"Josh Assing" wrote in message
...
1st I want to say thank you to all that have chimed in with advise &
input.
THANK YOU.

Here's the info I think everyone wants:

1990 AM210 Larson

According to Larson:
Came with a 3blade 19 pitch prop (alum)

According to Larson & Mercruiser:
200hp v8 5.0l engine

According to Mercruiser:
WOT RPM goal: 4200-4600

Currently has a 4 blade 20 pitch prop (alum)

Flat water:
I can, at WOT, achive 4600-4800 w/o trim @ about 30-34mph

Trimming the outdrive -- I get 5400 RPM at about 43-48mph

w/ waves -- I can't trim it that much -- as the prop gets too much air -
and can
achieve 4800-5000 RPM @ 36-43 mph

so it seems I need to go up at least 1 in pitch -- maybe 2?

Any thoughts/input/ideas?
I've read that a 3 blade is more efficient; but more vibration is felt.
And
that you need different pitches based on what you want.


I want a good "all around" prop -- I'm not planning on towing or water
skiing;
but I would like to plane quickly; and have good power/speed with "bow
down" in
waves.

What would my choices be for 3 vs 4 blade prop?

THANK YOU for your time & input....

Cheers
-josh

What are you determining speed with? 30mph at 4600rpm with a 20 pitch prop
seems slow. (lots of slippage. If you know your final drive ratio you can
calculate your max speed at any rpm with your prop. Just remember a 20 pitch
prop moves forward 20" in every revolution. With a 1.6 ratio (I don't know
yours this is just an example) final drive your max speed would be about 55
at 4600rpm. Even at an inefficient 80 per cent you still should be doing
over 40.

You are not accounting for slippage which all props do. A 20 pitch prop will
move forward 20" in and ideal medium. Water is not an ideal medium.

--
Bill
Chesapeake, Va


"calhoun" wrote in message
...

"Josh Assing" wrote in message
...
1st I want to say thank you to all that have chimed in with advise &
input.
THANK YOU.

Here's the info I think everyone wants:

1990 AM210 Larson

According to Larson:
Came with a 3blade 19 pitch prop (alum)

According to Larson & Mercruiser:
200hp v8 5.0l engine

According to Mercruiser:
WOT RPM goal: 4200-4600

Currently has a 4 blade 20 pitch prop (alum)

Flat water:
I can, at WOT, achive 4600-4800 w/o trim @ about 30-34mph

Trimming the outdrive -- I get 5400 RPM at about 43-48mph

w/ waves -- I can't trim it that much -- as the prop gets too much air -
and can
achieve 4800-5000 RPM @ 36-43 mph

so it seems I need to go up at least 1 in pitch -- maybe 2?

Any thoughts/input/ideas?
I've read that a 3 blade is more efficient; but more vibration is felt.
And
that you need different pitches based on what you want.


I want a good "all around" prop -- I'm not planning on towing or water
skiing;
but I would like to plane quickly; and have good power/speed with "bow
down" in
waves.

What would my choices be for 3 vs 4 blade prop?

THANK YOU for your time & input....

Cheers
-josh

What are you determining speed with? 30mph at 4600rpm with a 20 pitch prop
seems slow. (lots of slippage. If you know your final drive ratio you can
calculate your max speed at any rpm with your prop. Just remember a 20
pitch
prop moves forward 20" in every revolution. With a 1.6 ratio (I don't know
yours this is just an example) final drive your max speed would be about
55
at 4600rpm. Even at an inefficient 80 per cent you still should be doing
over 40.

How much slippage do you account for? In my post I allowed for 20%. (80%
efficient) I thought the general consensus was about 10%.


"IBNFSHN" wrote in message
news:c7pZc.75270$wo.17696@okepread06...
You are not accounting for slippage which all props do. A 20 pitch prop
will
move forward 20" in and ideal medium. Water is not an ideal medium.

--
Bill
Chesapeake, Va


"calhoun" wrote in message
...

"Josh Assing" wrote in message
...
1st I want to say thank you to all that have chimed in with advise &
input.
THANK YOU.

Here's the info I think everyone wants:

1990 AM210 Larson

According to Larson:
Came with a 3blade 19 pitch prop (alum)

According to Larson & Mercruiser:
200hp v8 5.0l engine

According to Mercruiser:
WOT RPM goal: 4200-4600

Currently has a 4 blade 20 pitch prop (alum)

Flat water:
I can, at WOT, achive 4600-4800 w/o trim @ about 30-34mph

Trimming the outdrive -- I get 5400 RPM at about 43-48mph

w/ waves -- I can't trim it that much -- as the prop gets too much
air -
and can
achieve 4800-5000 RPM @ 36-43 mph

so it seems I need to go up at least 1 in pitch -- maybe 2?

Any thoughts/input/ideas?
I've read that a 3 blade is more efficient; but more vibration is
felt.
And
that you need different pitches based on what you want.


