On Mon, 22 Nov 2010 21:37:09 -0500, Wayne.B
wrote:

On Mon, 22 Nov 2010 17:49:24 -0800 (PST), Joe
wrote:

Have been on a hundred boats with 25-72 inch props and had to chain
them down many times to prevent damage to the gears. As I said the
power is massive and you had better have heavy chains and binders.

Joe, my trawler has 30 inch, 4 bladed props on 2 1/2 shafts. Can you
suggest a procedure for safely binding/chaining a shaft while
underway? I was thinking about something like 3 or 4 loops of 1 inch
line terminating in a block and tackle lead to an overhead beam.


Out of curiosity, why chain the shaft? Are you running on one engine?
And, if you are how is it working for you. I tried it and it simply
dropped the speed by about half :-(

Cheers,

Brice

On Tue, 23 Nov 2010 17:46:50 +0700, Bruce
wrote:

Out of curiosity, why chain the shaft? Are you running on one engine?
And, if you are how is it working for you. I tried it and it simply
dropped the speed by about half :-(

On our boat we can improve fuel efficiency by about 25% running on a
single engine assuming a speed of no more than about 1.1 SQRT LWL.

We have Detroit 6-71 2-cycle diesels which are not efficient at low
speeds. Running single engine gets operating RPMs up to a normal
level. This is useful on long passages in relatively light winds and
calm seas. If the wind kicks up we need more power to maintain speed
and stability.

On Tue, 23 Nov 2010 06:15:07 -0500, Wayne.B
wrote:

On Tue, 23 Nov 2010 17:46:50 +0700, Bruce
wrote:

Out of curiosity, why chain the shaft? Are you running on one engine?
And, if you are how is it working for you. I tried it and it simply
dropped the speed by about half :-(

On our boat we can improve fuel efficiency by about 25% running on a
single engine assuming a speed of no more than about 1.1 SQRT LWL.

We have Detroit 6-71 2-cycle diesels which are not efficient at low
speeds. Running single engine gets operating RPMs up to a normal
level. This is useful on long passages in relatively light winds and
calm seas. If the wind kicks up we need more power to maintain speed
and stability.

I've got littler engines and at cruise are running about 2,000 RPM on
both. Cutting one engine reduces speed by about half.

But you have, I believe a Grand Banks, which has a semi-planeing hull,
I think the company calls it, that can benefit from larger engines. My
boat is a displacement hull so additional H.P. isn't going to make a
vast difference.

You say "maintain speed and stability", do you have active
stabilizers?

Cheers,

Brice

On Wed, 24 Nov 2010 07:37:46 +0700, Bruce
wrote:

You say "maintain speed and stability", do you have active
stabilizers?

Yes, Naiads.

http://www.naiad.com/Product_Flyer_162-302.pdf

On Tue, 23 Nov 2010 06:15:07 -0500, Wayne.B
wrote:

On Tue, 23 Nov 2010 17:46:50 +0700, Bruce
wrote:

Out of curiosity, why chain the shaft? Are you running on one engine?
And, if you are how is it working for you. I tried it and it simply
dropped the speed by about half :-(

On our boat we can improve fuel efficiency by about 25% running on a
single engine assuming a speed of no more than about 1.1 SQRT LWL.

We have Detroit 6-71 2-cycle diesels which are not efficient at low
speeds. Running single engine gets operating RPMs up to a normal
level. This is useful on long passages in relatively light winds and
calm seas. If the wind kicks up we need more power to maintain speed
and stability.

Tough finding a solution to that.
Just a few thing things that popped into my head, probably none
practical.
Re-propping to get revs up on both engines - non-starter because
you're running 2 engines, and waste heat kills fuel savings.
Transmission that can run both props on one engine input.
Makes sense for cruising speed, but probably too expensive/complex.
Feathering props. Probably more drawbacks than gain.
Easily detached props. Read to dive far asea, hoist, and get caught
with only one prop when it squalls? Didn't think so.
My favorite lame-brain idea is streamlined remote operated prop cowls.
Close when prop not in use, open otherwise.
Insane.

Do you have trans lube/heat problems when freewheeling a prop?
If you lock it down, will you still get 25% fuel savings?
Lots of drag there.

--Vic

On Wed, 24 Nov 2010 09:48:30 -0600, Vic Smith
wrote:

We have Detroit 6-71 2-cycle diesels which are not efficient at low
speeds. Running single engine gets operating RPMs up to a normal
level. This is useful on long passages in relatively light winds and
calm seas. If the wind kicks up we need more power to maintain speed
and stability.

Tough finding a solution to that.
Just a few thing things that popped into my head, probably none
practical.
Re-propping to get revs up on both engines - non-starter because
you're running 2 engines, and waste heat kills fuel savings.
Transmission that can run both props on one engine input.
Makes sense for cruising speed, but probably too expensive/complex.

Running two engines is always less efficient than one engine,
everything else being equal. An engine in motion has lots of
frictional and parasitic losses - things like pumps, alternators and
valve trains for example. DD 6-71s have an additional parasitic loss
from spinning the blower.

Feathering props. Probably more drawbacks than gain.

Feathering props are good although complex, expensive and difficult to
repair in the boondocks.

Easily detached props. Read to dive far asea, hoist, and get caught
with only one prop when it squalls? Didn't think so.

Not on my boat although I understand that a guy with a GB49 went from
Hawaii to San Francisco that way.

My favorite lame-brain idea is streamlined remote operated prop cowls.
Close when prop not in use, open otherwise.
Insane.

Good out of the box thinking, just a few details... :-)

Do you have trans lube/heat problems when freewheeling a prop?
If you lock it down, will you still get 25% fuel savings?
Lots of drag there.

At slow trawler speeds it is not that big an issue. We start the
other engine once in a while to recirculate the transmission lube. I
also check the temp with a heat gun from time to time when I'm doing
my engine room checks.

In theory locking it down is more efficient than letting it spin.
Locking it down is potentially dangerous however unless a built in
shaft braking system is used.

Check out

http://www.cruisersforum.com/forums/...est-37969.html

It's a lot of posts on the Cape Town to Brittany test. The boat had
1,600 Watts of solar panels, a wind gen and a 22KW diesel generator.

The African Cats poster also stated, "Regeneration with the
motors/generators will be done as minimal as possible in order to keep
the best average speed."

There's about 9 pages of posts and it seems the solar was king, with
diesel coming in second.

Rick