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Old 10-07-2009, 20:01   #1
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Which Propeller?

The middle of last month, I posted a thread seeking the advice of forum devotees on which engine I should install in my 40,000-pound, 48-foot ketch. I thank all who responded for their input. I ultimately decided on the Beta Marine 90, which surprised even me, however, I preferred an engine without a turbocharger and that operated at a lower RPM. The Beta 90 reaches it's rated horsepower at 2,600 RPM. It's dimensions are similar to the engine that I'm removing. By the way, the cost to overhaul the Volvo exceeded the cost of the new Beta.

But now I'm facing a similar dilemma in choosing a prop. Whether I like it or not, it's going to have to be either a folding or a feathering as the transmission I've ordered is hydraulic and I'd have to install a shaft brake if I were to install a fixed-bladed prop, otherwise the prop would spin anytime we were under sail. Since the prop shaft is directly under my berth in my cabin, the noise would probably drive me (or my wife or both of us) nuts.

Of course, the Max Prop is one of the most popular choices but I'm not enthusiastic about the maintenance required annually. The Flexofold gets good marks in the test I found at http://www.propelspecialisten.dk/dow..._test_2008.pdf but the Gori 3-bladed folding prop got even better.

We cruise Mexico and it seems that we do more motoring than sailing so an efficient prop is very important. (It's easy to navigate in Mexico: You just head toward the direction the wind is coming from.)

What has worked for you? What hasn't worked? Thanks for taking the time to reply.

Fair winds and calm seas.
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Old 11-07-2009, 09:40   #2
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Of course, the Max Prop is one of the most popular choices but I'm not enthusiastic about the maintenance required annually.
The Max Prop requires no more maintenance than any other feathering prop, aside from lubrication every couple of years, something that is easily done in the water or on the hard.
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Old 11-07-2009, 10:29   #3
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We have had the Gori 3-blade for 3 years, including a year in the Med when we used it a lot. So far it's been great. We don't use the 2 different gears often. The overdrive seems to work best when motor sailing, but we seldom motor sail.
Maintenance is easy and quick. When we are out of the water for new paint I change the little rubber bumpers, anodes and lubricate.
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Old 11-07-2009, 16:29   #4
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We have a fixed 3 blade prop. nd love it. Maybe you shouldnt dismiss it completely till you get a shaft brake quote.
Fixed 3 blades will help a big boat better than a folding, won't it?
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Old 11-07-2009, 19:16   #5
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There was a previous thread where the quoted German report was discussed. An ongoing problem with many of these types of reports is they never manage to equalise the props, ie have all props sized allowing the engine to achieve full rated revs. There has just been another report published in May issue of Yachting Monthly, altho based on a smaller installation.
For low drag props my view is the folding props are the way to go, with the equal best (more or less) being flex-o-fold and Varifold, followed by the Gori. When I was selecting a prop I was thinking about the Flex-o-fold, but finished up selecting Varifold because the Flex was only supplied in 2" increments and I needed the 1" step. Note Flex-o-fold tops out at 24", whereas Varifold manufacture up to super yacht sizes. You will be told feathering props have better astern performance and this is generally true, however how much time do you spend going astern compared to ahead? The significant efficiency gains with the folding prop are well worth it.
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Old 12-07-2009, 10:16   #6
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We have a fixed 3 blade prop. nd love it. Maybe you shouldnt dismiss it completely till you get a shaft brake quote.
Fixed 3 blades will help a big boat better than a folding, won't it?
One problem with adding a shaft brake is that I'd then be dragging a 24" prop whenever I'm sailing. Since Rutea is a low-performance sailer, I'm reluctant to hamper her ability to get out of her own way.
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Old 12-07-2009, 10:24   #7
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I made a post that never appeared.

The idea of a folding prop is basically a scheme by engineers to extract lots of money from suckers.

First of all, why would anyone in their right mind install a mechanical device which requires you to haul you boat to service?

Second, when you think of all the things which slow your boat down... towing a dink, a fouled bottom, thru hulls the speed gained by a foldind prop in minuscule.

