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Old 22-04-2010, 13:03   #1
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Folding Props Suggestions for 40' Maverick Catamaran

I am having to decide on props for my new Maverick 400. I am wanting to put on folding props with three blades. I have a 40hp Volvo motor. From what I have seen there is no program that one can use for estimating the prop size for a catamaran, only monohulls. I would appreciate any experience or ideas people have on type of prop and size. I am looking at the Volvo folding three blader, they suggest an 18X13 but won't change the blades if they are the wrong size
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Old 22-04-2010, 15:49   #2
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Paul:

The diameter of your prop will be limited by the aperture size. Use maximum radius less 10%. Then the only issue is pitch. Most, maybe all feathering props let you adjust pitch. I know you said folding prop, but I would go with a feathering prop. You will get much better thrust in reverse with a feathering prop.

MaxProp is one of the best. One model will let you adjust pitch in the water without removing the prop.

David
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Old 22-04-2010, 16:28   #3
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Propeller Tests.

This is a review of various props which may help in decision making when looking at various props.

Gordon.


Test Results - Flexofold folding Propellers
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Old 23-04-2010, 00:53   #4
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Quote:
Originally Posted by Gordon View Post
This is a review of various props which may help in decision making when looking at various props.
That Yachting Monthly review behind your Flexofold link was excellent, thanks Gordon.

Paul, how's your propeller decision progressing? I must say I was stunned by the suggestion that fixed-blade prop(s) will add 4 hours to an 80nm passge. I knew drag was an issue, of course, but that suggestion makes it fairly dramatic for coastal cruisers.
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Old 23-04-2010, 03:40   #5
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Hi Don

I am gathering information at the moment, the problem none of the prop manufacturers want to make a clear suggestion for the size. I am trying flexofold at the moment to see if they will. Volvo gave a suggestion for a three bade folding prop but would not swop the props if they are the wrong size. I want to make sure I do get the right size in a folding or feathering type. I had a maxprop on my monohull which was great, interesting though that it did not fare that well in the test. I dont want to get the wrong size as it can potentially affect your warranty. From what I have seen it is often an excuse used by yanmar. I will give you feedback on the final outcome.
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Old 23-04-2010, 03:51   #6
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Paul, how's your propeller decision progressing? I must say I was stunned by the suggestion that fixed-blade prop(s) will add 4 hours to an 80nm passge. I knew drag was an issue, of course, but that suggestion makes it fairly dramatic for coastal cruisers.
Yes saw that too. Even if they are comparing the worse case, fixed 3 blade prop locked, against a folding 2 blade it does warrant some consideration. We pop across the channel a couple of times a year so even knocking off a couple of hours (fixed 2 blade rotating against 2 blade folding) would be a major gain.

Daglow the UK supplier want 918 for 2 blade folding 16x14 flexofold. Did try the European distributor but no reply. Need to find the old propshaft and measure the nut, taper and length now so the prop hub can be machined to match.

Looked at the Kiwi (similar price here) but we touch a muddy bottom at LW Springs so can't use it

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Old 23-04-2010, 04:33   #7
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Prop Size?

Hi paulrack,
We have gone through the same process for the Orana 44, also fitted with D2-40 Volvo engines. Flexofold recommmended 3-blade 17 x 12-3L with hub for saildrive,or the 2 blade 17 x 13L with hub. Very tempted with the Ausi $ and euro rate at the moment.

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Old 23-04-2010, 04:46   #8
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iv just fitted a kiwi prop last year and have gained a knot to aknot & half when sailing.The other good thing is you can adjust the pitch to suit the type of sailing or motoring yuo do
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Old 25-04-2010, 01:09   #9
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Hallo Paul , the Volvo props are not the highest efficient props on the market ,
If you want efficient go to Flex O fold 3 bladed props , and forget about the Volvo props a difference of 10 % in speed is possible this is both experience and the test results show the same http://flexofold.com/upload_dir/docs...onthly_low.pdf
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Old 25-04-2010, 04:23   #10
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You might also consider the Bruton Autoprop. It is the worst of the folding/feathering props for drag under sail, but it's still about one-fifth the drag of a fixed prop. It's also among the most expensive props.

