Prop clearance specs?
 

I have a alpha1 gen II outdrive.
As some of you know; I'm trying to reprop -- found a shop nearby that
rents demo props. They gave mea 15" prop (diameter) but I didn't try it as the
clearance between the prop blade edge and the cavetation plate was less than a
wire-coat hanger.

They said "it improves performance, use it anyway" My gut says that the
clearance is so small that it's begging for damage from a twig in the water.

Two people (one I consider knowledgeable and one from a shop I use regularly)
said "that's not enough clearance, should be about 10% of the prop diameter"

To me - -this sounds reasonable.

So; since the shop with the demo props doesn't want (for unknown reasons) to
give me a 14 or 14.5 diameter prop, I'm stuck with buying a new one; for that
reason; I'm looking to the NG for people that have "almost no clearance" between
the blade & the cavetation plate to see real-world experiences.

We're talking a SS prop. If I guy a prop; I'll probably go with aluminum 1st
(cheaper) while I experiement and then go SS once I settle on size & pitch &
blade count.

Thanks
-j

Prop clearance specs?
 

On Sat, 12 May 2007 11:47:05 -0700, Josh Assing
wrote:

Two people (one I consider knowledgeable and one from a shop I use regularly)
said "that's not enough clearance, should be about 10% of the prop diameter"

And ten percent of a 15 inch diameter prop would be what?

That is way to close for a number of reasons including cavitation.

What you are looking for is a 14.5/21p or thereabouts - might need a
19p - doubt if you will need a 23.

Prop clearance specs?
 

And ten percent of a 15 inch diameter prop would be what?

exactly - -it's not 3 mm


That is way to close for a number of reasons including cavitation.

that's what I thought -- the demo-prop-shop said "it will increase performance
by directing more water aft rather than up" seemed snake-oilish to me.


What you are looking for is a 14.5/21p or thereabouts - might need a
19p - doubt if you will need a 23.
well; wrong way -- I have 19pitch now; need to go down in pitch to 17 or 16.
(wot now = 4100, need to get it to 4400-4600)

Thanks
-j

Prop clearance specs?
 

"Josh Assing" wrote
My gut says that the clearance is so small that it's
begging for damage from a twig in the water.

Twigs care not for clearance. I have about an inch between my prop and
cavitation plate (which, I must point out is technically an anti-ventilation
plate). I hit a small twig a couple years ago and took a big chunk out of
said plate. http://users.adelphia.net/~blizzard3...ges/break2.jpg

Prop clearance specs?
 

On Sat, 12 May 2007 17:08:02 -0400, Gene Kearns
wrote:

On Sat, 12 May 2007 19:44:03 GMT, Short Wave Sportfishing penned the
following well considered thoughts to the readers of rec.boats:

On Sat, 12 May 2007 11:47:05 -0700, Josh Assing
wrote:

Two people (one I consider knowledgeable and one from a shop I use regularly)
said "that's not enough clearance, should be about 10% of the prop diameter"

And ten percent of a 15 inch diameter prop would be what?

That is way to close for a number of reasons including cavitation.

What you are looking for is a 14.5/21p or thereabouts - might need a
19p - doubt if you will need a 23.

1.5 inches? Mine is 1 inch with a 13.25 inch prop.

Suzuki puts a 14 inch prop on the same engine.... so, I'm figuring
that they are OK with 5/8 of an inch....

Yeah - I didn't quite say that correctly. In fact, I thought 1.5
inches was a little much - as in 10% seemed like a lot.

On the ETEC, it's a half inch.

Prop clearance specs?
 

On Sat, 12 May 2007 13:40:08 -0700, Josh Assing
wrote:

And ten percent of a 15 inch diameter prop would be what?

exactly - -it's not 3 mm


That is way to close for a number of reasons including cavitation.

that's what I thought -- the demo-prop-shop said "it will increase performance
by directing more water aft rather than up" seemed snake-oilish to me.


What you are looking for is a 14.5/21p or thereabouts - might need a
19p - doubt if you will need a 23.
well; wrong way -- I have 19pitch now; need to go down in pitch to 17 or 16.
(wot now = 4100, need to get it to 4400-4600)

Whoops - sorry - read that wrong. My bad.

I think you are probably close on that, but you might want to consider
having the rpm checked using a meter directly off the engine. I know
when I swapped engines on the Ranger, we couldn't get 5400 top end out
of the gage on the dash, but when we looked at the EMM, it was 5400 on
the nose. It was about the same RPM range you noted.

