Max Prop Issues -cavitation and poor performance

[epoxyman]

Hello All
I purchased a Cal 39 MK2 with a Yanmar 4JH4E (600 hrs). This engine should be able to get this boat up to hull speed without issue, however it is a labor to get close to 6 kts. 2500 rpm only about 5kts (dependent on tide and wind).

Boat came with a two blade feathering prop - 17in diameter at 16 deg pitch.
after a few months I find that when starting underway, there is a lot of cavitation noise that seems to go away if I put in reverse hard or just slowly up the rpms. I have dove on the prop 3 times this summer to make sure it is clean (appears clean throughout season).
I am thinking of dumping the MaxProp for a 3 blade Flexofold however I would love some input on these MaxProps. I know there are a lot of them out there and I know that I can send it back for reconditioning but I do not know the cost of this.
What say yee sailing community - Is the MaxProp headed for the briny deep???

[StuM]

When was the last time it was re-greased? It should be done annually.

[Bill O]

When you pull it to check and/or grease the prop as Stu suggested, you may want to re-pitch the prop. Doubt there is a cavitation issue unless you don't have any tip clearance and this would be evident upon inspection of tip or blade edge erosion if it was run like this for a while.

If you can't reach the 3000 rpm or more for your motor (don't know the continuous max rpm for your motor) then mostly likely you are over pitched. Check your motor in neutral to see if it reaches max rpms. Obviously only do this very quickly.

Also you may want to call PY Yacht (Max prop) with your specs as they will be fairly close to calculating the right pitch for your prop. Besides the normal boat spec have the trans ratios ready for the calculations.

Doubt you need a need prop unless you really want to spend some cash. A three blade will give you more torque to push up against strong head winds than a two, but then again you have a sailboat, so sail.


Bill O.

[DougR]

There are two things that prevent efficient propulsion with props like the Max Prop.
- the blades have no twist. This means that the pitch angle is the same from the hub all the way out to the tip, but this is not the way a prop should be built. Because both the hub and the tip have the same forward advance distance per revolution they both need to have the same pitch. But to have the same pitch along the blade, the angle of the blade to the hub needs to decrease as you move from the hub to the tip. Look at a fixed blade prop and you will see that the blade angle flattens further from the hub. So the Max Prop will be under pitched near the hub and over pitched at the tip.....not the best formula for efficiency, especially at higher loads.
- the blades have no airfoil shape, and this shape provides more efficiency than flat blades.

The prop on your boat is without a doubt very low drag under sail, but it doesn't have enough blade area to absorb the available horsepower, and it's being driven into cavitation.

I also have a Cal39 MK2 which originally was fitted with a Perkins 4-108 with a
2.5:1 ratio gear and an 18x14 two blade fixed prop. I replaced that prop with an 18x 13 X 3 blade Volvo folding prop which was slightly over propped and that engine /prop combination could drive the boat to its hull speed of about 7.5 Kts and then squat the stern until the exhaust buried!

A few years ago I repowered with a Volvo D2-55 engine ( same H.P. as your Yanmar) fitted with a 2:1 gear to compensate for lower engine RPM and keep close to the same shaft speed and the same prop. This engine/prop has no problem driving the boat to hull speed and easily cruises at 6.5+ Kts at 2200 RPM. (3000 max)

I think if you get rid of the two blade prop and fit a three blade folder, Volvo or Flexofold, you will find a significant increase in thrust and propulsion efficiency.

DougR

[billknny]

Originally Posted by DougR

There are two things that prevent efficient propulsion with props like the Max Prop.
- the blades have no twist. This means that the pitch angle is the same from the hub all the way out to the tip, but this is not the way a prop should be built. Because both the hub and the tip have the same forward advance distance per revolution they both need to have the same pitch. But to have the same pitch along the blade, the angle of the blade to the hub needs to decrease as you move from the hub to the tip. Look at a fixed blade prop and you will see that the blade angle flattens further from the hub. So the Max Prop will be under pitched near the hub and over pitched at the tip.....not the best formula for efficiency, especially at higher loads.
- the blades have no airfoil shape, and this shape provides more efficiency than flat blades.

Every word of what DouR says is true... And it doesn't matter a hoot in the real world. Having switched from fixed to maxprop installation, on two boats I can say there was no real decrease in motoring performance in forward, and a dramatic INCREASE in performance in reverse. There are so many other variables, the minor losses in efficiency that come from the design of a MaxProp, and most other feathering props, are lost in the noise.

MaxProps are very popular, for a good reason. They drive a boat well, yes, NOT perfectly well, but well, and have very low drag, and good close quarter handling, not so true for the folding props I have driven.

