Feathering props advice needed

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paul

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I've got a Moody 36 and am thinking of buying a feathering prop to help the tub go a little faster. The boat uses a volvo saildrive. Anyone had any good/bad experiences using feathering props on a saildrive? Which makes are best?
 
Hi Paul, I've been looking at a folding prop for my Centaur
there doesnt seem to be a lot to choose between them exept for price. Some of the American web sites have useful
discussions. Most of the manufacturers have their own sites.
 
There was a discussion on this recently, I asked for some suppliers names but didn't get any. Perhaps I'll have more luck this time. I think Harald S. was using a Danish make but didn't leave make. If you read this Harald S. can you help?
 
I researched this recently in order to improve the sailing performance of my 37 foot cruiser. The information I was given was that a fixed prop represented about 48 lbs of drag when sailing and this could be reduced to 8 to 10 lbs by fitting a feathering or a folding propeller. This would represent a reduction in overall drag of about 20% for my boat.

I did the rounds at the London boat show for both feathering and folding. The information I got was that feathering propellers were more complicated than folding and that you need to have a rope cutter to protect them, whereas in theory the folding blades should fold if you have forward motion thereby obviating the need for a rope cutter. Having been over one or two line (inadvertently) in my previous boat, Sigma 362 with folding prop, this does seem to be the case. the only time I ever got a line round the prop was when stationary and someone dropped a halyard over the side.
I checked with the builders of my boat (Najad) and they recomended a Flex-o-fold 3 bladed propeller, made in Denmark and imported by CJR propulsion (www.cjrprop.com) or phone 02380639366. I asked in the other forum and found another Najad owner who sang the praises of the Flex-o-fold but said that when you are going ahead and want to stop you need a good burst of revs intiallly to spread the blades in astern. CJR agree this is necessary. You will find that reply in the January threads except I think I mis-spelt Folding.
I also looked at the Gori, which has a website and a UK distributor, it is more complex and more expensive. The best of the feathering I thought was the Max Prop , Darglow Marine are UK distributors, but I did not keep all of the data. CJR also have a feathering prop, the Vari Prop and both types have sail drive versions so it might be a good place to start. I did not like the way the Vari prop blades were hung on the side of the boss, but that is personal.
One word of warning, My current fixed prop is an 18inch, but Najad advised me to fit a 17inch Flex-o-fold to prevent overstress on my gearbox, this on the advice of Yanmar. Perhaps the folding is more efficient in drive than the fixed prop.

My own thought is that the simplicity of the folding propellor probably means it is more robust. The article on the various feathering options did not make any recommendations but merely talked about how they worked and what the cost of the various options were. You can get all of that info from the various manufacturers websites.

Hope this all helps, I debated for about two weeks before reaching my decision which was not based on cost although in the out-turn the Flex-o-fold was the cheapest option

Good luck

Chris

Chris Stannard
 
Re: Feathering props prices

I've had quotes for a folding 14x9 2 blade- Flexofold £450 +VAT, Gori was £330, I think I'll go for the Gori!
 
Yes it was me with the danish make. And as Chris Stannard pointed out ,I ment the Flex-O-Fold and I'm very happy with it.

It was originally recommended to me by a guy who worked at Najad and had fitted it to his own boat. At that time the yards standard was VariProp, which is a feathering prop, hard to distinguish from the MaxProp.

I wanted something with even less drag and I was concerned about the lack of twist in the blades of the feathering props. I heard that due to the huge speed differnce, close to the hub versus far out at the tips of the blades, they become too much of a compromise when you get to larger diamaters. The result could be cavitation at the tips.

At that time I was thinking about fitting a Brunton Autoprop, but then changed to have them fit a flex-o-fold, given the recommendation.

Now after I had plenty of time and all the locks of the Caledonian Canal to play with it, I think it was a good decision. Seemingly Najad came to the same conclusion, as they now fit it as the standard on their larger boats, and offer it as an option on all others.

The comment I made about needing to be reved up quite a bit in reverse if you want to slow down quickly from faster speed forward. isn't a real big issue. If you know it, you know what to do, and if you go slow there is no need for such dramatic action. Like when I glide into a lock at 1 - 2 knots, I would just put it into the first grove of reverse when the lock doors were abeam of the helm. The engine doesn't even get above idle speed then and still the boat stops nicely where you wanted it to stop. I guess in such a case the prop only opens partially.

I'm sure some of the behaviour will depend on prop pitch, as with a large pitch and slow rotation the thrust pressure on the blades may be be stronger than the centrifugal force opening the blades. Though I think it is constructed in a way that also transforms some of the tourque into an opening force.

In my case the prop has a pitch of 13" and it develops a huge thrust in reverse. I wouldn't expect any more from a fixed prop. I played with this at anchor and going full reverse is almost frightning and the pull is plenty more than the 1100kg that the anchor windlass is supposed to pull as it stalls it easily. So, my biggest concern with a folding prop, the reverse power turned out to unwarranted.

It also does look very solid and robust, but only time will tell.
 
Re: More on Prices

For a three bladed folding prop I was quoted £900 for the Flex-o-fold and £1300 for the Gori. When it comes to parting with cash best check for the best deal for you.

Cgris

Chris Stannard
 
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