Prop tech advancements

[madhatter1]

So we all know a new set of props is in my future. Was trying hard to buy a new set of 4 blades but all have lead times that will not help me. Taking a step back and moving forward more slowly and not in a reactionary way.

Did plan on going to 4 blade props next year as I cruise the boat at 1800-1900 RPM's. 3 blades perform best at higher speeds and I will only ever run WOT with mechanic on board (performance testing, reading temps, etc.) and I believe the 4 blades should provide a bump in cruise speed. But then have heard "modern" props can provide even more gains. Now I don't think a new prop can take my 23 MPH cruise at 1850 to 26 MPH. But a 1-1.5 MPH pickup at same fuel burn would be sweet.

So what say the HOF group? Is there any tech I should be looking into? I was told (by General Propeller who did the calc off my last prop scan job and boat specifics) to go from 28x24.5 3 blades to 4 blade they should be 28x22 which seems light but maybe the 4 blades have that much less slip. If I did 22 pitch I would add a light or medium cup. Also considered going to bronze to save a few bucks but after much reading I see the Nibral blades are slightly thinner and flex less so going for Best performance think I need to stick with Nibral. Please offer all advice, opinions, and experience.

 

[Captain Ralph]

There is so much weird science to propellers.

Swamp logic offers; More blades in the water, more wetted surfaces, more contact to the water, more traction, less vibration.
Backside; more friction from the extra wetted surface, reduce in pitch required to counter less slip and extra drag.
Not even going to start how gear ratios can further help/hinder these issues variables..

Ever notice the latter Hatts with C32s? 8 skinny blades. It would be insane to use 8 full sized blades. To much drag.

From the swamp; Safe poker hand would be keeping what the factory (after lots of trial & error already) originally offered.
Or find a real propeller shop(s) and ponder what they think past factory and swamp logic...

Propeller logic is weird science..

 

[madhatter1]

Did not know that was you in weird science. Great scene.

 

[Captain Ralph]

Did not know that was you in weird science. Great scene.

Ask Paul and/or Don at TC Prop what their thoughts are. I think Paul is the owner.
They were always open in thought with us.

That pic was from 20 years ago. Working hard on our issues, on our our old Bertram then.
I still look for my thinking cap now days. Even when it is in use, by another.

 

[madhatter1]

Ask Paul and/or Don at TC Prop what their thoughts are. I think Paul is the owner.
They were always open in thought with us.

That pic was from 20 years ago. Working hard on our issues, on our our old Bertram then.
I still look for my thinking cap now days. Even when it is in use, by another.

In search of prop guru’s that can be trusted. Need real world info, not guesswork. Need the go to guys who know this stuff right. Gnomesayin?

 

[motoryacht lover]

I bought new 5 blades for my boat a number of years ago. My primary objective was reaching 2350 RPM.
The shop recommended whatever pitch and diameter. Their recommendation didn’t achieve 2350 and it took
2 adjustments to get it there. So try to negotiate that the shop has to make however many adjustments needed
To get to your max requested RPM.

 

[Pascal]

When I repowered my 53, the Cummins dealer had F&J run the numbers and they were absolutely spot on. Turned rated RPM and hit predicted speed

Turned out I didn’t have to buy new wheels as I had a spare set of 4 blade Nibrals which only need an Inch of pitch adjusted.

I was told that Nibral is the way to go on planning hulls.

 

[madhatter1]

So you can research this all day and only get bombarded by adds for props, especially sharrow. So I'll just ask here.

If I calculate my present pitch out (pitch" x RPM / trans ratio x 60 minutes / 12 (to get to feet) / 5280 x.8 (account for slip)) I get 23MPH. My actual crise there is 22-23. My guess at present slip with 3 blades is 20-22%.

Anyone know how much better slip is on 4 blades? To get same speed at recommended 22" pitch the 4 blades slip would need to be 11%

My guess is the 4 blades will have more slip than 11% so would a light or medium cup make up for the pitch at cruise speed?

Sorry for all the posts and questions. Got nothing better to do while we wait. Well other than drive to pick up borrowed props and maybe lunch with Scott this weekend.

 

[cww]

I switched from the factory federal/michigan DQ props to the newer DQX's with the scimitar-shaped high skew blades. My boat picked up almost 2 knots at any throttle setting over 1950. When not planing I don't notice any difference at hull speeds, but on plane there's a big difference. The boat used to struggle to get on plane plane, and sometimes wouldn't plane if I had full fuel and water, wasn't in shallow water where I picked up ground effect, and had a 90% clean bottom. That problem has been completely eliminated. It jumps on plane now. The boat also would also tend to fall off plane below 2050. Max RPM is the same as before, and as long as I have a clean bottom it stays on plane at 1950. I couldn't be happier, they really have improved the performance substantially.

My case was similar to yours, I needed a second set of props anyway and figured may as well get some newer technology if I was going to spend the money no matter what.

 

[rsmith]

If you have muff couplings the best thing you can do for performance is to go with one piece shafts. Pitch the props for the fuel water and load you normally run. Don’t pitch them for full fuel unless you that your typical mission profile. Tankering fuel unless you’re fishing 90 miles offshore on overnight trips or going somewhere where fuel is suspect or unavailable makes no sense and costs speed and efficiency.