that I can detect. It also can't steer
from propwash in forward. It must be moving for any steering to occur.
The prop (18-inch Martec) is 12 feet forward of the spade rudder and
fairly close to the keel, so it has little lever arm to turn the boat.

I assume that this is a sail boat, which would put this into a "large
rudder" catagory. Sailboats, by their very nature, need to be able to steer
at slow speeds without any thrust from the prop. Thus, they install a rudder
that is large enough to provide adequate steering at dead slow speeds.

A typical power boat, on the other hand, uses a very small rudder that is
located as close as possible to the prop. The rudder is rarely taller than
the prop is. Such a rudder is very effective when it can deflect the stream
of water that is being pushed by the prop, but has minimal effect when the
prop is not turning.

Yes, ours is a sailboat. We rented a canal boat once that had a
semibalanced barn door rudder clost to the prop. It could turn
practically in its own length. The appearance of the propwash suggests
the rudder completely covered the prop circle, shooting out the side
when hard over.



In reverse it did walk, but very predictably. As icing on the cake, it
also had a bow thruster.
Rod



Rodney Myrvaagnes NYC J36 Gjo/a


"Curse thee, thou quadrant. No longer will I guide my earthly way by thee." Capt. Ahab