best folding prop

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mariog

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Hi Guys need to change the prop on my MUMM36 powered by a Yanmar 2GM (20Hp) & saildrive which only motors to a maximum of 4.5 knots. As I need more speed was thinking of changing the prop. Was looking at the Gori simple 2 bladed prop or the more complicated Autoprop. Am begging for your suggestions or comments.
 
After researching all the brands at SIBS I bought a flex-o-fold 2 blade folding prop for my 20hp Volvo engine. Flex-o-fold are the latest designs, have unique features and are consequently the most expensive folders. However the difference in price with the competition was only about 20%, which I thought was worth it if you are getting the best.

As is often the case, you get what you pay for....
 
Just to add to the options, we chose a Gori 3 blade and are very impressed with it!

Like you I asked a lot of different owners all of whom said they they had chosen the best. I think they all work and are such an improvement over a fixed prop that all are satisfied. The only caution I heard was that some props do get through anodes at an alarming rate, but that may be local conditions.
 
I've got the Gori 3 bladed and I'm very impressed with it (at least it's performance as a prop). In forwards it is as good as a fixed 3 bladed, in reverse it is better. Just look at the profile of its blades compared with say the Maxprop.

You don't say what prop you currently have - but if you are looking for better performance under power I would avoid any 2 bladed prop (fixed or folding) and go for one of the better 3 bladed designs
 
I vote for Auto prop, as you don't have to "mess" with getting the pitch correct (self pitching). However, you did say folding in your post and you should note that Autoprop are not folding but feathering props. Expensive, but I'm on my second onw (changed boat) and am very pleased with overall performance and in particular the reduced prop-kick in astern (which was my main reason for changing).

Alan.
 
I also had a 2GM20 which was only giving 4.5kts max with a two blade "sailing" prop.
Repalced it with a Kiwi prop (three blades) and can now do 5.5kts. Part of the problem is that a 2GM20 only gives 14 to 16Hp depending on revs. Is your existing prop too small or too large!?
A Kiwi prop is particularly good if your gearbox has a higher ratio in reverse, due to it's greater pitch in reverse. This transforms close quarters manouvering. The blades also feather to water flow rather than shaft angle which must reduce sailing drag a lot. We can notice the difference especially in light airs. They are less expensive than the alternatives.
 
I think there is a bit of confusion here as although your title says "best folding prop", you mention an Autoprop, which strictly speaking is a feathering prop.

The first thing you need to do is decide whether you want feathering or folding. In my experience feathering tends to deliver better on motoring performance, whereas folding tends to deliver better on sailing performance. It also tends to be the case that folding propellors are more suited to smaller/lighter boats.

A Mumm 36 would be suited to either, so you have an open choice.

The pure feathering propellers include Maxprop, Kiwiprop etc. I would rate Maxprop as the best, but it is also the most expensive. The Kiwiprop does have a curious reverse characteristic that either works with your boat or not. I've heard in some isolated instances the Kiwi can cause engine overload problems in reverse.

Autoprops are a feathering variant out on their own that automatically adjust for pitch, which is at it's best when used in motor sailing mode. The downside is that the autoprop suffers the most drag of all the feathering/folding props (but still a lot less than a fixed prop).

Folding props offer the least drag, are still very effective forward, but are not so good in reverse (something like a maxprop is actually better in reverse than a fixed prop). I think this is one of the reasons why folding props are not suited to larger vessels. A lot of choices of brand are available, but one of the main reasons I went for the flex-o-fold is due to the dual gears that make the folding more smooth than single gears. The blade stops on the flex-o-fold are also the largest of all the models I looked at.

If all this is only adding to the confusion then the reality is that you will not go wrong with any of the props that are generally on the market.
 
When I had an Autoprop fitted to a Volvo saildrive I was extremely satisfied with the prop's performance but shocked at the rate of anode usage. I had to change the prop anode three times in one season. Part of the problem was with the anode design, which eroded from around the fixing bolts early in its life, leaving a large chunk of zinc untouched but also unattached to the propeller. Painting around the bolt holes slowed the process down but did not provide a solution. Brunton's suggested that it was a problem caused by local conditions but a friend of mine who keeps his boat a couple of hundred miles away suffered the same problem. We both ended up demanding our money back from Brunton's. I understand from Brunton's MD that they were developing an anode that can be changed from within the hull. This may have solved the problem.
 
I have pm'd a .pdf file which is a comparison of various folding and feathering props against a fixed prop.

Makes very interesting reading and was published in Yacht Magazine N°5, February 1997.

Probably a better way to make a judgement.

Regards

Donald
 
Afraid not - we hoped it would, but they do make it possible to put the shaft in and out of gear.
 
Mmmmm can't put it in gear as its a PRM box! Stopping freewheeling would have been a good justification for buying one!
 
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I have the 3 blade version and get 6-6.5 knots at 1800 revs in my 36 footer

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I have an Autoprop and get 6-6.5 knots at 1200 revs with our 40 footer. Even at 1000 revs we get about 5 knots!
 
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I have the 3 blade version and get 6-6.5 knots at 1800 revs in my 36 footer

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I have an Autoprop and get 6-6.5 knots at 1200 revs with our 40 footer. Even at 1000 revs we get about 5 knots!

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Oh dear - that's not good.

Who specified the prop for the boat? Probably worth having a discussion with them but I don't think there is much you can do about it without replacing either the prop or the gear box.
 
I can't remember from the last time I sailed one, but I would have thought a folding prop is the most likely to close automatically without freewheeling.

I have a folder on the new boat, but I don't get it for a couple of weeks still. Happy to report back when I try.
 
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