Perhaps you did not realize that Doug is a just a motor boat driver now.
He has some sort of motor boat with nasty osmosis problems -he's
posted lots of pictures of it.

Cheers

Capt. Neal® wrote:

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

Crossed purposes I see. I was thinking about the thrusters here. What is
the origin of term "back down" when talking about going astern come from
anyway -I was misled by it into thinking about manouvering with the
thrusters...

Cheers

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.

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

Is that to cut the sea grass?

Cheers

Gilligan wrote:

Counter rotating scythe propellers with electric drive.

Gilligan

"Bart Senior" wrote in message
...

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.

... 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.


Nav wrote:
Well we disagree there. Look at all the boats in your boatyard -what %
do not use electric thrusters?

Ah, I see the problem. You're confused about the subject.

Again.

The discussion is not about aux thrusters, which can be a trivial
fraction of main engine horsepower, but rather the main propulsion itself.

DSK

The net torque is zero, hence changes can occur quickly. The blade
configuration always has metal in the flow for maximum efficiency, no
chopping.

Anyone who knows anything about propellers knows sternwheelers are used to
cut seagrass.

Gilligan




"Nav" wrote in message
...
Is that to cut the sea grass?

Cheers

Gilligan wrote:

Counter rotating scythe propellers with electric drive.

Gilligan

"Bart Senior" wrote in message
...

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.

Thanks, it figures. I always knew Mr. King was no sailor.

CN


"Nav" wrote in message ...
Perhaps you did not realize that Doug is a just a motor boat driver now.
He has some sort of motor boat with nasty osmosis problems -he's
posted lots of pictures of it.

Cheers

Capt. Neal® wrote:

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

"Joe" wrote in message om...
Capt. Neal® wrote in message ...
I read the original post again and it just
says 150 foot mega yacht so it probably is
a mono-hull. I guess I was mixing it up with
Oz's thread about the big catamaran he just
bid on from the Greeks?

You could still build a nice tunnel drive into
the hull just forward of the rudder. That would
be my plan if I were filthy rich and were building
such a yacht. Actually, I think I would experiment
with a tunnel either side of the keel where it
fits to the hull. It would look somewhat like
a couple of jet engine nacelles on the tail
of a Gulfstream like this one
http://www.controller.com/images/con...e/00905032.jpg
but with smaller tunnels recessed into the keel.



And it would be an effective add on. However on something in the 150
yacht it would be a smart move to have a twin screw system. If
properly set up you can walk your stern left or right without any
thruster assitance just using your wheel walk. For a bow thruster a
simple 120 hp electric thruster would suffice in a tunnel. If money
were truley no issue than Id go all diesel electric including both
main screws and go with cort nozzles and variable pitch props able to
feather flat. Everything would sail by wire off a joy stick with
computer sail trimming, touch screen navigation and control thruout
the vessel.
But 150 foot is just so second class in today maga yacht scene. Id
build in the 225 footer range.

Joe


225 feet is about where steel comes into its own. Any smaller
than that and it's just too heavy for spritely performance.

I would go whole hog and have it made from stainless steel.
After all, the premise is you won the lottery and money is
no object.

CN

"Nav" wrote in message ...
Perhaps you did not realize that Doug is a just a motor boat driver now.

Not just any old "motor boat driver" if you please.

... He has some sort of motor boat with nasty osmosis problems -he's
posted lots of pictures of it.

Our boat has never had osmosis problems. Once again your bitterness &
spite has muddled the facts.


Capt. Neal® wrote:
Thanks, it figures. I always knew Mr. King was no sailor.

Yep. Keep on thinking that!

DSK

DSK wrote:

"Nav" wrote in message
...

Perhaps you did not realize that Doug is a just a motor boat driver now.


Not just any old "motor boat driver" if you please.

... He has some sort of motor boat with nasty osmosis problems -he's
posted lots of pictures of it.


Our boat has never had osmosis problems. Once again your bitterness &
spite has muddled the facts.


Your motor boat did not have blisters along the water line? Whose boat
was it?

Cheers

Capt. Neal® wrote:

"Joe" wrote in message om...

Capt. Neal® wrote in message ...

I read the original post again and it just
says 150 foot mega yacht so it probably is
a mono-hull. I guess I was mixing it up with
Oz's thread about the big catamaran he just
bid on from the Greeks?

You could still build a nice tunnel drive into
the hull just forward of the rudder. That would
be my plan if I were filthy rich and were building
such a yacht. Actually, I think I would experiment
with a tunnel either side of the keel where it
fits to the hull. It would look somewhat like
a couple of jet engine nacelles on the tail
of a Gulfstream like this one
http://www.controller.com/images/con...e/00905032.jpg
but with smaller tunnels recessed into the keel.



And it would be an effective add on. However on something in the 150
yacht it would be a smart move to have a twin screw system. If
properly set up you can walk your stern left or right without any
thruster assitance just using your wheel walk. For a bow thruster a
simple 120 hp electric thruster would suffice in a tunnel. If money
were truley no issue than Id go all diesel electric including both
main screws and go with cort nozzles and variable pitch props able to
feather flat. Everything would sail by wire off a joy stick with
computer sail trimming, touch screen navigation and control thruout
the vessel.
But 150 foot is just so second class in today maga yacht scene. Id
build in the 225 footer range.

Joe



225 feet is about where steel comes into its own. Any smaller
than that and it's just too heavy for spritely performance.

I would go whole hog and have it made from stainless steel.
After all, the premise is you won the lottery and money is
no object.


Stainless steel is not a cure all for corrosion problems -it's also
heavy for a yacht. Aluminum seems a more common solution.

Cheers