January 25, 2003
Ron Damsen wrote,
"Can anyone in the Fleet help I36 owner Vern Verling. His boat, Dream Catcher, is undergoing a repower at KKMI after cruising for a year in Mexico and would appreciate any input regarding installing a three blade Max Prop." His question is:
"IMPORTANT question..Do you have a max prop or know of anyone in the assoc that does? I read that someone had a three blade and really liked it. What size is it??????????
Vern's email is: Asklepios@aol.com
I do, being pushed by a Palmer P60, which is only an 18shp motor, not much
by today's perceived engine size needs, but in range by the two horsepower
per ton rule. So in my case a good prop match is more important than if
you're running 40shp, and can bury prop losses by turning up the whistle.
I've used a fixed two blade prop: good efficiency, but way too much
drag in light air. Then an old style Martech two blade folder; very
inefficient, expensive to change pitch, no backing oomph. But it will get
you out to the start line and back if you're a hardcore racer.
So I got a two blade MaxProp, presently on the boat. It's expensive, but has a nice feature: easy repitching (out of the water). I've fiddled with the pitch and now it's just right. They look sort of fragile, the edges are thin and ding easily, but they're used on high speed powerboats so they must be fairly tough. I've heard if you shift from ahead to astern at full rpm the steel puzzle pieces inside the hub that allow adjusting pitch can strip the bronze teeth. Not much of a problem when running 18hp. They require maintenance, refilling with grease every few hundred engine hours, out of the water old style, zerk fitting new style. Mine's been in service 13 years with no problems, but I haven't hit any logs either. It's always snapped open, feathering below 3kn is iffy. Once feathered, boatspeed can drop to 0kn with no opening.
Not sure if they're still made in Italy, but the whole thing used to be (is?) hand lapped so all the gear gimcrackery doesn't bind, and the grease doesn't get spun out of the housing. There's no gaskets, all metal to metal. Very tight tolerances compared to a floppy MarTech. Perfect balance right out of the box. If you break an interior part, the whole prop has to go to the shop, you can't just buy a replacement gear thingy.
The force which feathers the prop is not great at low boatspeeds because of the geometry, so the gearing must rotate freely. A spinning out of gear MarTech wants to keep spinning; a MaxProp wants to feather. The well written manual says you have to be going 5 knots at shutdown to ensure complete feathering.
The shaft should not turn when feathered, but leaving the engine in gear is enough if the transmission is not hydraulic, unlike the big brake needed with fixed blade props. The force to keep them closed is negligible (low drag), unlike a MarTech which, if one blade is straight down it will open at low boatspeeds. So there's no need to align the shaft after shutdown, although some say a two blader MaxProp should have blades at 6:00 and 12:00 because of shaft angle, the opposite of a MarTech. I think that's being picky.
They are not as efficient as fixed props, because the blades have no twist, i. e., they're flat as pancakes when viewed edge on. Therefore they cavitate a lot at certain rpms, sounds like a hyperactive christmas tree bubble-light. I saw an underwater view of twin MaxProps on a powerboat firing up and they shot a cylindrical shaft of cavitation bubbles the length of the boat comin' out of the hole. Of course they were running lotsa hp and rpm. My setup doesn't perform well in headwinds and seas, dropping to 3kn because of prop slip; don't know if it's a horsepower problem or the inefficient nature of a prop with no twist, a 3 blader might have less slip.
MaxProps are symmetrical so they back *better* than a fixed blade. I can stop in two boatlengths from hull speed, with wash gurgling up the cockpit scuppers. No change in prop walk. It catches kelp more than my other props, because when deployed, the blade edge which fairs into the hub projects out like a cleaver. Backing down on moderate infestations cuts weed right off (not poly rope); I haven't tried powering into a kelp bed with it yet, though.
As far as MaxProps and I36s go, there are some installation issues. Blade tip to hull clearance with my shaft length is only 1 1/2 inches with a twelve inch prop, and MaxProp didn't make 12" inch three bladers back then. MaxProps are best on larger boats with more room, because as prop size goes down, hub diameter doesn't decrease (the internal gimcrackery is the same size) which means an 8" MaxProp would be mostly hub and no blades. The added drag because of the unusually large hub (12" size) means a good MarTech folder probably has less drag. Some racing fleets rate featherers slower than folders just from the wetted surface standpoint.
Also, because the MaxProp completely encloses the end of the shaft (doesn't slide on, bolts on like a shaft zinc), the threads for the classic castellated shaft nut which holds a fixed or MarTech folding prop on cannot project much beyond the end of the shaft taper. Part of the shaft threads had to be cut off my shaft so the MaxProp would clear the shaft end, which means I may have to get a new shaft to switch back to the fixed or MarTech prop. OTOH, some Santa Cruz 70 sleds switch to fixed props for long deliveries, so hub work on a fixed prop might allow the remaining threads to catch a castellated shaft nut.
Sysnopsis: Maybe a 10% fuel consumption hit compared to a fixed prop. I'm happy, but I'm running a low horspower auxiliary. Don't know how performance would change when running a 25-35hp diesel. Back when I bought mine there weren't many low drag prop options on the market, now there's several new designs available which may be worth some research. $1,000 for a MaxProp two blade 12" prop is a lot of money, and the 3 bladers are more expensive. And, if you don't care about ultimate sailing performance, a fixed prop is hard to beat concerning cost, simplicity and durability. If money is no object, clearly a variable pitch prop while underway is the ultimate setup.
From Mike Reed:
I am not sure how I missed the beginning of this thread, but I did. Back in August, I went from a two bladed 8x11 fixed prop to a 3 blade 13" Maxiprop. I too am powered by a Palmer P-60 and can get up to about 6.25 knots at 1800 rpms. The prop was expensive, but in my mind, when I get on my Islander, I like to go quickly, either under sail or power. With the 2 blade, it didn't take much to slow the boat down drastically. With the Maxiprop, I loose a little headway with waves and wind, but nothing like with the fixed prop. The best improvement has been under sail however. Its difficult to put hard numbers to the results, but I'd venture to say that sailing performance has improved by at least 25%. And she backs quite smartly now.
I purchased my Maxi from PYI in Lynnwood, Washington. They are the manufacturer/distributor and were extremely helpful in helping me install the prop myself. I did have to take about 1/2 inch off of the threaded end of the shaft, but ran into no other problems whatsoever. The 13 inch diameter was pitched to 6 inches per their instructions and has been a perfect match. If you call them direct, ask them about reconditioned props as they have occassional trade-ins that they say they will discount quite nicely.
A good friend is running a 3 bladed Maxi on his Nordic 34 with a Yanmar deisel in it. He was the one who convinced me to try one. Another friend managed to find a three blade Maxi at the Seattle swapmeet this year and saved quite a bundle. He will be installing his on his Sabre 38 this spring when he hauls out.
A couple of other things about the props. First, there are two models, the least expensive is set to the desired pitch, assembled and then mounted on the shaft. The more expensive one allows the pitch to be set/adjusted by a diver in the water. Second, Mark mentioned steel parts, when I assembled mine, only the set screws were steel (of the stainless variety), the mechanism was all brass.
If you can get past the price tag, mine was about $2000.00, I really don't believe you will have any regrets going to a 3 bladed MaxiProp.
Mike Reed firstname.lastname@example.org
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