Prop Help Larson 18 ft

[rgood44]

Looking to get better out of the hole performance. Here are the essentials....

1) Performance issue you are trying to correct. ? Need better off the line performance. Better at pulling up skiers

2) Current prop manufacturer, model, aluminum or stainless and as a minimum. Solas aluminum 14.2 x 23

3) Current prop diameter and pitch (required). 23 pitch Diameter 14.2

4) Wide open throttle RPM and speed with an average load (very helpful) ? 4800-4900 (Boat does 52 on the GPS with the 23 pitch prop)

5) Engine/drive make, model, year, and HP - 2000 Volvo Penta 4.3GL (PERS) 190 HP - Volvo Penta SX sterndrive

6) Boat make model, year, length and weight - 2001 Larson 180 SEI - 18 foot, weight 2150 LBS

How far should I go down in pitch?

 

[fossill]

Re: Prop Help Larson 18 ft

I got the same boat but with the mercruiser 4.3L power package and the merc 14x23 oem aluminum 3 blade prop(4400 rpm and 48mph gps). Mine weighs 2375lbs though. I went to a merc 4 blade aluminum 14x20. WOT RPM's at 4600 with average load ( 4 pax/ full fuel /gear) and 48mph gps. Comes up on plane noticeably faster and runs way smoother. I could probably go to a merc 18 pitch prop to put it right at 4800 rpm at full load (Merc dont make an aluminum 19 pitch). I believe the Volvo powerplant is geared different than the Merc though so your outcome may be somewhat different.

 

[rgood44]

Re: Prop Help Larson 18 ft

I got the same boat but with the mercruiser 4.3L power package and the merc 14x23 oem aluminum 3 blade prop(4400 rpm and 48mph gps). Mine weighs 2375lbs though. I went to a merc 4 blade aluminum 14x20. WOT RPM's at 4600 with average load ( 4 pax/ full fuel /gear) and 48mph gps. Comes up on plane noticeably faster and runs way smoother. I could probably go to a merc 18 pitch prop to put it right at 4800 rpm at full load (Merc dont make an aluminum 19 pitch). I believe the Volvo powerplant is geared different than the Merc though so your outcome may be somewhat different.

Thanks. I am probably going to just drop down to a 21 pitch 3 blade and see what happens. I that does not work I am going to try a 4 blade.

 

[steelespike]

Re: Prop Help Larson 18 ft

I don't know what your max ratyed rpm is but you must be very close at 4,800-4900.
If you go to a 21 you'll have to be carefull about overreving.
I think a 4 blade 23 will allow better hole shot,stay on plane with less power,
generally run smoother,no worries of overreving.
A 4 blade 21 will do the same and might temper overeving a little.

 

[rgood44]

Re: Prop Help Larson 18 ft

I don't know what your max ratyed rpm is but you must be very close at 4,800-4900.
If you go to a 21 you'll have to be carefull about overreving.
I think a 4 blade 23 will allow better hole shot,stay on plane with less power,
generally run smoother,no worries of overreving.
A 4 blade 21 will do the same and might temper overeving a little.

Thanks for the advice - I guess I was wrongly assuming that a lower pitch would make my RPM's go down. This is frustrating because it looks like I have about the highest pitched 3 blade prop that you can get for that boat and I am near the top of my RPM range. I just checked my W.O.T and it is actually 4200 - 4600. I have to re-check this - maybe my tach is off (it is new though).

 

[hwsiii]

Re: Prop Help Larson 18 ft

Good, Spike is 100% right, buy a 23" pitch Solas Amita 4 blade aluminum prop and your RPM will drop by about 200 and your hole shot will be much improved, and your top speed should stay at least the same and possibly more as your prop slip right now is 19%, if your lower gear ratio is 1.66:1, please verify the gear ratio, and the WOT top speed you gave us is with your NORMAL load.


And use a mechanic's tachometer to check your RPM before you buy the new prop.



H

 

[rgood44]

Re: Prop Help Larson 18 ft

Good, Spike is 100% right, buy a 23" pitch Solas Amita 4 blade aluminum prop and your RPM will drop by about 200 and your hole shot will be much improved, and your top speed should stay at least the same and possibly more as your prop slip right now is 19%, if your lower gear ratio is 1.66:1, please verify the gear ratio, and the WOT top speed you gave us is with your NORMAL load.


And use a mechanic's tachometer to check your RPM before you buy the new prop.



H

Rechecked RPM's and I am actually at 4500 WOT. Should I still go with the 4 blade 23 pitch?. I believe that my gear ratio is 1.6. Thanks a million for your help!

 

[fossill]

Re: Prop Help Larson 18 ft

I'd be tempted to split the dfference and go to a 22

 

[hwsiii]

Re: Prop Help Larson 18 ft

Was that with your normal load, or were you running light.



H

 

[rgood44]

Re: Prop Help Larson 18 ft

Was that with your normal load, or were you running light.



H

Yes, normal load. 50 mph on the GPS

 

[Tail_Gunner]

Re: Prop Help Larson 18 ft

Rechecked RPM's and I am actually at 4500 WOT. Should I still go with the 4 blade 23 pitch?. I believe that my gear ratio is 1.6. Thanks a million for your help!

That makes sense..A 23 is a bit much for that boat.

22 gets 4700
21 gets 4900........