I assure you, your problem is NOT the design of MaxProp itself. It might not be sized or pitched correctly for your boat, but the MaxProp will give you performance in forward gear greater than 90% of what you get from a fixed prop.

I think I understand you to say that your engine can only get to 2500RPM at full throttle. That means either your prop is severely over-pitched, OR you have a problem with your engine.

If you have not greased the prop (the blades should swing with a fingers touch), that would be the place to start. If it is not fully feathering, or assuming the set pitch, because of friction that would cause you to be very unhappy with the unit.

[Terra Nova]

Your MaxProp is not setup properly.

[Halien]

I have a Max-Prop on my Tartan 33. The Universal 5424 frequently overheated running at 2600 RPM and 7 knots. I thought the prop was overpitched so I contacted PYI for their recommendation. They told me to increase the pitch, which seemed counterintuitive. I did it, and now in flat water I cruise at 6.8 knots at 2200 RPM, and the engine never overheats. Max RPM under load is about 2500 RPM, but that doesn't come with enough benefit to matter. In rough water I cruise at 6.5 knots at 2000 RPM, and the engine never complains.

If you send PYI an email with all of your details, they'll suggest a setting to begin with. Chances are it will be spot-on.

[Alita49DS]

What is the email address for whoever PYI are please?

Last time, a few years ago, when I wrote to whoever about the setting for my three bladed MaxProp I had a very pleasant conversation which got me precisely nowhere. The suggestion to try different settings seemed to overlook the fact that the prop was underwater and lifting a 49' boat is wallet damaging.

BTW, one thing that I can pass on about MaxProp is to only buy the genuine anode. It has a steel plate in it. The cheaper copies fall off in no time leaving just the set bolts. That is because the lugs erode away first.

[Jammer]

Originally Posted by Alita49DS

The suggestion to try different settings seemed to overlook the fact that the prop was underwater and lifting a 49' boat is wallet damaging.

I always thought they were supposed to be easily adjustable in-water by a diver.

[Halien]

Max-Props are easily adjusted underwater. In my case, the choices were either to get in the water myself, haul the boat just for the task, pay our regular diver to do it, or wait for the next scheduled haulout. I considered doing it myself, but octopuses, crabs, jellyfish, and curious harbor seals freak me out, so I had our regular diver do it. It cost about $100 on top of our regular bottom cleaning. I'm sure it took him about five minutes, but he's a nice kid trying to make a go of it, so it was a win-win. The least expensive option for me was a minor windfall for him.

[daletournier]

Some Maxprops are easily adjustable underwater, others have to be disassembled to change the pitch.

[Terra Nova]

Originally Posted by daletournier

Some Maxprops are easily adjustable underwater, others have to be disassembled to change the pitch.

This.

[oregonian]

Hello, One more consideration to explain the very poor performance. The prop MUST be assembled correctly for Right hand or left hand operation. Though you would think that that error would not be made, I have now seen it 4 times. Three times it was done by the boat yard. In one case the yard would not let the owner assemble the prop because of DIY policies. They assembled it Wrong. In another case, the symptoms were exactly as described by the OP. The boat owner assured me that the assembly was not wrong. Well! It was. Good luck. Please let us know your solution.

[SV Bacchus]

I have two from 2004 on our Cat and yes, the older ones need to be disassembled, partially, to adjust the pitch. I needed to send one in for service as it seemed to have excess play. It was rebuilt, quite reasonable $$ by PYI in Washington, and promptly returned with clear instructions of how to assemble and what pitch to use. They also have videos on their website.

I had a diver remove the prop for servicing and it had to be disassembled for removal. When it returned my diver and I watch the videos together, looked at the specs for pitch and he reinstalled it which required reassembly under the water.

Sounds like a lot to go through but it really wasn't and the diver had no problem. $75 to remove and $100 to reinstall in Marathon, FL.

I just have to say Man oh Man I do love those props! I don't really motor forward much to notice a lack of twist, I sail as much as I can. However, the reverse is fantastic and has saved my butt a couple of times! Love em, Love em, Love em!

Call PYI and ask for advice, they were very helpful to me throughout the process.

[daletournier]

Originally Posted by oregonian

Hello, One more consideration to explain the very poor performance. The prop MUST be assembled correctly for Right hand or left hand operation. Though you would think that that error would not be made, I have now seen it 4 times. Three times it was done by the boat yard. In one case the yard would not let the owner assemble the prop because of DIY policies. They assembled it Wrong. In another case, the symptoms were exactly as described by the OP. The boat owner assured me that the assembly was not wrong. Well! It was. Good luck. Please let us know your solution.

I'll second this, I had the same thought as I've seen it done. You can check this out underwater. There is a utube regarding this that will explain how to determine if it's correct.