2 Vs 3 blade folding prop

[DavidBolger]

I am still pondering which new prop to ask Santa for this Christmas. I will definitely be changing from my current fixed 2 blade to a folding or feathering prop. However, I don't know whether to go for 2 or 3 blades. Much has been said about the performance advantage (particularily in reverse of the 3 blade over the 2 blade while under power. But what about the performance comparison while sailing. I assume the 3 blade has more drag than the 2 blade but by how much? People talk about getting an extra 0.5 knot from a folding prop over a fixed prop but how much is it for a 2 blade or three blade.

I know the other major difference between the 2 balde and 3 blade is the cost but remember this is from Santa, so the cost issue doesn't arise.

Thanks

David

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[dulcibella]

If Santa is really in a generous mood, have you considered a Brunton Autoprop? They adjust pitch to suit load so that they are efficient over a much wider range of RPM, and the blades flip in reverse giving you great stopping power. Drag when sailing is also much lower than a 3-blade fixed prop.

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[DavidBolger]

Yes, the 4 models I am considering are
CJR - Flexofold
Gori
Auto prop
Max prop

But the same question applies, what are the sailing performance differences of a 2 blade compared to a 3 blade?

regards

David

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[Aeolus_IV]

As said some where else on this board recently folding/feathering props are about 5% drag of fixed prob - the bruntons auto-prop about 15%.

Given a choice (and Santa were buying me a new prop) - I'd go for 3-blade Gori folding prop. Well I can dream, can't I? The 2-blade version I have is very good indeed.

Regards, Jeff.

<hr width=100% size=1><A target="_blank" HREF=http://users.swing.be/FDB/centurion/index2.html>Centurion 32 Web site</A>

 

[snowleopard]

the 3 blade will maybe give you 7% of the drag of a fixed prop compared to 5% for a 2-blade, i.e. insufficient difference to detect. the real issue is the relative efficiency under power.

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[BobE]

I find this a strange thing... Surely someone has done some properly contolled evaluation of the drag at varying speeds of the different types of props and of course also the mechanical efficiency of them when driving in Fwd and Reverse?

My boat came with a Darglow 3 bladed feathering prop and I have no idea what diff. it makes over a fixed or folding...
As I remember the ungeared folders we raced with in the 70's ( I hear Jimi telling me to get modern) didn't work too well in reverse and we put rubber bands on them to stop the bottom blade opening if it somehow got rotated to the lower side of the shaft (Low speed drag).. It was really cold in the water off Cowes B4 the Fastnet. But made the crew feel better. ('cept me I was, as ever, the sucker.)
Cheers Bob E...

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[Sans Bateau]

We have used a two bladed folding prop for some time, Gori and more recently Volvo. I cannot speak for a three bladed prop, you soon get used to the slight delay in reverse/stopping, but never enough to cause any problem. How much more % is a three blade to buy? Don't forget you will only get a small % of use out of any prop, you should be sailing. Is there some other goodies you need, that you can buy with the saving?

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[Keith]

I see from your Bio that you quote"enjoy a spot of racing" are you buying the prop with this in mind? if so how will it affect your rating? I tend to agree with snowleopard for the rest of it you will hardly notice the difference in drag between two or three blades, the biggest difference is the amount of "grunt" a three blader will give you, and you may notice that the boat is smoother with less vibration with three blades.........keith

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[pragmatist]

We reckon changing from 2-bladed fixed to 3-bladed fixed has cost us about half a knot. We never intended to do this - the yard even had the Volvo folding prop in stock when they discovered there was insufficient room to fit it ("negative space" as the young engineer said !) . We are still considering VectraMarine Kiwi Feathering Prop - it's a fraction of the price of a Brunton. But no-one on the PBO forum replied to a post about it - so if anyone has any experience of them we'd be very pleased to hear.

The wonderful thing about the 3-blader is that we CAN STOP ! This was quite novel and removes some of the "little discussions" we used to have about pontoons and marinas !

<hr width=100% size=1>a pragmatist is a sailor who now believes it will _always_ rain

 

[Robin]

We inherited 3 bladed Brunton with our latest boat and rate it very highly. The original owners fitted the Brunton as a replacement for a 2 bladed folding prop which we still have as a spare, they were unhappy about the performance of the folding one under power but delighted with the Brunton under both sail and power as are we. The big advantage with the Brunton is that it is self pitching, so there is no problem finding the right diameter/pitch combination to the last inch since the prop self adjusts anyway. We have friends who fitted a Max-Prop which has adjustable pitch but had to be lifted out to adjust it many times before they got it right, they couldn't fit the Brunton for some reason, clearance from the rudder I believe. We have since spoken with another owner of a Sun Legende 41 like ours with the same engine, and under power for the same revs we not only cruise 0.75kt faster but use less fuel than he does with a 2 bladed fixed prop.

