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