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Old 27-08-2018, 18:44   #31
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Re: Max Prop Issues -cavitation and poor performance

Out of curiosity, How clean is the bottom?
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Old 27-08-2018, 20:53   #32
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Re: Max Prop Issues -cavitation and poor performance

Can you reach close to the engines max rpm of 3000 In gear? If not, the prop is over pitched and needs to be adjusted, or the bottom or running gear is fouled.

I've had excellent service with Maxprops on a couple of boats, but they were 3 blade.
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Old 28-08-2018, 02:25   #33
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Re: Max Prop Issues -cavitation and poor performance

Yes I can get close to the max rpm of 3000 for the 4JH4E, but I only see about 6 kts at that max rpm. Additionally, this low speed output was from the very beginning when the boat was launched (with a just preped bottom).
True after a summer in Maine there is some algea / slime on the bottom.

The speed issue was from the beginning, but the cavitation sound at start has only been the last month - I would believe now that this is probably due to not having been greased at the beginning of the season by the PO, and the two blades are probably not fully opening under low (1600 - 2200) rpm.

From the picture I attached - can anyone tell me if this is the Old Classic prop?
IF so were there known issues with these props for power and deployment?
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Old 28-08-2018, 08:05   #34
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Re: Max Prop Issues -cavitation and poor performance

I doubt there is an issue with the blades fully opening. The gears would have to be jammed with something. If it only partially opened you would probably have vibration too. It maybe that a 2 blade prop was a poor choice for your boat, Maxprop or not.
No pic attached.
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Old 28-08-2018, 08:10   #35
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Re: Max Prop Issues -cavitation and poor performance

I had a thread here on CF a couple of weeks ago about issues I was having with the Max Prop...

I have a 3-blade Max Prop (which I am told is noticeably superior to the 2-blade version, but I know people that are quite satisfied even with the 2-blade), and my experience with it has been very positive, provided that it feathers correctly. In general, the Max Prop has very positive feedback from users; it is a very well designed piece of equipment (and they certainly make you pay for the engineering...), but it requires some maintenance, as most precise mechanisms do.

From what you describe, it sounds like your Max Pro needs servicing; re-greasing for sure, as others have pointed out.

In my experience, it is relatively easy to find people who can service the Max Pro (even re-pitch it) while the boat is in the water, and the service is relatively affordable (re-greasing is very simple, re-pitching is quite complex, but very doable), at least compared to hauling the boat out, servicing the prop, and getting the boat back in the water.
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Old 28-08-2018, 17:25   #36
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Re: Max Prop Issues -cavitation and poor performance

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I'm having a bit of difficulty with that logic
Agree with you Stu, my diver had never done it before. That is why he and I watched the videos together. He had no problems at all installing the prop; maybe he was "extra gifted?"
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Old 28-08-2018, 17:51   #37
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Re: Max Prop Issues -cavitation and poor performance

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I always thought they were supposed to be easily adjustable in-water by a diver.
They are, if your diver knows what he's doing.
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Old 28-08-2018, 17:58   #38
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Re: Max Prop Issues -cavitation and poor performance

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Originally Posted by epoxyman View Post

From the picture I attached - can anyone tell me if this is the Old Classic prop?
IF so were there known issues with these props for power and deployment?
Yes, that is a 2-blade Classic. There are not a lot of this particular model out there and I have to wonder why the PO went with a 2-blade model as opposed to a 3-blade model. Your boat is hardly lightweight.
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Old 03-09-2018, 07:28   #39
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Re: Max Prop Issues -cavitation and poor performance

If you go from neutral to full power, slowly, does it cavitate ? That is good practice in any event. Is it possible that it doesn't always open evenly ? Download a little spreadsheet called propking.xls to check pitch/diameter for your boat.
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Old 03-09-2018, 08:46   #40
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Re: Max Prop Issues -cavitation and poor performance

There are two versions of the Max Prop, one can be adjusted (newer version) under the water. The "classic" needs to be done out of the water. Find which one you have here:

PYI Inc. | Max-Prop Automatic Feathering Propellers

You have a 3000 rpm engine. Adjust the pitch until you can just comfortably reach 3000 at full throttle on flat water with a clean bottom. Your real max throttle may be more like somewhere between 27-2900 depending on fuel consumption, vibration, etc. Rarely will you run at absolute full unless you are fighting current or whatever.

