The Right Prop?

[Span 24]

I have a 2003 Starcraft Aurora 2000 Deckboat with the following specs:

Length : 20?4?
Beam: 8?6?
Draft: 29"
Deadrise: 13
Dry Weight: 2,325 lb. (boat only)
Engine: Volvo-Penta 4.3GL
Outdrive: Volvo-Penta SX-M
Prop: Volvo-Penta 15x17

Load for this trip:
Fuel: 45 gallons
Cargo: 250 lbs
Persons: 5 totalling 1100 lbs

Maximum attainable RPMs (WOT): 3800 RPM
Maximum attainable speed: 38 MPH
Time to plane: 5-8 seconds

I only recently purchased the boat. I have had her out several times under differing loads and am finding that I simply cannot get the recommended WOT RPMs called for by the engine manufacturer. I am concerned that the prop is wrong. The engine seems to run just fine. There is just the slightest bit of vibration until we get on plane but I assume this to be normal (kinda like driving a Pontiac Vibe or Ford Escort). The boat does seem to produce quite a large wake, even on plane. I am comparing it to similar boats I see on the water.

Do these numbers seem normal? What might I do to get her to the correct numbers.

My local Marina mechanic told me that they could take my current prop in and drop the pitch to 15.

Any advice is appreciated!

Michael

 

[trswenson]

Re: The Right Prop?

The Mariner - Admiral types may see it different, but it seems to me you're a little slow to plane and and can't quite get WOT specs (what R they?). So proping down in pitch will help, but will also cost you top end.
Assuming your prop is a 3 blade aluminum...? I found 4 blade props get me out of the water significantly quicker, especially when pulling but I suffer top speed ( & don't care).
What does the shop mean by taking your prop in and making it a 15? They actually gonna modify it? Do you already have a spare? Maybe buy a 15P aluminum and have one as a spare
best of luck...

 

[Span 24]

Re: The Right Prop?

The Mariner - Admiral types may see it different, but it seems to me you're a little slow to plane and and can't quite get WOT specs (what R they?). So proping down in pitch will help, but will also cost you top end.
Assuming your prop is a 3 blade aluminum...? I found 4 blade props get me out of the water significantly quicker, especially when pulling but I suffer top speed ( & don't care).
What does the shop mean by taking your prop in and making it a 15? They actually gonna modify it? Do you already have a spare? Maybe buy a 15P aluminum and have one as a spare
best of luck...

The prop is three blade, aluminum. The VP WOT specs are 4200-4600 RPM.

The mechanic indicated that they could re-work the prop and adjust the pitch from 17 to 15. I assume that this is possible and he made it sound quite typical.

I have two props, both Volvo-Penta 15x17 aluminum.

 

[trswenson]

Re: The Right Prop?

since ya have two of the same might as well have the shop work one down to a 15P and test 'em out. You do need less pitch just by the WOT variable. Have a good season!!

 

[hwsiii]

Re: The Right Prop?

Span, if your motor is 190 horsepower and your gear ratio is 1.5 to 1 then changing the prop to a 15" pitch will increase your RPM to right at 4,300 with the total weight you are carrying right now at 4,100 pounds. When you are carrying less people and weight your RPM and speed will go up as well.
But the theory that you will lose top end speed by doing this is wrong, that only happens in theory if you have a 15" prop that can't turn any more RPM than a 17" prop. By changing from a 17" prop that can only turn 3,800 RPM to a 15" prop that will be able to turn 4,300 RPM the speed will stay relatively the same because of the increase in RPM. Right now I am showing your prop slip at 7% with the 17" prop at 3,800 RPM and 38 MPH.
Here are the numbers.

Prop Change

Prop Slip

H

 

[steelespike]

Re: The Right Prop?

If that is a typical load for you then you should prop for that.As H says a
15 will put you about right.Just keep in mind when running light you will need to watch your rpm.Repitching will work fine and you won't be able to tell much difference from a factory 15 but a repitch is a bit of a comprimise.
A prop change is an oportunity to up grade.Check out the Turning Point props. Stainless performance at aluminum prices.Probably not a huge improvement over new aluminum prop but better than a reworked prop.

