folding propellers

[Guest]

I am owning a Dufour 35 Classic equipped with a Volvo Penta 35 saildrive and the standard 2 blades fixed propeller.
The boat is mainly used for family cruising, club racing activity being marginal, and normally mostly under sail, as much as the wind allows, the engine being used almost only when there is no wind or for harbour manouvering.
I am considering to install a folding propeller for increasing the daily mileage range, I believe it can be interesting considering that speed gain under sail could mean several miles per day.
A 3 blades folding propeller should assure better thrust and power than 2 blades in emergencies and, becouse of the family use, colud be a convenient choice.
Between the 3 blades folding propellers available, two models seems to be more reasonably priced: the Volvo and the JProp.
The Volvo may, in theory, have been "calibrated" by the producer with its own engines, but other elements may influence the performances and its design is so different from any other available.

I would be gratefull to hear opinions about the possible choices and personal experiences regarding this concern with similar boats.

More, is there any report based on real hard data - tests - (resistance under sail, thrust, power forward and in reverse...) avilable on the press ?

Thanks in advance and regards from sunny Adriatic

 

[Sinbad1]

Sailing Today did an analysis of the various props last year. Pick up any copy and they do a mini summary of all products tested. This will tell you which back issue you need.

 

[LeonF]

I sail A Sigma 33 OOD on the Thames, and have a two bladed folding prop. I don't plan to change as the loss of that little bit of vibration when folded is noticeable, and it probably adds about half a knot to my boat speed. I have also managed to punch a powerful ebb.

L.A.R.Ferguson

 

[Chris_Stannard]

I have just fitted a 3 bladed Flex-o-Fold from CJR of Southampton, although the prop is made in Denmark. Although I have a conventional shaft the Flex-o-Fold is made for stern drive as well.

I have experienced no loss of performance under power, I previously had a fixed three bladed prop. The boat is also just as manouvreable astern. Under sail the improvement is dramatic, giving at least half and probably three quarters of a knot greater boat speed. This agreed with the statements made by many of the folding and feathering prop agents at the Boat Show, that a folding propellor would reduce the hull drag by about 20-25% overall, it may be less for a two bladed propeller.

The only thing to watch out for is that the prop should be sized to allow the engine to run at maximum revs, I had to reduce my original 18 inch to 17 inch to meet the engine manufacturer's recommendation.

The only problem I encountered was late delivery from the manufacturer. You can find CJR on the web if you are interested

Chris Stannard

 

[Guest]

Two boats, both with folding 2-blades:

Boat 1: Flex o fold - hopless astern, marginal increase in speed under power, ok sailing.

Boat 2: Gori - ok astern, 2.5 kts extra under power! and cheaper than the flex o fold to boot.

 

[PeterGibbs]

Given your description of the boat and the type of sailing, you are projecting a 10-15% improvement in water speed by going to a folding prop. Highly unlikely, except in the lightest winds when drag plays a more significant part.
With any kind of wind ( 15 knots + ) your type of vessel will achieve hull speed whatever the prop.

3 blades will give noticeably more thrust in both directions if manoeuverability under power is an issue. Why not a fixed blade? - so much cheaper and more reliable. Spend the change on a good rope cutter!

If you freewheel the 3 blader which, with Volvo you often can (I have an S leg and the book says so) your drag factor will not outweigh the advantages of a 3 blader.

PWG

 

[Guest]

thanks everybody for your answers

happy sailing