If the engine overheats at full throttle you have other issues like old impeller, clogged intakes, stainers, dirty heat exchanger, etc.
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Old 03-09-2018, 10:49   #41
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Re: Max Prop Issues -cavitation and poor performance

We have a couple of divers who have experience reinstalling the Classic Max-Props underwater. Kudos to them as it was a challenge for me on the hard. Experience counts a lot. I would not want to be the first for a diver who had never done it but some people are better at this things then I am.
As to Max-Props in general, I had one on my Whitby with an 80hp Ford Lehman engine and BW trannie. When I got the boat and ran it a couple of years I finally figured out the prop was pitched incorrectly. When I found out the correct pitch I increased my speed a whole knot at the same RPMs and decreased my fuel usage almost 1/4 gal per hour. It was amazing.
And the reverse in Max-Props is outstanding.
My current fixed prop is over-pitched as I was getting black exhaust and could not make RPMs. Rather than getting it repitched or replaced I bought a Max-Prop which I picked up direct from Max-Prop at their facility. I live north of them so it was easy.
I looked at the Flexofold and almost went with it, but after a lot of research I thought it would do the job with similar properties except in reverse. However their customer service was downright rude and if you got the pitch wrong tough bananas. You would have to buy a new one.
The Max-Prop guys have some of the best customer service I have ever experienced. I still need to install my new prop. I am excited to do both for the new efficiency I will get and also the added (and controllable) better reverse bite. I have a lot of trouble with my boat getting it in my slip stern in.

I spent the extra bucks to get the new model which allows the pitch to be changed underwater easily. They do need to be greased regularly. They are a beautiful piece of equipment. Sturdy, well made, and just a joy to hold. Heavy though and they do need a lot of extra clearance from the end of your shaft so make sure you have enough so the prop will fit.
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Old 03-09-2018, 11:13   #42
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Re: Max Prop Issues -cavitation and poor performance

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I considered doing it myself, but octopuses, crabs, jellyfish, and curious harbor seals freak me out,
Chuckle....
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Old 03-09-2018, 11:13   #43
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Re: Max Prop Issues -cavitation and poor performance

My experience with props led me to a few conclusions.... the most important one for me was the maximum hull speed under way (especially under power) and as I recall it is the square root of your WATERLINE length X 1.4 or 1.2 depending on size of keel... and the other conclusion I came to (after a LOT of hard work and expense) was, there must be a lot of water clearance between the prop and the hull, to avoid speed-robbing cavitation, regardless of type of prop.. I built my boat and after sailing virtually around the world I finally decided to take the prop off and with an angle grinder, cut away a fairly sizeable chunk of the area around the boat to widen the prop aperture, and then re fiberglass the area...I put on the recommended size three bladed prop to work with my Vetus 24 HP engine and I was BLOWN away by the extra power and speed Good luck and explore all options...
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Old 03-09-2018, 13:43   #44
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Re: Max Prop Issues -cavitation and poor performance

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

If you have “classic” Maxprop, one of the first generations, it needs to be taken apart to change the pitch. It’s difficult even doing it on a work table if you have a three blade because the blades gears and hub need to be meshed together at the right pitch. A third hand would be helpful. Doing it in the water is theoretically possible but practically virtually impossible.
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Old 03-09-2018, 14:26   #45
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Re: Max Prop Issues -cavitation and poor performance

I have had a number of folding and feathering propellers and they all provide increased speed under sail. Unfortunately they also are complex in design and require maintenance.
I currently have a 20" max Prop in the garage which PYI says can not be overhauled. No more Max Props ! In its place I installed a Auto Steam which has easily replace nylon bushings and is all 316 stainless. I obtain 7.3 knots at 2200 rpm with a Yanmar 4jh2te 75 hp engine in my Tartan4600.
For good performance under sail and great motoring performance I recommend a Autoprop. Radical in design, but with twisted blades it motors great. I had an 18" Autoprop on my Hylas 45.5, with a 62 hp Yanmar I obtained 7.4 knots at 2200 rpm. The previously installed fixed 3 blade produced 6.5 knots at 2800 rpm. I did two trips down the ICW and to he Bahamas plus 9 years of local cruising with no problems.
Some early Autoprops did have some issues, but these have been corrected.
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