But for those two disadvantages you get the best motoring performance of any prop, the most thrust ahead or, especially, astern, and very little prop walk.

Best of all, the prop is self-pitching -- it's like an automatic transmission. It will "upshift" if you are motosailing, or if you back off the throttle in calm water. This also means that the prop is less demanding of being pitched exactly right for your boat. It will find the right "gear" for the conditions.

It will also "downshift" when loads increase -- like going into seas or wind. This makes it almost impossible to lug the engine.

Oh, one more disadvantage -- it will also "upshift" if you are trying to maneuver at low speeds, making it impossible to get the speed down in gear even at idle. Our boat does about 4 knots at idle, and to go any slower you have to shift in and out of gear, which is a certain PITA.

All in all we love ours. Remember, though, that you will lose a part of a knot under sail, compared to the slickest of the folders.
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Old 25-04-2010, 07:32   #11
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I would definitely take a look at feathering props as well as folding. As pointed out above, not quite as streamlined, but typically much better performance under power, particularly in reverse around docks. We have been very happy with our Autostreams. Here's an interesting comparison of feathering and folding props by someone who sells both.

Seahawk: Feathering, Folding or Fixed Propeller?

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Old 25-04-2010, 09:08   #12
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One of the other things you should factor in is the complexity of the installation and whether you can do that (as well as change them out) in the water. Some of these props have a number of very small bits that result in them requiring a haul out. Others are relatively simple and although you might not want to do it, you could change them out in the water with care.

We've been quite happy with our 2 bladed Flexofolds. They perform well, are pretty simple and I prefer the folding over the feathering, as they are less likely to catch a crab pot or other floating junk. Although I haven't had to work on them in the water, it is possible to do so, as long as you have the correct type of Locktite or the "special screws" provided by Flexofold.

No matter which one you choose, you will be pleased with the results under sail.

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Old 25-04-2010, 10:22   #13
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One of the other things you should factor in is the complexity of the installation and whether you can do that (as well as change them out) in the water. Some of these props have a number of very small bits that result in them requiring a haul out. Others are relatively simple and although you might not want to do it, you could change them out in the water with care.

We've been quite happy with our 2 bladed Flexofolds. They perform well, are pretty simple and I prefer the folding over the feathering, as they are less likely to catch a crab pot or other floating junk. Although I haven't had to work on them in the water, it is possible to do so, as long as you have the correct type of Locktite or the "special screws" provided by Flexofold.

No matter which one you choose, you will be pleased with the results under sail.

ID
That's another advantage of folders I forgot to mention -- les likely to catch a line from a crab pot. That can ruin your whole day.

So that and more streamlined, are the two advantages of folders.

Big disadvantage of all complex props is that they require maintenance and can break (throw a blade). I had a folding prop throw a blade on me in the Windward Islands on a charter boat -- it was not fun.

But compared to dragging a regular fixed prop behind you while you're trying to make speed under sail -- forget it. Of course it's worth the expense, maintenance, and risk of thrown blades.

It's also worth noting that the best complex props are actually better than fixed props when motoring. A fixed prop presents trailing edges of the prop blades to the water in reverse -- the better complex props turn the blades all the way around, and thus work much better in astern. Personally, I would never go back to a fixed prop (although we do keep one as a spare -- just in case).
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Old 25-04-2010, 11:33   #14
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Have had both Flexofold and Maxprop. Both appear to give same advantages in forward and when under sail - but in reverse the Maxprop is MUCH better and it would be my choice of the two.
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Old 12-05-2010, 03:17   #15
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I am gathering information at the moment.
How's the propeller search going Paul?

After some chatting around mates here, I should throw an Aussie prop into your 'mix', if you haven't already considered it of course. It seems Austral Propellers are well regarded here, with both folding and feathering versions and they appear willing to recommend sizes for the folding props as well as compatibility with Volvo & Yanmar for the feathering models. The Austral website is...

2B & 3B Fixed, Folding & Feathering Sailboat Propellers

Gordon, did you look at Austral for your Orana?
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