Max Prop Pitch

[mthackray]

I have never been convinced that my MaxProp pitch is properly set. I have a 2007 Jeanneau 39i with a 40 hp Yanmar, purchased by me in 2019. The MaxProp is a 3-blade Classic. I get great gas mileage, but have never been able to get anywhere near hull speed, even at higher engine rpm’s. Running at 2800 rpm, I cruise on calm water at about 6.5 knots, at 3000 rpm about 6.8 knots.

The previous owner left the Maxprop manual, and in it is a note by the installer, Marine Service Center: “Pitch was set and tested at 22degrees RH N-D, ~3100 rpm FLFT, ~3400 WOT”
I’m not sure what FLFT means. I did confirm with an external tachometer that the Yanmar Tach was reasonably accurate (about 2.4% high).

The original Jeanneau prop was in the garage. It is a Radice with the following stamped on it:
   ER 17 * OR 13 * OE13OC
   PR 06/08912
I have not been able to find info on the web on how to interpret these numbers, but with some rough measurements, I believe it is 17” diameter, 13” pitch.

If this diameter and pitch is correct, then the MaxProp manual does say 22 degrees is the correct setting. It also says “A two degrees change in blade angle will change the engine RPM by 13-15% at the same boat speed.”

Any folks with MaxProps on their 39i and what pitch is it set at? Or conversely, should I be get more speed with a different setting? But would this sacrifice fuel efficiency?

Any comments welcome. I’m just figuring out how all these propeller variables play together.

[zaphod]

Assuming your bottom and your prop are clean you should be able to get more speed than that. My 39i will do 6.5kts @2000rpm, 7.5kts@2500rpm, and over 8.5kts@3200rpm. That is with a Flexofold 3 blade, but the numbers were similar with the old 3 Blade ZF fixed prop.

According to the specs for the 3JH4E engine, max power is at 3000rpm, so the fact that your engine revs to 3400 tells me it might be under-propped.

[sitara]

From what I have learned the prop pitch should be set to allow close to maximum engine revs at wide open throttle (WOT). My boat came with a factory fixed prop and would only ever reach 3200 rpm WOT. Our local Yanmar supplier recommended changing the prop and I now have an Autostream feathering prop.  I have adjusted the pitch over the years to get 3400-3500 rpm WOT. This setting allows the engine to develop its maximum power. Changing from fixed prop to feathering did result in a loss of speed under motor but much enhanced performance under sail. I normally cruise at about 2800 rpm and get about 6 knots. Engine is a 3YM30.

[bereboot]

I also have a 39i and installed 3 years ago a maxprop (easy).
The factory settings were forward motion pitch: 20°, backwards motion pitch 21°, which i altered to 23°.
I have no problem obtaining the desired speed, and go at 8,5 knots full throttle.
The advantage of the maxprop is that you can easily change the pitch.
I presume your initial setting is not correct.

[mthackray]

All,

Thanks for the comments.

As Zaphod says, I agree that I might be under-propped as I can’t get anywhere near hull speed under full power. I assume “under propped” means too little pitch, and the pitch should be increased. My MaxProp is the older model “Classic” which requires dis-assembly to change pitch. So I’ll need to do this the next time the boat is pulled out. If my prop is set to 22 degrees as the installer note says (to be confirmed), than to increase the pitch, I would need to change to 24 degrees or more.

Interestingly, Bereboot you say yours is set to 20 degrees. Maybe it is a different diameter, or the “Easy” model uses a different pitch.

I will contact the PYI folks here in my state of Washington and see what they say.

[bereboot]

The size of my maxprop easy is:
3B: number of blades
85: hub in mm
457: diameter of propeler in mm (=18 inch)
Iso30: Propeller shaft 30mm tapered

There is a very informative instruction manual on the site of maxprop, how to change the pitch versus rpm.

[mthackray]

I contacted PYI today (the US supplier of MaxProp). They are very responsive; I got a call back within 30 minutes of sending an email with a description of my issue. They said that the recommended diameter MaxProp for my boat and engine setup is 16” diameter with a 20 degree pitch. If I have a 17” diameter prop, then the pitch should be set at 18 degrees. 

So, things aren’t adding up. The note from my install says 22 degrees. A setting higher than the recommended 18 to 20 degrees should lower the rpm at the same speed.

The next time I haul out, I need to measure the diameter, and do a bit of disassembly to check the current pitch setting.  If it really is 22 degrees then why am I so under propped? The PYI fellow agrees that something is not right. 

More investigation needed.

[rene460]

Hi Mthackray, I think you are on the right track contacting the local reps. They are pretty good at supplying reliable information. So the next thing to do is to check the diameter and pitch setting you actually have.

I would also suggest you go out one calm morning and test the wide open throttle rpm reached, and (mainly for interest), the boat speed at this rpm. Do check your engine manual and note the maximum continuous rpm specified for your engine model, watch the rpm as you open the throttle and don’t go more than around 10% over that specified rpm. If you are reaching this rpm before you get to wide open throttle, that is a sure sign you could do with a bit more pitch.

