Next prop recommendation - 5.0L Gxi SX drive

[bhollehday]

Ive got a 2006 Larson Senza 206 that I use for towing and cruising. The recommended WOT ROM range is 4600-5000. I have a 14.5x17 4 blade aluminum that WOT RPM is at 4500 and about 40mph. My 15x16 4 blade aluminum was WOT at 5100 RPM (I had to pull off a smidge to keep it at 5000). I need to buy another prop and want to jump out of the water with the most top speed. The 16 felt a lot more jump and pull and I didnt get more than 1-2mph on top speed with the 17. Could I go with a slightly larger diameter 16p to bring the RPM down?

 

[Scott Danforth]

Cant have both...you get holeshot or top speed. Pick one

 

[bhollehday]

Cant have both...you get holeshot or top speed. Pick one

I guess what im asking is what direction would I go with the diameter and in what size in order to bring the RPM's down about 200 RPM at WOT with the 16 pitch prop

 

[Scott Danforth]

generally 1" of pitch is about 200 RPM at the top end. the 4th blade is about another 100 rpm compared to a 3 blade. however in your case something doesnt add up. you should have only dropped about 200 RPM with your new prop

either you went with a different style of prop that is more agressive such as blade design, etc. diameter has minimal effect. it is primarily blade design and pitch.

you may have also lost a cylinder (bad plug,etc) since you dropped 600 RPM

I would personally go with a 17P 3-blade

 

[dingbat]

Cant have both...you get holeshot or top speed. Pick one

interesting you would say that..I got better hole shot and better top end going with a different prop design on my recent prop swap. If anything my performance loss was at mid-range.

 

[Sea Rider]

If that were my combo would stay with current 15x16 4 blade aluminum prop. +100 wot rpm over revving from max wot range is nothing. Will be interesting to know how loaded was the combo when achieved 5100 wot rpm.

That rule of thumb that states constant +,- 200 wot revs is a falacy. Have seen those numbers on very heavy boats, not recreational though. This is another clear example achieving + 600 wot revs with only one less pitch. I have achieved 500 to 1000 wot revs increase running under powered OB's on light boats with 3 blade props and 1- 2 less pitches as currently loaded.

You can experience increasing hole shot along top end speed at same time if going from a prop spinning around the lugging range with next less pitch prop that revs towards middle range. Middle range towards full wot range it's a different scenario as stated by Scott and becomes a matter of which you preffer : Best hole shot or best top end speed by playing with pitches while maintaining same 3 or 4 blade props from previous one.

Happy Boating

 

[bhollehday]

If that were my combo would stay with current 15x16 4 blade aluminum prop. +100 wot rpm over revving from max wot range is nothing. Will be interesting to know how loaded was the combo when achieved 5100 wot rpm.

That rule of thumb that states constant +,- 200 wot revs is a falacy. Have seen those numbers on very heavy boats, not recreational though. This is another clear example achieving + 600 wot revs with only one less pitch. I have achieved 500 to 1000 wot revs increase running under powered OB's on light boats with 3 blade props and 1- 2 less pitches as currently loaded.

You can experience increasing hole shot along top end speed at same time if going from a prop spinning around the lugging range with next less pitch prop that revs towards middle range. Middle range towards full wot range it's a different scenario as stated by Scott and becomes a matter of which you preffer : Best hole shot or best top end speed by playing with pitches while maintaining same 3 or 4 blade props from previous one.

Happy Boating

The 17p was likely loaded up with a couple more people than the 16p was. Its got new plugs and everything is running good. Props are the same, 16p has glossy powder coated finish and the 17p had a dull flat anodized finish only difference I can see. The 17p is a Solax:

https://www.wholesalemarine.com/sol...ENshiKCtbvM7zHEfAtd_of5UlkiqsdgEaAn6pEALw_wcB

And the 16p is a Michigan Wheel Vortex:

https://www.deepblueyachtsupply.com/michigan-wheel-vortex-992202

I was always told to stay 4 blade if I wanted to get the pull out of the hole. What kind of performance differences did you see between the two?

