DSK wrote:
otnmbrd wrote:

It's a "general" rule that boats with Korts tend to lose some backing
efficiency over their un-Korted brothers .....couldn't explain why
(whether it's the shape of the nozzle or design of the prop, or both)


Probably the nozzle- you could make the nozzle symmetrical, but it would
cost some efficiency in forward motion. The question is would it still
be more efficient than an un-nozzled prop.

A Z-drive or Azipod would be cool... no such thing as reverse, it's
always in forward! Just swivel the whole thing around just like a video
game.

Fresh Breezes- Doug King


G The problem would arise if you were using a single Z-drive unit. As
it was swiveling, it would give a nasty steering component unless you
stopped the prop, first.

otn

There's no need for variable pitch -which is why you don't see it in
mega yacht thrusters


Cheers FT.

DSK wrote:
Bart Senior wrote:

2 points

After hitting the lottery for big bucks, you have nearly completed
your 150' new sailing mega yacht. Included on your new toy are both a
bow and stern thrusters--for side-to-side control..

What sort of prop would you want if you were concerned about precise
speed control, and being able to back down nearly instantaneously?

Money is, of course not a concern.


Hydraulically controlled variable pitch.

BTW is this 150' yacht equipped with a rack of racing dinghies and a
retractable artificial beach?

Fresh Breezes- Doug King

Doug,

There's no need for the complication of variable pitch. A reversing
motor (electric or hydraulic) is all that is needed. Hence for this
size vessel you see symmetric 4 blade props. The small increase in
efficiency gained by having variable pitch is not worth the extra
complication.

Cheers


DSK wrote in message ...
Bart Senior wrote:
2 points

After hitting the lottery for big bucks, you have nearly completed
your 150' new sailing mega yacht. Included on your new toy are both a
bow and stern thrusters--for side-to-side control..

What sort of prop would you want if you were concerned about precise
speed control, and being able to back down nearly instantaneously?

Money is, of course not a concern.

Hydraulically controlled variable pitch.

BTW is this 150' yacht equipped with a rack of racing dinghies and a
retractable artificial beach?

Fresh Breezes- Doug King

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.

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.

Actually CPPs are slightly less efficient, ideally, than conventional
props becuase of the bulky hubs. However, in real world conditions, they
often achieve greater efficiency by being able to trim the prop to match
sea/wind conditions to engine load.

Fresh Breezes- Doug King

As a sailor you should be more concerned with trimming sails.

Leave the motors to the likes of Captains Shen and otn.

Captain Neal
(a member of an elite group)

"DSK" wrote in message ...
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.

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.

Actually CPPs are slightly less efficient, ideally, than conventional
props becuase of the bulky hubs. However, in real world conditions, they
often achieve greater efficiency by being able to trim the prop to match
sea/wind conditions to engine load.

Fresh Breezes- Doug King

Capt. Neal® wrote:
As a sailor you should be more concerned with trimming sails.

I can do that, too.

DSK

Nav wrote:
There's no need for variable pitch -which is why you don't see it in
mega yacht thrusters


Cheers FT.

I believe the discussion regarded the Main Engine, not the thrusters

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

otnmbrd wrote:

Nav wrote:

There's no need for variable pitch -which is why you don't see it in
mega yacht thrusters


Cheers FT.


I believe the discussion regarded the Main Engine, not the thrusters

I thought it was 'bout the whole propulksion package 'cos he mentioned
dual thrusters. If just about main engine that's a really boring question.

Cheers

DSK wrote:

Bart Senior wrote:

2 points

After hitting the lottery for big bucks, you have nearly completed
your 150' new sailing mega yacht. Included on your new toy are both a
bow and stern thrusters--for side-to-side control..

What sort of prop would you want if you were concerned about precise
speed control, and being able to back down nearly instantaneously?

Money is, of course not a concern.


Hydraulically controlled variable pitch.


For main prop definitely CPP. I'm not sure I'd want just hub hydraulic
control though. Might be better to have a servo that can be overridden
by human muscles -just in case.

Cheers