Folding versus feathering props

[Sans Bateau]

The main benefit of a folding prop over a feathering prop is, with possibly a few exceptions the very low drag of a folding prop, plus a folding prop is far less likely to pick up ropes, weed, fishing lines etc.

Some of the comments regarding the poor performance of folding props in reverse may be true of some folders, but should not be applied to all. Also someone suggested that two bladed folders are a little inefficient in forward drive.

Speaking as someone who has always had a folding prop, I can partly agree with the above comments, however, relying on the findings of the Yachting Monthly test that was carried out around 2 years ago, I fitted a Darglow FlexOfold 2 bladed prop at the start of this season. Because of a lack of wind (yes really!) this season I have had to motor getting on for 100 hrs. The boat cruises effortlessly at over 6knts with only 2250 rpm. As for reverse thrust, yes there are few seconds whilst the prop grips, but I have never had a problem stopping or reversing into a berth. Its such a short delay, once you are used to it its hardly noticeable.

If you get to read the Yachting Monthly report you will see that the FlexOfold, even in 2 blade design, fared better than the original fixed prop, and some feathering props.

 

[colhel]

Why would folder be less efficient in forward drive?

 

[earlybird]

Why would folder be less efficient in forward drive?

There's no fundamental reason IMO, but it probably comes down to blade area. I've had 2 boats with 2 bladed Radice folders, a popular make, possibly because of its relatively low cost. They seem to have fairly narrow chord blades, and I suspect many comments about folders in general refer to this type.
My present Flex-o-fold has noticably broader blades and seems more efficient than the Radice.

 

[Neil_Y]

Is it all worth the trouble (if you don't race)

For cruising I prefer a fixed, neglegible difference between a two bladed fixed and volvo folding on my 40' boat.

How often are you bothered with a speed difference of half a knot, setting the sails correctly or having the right ammount of sail up is more significant, as is sail trim.

If we had wind we towed a generator and never noticed the drag/loss of speed, in lighter winds we had more sailing which we enjoyed, if we were really in a hurry then on went the motor and she went far better with the fixed prop than the folder (bigger blade area)

Having said al that as an engineer I like the darglow featherstream.

 

[Cantata]

My boat came with a Flexofold 2-blade which was OK ahead but poor in astern (the design has since changed, though, blades are a different shape these days). I also used a Volvo 3-blade folder for a few years which was a very good all-rounder although too big for the boat (I acquired it cheaply).
This year I reverted to the original-fit 3-blade fixed prop which I found in the bottom of the cockpit locker. Apart from my unease about drag (I don't race but I like efficiency) it has been a total revelation, instant response ahead and astern, it just works. Perhaps I don't need a folder/featherer at all.

 

[cmedsailor]

For cruising I prefer a fixed,[/img]

With 2-blades or 3-blades? In other words will you consider their performance equal/adequate for cruising?

 

[Sailfree]

Best prop for going forwards is a standard fixed shaped prop.

Best prop for motorsailing is an Brunton autoprop as pitch adjusts to work required but it hesitates most before going astern. Has greater drag than folding and feathering.

Best prop for minimum resistance when sailing is a folding prop. Modern designs improve astern performance but still "weakest" of all for astern power. Folders have least likelihood of picking up a rope when sailing

Best prop for going astern is a feathering prop as blades completely reverse in direction. Has next minimum drag after a folding prop but flat blades mean it cannot be 100% as efficient going forwards. Kiwi prop is cheapest but astern pitch cannot be adjusted and limited in power handling ability.

On charter boats heavy use soon reveals any weakness in the design/materials. Had 2 Volvo folding props on my 2030 in 1st year (1998) before Volvo gave me my money back with tacit admission not suitable for heavy use 500hrs/yr! I would now only go for Varifold or the Variprop. Had a Variprop on last 2 boats and consider it the best compromise for my requirements. My current one is a 4 blade feathering Variprop, its can handle 75HP and now done over 2200hrs on my charter boat. Its almost as good going forwards as the original 3 blade fixed prop, in fact have found no discernable difference (does 10kts), Pitch both forwards and astern can be adjusted from outside prop for maximum efficiency for engine/hull characteristics (maxiprop you set pitch only during assembly). Best feature for me is the maximum power astern - can stop boat from 6kts in own length and maximum power to get off the putty or get out of jail card when misjudging a berthing - an real asset on a charter boat. One boat on our fleet tried a Kiwi prop and gave up but others with light use like them. I get the impression that owners of 30hp engine and less are happiest with Kiwis.

As others have said all boats and all propellers are a compromise. I have difficulty believing advice from people that say Prop "A " is best in all respects.

If anyone that has a circa 40' boat 40HP saildrive I have a new Variprop feathering prop sitting on my shelf waiting for my next boat if I downsize.

 

[Neil_Y]

With 2-blades or 3-blades? In other words will you consider their performance equal/adequate for cruising?

I've sailed an old Bav 390 with two bladed fixed on sail drive and a Rival 38 with three blade fixed, with many hours motoring. If they are the right pitch/size for the engine boat you'll get a bit more grunt to stop the boat with more blades ( I believe) but in pactice they both work.

I did like the feel of the fixed prop after the volvo folding two blade on the Bav, parking fealt much easier. I motored around 500 hrs a year and also found the Volvo folding needed periodic maintenance in that time. I changed as the folder threw a blade off in Ribadeo harbour whilst parking which was interesting as it was supposed to stop the boat when it decided to go for a swim.

 

[BlueSkyNick]

Gearbox ratios

Feathering and folding props seem to have been done to death in recent weeks, and I started a previous thread about engine power versus displacement. What about the bit in the middle?

Having decided on a Beta 38, Flexofold 2 blader, what are the criteria for deciding on the gearbox ratio ?