Prop Suggestions Needed

[Seaswirl89]

Boat/Motor: 1989 seaswirl spyder 202 (20’ length) with an OMC 4.3L 190HP V6
Boat mechanic did a preseason tune up and everything checked out, in other words no issues that are known of

Props used: 14.5”x19degree aluminum. Didn’t make it to 4000rmps at a lake at 6000’ elevation(I believe it was around 3600/3800 rmps if I remember. MPH obtained was +- 38mph at WOT
15”x17 degrees aluminum: Will get up to 4000 rmps at 5000’ elevation lake (hasn’t been tested at 6000’ elevation) at WOT for 20 or so seconds. This prop has better hole shot than the 19 degree prop. MPH was not tested. I like this setup pretty good but RMPs not ideal (I believe I need to be 4200-4800)

What I would like to do: Good hole shot for wakeboarding and quick to get on plane from lakes at 4000’-7000’ elevation. Run the engine in its optimal RMP range at WOT (need 200-400rpm additional over the 17 degree prop assuming Tac gauge is accurate) to increase motor longevity

Should I get: a smaller diameter prop with the same 17 degree pitch? Or same 15” prop but lower degree pitch?

 

[Scott06]

Boat/Motor: 1989 seaswirl spyder 202 (20’ length) with an OMC 4.3L 190HP V6
Boat mechanic did a preseason tune up and everything checked out, in other words no issues that are known of

Props used: 14.5”x19degree aluminum. Didn’t make it to 4000rmps at a lake at 6000’ elevation(I believe it was around 3600/3800 rmps if I remember. MPH obtained was +- 38mph at WOT
15”x17 degrees aluminum: Will get up to 4000 rmps at 5000’ elevation lake (hasn’t been tested at 6000’ elevation) at WOT for 20 or so seconds. This prop has better hole shot than the 19 degree prop. MPH was not tested. I like this setup pretty good but RMPs not ideal (I believe I need to be 4200-4800)

What I would like to do: Good hole shot for wakeboarding and quick to get on plane from lakes at 4000’-7000’ elevation. Run the engine in its optimal RMP range at WOT (need 200-400rpm additional over the 17 degree prop assuming Tac gauge is accurate) to increase motor longevity

Should I get: a smaller diameter prop with the same 17 degree pitch? Or same 15” prop but lower degree pitch?

I think you will loose 15-20% power at these higher elevations and your carb will need rejetting if it hasn;t been set up for these elevations. De rated for altitude you probably only are making 160 or so hp on a faily decent sized boat.
Try a 15" pitch or if wakeboarding is your thing try a 4 blade in a 15" pitch. For holeshsot nothing beats a 4 blade.

 

[Seaswirl89]

I think you will loose 15-20% power at these higher elevations and your carb will need rejetting if it hasn;t been set up for these elevations. De rated for altitude you probably only are making 160 or so hp on a faily decent sized boat.
Try a 15" pitch or if wakeboarding is your thing try a 4 blade in a 15" pitch. For holeshsot nothing beats a 4 blade.

Thanks for the info. Back in 1989 the boat was bought new at this elevation and hasn’t left so I believe it was setup for it. It seems to run and idle well so I feel like it’s been jetted for this elevation.

So if I lose 15-20% of my power due to elevation, that doesn’t mean I lose WOT rmps correct? I just lose the ability to turn a normal pitch (17 or 19 degree) at motor spec WOT rmps correct?

 

[Seaswirl89]

Thanks for the info. Back in 1989 the boat was bought new at this elevation and hasn’t left so I believe it was setup for it. It seems to run and idle well so I feel like it’s been jetted for this elevation.

So if I lose 15-20% of my power due to elevation, that doesn’t mean I lose WOT rmps correct? I just lose the ability to turn a normal pitch (17 or 19 degree) at motor spec WOT rmps correct

I think you will loose 15-20% power at these higher elevations and your carb will need rejetting if it hasn;t been set up for these elevations. De rated for altitude you probably only are making 160 or so hp on a faily decent sized boat.
Try a 15" pitch or if wakeboarding is your thing try a 4 blade in a 15" pitch. For holeshsot nothing beats a 4 blade.

And when you say 15 degree pitch prop, what diameter of prop? 15 inches?

 

[Scott06]

And when you say 15 degree pitch prop, what diameter of prop? 15 inches?

Dont sweat the diameter that is for the prop designer to figure out. I belive the rule of thumb is 2" pitch decrease per 3000 ft of elevation increase . Was the boat ok with a 19" at sea level or close to it

 

[Seaswirl89]

Dont sweat the diameter that is for the prop designer to figure out I forget the rule of thumb is 2" per 3000 ft of elevation. Was the boat ok with a 19" at sea level or close to it

The previous owner never had it below 4000’ elevation and I’ve never had it below 5000’ elevation. The previous owner said the 19” was the speed prop and 17 was for skiing. I ran the 17 yesterday and think there’s still room for improvement because it only get to 4000 rmps at WOT

 

[Seaswirl89]

Bump

 

[Scott06]

The previous owner never had it below 4000’ elevation and I’ve never had it below 5000’ elevation. The previous owner said the 19” was the speed prop and 17 was for skiing. I ran the 17 yesterday and think there’s still room for improvement because it only get to 4000 rmps at WOT

Ok so based on what you are showing for rpms and stated good running condition drop 2” in pitch

 

[Seaswirl89]

Ok so based on what you are showing for rpms and stated good running condition drop 2” in pitch

Thanks for the info, I’ll start looking for a 15 degree pitch prop that is 15” in diameter

 

[Scott06]

Thanks for the info, I’ll start looking for a 15 degree pitch prop that is 15” in diameter

Again dont worry about the diameter. Typically diameter will go up as pitch goes down in the same prop. Your safest bet would be to stay with the same prop just go down one step in pitch. If you can find a local prop shop that will let you try before you buy that is also a good route