 

[Span 24]

Re: The Right Prop?

Thank you all for your valued input! I think that I can speak for the majority of the folks like myself who are new to boating when I say that I am very pleased that I do not have to pay for the assistance I get from these forums. Your experience and willingness to help are priceless!

I will take the prop in to be re-pitched and 'see what I get'.

Regarding the rework (changing the pitch), can anyone shed some light on the process for me? When SteelSpike says that it is a compramise between changing the pitch on an old prop and buying new what does he mean? Other than the obvious weakness of a reworked aluminum prop what is different?

Thanx again!

Michael

 

[Tail_Gunner]

Re: The Right Prop?

I have a 2003 Starcraft Aurora 2000 Deckboat with the following specs:

Length : 20?4?
Beam: 8?6?
Draft: 29"
Deadrise: 13
Dry Weight: 2,325 lb. (boat only)
Engine: Volvo-Penta 4.3GL
Outdrive: Volvo-Penta SX-M
Prop: Volvo-Penta 15x17

Load for this trip:
Fuel: 45 gallons
Cargo: 250 lbs
Persons: 5 totalling 1100 lbs

Maximum attainable RPMs (WOT): 3800 RPM
Maximum attainable speed: 38 MPH
Time to plane: 5-8 seconds

I only recently purchased the boat. I have had her out several times under differing loads and am finding that I simply cannot get the recommended WOT RPMs called for by the engine manufacturer. I am concerned that the prop is wrong. The engine seems to run just fine. There is just the slightest bit of vibration until we get on plane but I assume this to be normal (kinda like driving a Pontiac Vibe or Ford Escort). The boat does seem to produce quite a large wake, even on plane. I am comparing it to similar boats I see on the water.

Do these numbers seem normal? What might I do to get her to the correct numbers.

My local Marina mechanic told me that they could take my current prop in and drop the pitch to 15.

Any advice is appreciated!

Michael

That description should be made a sticky...very well done. I could be wrong here but something doesnt sound right..to get to the mfg's recomended spec of 4600 @ WOT it goes as follow's..
17@3800
16@4000
15@4200
14@4400
13@4600
Technical data Engine4.3GL-DProduction period2004-2005Operation4-strokeCylinder configurationV-6Bore (in.)4Stroke (in.)3.48Compression ratio9.3:1Displacement (cu. in.)262Power (hp)190Max engine speed (rpm)4600

http://www.volvo.com/volvopenta/na/...duction_engines/out_of_production_engines.htm


1. check your tach
2.check your timing and state of engine tune
3. check your hull any build up

 

[hwsiii]

Re: The Right Prop?

Tailgunner, the reason I chose the 15" prop for him is his 3,800 RPM at 38MPH is with 5 people weighing 1,100 pounds total, and he says he runs with varying loads. So I figure when only has a couple of people on there and loses that extra 700 pounds of weight and only half his fuel minus another 140 pounds he will most probably be turning the full 4,600 RPM, but if he has a 13" pitch he will be over revving in my opinion. My software shows he should be running a 16" pitch at that time.

 

[Span 24]

Re: The Right Prop?

Tailgunner, the reason I chose the 15" prop for him is his 3,800 RPM at 38MPH is with 5 people weighing 1,100 pounds total, and he says he runs with varying loads. So I figure when only has a couple of people on there and loses that extra 700 pounds of weight and only half his fuel minus another 140 pounds he will most probably be turning the full 4,600 RPM, but if he has a 13" pitch he will be over revving in my opinion. My software shows he should be running a 16" pitch at that time.

I find that I like the idea that I can take one of the two props that I already have (VP 15x17s) and change the pitch to try to put me at the bottom of the WOT RPM range with what will probably be my average load with little danger of over-revving if someone falls out or gets kicked out. This is cheaper than buying a 14" to begin with and if it turns out that I need the additional RPMs then I can always purchase a 14" later for when I really wanna party!

Michael

 

[steelespike]

Re: The Right Prop?

