"Jeff Morris" wrote in message
...
Shen44 wrote:

LOL don't hold your breath waiting.
To date, I haven't seen the final NTSB report of this incident (Jeff
seems to
find these more easily than I [hint]), so I won't comment as to the
validity of
a Federal courts findings.


It takes a few years for the NTSB reports to be published. Here's the
current list:
http://www.ntsb.gov/Publictn/M_Acc.htm

The CG reports are harder to track down. And the court findings are
buried in the various appeals courts.

Great link. Didn't realize there were so many vessel/bridge allisions
resulting in fatalities.
John Cairns

Subject: Seamanship Question #15 Props
From:

The issue of whether the city's liability can be drastically limited for the
crash turns on whether the ferry management had
"privity or knowledge" of the negligence that led to crash. The ferry pilot,
Richard Smith, pleaded guilty in August to seaman's
manslaughter charges, admitting he passed out at the wheel from fatigue and
the effects of medication.

Like I said, the man was not fit to pilot that ferry . . . Damned druggie!

The above is from:


http://www.newsday.com/news/local/ne...58041.story?co
ll=ny-nynews-headlines

Now do I get that apology?

CN

ROFL NOT a chance!
When the NTSB report comes out ( I believe Jeff's right .... too early for this
one) I'll decide whether you made a lucky guess or not.
Till then, take any news reports and politically motivated court decisions and
stick them where the sun don't shine.
Cheer up, though, you could be partially correct ... if so, not from any first
hand knowledge on your part.

Shen

Subject: Seamanship Question #15 Props
From: Jeff Morris
Date: 11/26/2004 10:29 AM Pacific Standard Time
Message-id:

I'll take some of those points - It was me, not Neal, that pointed out
that the gearing could well be different in reverse. I also pointed out
that it would be easily noticeable.

Curiously, his first answer, that the prop was mounted backwards, may
have been a better answer. That doesn't change the handedness, but if
the blade is not symmetrical it will affect the efficiency.


Wish I had a prop handy.
My own feeling is that different gearing is a rarity. However, props are
designed to be most efficient when ahead, which means less efficient when
astern, so basically I agree.

Shen

Shen44 wrote:
Subject: Seamanship Question #15 Props
From: Jeff Morris
Date: 11/26/2004 10:29 AM Pacific Standard Time
Message-id:

I'll take some of those points - It was me, not Neal, that pointed out
that the gearing could well be different in reverse. I also pointed out
that it would be easily noticeable.

Curiously, his first answer, that the prop was mounted backwards, may
have been a better answer. That doesn't change the handedness, but if
the blade is not symmetrical it will affect the efficiency.



Wish I had a prop handy.
My own feeling is that different gearing is a rarity. However, props are
designed to be most efficient when ahead, which means less efficient when
astern, so basically I agree.

I can't say about ALL small diesels, but Yanmar is one of the most
common. Here's the spec sheet for the new 30HP, which, with its
siblings, may become the most common engine of its size fitted in the US.
http://www.yanmarmarine.com/products...0_TechData.pdf

While the saildrive gearing is symmetrical, the normal transmission has
three gearing options, none of which are symmetrical.

I remember an article (by Pascoe, I think) about a large power boat that
used reverse gear to have a counter-rotating prop. The shift linkage
was reversed, of course. The owner couldn't figure out why the
transmission needed service every 50 hours.

While the saildrive gearing is symmetrical, the normal transmission has
three gearing options, none of which are symmetrical.

I remember an article (by Pascoe, I think) about a large power boat that
used reverse gear to have a counter-rotating prop. The shift linkage
was reversed, of course. The owner couldn't figure out why the
transmission needed service every 50 hours.

Interestin. G we learn something new everyday.
I do note the reduction difference is not all that great between ahead and
astern and would have to wonder how noticeable the difference would be, versus
putting the prop on backwards. I also have a problem seeing how someone could
put the prop on backwards, other than in a twin screw application.

Shen

True. 2 points to you Jeff.

Would you know if tapering the shaft is the
standard? I haven't seen any otherwise, but my
experiece is limited to puling props on only a few
boats.

I was wondering if some shafts come straight with
just a key way to lock them in position?

Bart Senior

Jeff Morris wrote

I'll take some of those points - It was me, not Neal, that pointed out
that the gearing could well be different in reverse. I also pointed out
that it would be easily noticeable.

Curiously, his first answer, that the prop was mounted backwards, may
have been a better answer. That doesn't change the handedness, but if
the blade is not symmetrical it will affect the efficiency.

Joe wrote:
(N1EE) wrote in message . com...

(Joe) wrote


(N1EE) wrote



Joe,

Have you considered that the previous owner of a
boat might bave screwed up and put the wrong prop on?

Yes

Then you as the new owner might make the false assumption
that replacing the prop, with an indentical one, would be
a solution.

No, if it slipping as defined by cavitating then its pitch is to
great.
And if I put another opposite rotating prop on it would not be
IDENTICAL.

Joe, you've been drinking TOO, not "to" much.



And I can not think of any marine transmission that does not have the
same ratio forward and reverse.

It shows how limited your experience is then doesnt' it?



Name one marine transmission that has a diffrent ratio in recerse than
it has in forward.

I already posted a link to one of the most common small marine engines.
Their transmission uses different ratios for all options, except the
saildrive.
http://www.yanmarmarine.com/products...0_TechData.pdf




That would be a big mistake by the mfg. Can you guess why?


So I checked the bigger Yanmar, such as the one used by the PDQ
Powercat. This is offered with the Hurth ZF30 which uses different
ratios for fwd/asn, but is clockwise only. If you want a
counter-rotating pair, there are several with the same ratios, including
the ZF25, which is what PDQ uses. Of course, this is of little interest
to most sailors - even catamarans don't usually use counter-rotating props.

http://www.yanmarmarine.com/products...E_TechData.pdf