On 2007-11-20 22:35:18 -0500, Wayne.B said:
On Wed, 21 Nov 2007 00:46:44 GMT, Jere Lull wrote:
I've always wondered... Why not put a feathering prop on at least one
of the shafts?
It's a good thought and one that I might consider if I have to reprop
again sometime in the future. Do you have any idea how they work? Is
the pitch adjustable in some way or do they just self-feather from the
force of the water like a folding prop?
They self-feather from the force of the water. The blades reverse to a
different pitch in reverse, thus vastly improving the "brakes". The
blades are geared, so it's nothing like a folding prop. If you punch
reverse, you'll have it in spades.
We have the "cheaper" AutoProp that requires taking the hub apart to
re-pitch, but they have one that can be re-pitched in the water by
adjusting the hub.
The Autoprop is self-pitching to the load, so will have a more linear
power/rpm curve, and a bit more load at lower RPMs.
The other important issue is reliability. If you are docking a 60,000
lb boat in close quarters you *really* want to know that forward and
reverse are working exactly as planned. There is no fending off by
hand if something goes wrong. The reality of today's boat insurance
market is that if you have an expensive liability claim from damage to
another boat, you are probably going to get cancelled and have trouble
finding another policy. You pretty much have to self insure for all
but the very largest losses these days.
I believe you'll find that you'll need a less throttle to maneuver and
a closer correlation between forward and reverse settings.
I suppose it's possible to break one, but they're built pretty heftily
and seem to survive charterers' errors. In fact, I don't believe I've
heard of one breaking, though I suppose they get dinged as often as
fixed wheels.
I'd check with the manufacturers, of course, for suitability, but if
they're building them 3'+ in diameter, they're putting them in some
pretty big boats.
--
Jere Lull
Tanzer 28 #4 out of Tolchester, MD
Xan's pages:
http://web.mac.com/jerelull/iWeb/Xan/
Our BVI trips & tips:
http://homepage.mac.com/jerelull/BVI/