21' larson prop size?
 

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.

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

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.

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..

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....

---
Remove x's to send.

Thanks.

Now I just gotta figure out what the RPM range is & all that jazz.
I'd rather have better top end & fuel economy...

-josh

On Thu, 26 Aug 2004 21:33:03 GMT, Jack Redington
wrote:

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..


---
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:

Thanks.

Now I just gotta figure out what the RPM range is & all that jazz.
I'd rather have better top end & fuel economy...

-josh

On Thu, 26 Aug 2004 21:33:03 GMT, Jack Redington
wrote:


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..



---
Remove x's to send.

The recomended rpm's (high end) will be with the manufactures
documentation. If you don't have it you can get it from whoever made the
power plant.

Capt Jack R..

The recomended rpm's (high end) will be with the manufactures
documentation. If you don't have it you can get it from whoever made the
power plant.

Thanks -- I'll try to find them -- it's a mercruiser mcm 5.0litre "AlphaOne"
engine

cheers!
-josh

---
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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....

---
Remove x's to send.

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

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.

I believe it should be 4200-4600 rpm.

--
Bill
Chesapeake, Va


"Josh Assing" wrote in message
...
The recomended rpm's (high end) will be with the manufactures
documentation. If you don't have it you can get it from whoever made the
power plant.

Thanks -- I'll try to find them -- it's a mercruiser mcm 5.0litre
"AlphaOne"
engine

cheers!
-josh

---
Remove x's to send.

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

Josh Assing wrote in message . ..
The recomended rpm's (high end) will be with the manufactures
documentation. If you don't have it you can get it from whoever made the
power plant.

Thanks -- I'll try to find them -- it's a mercruiser mcm 5.0litre "AlphaOne"
engine

If its this motor:

5.0 MPI - 260 HP


Then WOT=5000 rpm

att

Josh Assing wrote in message . ..
Thanks.

Now I just gotta figure out what the RPM range is & all that jazz.
I'd rather have better top end & fuel economy...

RPM ... see my other reply...

If you do skiing then you should keep the low pitch prop on there. If
not get a prop with normal pitch for this boat.

With a propeller boat you might want to have 2-3 different props for
different uses and put on the prop for the day, depending what you do.

(One spare with tools to put it on should be in the boat)

Matt

I have a 18Sei w/ 3.0 Litter. Came with a 17 inch. Too much throttle left.
19 is perfect. 21 was too much.

Mike

"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.

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...


---
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.

Thanks -- I'll try to find them -- it's a mercruiser mcm 5.0litre "AlphaOne"
engine

If its this motor:

5.0 MPI - 260 HP


Then WOT=5000 rpm

5.0 mmc -- mercruiser said it's a 200hp & 4200-4600

---
Remove x's to send.

I planned on putting this prop in the boat for "spare" -- but I want a better
"all around" prop for day-to-day usage -- as we plan on leaving it in the
water...

On 27 Aug 2004 12:30:27 -0700, (Matt Lang) wrote:

Josh Assing wrote in message . ..
Thanks.

Now I just gotta figure out what the RPM range is & all that jazz.
I'd rather have better top end & fuel economy...

RPM ... see my other reply...

If you do skiing then you should keep the low pitch prop on there. If
not get a prop with normal pitch for this boat.

With a propeller boat you might want to have 2-3 different props for
different uses and put on the prop for the day, depending what you do.

(One spare with tools to put it on should be in the boat)

Matt


---
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
...


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.

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


---
Remove x's to send.

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


---
Remove x's to send.

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.

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.

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.

You are correct. That's what I get for not reading close enough. Typical
slippage is 15-20%. Now you got me thinking, I wonder what the difference is
between fresh and salt water.

--
Bill
Chesapeake, Va


"calhoun" wrote in message
...
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.