When you rework a prop pitch you change the blade dynamics moving the
thrust point on the blade etc. to keep it simple.There are other more subtle
changes more difficult to describe for me.Could you tell the difference
between a retooled 17 and a factory 17 probably not without some careful testing.There are other procedures as well if a prop is cupped and you need more rpm you can remove some cup with very favorable results.You can add or remove cup and move it around. A stainless allows more fooling around
aluminum not quite so.

 

[MikDee]

Re: The Right Prop?

Span, Is that your specs with 5 people on board? 38mph @3800rpm? If so I would say that you would need a 15" pitch prop which should raise your rpm to about 4200, which is just fine, Right into the bottom of your recommened rpm range. Theoretically then, with a light load you should be at 4600-4800rpm, the top of your recommended rpm range. This sounds just right to me

You may even pick up more speed under load, because you are taking some stress off your engine, but I don't know how a re-worked (re-pitched) prop would work, because I have no experience with them.

 

[Tail_Gunner]

Re: The Right Prop?

The boat is relatively light.... the deepest gears for that combo is 1.66....I think you will find most 18-20' boat's running that combination will turn a 18-23" prop...19 being a norm.

It is not all unusal for a boat tach's to be off 3-500 rpm at all...I find it a bit out of the normal range is all....Most 18-19' boat with a 3.0 turn a 18...I guess i am saying something is a miss..

As to the rpm @ wot going to the top of the ban almost universally assures's the person of top overall performance and the motor working at it peak effeicny.. which is about 3200 ..

I truly believe that the 17 should push that boat to 4600 with the load and a 19 being the norm (light load) With that being said i am trying to suggest to check your tach @ 1000....25000.....3500 for accuracy and if it is on so be it..if not your spending money in the wrong direction

 

[Span 24]

Re: The Right Prop?

Span, Is that your specs with 5 people on board? 38mph @3800rpm? If so I would say that you would need a 15" pitch prop which should raise your rpm to about 4200, which is just fine, Right into the bottom of your recommened rpm range. Theoretically then, with a light load you should be at 4600-4800rpm, the top of your recommended rpm range. This sounds just right to me

You may even pick up more speed under load, because you are taking some stress off your engine, but I don't know how a re-worked (re-pitched) prop would work, because I have no experience with them.

Yes, this is with 5 people on board. I figure this to be a 'normal' load for us. We purchased the deckboat because we love to take family and friends out to ski and cruise. The deckboat is perfect for a half-dozen adults and a few chip-nippers.

I did verify last evening that the throttle is opening fully because this was a question. I think that the engine is running fine. I have to believe that the dealer had to replace the prop and just stuck the 15x17 on to sell it.

At only $30 for the pitch rework, trying a rework to 15" first just makes sense. If it turns out that we still have too much pitch I can purchase a 14". My prop library would them consist of:

15x17
15x15
15x14

This should about cover any outing and I should never find myself without prop-age!

Michael

 

[MikDee]

Re: The Right Prop?

The boat is relatively light.... the deepest gears for that combo is 1.66....I think you will find most 18-20' boat's running that combination will turn a 18-23" prop...19 being a norm.

It is not all unusal for a boat tach's to be off 3-500 rpm at all...I find it a bit out of the normal range is all....Most 18-19' boat with a 3.0 turn a 18...I guess i am saying something is a miss..

As to the rpm @ wot going to the top of the ban almost universally assures's the person of top overall performance and the motor working at it peak effeicny.. which is about 3200 ..

I truly believe that the 17 should push that boat to 4600 with the load and a 19 being the norm (light load) With that being said i am trying to suggest to check your tach @ 1000....25000.....3500 for accuracy and if it is on so be it..if not your spending money in the wrong direction

TG, the boat is about 3990lbs total, with 5 people, 45 gals of gas, & 250lbs cargo,,, I don't consider that light? and it was doing 38mph @ 3800rpm, so he's not far off the low end of his rpm range Fully loaded with a 17" pitch prop. Granted, it'a strong motor, but it's only a V6

 

[Tail_Gunner]

Re: The Right Prop?

