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Old 07-07-2010, 16:28   #1
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Martec MkIII Elliptical Folding Prop

Hi again all, anybody care to comment on the folding prop?

From a safety stand point, I will be mostly cruising. I have been told that docking and maneuvering in tight corners might be easier with a conventional three bladed prop. I've also been told if they fail, well, of course you're in trouble... I've also been told the conventional prop will have more power and generate perhaps more thrust (10-15%)... better speed under power, less fuel consumption...

However, I find the speed gain under sail very appealing: around 0.75 knots VMG is not negligible or am I too greedy vs. safety conscious?

I have a Wauquiez 45, both props available, and will be cruising the Bahamas for 6 months.

Your comments if you please!

Cheers, PJAZZ.
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Old 08-07-2010, 21:37   #2
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I'm spinning a Martec elliptical two-blade folding prop on a Perkins 4-108 powered 21500 pound 45' sailboat, and what you describe is about right as regards how the prop works:

1. forward speed under sail is .75 to 1 knot faster than with fixed prop
2. forward speed under power drops by about the same
3. you have to plan way ahead for using reverse - folding props are trying to close themselves when spun in reverse, and you're hoping centripal force will keep them open
4. power is about the same as a two blade prop in forward
5. power is way less than a three blade prop (again, in forward)

I'm planning a re-power of the boat (Perins 4-108 out, Yanmar 4JH5E in) and will be installing a MaxProp 3 blade feathering prop at that time. If you want power in gear for motoring, but keep the sailing performance - you're looking at a feathering propeller.

At least those are my thoughts...

- rob/beetle
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Old 08-07-2010, 21:42   #3
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Folding, especially non-geared, props are really aimed at racers who don't care about motoring performance. They are often swapped out for deliveries.
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Old 08-07-2010, 21:59   #4
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G'Day pjazz,

While I agree that reverse thrust with any folding prop is a bit puny, there is no reason that performance going forward will be any worse than with a fixed prop.
In fact, it may be better than with a typical "sailors" two blade fixed prop, because the designer of the folder doesn't have to skimp on blade area in order to minimize drag.

In your case the Martec Elliptec is a well designed folder, and will be quite efficient in cruising conditions. It may not have as much static thrust as your 3 blade fixed, which means less thrust when trying to get off a mud bank or towing another vessel, but if PROPERLY matched to your eng/tranny should give equal top speed and fuel economy. It does lack gearing between the blades which can cause problems, especially as the prop bushings wear a bit.

The feathering prop on the other hand, is inherently LESS efficient than either a folder or fixed prop because their blades can not have any "twist" built into them. One real world example -- we switched from a two blade Martec Elliptec to a three blade Autostream feathering prop. Had much greater thrust in reverse and when stalled (static) in forward, but our fuel economy was reduced by 25%. A PITA for a boat with limited tankage as that one was.

So, it boils down to what you consider more important -- performance under sail or under power. Take your choice!

Incidentally, after trying lots of combinations, we've settled on a three blade Flex-O-Fold folding prop. Better reverse thrust (but still not great) and excellent powering performance coupled with minimal sailing drag. We like it!

Cheers,

Jim and Ann s/v Insatiable II lying Manly Qld Oz
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Old 08-07-2010, 22:31   #5
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Just a personal preference but I would not replace a fixed prop with a folding prop. The folding prop compromises forward thrust because it relies on centrifugal force to remain unfolded in reverse.

If the .75-1kt is important enough for sailing performance I would go with a feathering prop.

We switched from a folding prop to a feathering prop. We picked up 2 1/2 knots in forward motoring and a ton of control in reverse. With the wind up in a marina or anchorage I like the better control the feathering prop provides.
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Old 09-07-2010, 06:09   #6
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We have a Gori folder, rather than the Martec, but we have never had any difficulty with either forward or reverse under power. We have no difficulty achieving hull-speed at roughly 3,000 RPM and no difficulty slowing the boat or backing her when necessary. FWIW...
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Old 09-07-2010, 09:50   #7
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We changed from two blade folding Martecs to two blade folding Flex-O-Folds and were much happier with the performance in reverse.
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Old 09-07-2010, 10:21   #8
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Two blade flex o fold start at £1000 over here, otherwise we would have one too.