I have had a 2 blade fixed prop for 24 years - no problems whatsover and I sail faster than many boats with longer waterlines.

Keep is simple, don't waste your money and get a fixed blade prop. The work fine in forward and reverse. Mine 2 blade aligned itself when sailing and presents very little drag.

Ignore the hype and rubbish about gaining .1 knots.
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Old 12-07-2009, 11:50   #8
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Defjef brings up a good point. A fixed-blade propeller offers a lot of simplicity and economy. However, the type of cruising we do involves a lot (too much) motoring. When we were returning last month from Mexico, we were frequently bashing into 25-knot winds and 6 to 8-foot seas. Most propeller engineers would suggest a large 3-blade prop for those conditions. Also, dragging a fixed-blade prop of that size when sailing would likely slow the boat down more than a tenth of a knot and letting the prop freewheel is not a good solution as it doesn't reduce the drag that much, adds a lot of wear to the transmission and creates a lot of noise (the prop shaft runs right under my bunk).

Feathering and folding props also have the advantage of minimizing prop walk. We have provided many hours of entertainment to those watching us try to dock Rutea up and down the west coast of North America as in reverse, she has a mind of her own. Eliminating or at least minimizing that would reduce some of the embarrassment.

But is it worth spend five times the cost of a fixed blade prop for the feathering/folding? Great question.
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Old 12-07-2009, 11:57   #9
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First of all, why would anyone in their right mind install a mechanical device which requires you to haul you boat to service?
Clearly a statement made either in ignorance or by someone too cheap to buy improved technology (i.e.; a folding prop.) There is virtually no service to a prop (any prop, be it fixed, folding or feathering) that cannot be performed while the boat is in the water.
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Old 12-07-2009, 12:03   #10
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I can't speak for other boats but this is our experience with the 24" MaxProp aboard Jedi: after setting sail and shutting down the engine, the prop turns until I shift the gearbox into fwd or rev gear. This immediately gives me one full knot extra speed. I can only guess about the difference between a turning prop and one that is stopped with a shaft break.

We love our MaxProp but on boat shows I always stop to admire the Gori 3-blade prop. The only negative I heard about was it's performance in reverse. Maybe they improved that?

cheers,
Nick.
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Old 13-07-2009, 14:34   #11
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I couldn't service a max prop in the water up here in LIS for the following reasons:

I need glass to see and would have a heck of a time seeing under those conditions

I don't have diving gear.

I don't know where you put tools and parts and so forth.

Can someone take a max prop apart, repair it, adjust it and put it back together underwater? Sure, diving mechanics can.... But that's not me and I don't want to spend a few hundred dollars for that... assuming I could find one who knows what he's doing.

I have enough trouble working in the air, with plenty of light and a reference manual... let alone underwater.

Our fixed 2 blade has little drag and pushed the boat very well into 20 knots and seas... not 6+ knots, but we would probably crack off and motor sail and tack.
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Old 13-07-2009, 16:06   #12
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I couldn't service a max prop in the water up here in LIS for the following reasons...
Those are reasons you couldn't or wouldn't service a Max Prop in the water. Doesn't mean it can't be done, which is what you stated previously.
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Old 13-07-2009, 17:10   #13
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Ignore the hype and rubbish about gaining .1 knots.
Like Nick, we gain an entire knot of speed when our (Volvo) props are folded vs open. I don't consider that inconsequential, but others might.

Mark
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Old 13-07-2009, 17:12   #14
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Also, you don't have to take it apart. That is something we do once every 5 years ro so, only to find we didn't need to take it apart at all.

Under water: just put the greasenipple(s) on and let the grease gun have a go at it. I do that without scuba gear once a year or so.

cheers,
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Old 13-07-2009, 17:20   #15
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Aloha Mark,

1 knot speed extra in 24 hours means 24 nautical miles. Simple calculation that justifies, to me, a bit of extra mechanicals and cost.
Thanks for your post.
Kind regards,
JohnL
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