TG, the boat is about 3990lbs total, with 5 people, 45 gals of gas, & 250lbs cargo,,, I don't consider that light? and it was doing 38mph @ 3800rpm, so he's not far off the low end of his rpm range Fully loaded with a 17" pitch prop. Granted, it'a strong motor, but it's only a V6

http://www.boatinglife.com/article/Reviews/Starcraft-Aurora-2000-IO


PERFORMANCE
Test Engine: MerCruiser 5.0L.....
Test Prop: 15 x 17, aluminum
Test Load: Fuel (25 gal.); People (425 lb.)
Top Speed: 41.4 MPH @ 4,900 RPM
Time to Plane: 3.1 sec.
Time to 30 MPH: 7.8 sec.
Minimum Planing Speed: 18 MPH @ 2,600 RPM
Noise at Idle: 63 db
Noise at 30 MPH: 81 db
Cruise Stats: 81 db; 31.5 MPH @ 3,600 RPM

POWER CURVE
RPM MPH
600 3.5
1,000 5.5
1,500 7.0
2,000 8.9
2,500 16.0
3,000 25.3
3,500 30.8
4,000 34.8

4,500 39.0
4,900 41.4




Maximum attainable RPMs (WOT): 3800 RPM
Maximum attainable speed: 38 MPH
Time to plane: 5-8 seconds


TG:That description should be made a sticky...very well done. I could be wrong here but something doesnt sound right..to get to the mfg's recomended spec of 4600 @ WOT it goes as follow's..
17@3800
16@4000
15@4200
14@4400
13@4600



...Know you may unerstand my confusion..and asking for a tach check. By the numbers the 13 should hit the mark...Way to small ...but then again as always...Stickly a Opinion..

 

[carter7979]

Re: The Right Prop?

Just bought my first boat guys...16' peterborough with deep v-hull. Has a older 70's 85hp johnson on it with no starter or prop...anyone have these parts for sale? and is it even worth fixing..thanks

 

[Tacklewasher]

Re: The Right Prop?

Start a new thread for this please Carter.

 

[MikDee]

Re: The Right Prop?

http://www.boatinglife.com/article/Reviews/Starcraft-Aurora-2000-IO


PERFORMANCE
Test Engine: MerCruiser 5.0L.....
Test Prop: 15 x 17, aluminum
Test Load: Fuel (25 gal.); People (425 lb.)
Top Speed: 41.4 MPH @ 4,900 RPM
Time to Plane: 3.1 sec.
Time to 30 MPH: 7.8 sec.
Minimum Planing Speed: 18 MPH @ 2,600 RPM
Noise at Idle: 63 db
Noise at 30 MPH: 81 db
Cruise Stats: 81 db; 31.5 MPH @ 3,600 RPM

POWER CURVE
RPM MPH
600 3.5
1,000 5.5
1,500 7.0
2,000 8.9
2,500 16.0
3,000 25.3
3,500 30.8
4,000 34.8

4,500 39.0
4,900 41.4




Maximum attainable RPMs (WOT): 3800 RPM
Maximum attainable speed: 38 MPH
Time to plane: 5-8 seconds


TG:That description should be made a sticky...very well done. I could be wrong here but something doesnt sound right..to get to the mfg's recomended spec of 4600 @ WOT it goes as follow's..
17@3800
16@4000
15@4200
14@4400
13@4600



...Know you may unerstand my confusion..and asking for a tach check. By the numbers the 13 should hit the mark...Way to small ...but then again as always...Stickly a Opinion..

Test engine:Mercruiser 5.0 TG! Span24 has a 4.3V6

And Fuel (25 gal.); People (425 lb.) Span24 had -Fuel: 45 gallons
Cargo: 250 lbs, Persons: 5 totalling 1100 lbs

I still say, a 15" pitch prop

 

[Tail_Gunner]

Re: The Right Prop?

Yes and his v6 is out performing the v8 coupled with 600lbs or more weight..Opp's drop a hun for the 6..