DSK wrote:
Farr1220 wrote:

Doug,

There's no need for the complication of variable pitch.


Well, sure. There's no "need" for the boat at all.

... A reversing
motor (electric or hydraulic) is all that is needed.


And that's simpler than a CPP?

... Hence for this
size vessel you see symmetric 4 blade props.


Sometimes 5 blade.

... The small increase in
efficiency gained by having variable pitch is not worth the extra
complication.


Bart wasn't asking about efficiency, he was asking about
controllability. An electric drive may be on par with the controlled
pitch for quick & easy reversing, but they're much less common... the
ones I know about have a bad reputation for being troublesome.

Well we disagree there. Look at all the boats in your boatyard -what %
do not use electric thrusters? I think electric is the most common
installation on yachts. I've not seen any alternative to electric and
hydraulic. What have you got in mind?


As for a hydraulic motor, if you think these are efficient and
trouble-free then I suggest you get some experience with them. It would
be at the bottom of my list for almost any power application.


I said that efficiciency is not an issue for a thuster. Now for
reliability, hydraulic are are no worse than electric motors in hostile
(SW) environments (look at what working fishing boats use to retrieve
gear if you want insight to reliability). That reliability is why
hygraulic power is used so much on mega yachts for furling gear, winches
and rams. But think on this: The hydraulic power will certainly be
there on this size yacht so why not use it? There is no reason to throw
money away when such a simple solution presents itself.


Cheers