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


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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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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.


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