I want a good "all around" prop -- I'm not planning on towing or water
skiing;
but I would like to plane quickly; and have good power/speed with "bow
down" in
waves.

What would my choices be for 3 vs 4 blade prop?

THANK YOU for your time & input....

Cheers
-josh

What are you determining speed with? 30mph at 4600rpm with a 20 pitch
prop
seems slow. (lots of slippage. If you know your final drive ratio you
can
calculate your max speed at any rpm with your prop. Just remember a 20
pitch
prop moves forward 20" in every revolution. With a 1.6 ratio (I don't
know
yours this is just an example) final drive your max speed would be about
55
at 4600rpm. Even at an inefficient 80 per cent you still should be doing
over 40.

What are you determining speed with? 30mph at 4600rpm with a 20 pitch prop
seems slow. (lots of slippage. If you know your final drive ratio you can
calculate your max speed at any rpm with your prop. Just remember a 20 pitch
prop moves forward 20" in every revolution. With a 1.6 ratio (I don't know
yours this is just an example) final drive your max speed would be about 55
at 4600rpm. Even at an inefficient 80 per cent you still should be doing
over 40.


GPS -- so I'm pretty sure it's accurate -- I don't know what my final ratio is.




---
Remove x's to send.

To properly prop your boat you need to know what the WOT (wide open
throttle) range is for your motor. Then you need to know what RPM you now
turn (with a normal load) at WOT. It is usually just a matter of adjusting
the pitch up or down.

--
Bill
Chesapeake, Va


"Josh Assing" wrote in message
...
We just picked up a larson power boat - the PO said it had a "ski prop" on
it;
but if we put the "stock" prop on; the boat would be faster....

I don't know much about props; but I thought props were 'designed' for
engine &
boat -- and couldn't (shouldn't) be swapped about....

is this true? if so; what should the proper prop be for the boat?

Thanks
-josh


---
Remove x's to send.

How do I find this information?

On Thu, 26 Aug 2004 16:58:34 -0400, "IBNFSHN" wrote:

To properly prop your boat you need to know what the WOT (wide open
throttle) range is for your motor. Then you need to know what RPM you now
turn (with a normal load) at WOT. It is usually just a matter of adjusting
the pitch up or down.


---
Remove x's to send.

Josh Assing wrote:

How do I find this information?


From the engine manufacturer... AND/OR, if you give us all information
about your boat & engine, there are people in the NG who can pull their
attention away from politics & back to boating long enough to impart
some good advice, even some expert knowledge...!

Rob




On Thu, 26 Aug 2004 16:58:34 -0400, "IBNFSHN" wrote:


To properly prop your boat you need to know what the WOT (wide open
throttle) range is for your motor. Then you need to know what RPM you now
turn (with a normal load) at WOT. It is usually just a matter of adjusting
the pitch up or down.



---
Remove x's to send.

From the engine manufacturer... AND/OR, if you give us all information
about your boat & engine, there are people in the NG who can pull their
attention away from politics & back to boating long enough to impart
some good advice, even some expert knowledge...!

Thanks.

found out that the engine is rated for 4200-4600 rpm at WOT. It left the
factory with a 14.5x19 prop (3 blade) it currently has a 20pitch 4 blade. it
tops out at like 35; but the data I've found said the boat should reach 45-50.


---
Remove x's to send.

What are your current wide open rpms w/ 2 people on board and full of fuel
(or what condition do you know the wide open rpms).
What is the current 20 pitch 4 blade prop. Is it SS, aluminum, plastic.
What brand/model.

Usually a 4 blade is the best all around prop. Especially if your turning
the right amount of rpms. I doubt you are though.

My guess is a good 18 4 blade SS would be about right for this boat not
knowing the info above.

--
Tony
my boats at http://t.thomas.home.mchsi.com

"Josh Assing" wrote in message
news


From the engine manufacturer... AND/OR, if you give us all information
about your boat & engine, there are people in the NG who can pull their
attention away from politics & back to boating long enough to impart
some good advice, even some expert knowledge...!

Thanks.

found out that the engine is rated for 4200-4600 rpm at WOT. It left the
factory with a 14.5x19 prop (3 blade) it currently has a 20pitch 4 blade.
it
tops out at like 35; but the data I've found said the boat should reach
45-50.


---
Remove x's to send.

Josh Assing wrote:
We just picked up a larson power boat - the PO said it had a "ski prop" on it;
but if we put the "stock" prop on; the boat would be faster....

I don't know much about props; but I thought props were 'designed' for engine &
boat -- and couldn't (shouldn't) be swapped about....

is this true? if so; what should the proper prop be for the boat?

Thanks
-josh


---
Remove x's to send.

I bet by ski-prop they mean it has a lower pitch. Thus better whole shot
for popping out folks out of the water and dragging them less. You would
lose a little top end. As long as you don't run the boat in excess of
recomended rpm. It would be fine.

Capt Jack R..