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Old 03-07-2006, 08:33   #1
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What Prop?

What propellors do people have on their cruising cats, and are you happy with them?

Fixed, folding, feathering etc etc?

I am thinking a folding prop may be OK (30HP volvos) and cheaper than an Autoprop but is 'reverse' good enough for marina manouvers on engines?
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Old 03-07-2006, 10:11   #2
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Autoprop wuld be my choice on a prop that stays in the water.

much prefer to be able to lift it out of the water.
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Old 03-07-2006, 23:28   #3
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For a folding prop check out the Flex-o-Fold line. About half the price of a feathering variable pitch prop. Auto Props may be great but a little pricey especially when you have to buy two. I would not consider putting a fixed prop on a multihull. At high speeds a fixed prop may create enough turbulance to affect the rudder.
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Old 04-07-2006, 02:32   #4
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Ah, Steve, but do you use them, and what is reverse like?
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Old 04-07-2006, 14:25   #5
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Folding Props

Hi Moby,

We have Volvo 3 blade folding props on our twin 55hp engines. Very pleased with performance ahead and astern, maybe slightly less efficient in astern but hardly noticeable (maybe more to do with hull shape).

No noticeable delay in drive either way even at low revs so blades obviously fold out asap. Certainly no problem for tight manouveres in marinas especially with two engines to help out. Main problem in marinas for us is windage on the bows, they tend to get blown off in crosswinds - I don't think the type of prop will make any difference to this problem, we just plan our moves to account for it.

Can't really comment on the impact on sailing performance since I have never had fixed props, however the Volvo props are a work of art and do fold up into a very small package so they must be a hell of a lot better than fixed props especially as sailing speed increases.

Only downside we have is the need to change anodes regularly (3 - 4 months) at about 10 per prop. This may be more to do with our marina (Holyhead) that has a reputation for being tough on anodes. I have added an isolating transformer and antifouled the blades now so hopefully this will improve the life span. At least it is easy to park a cat on the beach to check or change the anodes so not too big a problem.
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Old 04-07-2006, 19:47   #6
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I have 3 bladed fixed props on my cat. They don't interfere with the rudder at all. What they do do is slow down the sailing. When I am motor sailing, I only use one engine. Takes half the fuel that way. But, I can also feel vibration in the prop coming from the engine that is not working. This more than anything makes me think a folding prop would be just the thing.

I have looked at most of the folding props available for the sail drive. The major thing I have to say is that they are all expensive options times 2. Perhaps one of these days they will find themselves on the top of my list. Meanwhile the three-bladed props are providing excellant service, and they are inexpensive.

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Old 04-07-2006, 23:04   #7
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At normal sailing speeds you will not notice any problem with the fixed prop affecting the rudder. My concern is at higher surfing speeds. My tri is capable of surfing at 15- 20 knots and the designer warns against fixed props creating turbulence at these speeds. I can sympathize with the cost issue but dragging around two fixed props would be too much drag for me.
I have a two blade Volvo Saildrive folder and it is just adequate in reverse but I think this may be common for most two blade folding props. It is well built and designed. I made a trip that required alot of river travel but also several hundred sailing miles so I put on a fixed three blade that had been lurking in the bilge for years. Performance in forward and reverse was noticably improved but sailing performance was also affected. In conditions that I could expect speeds of 13-14 knots we could not get her past 11-12. I did like the three blade for motoring so I ending up getting a three blade folder but have not had the chance to use it yet.
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Old 05-07-2006, 01:19   #8
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Thanks for replies. Brunton Auroprop has good reports but V. expensive x 2, rather than just expensive x 2.

The Flex-o-fold website claims 2 blade (fixed or folding) prop. is more efficient than three blades: 3 blade just give more acceleration.
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Old 05-07-2006, 05:29   #9
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Someone said "pleased with performance ahead and astern, maybe slightly less efficient in astern but hardly noticeable (maybe more to do with hull shape)."

Props are designed to be more effecient in one direction (forward) than the other. The blades are not normally a simple helix. Since we tend to use them forward a LOT more than astern that makes sense. That is also why prop walk is normally more noticable in reverse.

Fixed vs. Folding. If you are a serious racer, folding is worth the cost. As a cruiser, I'll take the lower cost and effeciency of a fixed prop.

If your replacing anodes often in a marina setting, consider an galvanic isolator (mine is a Guest Model 2433-P) to reduce problems with stray currents from other boats or the marina itself.

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Old 05-07-2006, 06:54   #10
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Props are designed to be more effecient in one direction (forward) than the other
Not true of the autoprop, where the blades reverse direction, so they are as efficient going astern as ahead

That can clearly be seen in the videos here: http://www.autoprop.com/autoprop/int...nal/video.html
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Old 05-07-2006, 10:50   #11
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Neat video. I should have said the vast majority of props are . . .

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Old 05-07-2006, 19:54   #12
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We have the Volvo folding 3 blade props on our catamaran and they work well in both forward and reverse. I just threaded the boat through a tight maze of a marina this morning using only the throttles for steering, and reverse worked as well as forward.

Mark
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Old 05-07-2006, 20:04   #13
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I have been struggling with this decision for my trimaran. I have a 3 blade fixed, but would like the extra speed. Still, I like the simple reliability of the fixed prop. Sunday, I got my answer. I was in a race on a 47' Piver with a fixed prop. At 8kts, it started to vibrate. At 12 kts, it sounded like the engine was running, and at 15, it was just plain nerve racking. On a mono, it is a minor difference in speed, and more of an annoyance than anything else, but on a multihull that is regularly hitting speeds over 10kts, it is a problem waiting to happen. I will be going with the folding prop. I have looked at the feathering props, and they are to complex for my taste, but they have certainly come a long way technologically.
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Old 05-07-2006, 21:07   #14
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I have fixed 2 bladed on my twin Yanmars. They freewheel when sailing (yes, it's OK) and according to the performance charts offer minimum drag under sail. Under power, they are adequate.

Oh yeah... they're cheap!!

Rick in Florida
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Old 06-07-2006, 08:21   #15
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I dont like the thought of one 'sea anchor' under me on a monohull, so two on a cat is even worse. Therefore I am sure I will not have fixed props, but am still debating the merits of folding v feathering.

I like the - theoretical - slipperyness of folding props (when folded) to nets, fishing lines and so forth, (and would not freewheel a fixed prop) and agree the simpler design and price is appealling. I have had a folding 2 blader on a monohull and that seemd to work fine, both forward and in reverse.

As long as you CAN manouver with folding props, that seems to be way to go. I have heard about anodes on Volvo props needing frequent replacing in several cases now (or is that one case several times? I can never be sure on the internet)

any other feedback welcomed.
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