Now lets look @ 4 blades..Better all around midrange and hole shot lower planeing speeds..etc. That is where 95% of boating occurs

22 gets 4500
21 gets 4700
20 gets 4900

Convert to ss 3blade

22 gets 4500
21 gets 4700
20 gets 4900

4 blade ss
20 gets 4700
19 gets 4900
18 gets 5100

Those numbers should be right...But lets have some fun and talk about it...Your hull is a 21 degree i assume...and the motor is it a 4 or 2 barrel carb...How many people were in the boat when you made that run..

 

[rgood44]

Re: Prop Help Larson 18 ft

That makes sense..A 23 is a bit much for that boat.

22 gets 4700
21 gets 4900........


Now lets look @ 4 blades..Better all around midrange and hole shot lower planeing speeds..etc. That is where 95% of boating occurs

22 gets 4500
21 gets 4700
20 gets 4900

Convert to ss 3blade

22 gets 4500
21 gets 4700
20 gets 4900

4 blade ss
20 gets 4700
19 gets 4900
18 gets 5100

Those numbers should be right...But lets have some fun and talk about it...Your hull is a 21 degree i assume...and the motor is it a 4 or 2 barrel carb...How many people were in the boat when you made that run..

Seems like all is pointing to a 4 blade.... I had two adults (including me) and two kids (6 and 10) in the boat. Question is now - do I go with the 23 pitch 4 blade or the 21 pitch 4 blade?

 

[Tail_Gunner]

Re: Prop Help Larson 18 ft

Volvo Penta 4.3GL (190-hp) Fast FactsPropshaft HP 190-hpConfiguration V-6Displacement 4.3 LBore & Stroke 4.00 & 3.48Base Engine Weight 882 lbs. w/ DPS 874 lbs w/ SXLength/Width/Height 32.5/29.8/20.3Max RPM@WOT 4600 rpmVolvo Penta 4.3GL (190-hp) Fast FactsPropshaft HP 190-hpConfiguration V-6Displacement 4.3 LBore & Stroke 4.00 & 3.48Base Engine Weight 882 lbs. w/ DPS 874 lbs w/ SXLength/Width/Height 32.5/29.8/20.3Max RPM@WOT 4600 rpm

Ummm that 4600 WOT.. factory spec soo a 21. There must be some kind of valve train difference between the FI models and carbed...maybe its the carb gimme a sec

Ok are you sure that is pers or pefs there seems to be a big diff

http://www.volvopenta.com/volvopent..._engines/Pages/out_of_production_engines.aspx

http://www.volvopenta.com/volvopent..._engines/Pages/out_of_production_engines.aspx

If this seems trival there is a 4-500 rpm difference going on here could make a big diff..

 

[rgood44]

Re: Prop Help Larson 18 ft

Volvo Penta 4.3GL (190-hp) Fast FactsPropshaft HP 190-hpConfiguration V-6Displacement 4.3 LBore & Stroke 4.00 & 3.48Base Engine Weight 882 lbs. w/ DPS 874 lbs w/ SXLength/Width/Height 32.5/29.8/20.3Max RPM@WOT 4600 rpmVolvo Penta 4.3GL (190-hp) Fast FactsPropshaft HP 190-hpConfiguration V-6Displacement 4.3 LBore & Stroke 4.00 & 3.48Base Engine Weight 882 lbs. w/ DPS 874 lbs w/ SXLength/Width/Height 32.5/29.8/20.3Max RPM@WOT 4600 rpm

Ummm that 4600 WOT.. factory spec soo a 21. There must be some kind of valve train difference between the FI models and carbed...maybe its the carb gimme a sec

Ok are you sure that is pers or pefs there seems to be a big diff

http://www.volvopenta.com/volvopent..._engines/Pages/out_of_production_engines.aspx

http://www.volvopenta.com/volvopent..._engines/Pages/out_of_production_engines.aspx

If this seems trival there is a 4-500 rpm difference going on here could make a big diff..

Tail Gunner - Thanks for taking the time to answer my questions!

I looked at my serial numbers again and the motor is a 4.3GL PEFS. My drive is volvo penta SX-M 1.79. I assume that the 1.79 is the drive ratio if so I said it was a 1.6 above. Maybe this solves that puzzle?

 

[Tail_Gunner]

Re: Prop Help Larson 18 ft

Tail Gunner - Thanks for taking the time to answer my questions!

I looked at my serial numbers again and the motor is a 4.3GL PEFS. My drive is volvo penta SX-M 1.79. I assume that the 1.79 is the drive ratio if so I said it was a 1.6 above. Maybe this solves that puzzle?

20p baypro 11 in a four blade ss or a 21p in a 4 blade alum...

http://boatpropellers.iboats.com/Vo...20521/?**********=314045279&*******=920181559

http://boatpropellers.iboats.com/Vo...23343/?**********=314045279&*******=920181559


That 1.79 gear ratio was a big factor...1.66 and take those props down 1 inch

 

[rgood44]

Re: Prop Help Larson 18 ft

20p baypro 11 in a four blade ss or a 21p in a 4 blade alum...

http://boatpropellers.iboats.com/Vo...20521/?**********=314045279&*******=920181559

http://boatpropellers.iboats.com/Vo...23343/?**********=314045279&*******=920181559


That 1.79 gear ratio was a big factor...1.66 and take those props down 1 inch

Just put on the alum. 21p 4 blade. I hope to have it out this weekend. I will report back with the results.

Thanks again for your help!

 

[rgood44]

Re: Prop Help Larson 18 ft

As an update (Thanks Tail_Gunner!) The 4 blade works great - really did not lose any top end and much better low end. Better getting to plan as well! Running at 4500 WOT perfect!