An interesting article on folding and feathering props:

http://www.flexofold.com/upload_dir/...onthly_low.pdf

Pete
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Old 09-07-2010, 16:28   #9
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Quote:
Originally Posted by Ex-Calif View Post
Just a personal preference but I would not replace a fixed prop with a folding prop. The folding prop compromises forward thrust because it relies on centrifugal force to remain unfolded in reverse.

If the .75-1kt is important enough for sailing performance I would go with a feathering prop.

We switched from a folding prop to a feathering prop. We picked up 2 1/2 knots in forward motoring and a ton of control in reverse. With the wind up in a marina or anchorage I like the better control the feathering prop provides.
G'Day Ex C,

Wait a minute! How can the fact that folders rely upon centrifugal force to stay open in REVERSE compromise their thrust going forward????

And, if you gained 2 1/2 knots in forward speed by changing from folder to featherer, there MUST have been some serious defect in the folder -- wrong diameter or pitch, missing blade (!), or such.

As I posted above, our experience has been very different in that respect.

The good manuvering performance in the marina is certainly a benefit, but whether this outweighs the sailing attributes and the inefficiency of the feathering prop is a personal decision that rest upon the type of sailing that you do.

Cheers,

Jim
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Old 09-07-2010, 20:26   #10
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The prop I had was standard issue with the Volvo saildrive. I didn't design it but the only conclusion I can reach is the pitch in forward was seriously compromised in this design.

A larger pitch would create larger forces in reverse tending to fold the prop.
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Old 03-12-2011, 02:17   #11
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Re: Martec MKIII Elliptical Folding Prop

Bit late on the pick up here, but have just lost a fixed prop off my 38ft cat and have some Martec folders as spare that the previous owner said not to put on . To dangerous and hard to use.
They are eleptics , but have no idea of how old , the boat is 11 years.
I have already got a few ideas of best use , but thought I would try you guys out since you would now have even more idea of operating procedures.
eg what is the best way to get reverse while docking , side on in a cat.
It was recommended to put into idle , then use quick bursts of throtle, planning your manouver as they are a bit slower to respond.
I have yet to fully test them out , but am getting way more cruising speed than the fixed props that were on there.
Fixed - 2 blade 13/12P
Folders- 2 blade 15/ 10P
Big difference. Have not yet tested WOT.
Darren
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Old 03-12-2011, 04:17   #12
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Re: Martec MKIII Elliptical Folding Prop

Darren -
I think the biggest difference comes when trying to slow the boats' forward speed. If you are going faster than idle speed it takes some distance (and frequently lots of revs) to arrest the boats' forward motion and get her started going backwards. Just plan ahead and allow for having "weak brakes". Trying to overcome a current from a stopped position also requires time when going astern.
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Old 03-12-2011, 21:37   #13
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Re: Martec MKIII Elliptical Folding Prop

I started this thread almost a year ago... cruised the US east coast and Bahamas for 8 months full-time. I elected to keep the Martek folding prop mainly because I am from a sailboat racing background and sailing speed was always important to me. I had it rebuilt by Martek (approx $500), new pins and bushings, and re-polished.

Turns out that the prop was very efficient (8 knots at 2200 rpms) and absolutely flawless in reverse situations with virtually no "propwalk".

I can't comment on other types or configurations of props, but this one serves me quite well and I am very pleased with it. Maybe it's the combination of boat (1993 Wauquiez 45) powered with a 54hp Yanmar 4JH4E and the transmission (the transmission is a ZF15MIV with the 2.13 ratio) and the 2 blade 22X13 folding Martek that do it. Everything seems to mesh together very well.

Only negative point is the sound of the blades opening up ( slight metal "bang") heard when putting it in gear. Some have said that this may cause some premature wear on the tansmission... will have to wait and see.

Cheers.
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Old 13-03-2013, 07:34   #14
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Re: Martec MkIII Elliptical Folding Prop

Hi Gang ,
Lots of info above Iam currently running a fixed two blade on a cal 39 it goes well motoring but just about to sail across the pacific so looking at options putting in a new gearbox also.
Gorrie recommend a 18x13 rh for my boat

i have a chnace to get a well priced Martec two blade rh 18D x 12 p3 so minimal diff in pitch will it work ? i dont really like the shaft turning all the time.... and the extra 20 odd miles a day can be very handy to P
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