<hr width=100% size=1><font size=1>Sermons from my pulpit are with tongue firmly in cheek and come with no warranty!</font size=1>

 

[FullCircle]

I am going for the Kiwiprop 3 blade feathering, as it does have some strong devotees out there (and a few raspberries too). At 800 quid with a free spare blade it looks a very good proposition for extended trials on my new SO35 lift keel. I like the simplicity of the operation, and the use of modern structural plastics, which at least dont have much in the way of galvanic corrosion. It remains to be seen how robust it proves at sea. As I had one blade of a Gori fall off, it can't be any worse.
I am told that it is very hydrodynamically efficient as its light weight and action allows it to position itself for lowest flow when sailing.
We shall see.

Jim

<hr width=100% size=1>Jeanneau 35 - only 13,272 lbs displacement, not even 6 tons,what a lightweight!!!

 

[Robin]

Anything which came with a 'free' spare blade would worry me, it must mean they think it is necessary or why increase your material costs by 25%!

<hr width=100% size=1><font size=1>Sermons from my pulpit are with tongue firmly in cheek and come with no warranty!</font size=1>

 

[Stemar]

Vague memories of seeing some publicity, possibly their website, where they say that the spare blade is in case of damage by hitting something, though I also have a vague memory of a claim that the plastic blades are less liable to damage than bronze.

Generally even with high-tech plastics, I think material costs are minmal compared with design and tooling, so it makes sense.

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[Rigger]

I am considering fitting a feathering prop and trying to choose between the kiwi , cjr,and gori props. Unfortunatley the auto-prop wont fit without "surgery to the rudder" according to brunstons. I am a bit concerned re the need to adjust the pitch as I only lift out once a year so any slight adjustments would be done on an annual basis. What are the chances of getting it right first time,and do any of the 3 props have any greater merit over the others in this area??

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[GeoffW]

I have a 2 bladed folder on a Konsort. Fine in forward gear, but no stopping power when put astern, also kicks like a mule to port initially when put astern.

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[BobE]

I don't believe prop walk is any different on folding fixed or feathering props, or is it ??
Bob E..

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[Robin]

Well I guess the good news is that they ARE adjustable, normal props are not though they can be altered a little by expert machine shops. When we fitted a new engine on our previous boat I spent hours and hours studying prop formulae, reading books, programs and bugging the engine and prop people trying to calculate the ideal size. In the end I worked it our myself and actually managed to get it spot on first time, ie we could just pull max revs in gear under load. I think one of them can be adjusted by a diver but I'm not sure which, otherwise it is a lift out or dry out job. One friend with a Victoria 34 was really struggling and could only get 4kts, he was in an out more times than Blunket!

<hr width=100% size=1><font size=1>Sermons from my pulpit are with tongue firmly in cheek and come with no warranty!</font size=1>

 

[billmacfarlane]

I had a 3 bladed Volvo prop folding drive on a SL 120 saildrive. When I bought the boat I was told that there was an outstanding issue with the set up as the anodes were rotting too quickly. Much to my surprise 18 months later I got a letter from Volvo offering to change my prop which duly happened. I should add I was very happy with the performance of the original. The new one is crap. Talking to other Maxi owners, it hasn't solved the anode problem and the performance under engine is horrible. I've lost about 0.5 knots of boat speed. I'm almost certainly buying a 3 bladed feathering Kiwiprop. I know of a least one other Maxi owner who is very happy with his. I reckon I'll go the same way.

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[bedouin]

I've got the 3 bladed Gori - and I doubt if there is significant increase in drag over a 2 blader (not impossible it is less). Certainly I wouldn't have thought that the difference in drag should have a significant influence over the buying decision.

I considered all the props on your list, but eventually chose the Gori as the only one that was appropriate in my somewhat unusual installation. It is an excellent prop and you won't be disappointed with the performance (especially in reverse) but it is expensive.

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[Stork_III]

I had VP 2 blade folder on HR31, OK in flat water, NG in chop or at all in reverse.

Fitted VP 3 blade folder in summer, extra 1 knot ahead, miles better in chop, and the bloody thing goes or stops when in reverse. No noticable difference to sailing.

Best £800 spent this year, even got 15% discount on VP price as prepared to wait 2 weeks for special order at Volspec.

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