Max Prop or Not?

[Dockhead]

Originally Posted by a64pilot

From my understanding that is exactly what it is supposed to do, and ideally what I want, sort of functions like a CVT on a car. Have you had any service problems? I've read about bearing failures, don't know if that was only the open to water bearings, or the newer, greased bearings, or if it's internet hype as I've never seen an Autoprop.
So far sounds like what I'm after, and I got a price that is close to a Max Prop

Yes, it is like a CVT on cars, which produces another disadvantage -- you can't motor slowly with them. At idle speed, my boat still goes at 3 or 4 knots, because the blades pitch up. This does create some problems maneuvering in harbor, which you won't have with the Max Prop, since the pitch is fixed and you can reduce thrust all the way to zero by reducing RPM. I sometimes have to shift in and out of gear if I need to maintain a speed of under 3 knots.

But motorsailing it is pure magic. It is so good motorsailing that you will do this a lot more than you did before. Normal motoring in normal conditions you won't notice any difference to regular feathering props like the Max Prop.

As to the bearing failures -- there was a factory defect on a certain run of the old open bearing types, which resulted in a factory recall. Since then no reported failures. I had the open bearing type on my old boat, but before the run with defective retaining rings, so no problems at all in 20,000 miles. On my new boat, I have the sealed type (which unfortunately you have to grease, as a result). No problems at all in another 10,000 miles. The Autoprop is the predominant propeller on cruising boats in the UK. It was fitted standard to my boat. But that being said, the Max Prop also has a fanatical following -- never heard anyone say a single bad word about them.

[dohenyboy]

J prop looks better


Sent from an undisclosed location on the high seas or from the lounge chair by the pool, you decide.

[nhschneider]

First, I owned an Autoprop that came with the sealed bearings. After 2 significant failures in a relatively short period of time, I got rid of it. Yes, I had followed all of the maintenance guidelines.

When we repowered, our new Beta Marine 90 engine came with a hydraulic transmission and because we have a center cockpit/aft-cabin layout, it was essential that the prop not turn while sailing. I chose the Gori prop for several reasons:

1. Its folding design means virtually zero drag while sailing.
2. There is no annual maintenance.
3. The reverse attitude of the blades increases the pitch by about 25%. This can mean maneuvering in tight places is easier. If you choose, you can force the blades into the reverse attitude and drive the boat forward. Gori calls this 'overdrive' and means you can run your engine at substantially lower RPM and get the same SOG as if the blades were in the forward attitude.
4. The Gori comes with its own prop puller.
5. The Gori costs less than the Max Prop.

I can appreciate that Max Props have the ability to adjust their pitch but determining the correct diameter and pitch for a hull/engine/transmission is not difficult.


We have over 35,000 miles on our Gori prop and are delighted with it.


Fair winds and calm seas.

[roverhi]

On an Island Packet with the prop buried in deadwood at the end of the full keel, doubt you are going to gain much in sailing performance. Certainly not enough to justify the expense and complexity/trouble of a feathering prop. If it was a fin keel boat with the prop hanging out naked in clear water, it would make a difference. Once again, maybe not worth the expense and possible problems on a cruising boat, though. If you could justify it in improved engine performance, might be worth it. I'd want to talk with another IP owner who had done a before and after comparison before investing the money.

Doubt that anyone can get definitive results of the benefits of fixed vs folding/feathering prop without sailing two identical boats, except for the props, side by side in varying conditions. Sailed three different Westsails in ideal reaching conditions, two with large three bladed fixed props and one with a two bladed prop that was locked vertical and hidden behind the deadwood, almost the same as removing the prop entirely. Had the best days run of 181nm on one boat with the 3 blade prop. The best days run with the two blade hidden behind the deadwood was 177nm. The other 3 bladed equipped boat did 176nm. Mileage was measured by the same Walker Taff Rail Log.

[Jim Cate]

Neither of these has the efficiency, or low drag of a Max-Prop, but price wise, the 2 together, are cheaper than a Max-Prop.

I hate to throw cold water on the subject, Andy, but Max Props, or ANY feathering prop of similar design is LESS efficient than either a fixed or a folding prop. We've been over this here on CF so many times... feathering props must, because of their reversing blade design, have zero twist in the blade shape, whilst the others are free to twist the blades to improve efficiency. This means that while the feathering prop can indeed generate high static thrust, it takes more shaft HP (and fuel burn) to generate the thrust than a prop with twisted blades.

As an example, on our previous boat we switched from a Martec Elliptic two blade ( a very efficient prop for its day) to a three blade feathering prop. Our ability to stop the boat in reverse, or pull off of a sand bank was indeed improved, but our overall fuel milage was degraded almost twenty five percent! I was not aware of this when I made the change, and was pretty disappointed (that boat had small fuel capacity, and it impacted our motoring range severely).

Finally, I'll add my endorsement for the Auto Stream if one wants a feathering prop. IMO they are a better design than Max, and, at least here in Oz, quite a bit cheaper to buy.

Cheers,

Jim

[Neptune's Gear]

I had a 3 blade folding Volvo. Fancy looking curved thing. However, I got sick of it because to change the anode the whole prop had to be disassembled. I went (back) to a kiwi prop - simple, low cost feathering prop. i like it. Perhaps you might consider them?

[colemj]

Originally Posted by roverhi

Doubt that anyone can get definitive results of the benefits of fixed vs folding/feathering prop without sailing two identical boats, except for the props, side by side in varying conditions.

I don't know about that. How about sailing your own boat for a while with fixed prop and then with folder/feathering? On our boat with folding props, sometimes the props do not fold when the engine is shut down. They fold when the gear is put into reverse and stops their spinning. In these cases, we easily measure 0.5kt increase in speed for each prop after folding.