Note there is no direct relationship between boat speed and engine rpm, unlike your car for example. The propellors job is to produce thrust from the engine power, and the boat will go at the speed determined by the hull drag. Clean, smooth hull gives higher speed, heavy fouling will slow you down, even at the same rpm and thrust. A correctly sized propellor will use the maximum available engine power at the maximum engine speed, the wide open throttle test is a good indicator of that situation.

It is best to do the test soon after the boat returns to the water with clean hull, fresh anti fouling and the propellor also clean and not damaged. However, as you are now in the water, might as well do the test as is. Repeating the test after lift out and clean will be informative about the effect of the degree of fouling, and help you judge when hull cleaning is required. Even a tiny barnacle or minor damage will greatly degrade your propellor thrust and may dramatically increase the load on the engine, and hence reduce the wide open throttle rpm. However it seems from earlier posts you may be reaching the specified rpm before wide open throttle so incorrect pitch seems more likely in your case.

I am not sure what the adjustment method is on the Maxprop. I had an Autostream like Sitara, where it is adjusted by set screws with lock nuts, separate screws for forward and reverse. It turned out spot on just as set by the factory when they supplied it, so I did not need to adjust it further. As you seem to be getting a fair few more revs than specified, an adjustment seems necessary. It will be interesting to see the results of your checking propellor dimensions and pitch when you are able to lift out.

Please do come back and tell us all what you find.

Rene460

[bratwurzt1]

Jun 1, 2023 3:18:07 GMT mthackray said:

I contacted PYI today (the US supplier of MaxProp). They are very responsive; I got a call back within 30 minutes of sending an email with a description of my issue. They said that the recommended diameter MaxProp for my boat and engine setup is 16” diameter with a 20 degree pitch. If I have a 17” diameter prop, then the pitch should be set at 18 degrees. 

So, things aren’t adding up. The note from my install says 22 degrees. A setting higher than the recommended 18 to 20 degrees should lower the rpm at the same speed.

The next time I haul out, I need to measure the diameter, and do a bit of disassembly to check the current pitch setting.  If it really is 22 degrees then why am I so under propped? The PYI fellow agrees that something is not right. 

More investigation needed.

We had our 3 blade 17" set at 18 degrees as the previous owner suggested and we would only ever hit 5 knots. After speaking with PYI and giving them our boat info including the gear ratio on the transmission they suggested 20 degrees. We now hit hull speed when under power. We rub the rpms at 2500/2700. How clean is your bottom?

[mthackray]

rene460 and all. I will do another test of rpm versus hull speed soon. My previous testing has been done with a clean hull and I am confident in the numbers. I had the bottom paint redone about a year ago, and just last week had a diver check the hull, prop and anodes in my marina. (I have hard, non-ablating bottom paint, so he was able to clean the hull in the marina).

I have the MaxProp Classic which requires dis-assembly to change the pitch. I keep the boat at Bainbridge Island, Washington. It is a beautiful place to have a boat, but unfortunately no boat yard here. So it requires a trip to somewhere else on Puget Sound to pull the boat. Thus this process of pulling the boat, checking the diameter and changing the pitch, doing a sea trial (then maybe doing it again) is rather arduous.  I hope I can pull the boat, do the measurements, then talk with PYI/Maxprop live, make any adjustments and then back into the water, all this done once.

I'll let everyone know the results once complete, but it may be awhile in the future.

Thanks again for all the comments.

[MartyB]

If you can get to Edmonds easy enough, you can do your own work in the yard. PYI is maybe 20-30 min north of the marina at SW corner of Paine Field. They have parts in stock you can get if you drive in.

As noted, something does not add up.

As I type, if you have prop speed on a max prop, IIRC, the spec is to increase the pitch one setting due to the thickness of the material.

Marty

[mthackray]

MartyB, good suggestion. Edmonds is about 15nm from Bainbridge (as I’m sure you know) and could be a nice stop on a trip up to Deception Pass and onward.

[mthackray]

This is a follow up post on my MaxProp pitch.

As mentioned, I have always felt my boat was under-propped as I couldn't get hull speed, even at WOT.  Plus, at WOT, the engine ran at 3400 rpm where as the spec for max throttle was 3000.

I pulled the boat last week.  The prop is a MaxProp Classic, three blade, 17" diameter.  I disassembled the prop and confirmed that the settings at install was a 22 degree pitch.  I increased the setting to 24 degree pitch.

On the motor home, I got much closer to the desired performance with the new setting.  I got approximately 7.8 knots and WOT is 3200 rpm.  Note that during the haul-out the bottom and prop was cleaned.  I need to confirm these numbers, as there was a bit of current flowing and I didn't have my speed paddle wheel installed because of the haul-out so these numbers are SOG plus current estimate.

In summary, I lowered the rpm at WOT and increased the speed by about 0.75 knots at any given rpm.  Hull speed is 7.9 knots, so 7.8 knots is very close and within measurement error.

[MartyB]

Where did you pull out or get the work done at?

Good to know results are better than they were.

Marty

[mthackray]

I had the boat hauled at Seaview Boatyard at Shilshole.  Besides the MaxProp work, I was having new sails installed from Ballard Sails, also at Shilshole, so it made sense to combine.