Ive got auto leveling tabs that help jump the boat onto plane. The 5.0L GXi seems to have a good amount of power. I also will be putting in a tuner that gives some more performance from modified air/fuel maps next. Would I get a small amount less holeshot with higher top end speeds with a 3 blade?

 

[Sea Rider]

Can't answer that complex question have 0 experience with 4 blade props. I always go per prop maximizations with 3 blade alum OEM props. 1 less pitch while maintaining same diam prop is a day night difference in performance depending which side of the boating fun you want to fine tune.

On 3 blade props applies same concept, less pitch higher wot rpm. increases hole shot with slight tiop end decrease speed, more pitch, decreases hole shot with slight top end speed increase.

Each prop manufacturer has their own parameters, much better would be testing same brand pros in the 3-4 blade range playing with pitches. Mixing prop brands with same diam, blades, pitch will give different rpm performance results.

Correct deck weight distribution along proper trim accounts too for faster hole shot while propped right.

Happy Boating

 

[Maclin]

For a 5.0 fuel injected engine in a 20 footer, seems like it is down on power to me. Maybe the tabs are not flattening out at speed. Are you using the trim up? Is the spray back on the hull with bow up a few degrees? Feeling is it should be able to swing a 19p under load and for towing. Anybody else think this?

 

[porscheguy]

For a 5.0 fuel injected engine in a 20 footer, seems like it is down on power to me. Maybe the tabs are not flattening out at speed. Are you using the trim up? Is the spray back on the hull with bow up a few degrees? Feeling is it should be able to swing a 19p under load and for towing. Anybody else think this?

I think you might be on to something here.

It sounds like the boat is propped to pull max rpm with a full load of people onboard.

Theres videos of this model boat on YouTube running at 48-50mph.

I’m thinking it needs to be tested without smart tabs, and using a 3 blade 19p and 1-2 people onboard at most.

 

[89retta]

Have to agree that you have some engine problems. I have a 4.3 Volvo GXI and run a 4 blade Turning point prop 4800 rpm and 45 mph. Also when I put my 17 pitch 4 TP prop on I have to watch the rpms as it will hit the limiter easy

 

[bhollehday]

I think you might be on to something here.

It sounds like the boat is propped to pull max rpm with a full load of people onboard.

Theres videos of this model boat on YouTube running at 48-50mph.

I’m thinking it needs to be tested without smart tabs, and using a 3 blade 19p and 1-2 people onboard at most.

What do you mean pull max rpm? With my 16p? It seemed to be the same when I was without the smart tabs. I can pull them up and then try some different props at a local shop.

 

[bhollehday]

For a 5.0 fuel injected engine in a 20 footer, seems like it is down on power to me. Maybe the tabs are not flattening out at speed. Are you using the trim up? Is the spray back on the hull with bow up a few degrees? Feeling is it should be able to swing a 19p under load and for towing. Anybody else think this?

No trim is full down with 16p and with 17p I will trim up and maybe get 44. What do you mean by spray back on the hull?

 

[QBhoy]

I honestly think sometimes it’s too easy to get lost and out of hand with obscure props. 4 blades are good for certain applications, there is no doubt...but on most occasions and I’d think certainly this one, a good and well chosen 3 blade would be just right. 4 blades for me just complicate the reference point and should only be considered for the out of the norm circumstance and when specific requirement are needed. They usually mean bigger than normal diameter, rpm and performance characters, making it hard to go back to basics and spec a normal 3 blade.
Im not sure what your gear ratio is, just one of the variables that make it difficult to make a guess. Also to be considered is if your figures where taken when trimmed out or what weight you normally have in the boat etc etc.
The figures given don’t seem to ring true with the norm. It seems you have recorded a hike of 500+ rpm by just 1” change of pitch. That’s strange.
Not trying to be difficult, just perhaps pointing out the mystery and variables that are involved.

 

[Maclin]

Is the bow up, and the spray well back of the helm with no porpoising, that will show proof of a good trim up level when cruising.

 

[bhollehday]

Is the bow up, and the spray well back of the helm with no porpoising, that will show proof of a good trim up level when cruising.

"spray well back of the helm with no porpoising" not sure what you mean