Prop selection
 

OK, the engine arrives next week. Everything is in readiness. The
Aquadrive thrust bearing is in place and the shaft and coupling are on
but I find I have some extra shaft aft of the strut. It will be a
simple matter to pull the shaft, chop off a couple of inches and mill a
new keyway. Much easier to do before the engine is installed. BUT
then there is the little matter of prop to hull clearance.

Other than knowing that I needed an 18x14 prop I was not going to decide
on a make just yet but there are some major dimension differences
between prop makes. I am wavering between the Maxprop, the Martec
Autostream and the Gori 3 blade. I can chop as much as I want of for
the Gori because the blades are way aft of the shaft nut but the
Autostream has a lot less room to play with and the Maxprop even less.

SO I am looking for feedback on these 3 props. I am fairly familiar
with the Maxprop but does anyone have experience with the Gori or the
Autostream? I am leaning towards the Gori but it is a fixed pitch and
if I get it wrong it has to go back to Denmark to get adjusted. There
is a $1K spread in prices to be considered too.


--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

Prop selection
 

I've made my thoughts on this very clear in a recent thread -- I'd buy the
traditional MaxProp three blade in a second and never look back. I'd also
consider going an inch or two smaller in diameter (and up in pitch) since
you're not near square and a principal contributor to noise and vibration is
blade to hull distance -- every half inch counts.

You say, "other than knowing that I needed an 18x14" -- if you "know" the
exact prop for a boat that has yet to be launched, you're more confident
than I would be. There are all sorts of uncertainties, including weight of
stuff varying from local cruising to voyaging. The MaxProp is, as you know,
adjustable pitch. While they make one that can be easily adjusted
underwater, it's more money, and even the traditional one can be adjusted
underwater if you have good hands.

Of course, the MaxProp is made in Italy, and you've owned a Ferrari. PYI,
however, are great, and stock everything you might need, which is one reason
I'm probably going with Python Drive rather than AquaDrive.


--
Jim Woodward
www.mvFintry.com


..
"Glenn Ashmore" wrote in message
news:aFTqb.10767$62.6354@lakeread04...
OK, the engine arrives next week. Everything is in readiness. The
Aquadrive thrust bearing is in place and the shaft and coupling are on
but I find I have some extra shaft aft of the strut. It will be a
simple matter to pull the shaft, chop off a couple of inches and mill a
new keyway. Much easier to do before the engine is installed. BUT
then there is the little matter of prop to hull clearance.

Other than knowing that I needed an 18x14 prop I was not going to decide
on a make just yet but there are some major dimension differences
between prop makes. I am wavering between the Maxprop, the Martec
Autostream and the Gori 3 blade. I can chop as much as I want of for
the Gori because the blades are way aft of the shaft nut but the
Autostream has a lot less room to play with and the Maxprop even less.

SO I am looking for feedback on these 3 props. I am fairly familiar
with the Maxprop but does anyone have experience with the Gori or the
Autostream? I am leaning towards the Gori but it is a fixed pitch and
if I get it wrong it has to go back to Denmark to get adjusted. There
is a $1K spread in prices to be considered too.


--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

Prop selection
 

"Jim Woodward" jameslwoodward at attbi dot com wrote in message
...

I've made my thoughts on this very clear in a recent thread -- I'd buy the
traditional MaxProp three blade in a second and never look back. I'd also
consider going an inch or two smaller in diameter (and up in pitch) since
you're not near square and a principal contributor to noise and vibration
is
blade to hull distance -- every half inch counts.

I wouldn't go smaller if possible. Prop efficiency is related to diameter
to some power (^2 or ^3 I can never remember). So "an inch or two" would be
huge difference in efficiency - and a 16" prop is too small for the engine
size Glenn is installing.

I think that you can just compare prop dimensions and see what tip
clearance you can get. If you can get 20% of prop diameter great.

No opinions on the props under considerationj other than I don't like Max
props flat blades with no twist.

I might have to consider a similar propblem in a few years. I'll let the
group know in a week or so what the next boat might be :)


--
Evan Gatehouse

you'll have to rewrite my email address to get to me
ceilydh AT 3web dot net
(fools the spammers)

Prop selection
 

Complicated subject. Knee jerk comment -- I really worry about vibration.
Mea culpa. Sorry.

Dave Gerr (Propeller Handbook, International Marine, 1989) is not super
helpful here. "Assuming we settle on the acceptable minimum diameter ...
there are few disadvantages of [a smaller propeller] at cruising speed and
above." I read him (as para-quoted above and in other places) to say that
there is a minimum below which THOU SHALT NOT GO, but above that, diameter
is less important -- not Evan's second or third power to efficiency.

So, I should have said, "really worry about tip clearance" as insufficient
tip clearance will eliminate the advantage you get from the AquaDrive. Gerr
suggests 10% (of the diameter between the tips and the hull) absolute
minimum, 15% probably OK, 20% best.




--
Jim Woodward
www.mvFintry.com


..
"Evan Gatehouse" wrote in message
...

"Jim Woodward" jameslwoodward at attbi dot com wrote in message
...

I've made my thoughts on this very clear in a recent thread -- I'd buy
the
traditional MaxProp three blade in a second and never look back. I'd
also
consider going an inch or two smaller in diameter (and up in pitch)
since
you're not near square and a principal contributor to noise and
vibration
is
blade to hull distance -- every half inch counts.

I wouldn't go smaller if possible. Prop efficiency is related to diameter
to some power (^2 or ^3 I can never remember). So "an inch or two" would
be
huge difference in efficiency - and a 16" prop is too small for the engine
size Glenn is installing.

I think that you can just compare prop dimensions and see what tip
clearance you can get. If you can get 20% of prop diameter great.

No opinions on the props under considerationj other than I don't like Max
props flat blades with no twist.

I might have to consider a similar propblem in a few years. I'll let the
group know in a week or so what the next boat might be :)


--
Evan Gatehouse

you'll have to rewrite my email address to get to me
ceilydh AT 3web dot net
(fools the spammers)