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Old 18-01-2010, 13:05   #1
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Folding Prop for Cruising Boat?

I have an opportunity to buy (inexpensively) the correct sized Martec Eliptec for my great lakes, 34' boat with a Yanmar 3GM. It'll give me an addl. 1/2 to 3/4 knot. I plan to have Martec look it over and re-build it as needed. Please help me understand why this is a good/bad idea. Thanks.
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Old 18-01-2010, 13:18   #2
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folding props cause less drag going forward ( sailing) and perform ok when under power in forward, however they do not work as efficiently in reverse.
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Old 18-01-2010, 14:09   #3
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I believe Martech have flat blades which don't work well in reverse. There are other folding props which have variable pitch which work much better in reverse (Gori is one manufacturer)

I would say for cruising it depends on a few issues...can you lock the prop (a hydraulic transmission won't)...what type of transmission you have...some don't like freespinning for long periods.

Does the locked prop cause turbulence over the rudder reducing the effectiveness of the rudder?

Do you like to race?

Do you like to dock (i.e. reverse)?
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Old 25-01-2010, 22:07   #4
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If you now have a fixed two blade you won't see much difference going forward. In reverse you will need to learn to initially rev motor to engage blades after that learning curve hump is passed you will probably do fine if you are a reasonably good boat handler. Under sail just put trans. in reverse and you will get some added speed. There is a small increase in maintanance not much. Ultimate reliability is less than fixed prop but adequete for vast majority of sailors. If you are going to the outer world podunk bring your fixed prop just in case.
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Old 26-01-2010, 02:40   #5
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G'Day Sailstoo,

First, I think that LuvToSail is confusing folding and feathering props. The Martec Elliptec is a folder for sure, and is pretty efficient going forward. As with all folders, static thrust in reverse is pretty poor. One design drawback in the Martec is that the blades are not geared together as many others are. This means that sometimes only one blade opens when forward is engaged, and severe vibration follows. This usually can be corrected by a momentary burst in reverse. Not a big deal, but can be awkward.

We had an Elliptec two blade on Insatiable One some years ago, and cruised thousands of miles with it. When it finally wore out to the point that no one wanted to rebuild it again for us we went to a three blade feathering prop. Much more static thrust in both directions, but due to the flat blades inherent in these props their efficiency is poor, and we suffered a significant loss in fuel economy (like 25%) which I wasn't keen on.

But, the increase in sailing performance is well worth the small difficulties in these props. You won't find too much change in ghosting conditions (where skin friction is the main source of drag) or in hull speed conditions (where wave-making is eating all the power), but in that large inbetween range it really helps!

And don't worry about the prop spinning while sailing: simply putting the tranny in gear briefly stops the prop, which promptly folds flat and can no longer generate any torque to spin the shaft.

So in this cruiser's opinion... go for it and enjoy!

Cheers,

Jim and Ann s/v Insatiable II lying Broken Bay NSW Oz
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Old 26-01-2010, 08:22   #6
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We switched from Martec to Flex-o-Fold and were much happier with the response in reverse. Both props were 2 blade folders.
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Old 26-01-2010, 10:57   #7
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I installed a flex o fold 2 blade folding prop driven by my 3GM on my 30' 4 years ago.
I sail mostly in western Long Island Sound with mostly light air in July and August.
The folding prop has helped much in these conditions, approx 1/2plus knots plus
more momentum after coming about...have no problem in reverse.
Can't compare to Martec, but much happier than fixed 2 blade.
I do not race. Hope this helps.
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Old 26-01-2010, 11:28   #8
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I'm backing all other suggestions you go with a folding or feathering prop - but if you've the chance to get a geared folding then suggest you do so.
I am sure you'll learn to handle the inefficiencies of such a prop when under engine but as other shave said - the real benefit is when sailing.
Sail out at 8 am on a day trip of 40 miles at 5 knots with a fixed prop and you'll be in by 4 pm. A same boat with a folding that can make 5.5 knots under sail gets in just after 4 pm. Giving them time to wash down, clean up, and enjoy a beer when watching you dock. Worth every penny.
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Old 26-01-2010, 11:41   #9
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Quote:
Originally Posted by Jim Cate View Post
G'Day Sailstoo,

First, I think that LuvToSail is confusing folding and feathering props. .....


