Need Help From You Guys That Have Prop Efficiency Calculators

[harringtondav]

You go stainless and quality. Like a tempest plus 3 blade or an enertia 3 blade.

Thanks
I know SS would improve performance. I've got a hunch my 250 hp is overpowering and flexing the aluminum blades.
The SS price doesn't scare me off. But we boat in the hazardous, trashy upper Mississippi river, and every bent prop shaft I've had came from a SS prop impact. ...aluminum acts as a fuse. I was equipped to R&R Alpha II prop shafts, but not so much with our new VP.
...but I recon I'll spend the equivalent of a high quality SS prop finding the 'best' alum prop. ...then use that learning and buy a SS prop for high water and when my son isn't at the helm.

 

[QBhoy]

Thanks
I know SS would improve performance. I've got a hunch my 250 hp is overpowering and flexing the aluminum blades.
The SS price doesn't scare me off. But we boat in the hazardous, trashy upper Mississippi river, and every bent prop shaft I've had came from a SS prop impact. ...aluminum acts as a fuse. I was equipped to R&R Alpha II prop shafts, but not so much with our new VP.
...but I recon I'll spend the equivalent of a high quality SS prop finding the 'best' alum prop. ...then use that learning and buy a SS prop for high water and when my son isn't at the helm.

I’d like to think that the sacrificial hubs in stainless props these days, usually do a good job of not damaging a prop shaft. Not sure it’s even much of a worry these days. Long gone are the days of stainless props being hard splined onto prop shafts.
if you’re in mind to reduce prop slip and get as efficient a set up as possible…there is no getting away from the fact, you’ll need a good 3 blade stainless prop to do it. Simple as that really.

 

[harringtondav]

I’d like to think that the sacrificial hubs in stainless props these days, usually do a good job of not damaging a prop shaft. Not sure it’s even much of a worry these days. Long gone are the days of stainless props being hard splined onto prop shafts.
if you’re in mind to reduce prop slip and get as efficient a set up as possible…there is no getting away from the fact, you’ll need a good 3 blade stainless prop to do it. Simple as that really.

Agree. Getting the correct SS prop dialed in can be pricey if I don't nail it the first try. Diameter and pitch decisions still have me wringing my hands. The only thing that made sense with my 21P=>23P experiment was a 500 rpm decrease in WOT rpm.

 

[QBhoy]

Agree. Getting the correct SS prop dialed in can be pricey if I don't nail it the first try. Diameter and pitch decisions still have me wringing my hands. The only thing that made sense with my 21P=>23P experiment was a 500 rpm decrease in WOT rpm.

Haha. As you’ll know…prop perfection is something you can spend years and thousands on…even then…always a black art. Personally I’ve found that it’s essential to get good base numbers and data from the likes of a known (or as known as things get) entity prop like a black max or laser 2…then go from there. They are about the most predictable props for gaining good data, I’ve come across. Always know where you stand with them. Then personally I’ve used that to make a calculated as possible investment in a prop like a tempest, enertia or similar. Managed to get two of the quick boats down to about 3/4% and even a deep v cuddy down to about 5/6%. I’d add that this took plenty of money to get right so far.

 

[Texasmark]

Thanks. ...same 17% slip the Merc racing calculator gave me.
My question is how do I reduce the slip % which is essentially the same with 21 and 23P three blade alum props.

Most aluminum props don't have trailing edge cupping...tip is bent slightly. This is a huge asset in "grabbing" the water and is especially noticeable on props run close to the surface like is the case on fast Bass Boats. SS props are usually cupped and have enhancement characteristics for other reasons. Even though general rule of thumb is that cupping adds one inch of pitch to the prop, the streamlining effects of SS props probably overcome that effect meaning you can run the same pitch and get better performance.

If you get a SS prop with ports (holes under the leading edge of the blades) you get deliberate increasing of the prop slip in the Hole Shot making for faster to plane (HP develops faster) and better hole show for skiers and other water toys when pulling such. Once the boat gets up to speed, the water pressure seals off the ports and the prop acts like one without them. On one boat I had, when the prop locked up, it was like a stick shift automobile dropping into overdrive (RPMs dropped and speed increased) but an immediate change....neck popping of a mild nature....great sport.

A 3 blade Solace SS sells for about $250-275......a quality prop....don't know if it's ported in 3 blades. My 4 blade isn't but I don't need porting on my current rig.

 

[harringtondav]

Update: I purchased a Solas HR Titan 3 14.25" x 22P here at iBoats.
I think I'm as close to the sweet spot as I'll get.
WOT rpm = 5500 vs 5400-5800 spec. GPS speed = 55 mph.
Slip = 8%
Per @achris "The prop maketh the boat."

 

[achris]

What's the gearbox ratio?

 

[achris]

If it were me, I'd look at the 21". That should put you just on the top end of the recommended range, which is where those 4.3s prefer to be. They are great engines, but they don't do well at low speed with a big prop... They like to spin...

 

[harringtondav]

What's the gearbox ratio?

VP SX 1.91. (Please don't hate me. The VP 4.3 has too many advantages over the Merc 4.5)

 

[harringtondav]

If it were me, I'd look at the 21". That should put you just on the top end of the recommended range, which is where those 4.3s prefer to be. They are great engines, but they don't do well at low speed with a big prop... They like to spin...

Chris, the boat came with a VP alum 14.3 x 21. It pegged at 5800 rpm. I suspect it was rev limited. Slip was 17% WOT.
I'll recheck slip at 3500-4000 rpm with the 21P which is where I spend most of the time. WOT is interesting, but scares the wife.

 

[achris]

VP SX 1.91. (Please don't hate me. The VP 4.3 has too many advantages over the Merc 4.5)

I'd love to get out of Merc's clutches. But VP parts in Australia are just too expensive, and VP only had a very small market share, so even getting the parts is a problem...