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Max-prop, first impressions

Warren Holybee

Warren Holybee

Active Member
I splashed today and got to try the Max-prop on the way back to the marina. My first impressions.

17" max prop, set to 12.9 inch pitch.
Engine is a 50hp Volvo, with rated max RPM of 3400.

So the first thing I noticed, is that it is LOUD. There is a whole lot more water noise than with my older traditional prop. I can't even hear my engine over the noise at normal cruising speeds.

Speed was good, much improved over the old prop, and near what I was hoping for. Over 7 kt at 2000 RPM, and just shy of 8 kts wide open. Just over 6 kts at 1500 RPM, where my engine sips less than 0.5 gallons per hour. And the noise was bearable at that speed. That is good, because one of my goals is fuel conservation on multi-day motor trips (the doldrums, for example, or when I had to motor from Panama to SF against prevailing wind)

Reverse manners are really really good. There seems to be no noticeable prop walk at all. Before, the boat was totally uncontrollable, unless turning to port is what you wanted to do. Even using various techniques to work with it (quick bursts of forward to straighten out, etc.) were hopeless. However, there is much less stopping power while docking. But that is easier to deal with. Dock slowly, break early.

Wide open, my engine got to about 2800 RPM. Since it's rated for 3400 RPM and got there with the old prop (not even needing full throttle to do so) I suspect it's over propped at 12.9 inches. Not surprising, and I am ok with that given the performance in the range I usually run at (1500-2100 RPM). But I might back it down to the next setting, which is 11.6 degrees to see if that helps the noise.
 
Glad you got to splash today!

I don't remember any more noise with our Max Prop Easy. But we have a 16", pitched at 14" according to my notes.

We have a 3 blade ... is that what you have too?

I was so used to the extreme prop walk on the old propeller, it took some time to get used to near-zero prop walk.
 
Yes I have a 17" 3 blade. I went larger for more power motoring against large chop. The stock 16" really struggled. Maybe its not enough tip clearance in the aperture causing the noise. Maybe a 4 blade 16" would have been better. But others i think have the 17" and are happy.

I don't recall the formula, but a larger diameter would carry less pitch than smaller. So if you are at 14, that makes sense.
 
I have a 3 blade 16" MaxProp, set to 12" pitch. 35 hp Beta. Old Perkins drove a 16x11 3 fixed blade prop. I had hoped to reduce the prop noise, but I do not think I have. But it is not louder. And it runs the boat well, altho I do not get quite to hull speed (7.4) at Max rpm of 2800. I would have thought 17" is too big a diameter for the aperture we have. Is it a roar or a rumble?
 
I might describe it as both a rumble and a roar. I think the boat really needs a 17" prop, I might live with for now it and enlarge the aperture instead of going down to a 16". Plus, gowd damn the cost, I couldn't afford to change it. It would take me 2 weekends, the haul out alone would be $2k. With me doing all the labor. But I think a reduced pitch might help and that is simple to change in the water. The choices on a 17" prop are 11.6 and 12.9, with nothing between. The noise obviously increases a lot with RPM, and at 1500 RPM/6kts is loud but not terrible, probably similar to before while motoring at 6kts and a higher RPM.

I think the reason for needing the 17" prop is because of the thickness of the skeg and rudder. A pretty large percentage of the area of the prop is lost. Also, the blade shape of the Max-Prop is less efficient than a standard prop, and I wanted to compensate for that. I think that turbulence also causes more noise, regardless of prop size. But even without the aperture, when I played with various online prop calculators, I was often recommended an 18", which is clearly too big.

One of the things I really like is the easy pitch change. I could go to 11.6 now, or even lower. And then when I am going on a trip where fuel economy is important, swap the 12.9 back in. On much of my trip between Panama and SF I was using about 0.4 gallons per hour at 4.5kts and 1500RPM. Keeping that RPM and maybe bumping fuel to 0.5gph and up to 6 kts would be excellent. There are alot of complaints about my oddball Volvo engine, but it is really efficient, more even than I think the new computer controlled engines.
 
You seem to have it dialed in. You might want to read John Harries concerns about running a diesel at lower load. (Attainable Adventure Cruising). But since your Volvo got you around the world, it sounds as if you have it all figured out. I had no idea ,anyone marinized Volvos. Did you do it yourself?
 
The engine is a Volvo MD22p. It is an unusual Perkins block used in cars in the uk in the late 80s/early 90s. It was marinized by Perkins as the Perkins M50, then volvo repainted them and made some minor changes and sold it as the MD22 with many slight variations. Quite a few European production boats used them for a few years. Mostly have a good reputation for power and reliability, but really difficult to work on.

I don't know why the original owner repowered. Eliana might have sunk, as the sole and fuel tank were also replaced. But at the time the md22 was the standard Volvo engine offering.

It is electrically isolated (for use in aluminum boats) Has an oil cooler and a transmission cooler(volvo improvements i think). Doesn't need glow plugs to start but has them for sub freezing temps.
 
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