And don't worry about the prop spinning while sailing: simply putting the tranny in gear briefly stops the prop, which promptly folds flat and can no longer generate any torque to spin the shaft.

z
I was not referring to the difference between feathering and folding but more to what others are explaining that the Martech does not perform very well in reverse because the blades are very simple in design i.e.flat

this is the gori folding
Gori propeller

also the flexofold appears to be designed to improve the how well the prop works in reverse and over different ranges of speed with a better hydrodynamic shape that includes a twist

Also Hydraulic transmission won't lock the prop/shaft when in reverse gear
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Old 26-01-2010, 17:53   #10
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I have a Gori 2 blade folding (not particularly impressed) and will soon change to a Flexofold or Varifold.

Previous boat had a 3 blade MaxProp. Great quality.
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Old 26-01-2010, 18:53   #11
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G'Day LuvtoSail,

"I was not referring to the difference between feathering and folding but more to what others are explaining that the Martech does not perform very well in reverse because the blades are very simple in design i.e.flat"

Well mate, on the Martec Elliptec that I had the blades were definitely NOT flat, but properly designed with some twist. The Martec feathering props DO have flat blades, like all other feathering props that I have seen.

Cheers,

Jim

PS We have a three blade Flex-O-Fold on I-two now and are very happy with it. Smooth perrofmance in forward and reverse, a bit more thrust in reverse than with the two blade Gori that it replaced.
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Old 27-01-2010, 05:44   #12
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I switched from a factory installed 2 blade to a 2 blade Varifold when I started racing. In foward gear I'd say that the performance is equal or maybe just a tad better, in reverse not as good as the fixed though manageable. Last summer after waiting in a pleasure craft zone before entering locks I cast off and managed to get a bit over 4 knots in reverse at 3000RPM (Yanmar 2GM20F) backing into a 15 knot wind, my boat weighs about 9500 lbs.
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Old 27-01-2010, 10:20   #13
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G'day to Jim!

I have an older Martech 2 blade (flat like a pancake) on my SJ30 and it has almost NO reverse...we use it for racing mostly so not really an issue. It is nice to go fast!

On the Cal 46 it has a massive 26 inch three blade fixed prop...I would like to put a folding prop on that boat...some have recommended the 3 blade gori...but it sounds like the varifold or as you have mentioned a different martech might be worth a look (thank you).

In the case of this big cruising boat, yes an extra 1/2 K would be nice but the primary driver is the turbulence created over the rudder (reduced effectiveness) and that is a big driver. Also with the hydraulic tranny..you can't easily lock the shaft. Using a clamp (or vise grips) is dangerous as you might want to fire up the iron genny in an emergency ...quickly.
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Old 09-02-2010, 12:32   #14
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"....also the flexofold appears to be designed to improve the how well the prop works in reverse and over different ranges of speed with a better hydrodynamic shape that includes a twist

Also Hydraulic transmission won't lock the prop/shaft when in reverse gear..."


I recently changed from a Flex-O-Fold to a KiwiProp (long story but my old prop was too large for my Perkins 4-108) and I have no end of problems with it. Biggest issue for me is I can't stop it spinning. I have a hydraulic transmission too.....so it looks like I was sold a pup. The prepellor specialists we went to never mentioned that the Kiwiprop won't fold with a hydaralic trans and I have tried everything on the Kiwi Prop website to get mine to work. Now this makes sense!! Beware.

Cheers, Mike
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Old 09-02-2010, 12:55   #15
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G'Day MikeNZ,

I think that there is a solution to your problem. When shutting down the engine whilst sailing, briefly put it in reverse at idle speed. This spins the prop backwards. Then shut down the engine. The motion of the boat will try to spin the prop forwards. During the time when the rotation is stopped, the blades will fold, and then there is nothing to spin your shaft as you sail along.

Give it a try...

Cheers,

Jim and Ann s/v Insatiable II lying Broken Bay, NSW, Oz
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