Folding propellers

Dear all,

Hello. This is my first post on boatdesign.net - please excuse me if the question has been asked (and answered!) 1,000 times before...

I have decided to replace the fixed two-blade prop on my yacht with a feathering or folding type. Having looked at cost and performance, I've decided to go for a two-blade folder. Current front runners are both Danish: Gori and Flex-O-Fold.

Does anyone have any experience that would help me choose between them?

Thanks!

 

I don't have an answer for you but I am also interested to hear from those with the knowledge. My question is how much do you actually "gain" in efficiency by having a folding prop.? I know they are supposed to be less efficient when going astern.
Also they are more expensive then a fixed prop, so unless you were a serious long distance cruiser or into racing is the extra cost worth it?

Mychael

 

At 6knots you will gain at least half a knot of speed.

Yes, your "brakes" will be a lot worst

If you do a lot of cruising you should consider a self-adjusting pitch propeller (they fold too and have the same increased efficiency astern). They are more expensive but have a lot more advantages to consider.

http://www.propulsionalternatives.co.nz/autoprop.html

http://www.sailnet.com/collections/articles/index.cfm?articleid=matthe423

http://www.autoprop.com/

 

I've used the Flex-O-Fold for the last seven years. I've used Martec and Columbian (yes, they used to make a folder) on other boats. While I can't make a direct comparison (different engines and prop sizes), I believe the Flex-O-Fold is better at backing down than the others and at least as efficient going forward. Can't speak to the Goris.

 

Well - here's a more complete list of the props I've considered:

2 and 3 blade folding: Gori, Flex-O-Fold, Brunton Varifold
2 and 3 blade feathering: Brunton Autoprop, Maxprop; Kiwi; Autostream

The space for the prop is restricted - a 15" will allow for slightly more than 10% diamater tip clearance; a 16" prop breaks this rule, although it will fit. All my calcs suggest that, if I were to choose a 15" prop, I should go for three blades, in order to reduce the blade loading to an acceptable level.

Unfortunately, however, all three-bladers are beyond my budget, so it's two blades for me. That eliminates the Kiwi, Brunton and Autostream feathering props, and all the three-blade foilders, and leaves only the max prop two-blade feathering prop, and the various two blade folders.

I've decided to go for 16" and break the tip clearance rule. I wouldn't do this if my boat was flat bottomed, but she isn't - the hull forms a sharp V over the prop, so I'm assuming/hoping that the pressure impulses from the 2-blade prop passing rather close to the hull won't cause too much vibration.

I've rejected the two-blade Maxprop (a) because it's expensive and (b) because it's performance isn't that wonderful. Sure, you get the best possible performance in reverse, but the planar blades mean that they aren't very efficient and tend to cavitate strongly. Drag under sail is also (surprisingly) not especially fantastic.

So - I've whittled it down to a 16" two-blade folder. I'm going to accept the breakage of tip clearance rules, and live with the indifferent performance in reverse. Drag under sail is wonderfully low for more or less all makes, so far as I can see, and performance ahead is generally rather good - with maybe the Flex-O-Fold having the edge.

The only other consideration I've been alerted to is durability. Both the Gori and Flex-O-Fold are made from Nickel-Aluminium-Bronze (NAB) thus obviating most concerns about electrolytic corrosion (my old manganese bronze fixed prop has dezincified rather nicely). But some people seem to have experienced mysterious corrosion problems with the Gori. I can't explain this. And, some people have said that there are problems with pivot pins wearing out (making the blades a bit bit floppy) and the gear teeth work hardening, and sometimes breaking.

FWIW, my enquiries suggest that the Flex-O-Fold probably has the edge, although I don't know why.

So there ya go. I have a few articles, links and photos I could post, if people are interested...

Fuchsia

 

Fuchsia,
When you mention the "Kiwi" prop, do you mean the Bri-Ski?
If not, take a look at one, they are pretty nice.
www.bri-skipropellers.co.nz
Steve

 

RE: Props

How often will you use the boat? When I was researching I asked a couple folding prop retailers, How often does the folding mechanism need to be cleaned? What happens when it fouls and only partially opens or closes? Because it was at a boat show, one retailer ignored the question and moved on to another customer, the other retailer just said have the diver get it when he does his monthly bottom scrub. That was enough to keep me away from a folding model. I think if you are going to upgrade, feathering is the way to go, but you have one more mechanical thing under the water to foul and the extra expense. I would suggest excercise it regularly to keep it working properly. I chose to go with a fixed 3 blade Campbell, didn't see it on you list. www.westbynorth.com I have been very happy with the performance forward, back and sailing.

 

I've owned boats with folders for thirty-plus years and never had one fail to open (or close) due to fouling. Our boat is in the water all year but with minimal winter usage. Even so, all it usually needs in the spring is a good scrubbing. It's a non-issue to me.

 

You have overlooked the Luke and J-Prop...both good but expensive.

A question Fuchsia...is your prop in an aperature? Is it behind a keel? If so,setting up an ordinary two blade so that it can be locked in the verticle position behind the keel is very nearly as efficient as feathering.Much cheaper too.

 

Hi people, this my first go on a forum. I have a 30 ft sailing boat (carter 30) which had a "floppy" non geared folding prop. It worked reasonably well in reverse and ok as a brake. You had to remember to give a dab of reverse before forward as both blades didn't always open. This prop got bent and was replaced with a kiwi BRI-SKI 15" X 9" (re-pitched to around 8"). It is of almost NO USE IN REVERSE. I found this forum looking for a solution. Les

 

I've since had my boat out of the water and see it has a Geared prop.
So I am assuming it should be as efficient in forward as reverse.
Is that correct?
Mychael

 

If the gears ensure that both blades must open evenly (by the same amount), then it won't necessarily be ok in reverse because the thrust is trying to close them. I don't know why the "floppy" prop worked better but it certainly did. I have just e.mailed BRI-SKI props and am awaiting a reply. The BRI-SKI has the name stamped on the hub.
Les

 

Go the Gori

I have used folding and feathering props for 30 years and I can 100% recomend the Gori as being #1.
Make sure it is the square ended blades as it is much more efficient than the racing fully closed model when going astern.
With all models, make sure you get a very heavy outer blade model as it is the weight that holds the blades open while in reverse. If the tips are too light, then they grab the water and try to close up. Another good one was a Hendly from NZ

 

I thought the original Kiwi prop was from Blundells.
http://www.kiwiprops.co.nz/index.php
Kiwi prop has composite blades as opposed metal of the others. A significant difference I feel.
Only heard good things about them. My next choice on launching.
Roly

 

Roly...I hate to be the bearer of bad news but my best mate had one of those on and yes it performed like a bonza when motoring around..(why else would you have a good prop) but when we were sailing at over 9 knts, it would drag and re-open and ended up like a bucket. If it was left unlocked (in nuetral) it would free spin like mad. We only found this out while racing and it has since been replaced as we could not get it to feather at high speeds??????