Threw a new RPM gage in the dash - presto.

Just something to think about.

Prop clearance specs?
 

I've never had a tach go bad -- but I'll check it out with my old analog meter
and see what it ways...

On Sun, 13 May 2007 11:00:35 GMT, Short Wave Sportfishing
wrote:

On Sat, 12 May 2007 13:40:08 -0700, Josh Assing
wrote:

And ten percent of a 15 inch diameter prop would be what?

exactly - -it's not 3 mm


That is way to close for a number of reasons including cavitation.

that's what I thought -- the demo-prop-shop said "it will increase performance
by directing more water aft rather than up" seemed snake-oilish to me.


What you are looking for is a 14.5/21p or thereabouts - might need a
19p - doubt if you will need a 23.
well; wrong way -- I have 19pitch now; need to go down in pitch to 17 or 16.
(wot now = 4100, need to get it to 4400-4600)

Whoops - sorry - read that wrong. My bad.

I think you are probably close on that, but you might want to consider
having the rpm checked using a meter directly off the engine. I know
when I swapped engines on the Ranger, we couldn't get 5400 top end out
of the gage on the dash, but when we looked at the EMM, it was 5400 on
the nose. It was about the same RPM range you noted.

Threw a new RPM gage in the dash - presto.

Just something to think about.

Prop clearance specs?
 

Yikes; well; I still have my plate complete, save for a crack...
Still a coat hanger is what, a few mm's at most? heat up a prop and get it
spinning -- seems that space would be taken up in no time.

On Sat, 12 May 2007 23:15:46 -0400, "Ernest Scribbler"
wrote:

"Josh Assing" wrote
My gut says that the clearance is so small that it's
begging for damage from a twig in the water.

Twigs care not for clearance. I have about an inch between my prop and
cavitation plate (which, I must point out is technically an anti-ventilation
plate). I hit a small twig a couple years ago and took a big chunk out of
said plate. http://users.adelphia.net/~blizzard3...ges/break2.jpg

Prop clearance specs?
 

Are you completely sure the motor is running at it's best? You didn't give
much info but I'm thinking at one time the prop you have on it may have been
correct. I agree about the size, you want something between 14 and 14.5. I
think the 15s were common on the bravos. If you want to experiment buy used
props off ebay. You can resell them for about what you paid for them.

"Josh Assing" wrote in message
...
I've never had a tach go bad -- but I'll check it out with my old analog
meter
and see what it ways...

On Sun, 13 May 2007 11:00:35 GMT, Short Wave Sportfishing

wrote:

On Sat, 12 May 2007 13:40:08 -0700, Josh Assing
wrote:

And ten percent of a 15 inch diameter prop would be what?

exactly - -it's not 3 mm


That is way to close for a number of reasons including cavitation.

that's what I thought -- the demo-prop-shop said "it will increase
performance
by directing more water aft rather than up" seemed snake-oilish to me.


What you are looking for is a 14.5/21p or thereabouts - might need a
19p - doubt if you will need a 23.
well; wrong way -- I have 19pitch now; need to go down in pitch to 17 or
16.
(wot now = 4100, need to get it to 4400-4600)

Whoops - sorry - read that wrong. My bad.

I think you are probably close on that, but you might want to consider
having the rpm checked using a meter directly off the engine. I know
when I swapped engines on the Ranger, we couldn't get 5400 top end out
of the gage on the dash, but when we looked at the EMM, it was 5400 on
the nose. It was about the same RPM range you noted.

Threw a new RPM gage in the dash - presto.

Just something to think about.

Prop clearance specs?
 

On Mon, 14 May 2007 12:02:21 GMT, "jamesgangnc"
wrote:

Are you completely sure the motor is running at it's best? You didn't give
much info but I'm thinking at one time the prop you have on it may have been
correct. I agree about the size, you want something between 14 and 14.5. I
think the 15s were common on the bravos. If you want to experiment buy used
props off ebay. You can resell them for about what you paid for them.

That was my thought - something ain't right there.

Good idea on that eBay thing - although I'm not much of a eBay type.

Anybody know how selling on eBay works - per chance?

I've never done it, but I've got some motorcycle parts from my
youngest's GSX R600 - stock parts - that I want to get rid of, sell,
swap - whatever.