Adjusting MaxProp pitch

[smokey73]

My current Wide Open Throttle on my Hunter 40.5 is 3200 rpm (Clean hull, clean prop). Spec for the Yanmar is 3600 so I am a little over-proped right now.

I have checked the tach with a handheld photo tach and it is very accurate so I know its not a Tach vs actual problem.

On the next haul I am considering adjusting the MaxProp pitch, which has fixed points for adjustment. I am concerned that then next notch in adjustment may make me under-proped. Is it better to be over-proped (the amount I am 3200 vs 3600) or to be under-proped. Not sure what the next pitch adjustment would do but just wondering.

If someone has a Hunter 40.5 with a MaxProp what setting do you have it on right now and how is your WOT at that setting.

Thanks in advance

 

[Benny17441]

Allowing the engine to turn more than the maximum rated RPM is placing it at great risk of mechanical failure. Being underpropped would the greatest evil of the two. On the other hand the loss of 400 RPM at the top end makes that prop inadequate. I don't know how your boat is performing as far as operating at idle speed, accelerating or fighting against head seas. If it moves too fast at idle and the boat feels sluggish the prop could seriously affecting performance. Do consult with other h40.5 owners regarding how they are propped and how are their boats performing. If you cannot get it within Plus or minus 100 RPM I would look to replace that prop.

 

[RoyS]

You should readjust your pitch down one notch when you are hauled out. I have adjusted my max-prop several times and it is easy enough to do. Your engine has an internal speed limiter and you have your tach in any case so I would not use the prop pitch as an engine speed limiter. The prop pitch adjustment is really a trial and error effort and you are close already. One step down should be near perfect.

 

[Gunni]

We went with a slight "under propped" maxprop tune. Like Roy says, you have to pick a notch for the MP Classic, so it is a bit of a compromise. My concern was not loading the engine with too much pitch, which would be a factor at all RPM ranges, and lead to too much fuel, and thereby carbon. PYI was helpful in providing MP setting recommendations for my drive/boat.

 

[smokey73]

Thanks all,

Next time I have the boat hauled I'll adjust it down one notch and see what that does. I know there are fixed settings on the Classic and I was afraid if I went down one notch I'd be very under-proped, but it doesn't seem that way. If one notch down in pitch is too much I'll decide what to do on the next haul after that. I think a little under-proped is better than 400 RPM reduction that I now have. My manual says that every 2 degrees (which I assume is a notch) changes the rpm by 13% to 15%. So assuming I'm at 3200 rpm clean hull, clean prop right now one 2 degrees less pitch should put me at 3600 to 3680 so that should be about where I want to be. When I do it I'll post on what one notch actually achieved.

 

[Jerry Clark H356 SV Persi]

I just did what you are thinking of doing and think I am going back to my original setting. I was at 3400 WOT when my MaxProp was new in 2003 with 22 degrees setting. (Max RPM could be 3600) I just had a rebuild after 14 seasons and 1280 hours and went from 22 to 20 degrees and now can do 3600 max. My old (prior to needing the rebuild) cruise speed at 2750 RPM was 6.2 knots with a clean bottom. I expected to go faster on less fuel by reducing pitch to 20. I am still experimenting and will probably haul out and change it back to 22 in the near future. I haven't had the chance to fully check out what my speeds and RPM with the new settings are, but have an inclination I am not going to be better off than before. My limited tile with it seems to indicate slower speeds than previous.

I' ll let you know what happens after I make my decision.

 

[fstbttms]

Any Max Prop model can have its pitch adjusted while the boat is in the water. PYI can recommend qualified divers to do the work in your area.

 

[smokey73]

Any Max Prop model can have its pitch adjusted while the boat is in the water. PYI can recommend qualified divers to do the work in your area.

Thanks for the info. I'll call PYI. We do have 8 to 9 foot tides here with some pretty swift currents. Most divers here only work during slack water unless its an emergency so how long it takes might be a problem. From what I read in my manual the prop has to be partially disassembled to get change the pitch on the "Classic" and our water isn't all that clear. I'd hate to lose parts into the mud here as I'm sure they would be irrecoverable. I will probably have to get the boat hauled this winter or next spring for another bottom job so that may be the time to get the pitch changed. It's been at this pitch for at least 4 years and the engine hasn't seemed to suffer much so I'll probably wait until then.