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?

It is true

Prop pitch is somewhat like gearing in a car. If you pull more
(skiing) you need to gear down (lower pitch prop) giving you more
torque and less topspeed.

If you are cruising with a light load you dont need lower gear/pitch
and can have a prop with high pitch and go faster.

Getting the right prop and the right prop for the day/application can
be quiet the quest...

Matt

Prop pitch is somewhat like gearing in a car. If you pull more
(skiing) you need to gear down (lower pitch prop) giving you more
torque and less topspeed.

Hmm. I put a wrong prop on my fiberform years back and it just caused the boat
to "go fast" at idle; but at 1/2 throttle; it'd overheat & never go "faster"....
that's why I thought it was all designed "together"

If you are cruising with a light load you dont need lower gear/pitch
and can have a prop with high pitch and go faster.

and theoretically better fuel economy?


Getting the right prop and the right prop for the day/application can
be quiet the quest...

hmm. well; hopefully there's other Larson owners out there that can help....

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Josh Assing wrote:
-snip-



Getting the right prop and the right prop for the day/application can
be quiet the quest...


hmm. well; hopefully there's other Larson owners out there that can help....

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It really has little to do with being a Larson...

We have 3 different props for our Glastron, all for different days /
activities... I think you need to do some in depth research on prop
selection and not limit yourself to "21' Larson" owners...

Rob

activities... I think you need to do some in depth research on prop
selection and not limit yourself to "21' Larson" owners...


agreed; but a base to start from would be helpful; especially since it's out of
the water right now...


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Josh Assing wrote in message . ..
Prop pitch is somewhat like gearing in a car. If you pull more
(skiing) you need to gear down (lower pitch prop) giving you more
torque and less topspeed.

Hmm. I put a wrong prop on my fiberform years back and it just caused the boat
to "go fast" at idle; but at 1/2 throttle; it'd overheat & never go "faster"....
that's why I thought it was all designed "together"

There are limits ... there will be a few pitch and prop sizes that
work with your boat and different load condiditons.... others will not
make sense.

If you are cruising with a light load you dont need lower gear/pitch
and can have a prop with high pitch and go faster.

and theoretically better fuel economy?

Yes versus using a prop with very low pitch with a light load.


Getting the right prop and the right prop for the day/application can
be quiet the quest...

hmm. well; hopefully there's other Larson owners out there that can help....


has nothing to do with the brand, rather with HP, gear ratio, boat
shape and weight.

Matt

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


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A 2" change in pitch = 2-300 change in rpm's. A 4 bladed prop will give you
a better hole shot. You want the engine to run within recommended WOT. Its
your decision.

--
Bill
Chesapeake, Va


"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


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So; that'd be 6" change in pitch??

w/o backing; it makes the whole thing about pitch & bade "voodoo" vs any sort of
science related.

no difference betwen pitch of 3 vs 4 blades?

On Mon, 30 Aug 2004 22:24:19 -0400, "IBNFSHN" wrote:

A 2" change in pitch = 2-300 change in rpm's. A 4 bladed prop will give you
a better hole shot. You want the engine to run within recommended WOT. Its
your decision.


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Remove x's to send.

Nothing "voodoo" about it. Do a google search on props. There is tons of
info out there.

--
Bill
Chesapeake, Va


"Josh Assing" wrote in message
...
So; that'd be 6" change in pitch??

w/o backing; it makes the whole thing about pitch & bade "voodoo" vs any
sort of
science related.

no difference betwen pitch of 3 vs 4 blades?

On Mon, 30 Aug 2004 22:24:19 -0400, "IBNFSHN" wrote:

A 2" change in pitch = 2-300 change in rpm's. A 4 bladed prop will give
you
a better hole shot. You want the engine to run within recommended WOT.
Its
your decision.


---
Remove x's to send.

"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.