Prop walk with a Max Prop - Page 2 - SailNet Community
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post #11 of 20 Old 05-24-2011
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All props have prop walk in both forward and reverse. It cannot be avoided. It is not noticable when moving forward because the prop wash makes the rudder effective with even no way on. In reverse, this doesn't happen until the boat has enough motion to make the rudder work. As Rich said, tip clearance and boat design also play a big part.
Awaghorne: If you can make max rpms when in gear then you are not overpropped. Smoke at high power and unburned fuel could also be a sign of dirty/worn out injectors or a fouled prop
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post #12 of 20 Old 05-25-2011
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For what its worth, I've got a Maxprop in an aperture (skeg hung rudder). I get lots of walk in reverse. I didn't know the Maxprop was supposed to impact this.

To counter (for example if I need to back out straight from a narrow slip), I find cutting the wheel to counter the walk, and reversing aggressively until the rudder starts to "catch" allows me to back out straight. As soon as the rudder catches, I straighten it quickly before I start going the other way. Other times the walk can be useful. YMMV.
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post #13 of 20 Old 05-25-2011
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I've had a three-blade Max Prop for 21 years. Replaced a 3-blade fixed prop after a trip down the waterway from Annapolis to Ft. Lauderdale.

I immediately noticed:

1. no benefit in forward under power;
2. big benefit in reverse under power...the MaxProp made backing much more efficient; and
3. no decrease in prop walk compared to the 3-blade fixed prop.

Have thousands of inland and sea miles on this prop now. Love it. Absolutely reliable. The better performance in reverse allows maneuvering you just couldn't do with a fixed prop.

Bill
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post #14 of 20 Old 05-25-2011
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Prop walk is as much a charactoristic of the boat's hull, shaft angle, prop to rudder,prop to hull clearance as anything else. I can't understand how the prop guys can sell you on reduced prop walk with thier prop unless they significantly change the prop dia.
Bottom line, the prop is designed to produce thrust forces forward and reverse. In the process they also generate torque on the boat. some prop designs may change the torque some but not much. It's how a boat handles the torque that shows up as prop walk.
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post #15 of 20 Old 05-25-2011
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As the thread was resurrected by awaghorne to ask about fuel/soot on the transom, I doubt that has anything to do with the prop. It could be many other things, but not enough info to know.

As far as Max-Prop prop walk, I get a fair amount to port when initially powering into reverse, but it calms down when the rudder become effective. Reducing drag under sail is the only reason I care about the feathering prop.


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post #16 of 20 Old 05-26-2011
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Had out prop/tranny in N for tonights sail, finally on the downwind leg I kept noticing a hum the did not sound correct........prop was turning! put in reverse, gained 1/4-1/2 knot after the prop quit turning!

I do have a bit of prop walk to port, but if I am coasting, then idle the prop in R initially, then there is not as much prop walk.

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I drives me dinghy!
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post #17 of 20 Old 05-26-2011
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In a full keel boat with the prop in an aperture or a boat with the prop in an aperture in a skeg attached to the rudder the prop acts a bit like a thruster, pushing water sideways out of the aperture. You need speed in reverse to overcome this before the boat answers the rudder direction.

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post #18 of 20 Old 05-26-2011
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As far as Max-Prop prop walk, I get a fair amount to port when initially powering into reverse, but it calms down when the rudder become effective. Reducing drag under sail is the only reason I care about the feathering prop.
Our previous boat had a fixed three blade prop and had a lot of prop walk. Our current boat came with a maxi prop and the prop walk is nearly undetectable. It has a long fin keel and skeg hung rudder though, so I don't know whether it's the boat's bottom or the prop. I've heard several times that maxi props don't have much prop walk and thought that was the case with our boat, but it may have been a premature conclusion. Faster just put a maxi on his boat, so he may be able to shed some light on the matter.

Ray
S.V. Nikko
1983 Fraser 41
La Conner, WA


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post #19 of 20 Old 05-26-2011
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We have just gone from a 2 blade fixed prop to a 3 blade MAX. The improvement in smoothness and reduced vibration under power is considerable. It seems to me so far that there's less prop walk initially than we had with the old fixed prop, but our boat has always tracked well in reverse so the difference is not a big deal (in actuality I made good use of the prop walk we had, and may even miss it if it proves to be 'gone'.)

The bite and improvement in getting the boat moving in reverse is remarkable. The fact that the prop blades are not working backwards would, I imagine, explain this. Overall I'm very pleased but haven't had a lot of sailing weather to try out and quantify the reduction in drag under sail yet.

Ron

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post #20 of 20 Old 06-05-2011
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Further to previous post:

This weekend we've finally had a good try at sailing with this prop and the performance gain has been terrific. Really pleased.

As to the prop walk, it's still there but the boat starts moving aft so much earlier that the overall effect is reduced as the rudder takes over sooner.

The three blade smoothness under power is also a treat, as is the lack of feeling the swirl off the locked fixed blade on the rudder when sailing.

Ron

1984 Fast/Nicholson 345 "FastForward"

".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
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