Capt. JG wrote:
Back to more questions somewhat related to the Perkins 4-108. This
sailboat is a pig to back up. It really wants to prop walk to
starboard. According to the owner, it's got a fixed, 3-blade prop. I
believe the boat also has a folding prop aboard in a locker. Would
that help? Would tuning help? What do you think?

The simple type of folding prop which opens by centrifugal force has about
as much stopping power when reverse is engaged as a car with silcone-coated
tyres on sheet ice. Folding props of this type have one purpose and one
purpose only, to minimise the prop-drag on a racing boat. If you minimise
the drag you also lower the forward thrust of the prop, hence the maximum
speed under engine at a given revs.

Efficient props have more prop-walk than inefficient props, so you have a
price to pay for maximum thrust. Most sailors get used to the prop-walk of
their particular boats and allow for it. In most cases they learn to make
good use of it, such as when backing into a marina berth, the angle of
approach being controlled intitially by the prop-walk factor. Once the boat
gathers way, the prop walk is minimised and the rudder takes over.

If you use the boat only once a week or less, you would take about 3 years
to learn the secret, so practice is essential, which is why professional
fishing-vessel skippers are so good at it.

It would be possible to design a prop which did not "walk". The same prop
would have little or no forward or reverse drive, and would therefore be
useless. The answer can be seen in new liners like the QM2, 4 independently
rotatable pods, each powered by it's own motor. Such technology is rather
expenssive for a small boat, but you can fit a bow thruster, which is a big
help.