I agree with you that an IP will probably not see much of an advantage to a folder/feathering over a fixed.

Mark

[a64pilot]

Supposedly an IP will see on average about .5 kt sailing speed based on others report, but understand anyone who spends this kind of money will want to see some results, think of it as a Placebo effect. I can see as the older IP's had thicker keel cross sections, that it would be less drag difference than most boats.

Jim is exactly correct on the average feathering prop the blades are a Planar blade, that is flat, no airfoil, they are unquestionably less efficient, a theory is though that since they are very adjustable, that you can match the prop perfectly to the engine / hull and recover that loss in efficiency.
Having said that is seems the Max prop is bullet proof or nearly so and has a strong following.

Now as you guys know an IP's strong points are not light wind sailing and going to windward, I can see myself potentially motorsailing more possibly than others, and I really want to be able to do so at low RPM and engine load, essentially to take me from maybe three kts sailing to five motorsailing.
A normal fixed prop will have the engine turning about 1500 RPM to just get the prop pitch to equal boat speed with little to no thrust, to get decent thrust and increase boat speed to 5 kts or so, your going to have to turn at least 2500 RPM.
Now the engine is turning RPM, but at a low load as half the boats speed is coming from the sails, be nice to be able to turn say 1200 to 1500 RPM and put the engine under a little load, but the low RPM will keep noise and vibration down.
I think of the props available for my 4-JHBE, only the Autoprop will do that.

I think I can learn to snick her into neutral to keep the speed down when docking, I'm so overpropped now with my fixed prop that I have to do that anyway, just maybe not to the extent of the autoprop, but if I can idle at 4 kts, I'll learn to deal with that.

[Prairie Chicken]

Our new boat has an Autoprop. We are very pleased with it but have no experience with the folding props so can't offer a comparison. I do prefer the automatic feathering over the Max prop design though.

The manual specifies that to feather the prop while under sail you shutdown the engine whilst motoring in ahead gear, then leave it in ahead while sailing, and start the engine again with it still in ahead. We found we picked up a full knot of speed with the prop feathered.

The autoprop makes emergency stops very fast--they say within one boat length from 6 kts--and greatly improves power astern due to the reversing prop. We notice almost no prop walk. As Dockhead said, motoring very slowly may mean going in & out of gear.

I believe they aren't as popular as Max prop as they are perhaps the most costly option, or at least they used to be.



[a64pilot]

Originally Posted by Prairie Chicken

I believe they aren't as popular as Max prop as they are perhaps the most costly option, or at least they used to be.



Number I was given by AB for an Autoprop was very close to the number I got from PYI for a Max Prop. Either I was given a bad number ( I hope not), or maybe prices have come down.
I also think there is some that remember the problems that they had with "spitting blades", I for one don't want that to happen, I can see how serious damage could occur from that.

[FlightPlan]

I discussed Eco-Wind with the Rep at Miami Boat Show this year and he told me that it would not be much of an advantage with a displacement hull like mine. Now they have a 5 blade and I am looking at that to replace my 3 blade easy. The Eco-Wind has springs that provide resistance when the rpm's settle in. But in any kind of seas above 2 foot, the prop cannot settle back to a constant speed making the savings in fuel meaningful. I was hot to trot for it too. I thanked the rep for his honesty.


I like my Max-Prop and for stopping my boat, it is the greatest feature. (same thrust in reverse as thrust forward)

[GrandpaJim]

I've been digging into this myself lately. The best test I found was here:
https://yaffacdn.s3.amazonaws.com/li...LDINGPROPS.pdf

It does look like the Autoprop has significantly different, flatter torque curve than "non-autopitching" props be they fixed, folding, or feathering.

Comparison tests can be deceptive as the props are not always equally or correctly pitched for the boat. Calder does a good job mentioning that issue.

[silversailor]

Suggest you look at a Kiwi prop. Much less expensive that most other feathering props. Uses composite blades. I've been using one for 9 yrs on a Hanse 37 and very satisfied. Great service and response from Kiwi (NZ). No prop walk in reverse. Just leave tranny in neutral and she feathers while sailing.

[Loredo]

I can give you a direct comparison between the Maxprop and the Autoprop.
This spring I replaced the Maxprop on my Jeanneau 49 with an Autoprop.

My findings are:
8.2 Knots motoring speed. Consumption with the Maxprop 7.2L/H With the Autoprop 5.0L/H.
Engine speed at 8.2K with the Maxprop 2.900 Rpm, with the Autoprop 2.500 Rpm.

Max speed with the Maxprop 8.3K @ 3.000 Rpm increasing the R's further made only more noise.
Max speed with the Autoprop 8.7 K ( matches calculated hull speed ) @ 2900 Rpm. I did try 3.200 Rpm for a few minutes and saw 9. something on the GPS. I'm not interested in pushing the engine that hard for much longer.

Motorsailing there's simply no comparison!
I've been able to stay around 8 knots in a 8 knots aparent wind with the engine @ 1.200 Rpm several times. Using less than 2L fuel and hour.

The only disadvantage that I've noticed with the Autoprop is the drag compared to the Maxprop. Sailing in very light wind conditions I've lost about half a knot.

I have no idea how the Autoprop will hold up long term but it can't be worse (I hope!) than my personal experience with the Maxprop's I've owned.

Loredo

[a64pilot]

Loredo,
I hope mine when I get it works as well as yours has, of course I'll see smaller numbers as I'm a smaller boat, but the part throttle performance is what I'm after, being able to motorsail at lower RPM's. Other than range I'm not so concerned about fuel consumption, money these things cost, they will never pay for themselves in fuel savings,
but the lower RPM ought to increase engine life, and the increase in range would be nice.