New Propeller Advice

[Alex128]

I have a Folksong 25 (essentially a GRP Folkboat) It is a long keel boat with a stern hung rudder. I currently have a 3 bladed fixed prop and am looking to upgrade to a folding or feathering prop. After researching, it looks like either the Featherstream 3 blade or Flexofold 2 blade are the ones for me due to a combination of the small sized prop required/available, price and performance. As I am in the process of rebuilding my rudder a folding prop is less of a concern as I can adjust the rudder to accomodate the extra folded length if selected.
I have been adviced that a 2 bladed prop on a long keeled boat is not good, as when the blades go behind the keel then re-emerges it creates a druming vibration that is avoided with 3 bladed props, as there is always 2 blades in open water. Can anyone advice me if they have come across this problem, if the vibration/noise is significate, and any tips to avoid it. I would prefer the use the flexofold 2 blade prop as is a few hundred pounds cheaper and creates less drag. I hate motoring so the better the prop (least amount of drag) the better so I can carry on sailing, but also when I am motoring I dont want a deafing vibration. Thanks

[barnakiel]

First, make sure the folding thing will fit when folded - it will not in mine, so only a FATHERING thing will do.

Then, the Kiwiprop is OK and less expensive. If sailing o far and out take a spare blade, they can break, but it is easy to replace them.

The Maxi/Vari, etc. props are all said to be fine. they are expensive. In last year's Yachting Monthly there was a cross-manufacturer review and tests of like a dozen of the folding/feathering things. Get a copy. Or send me a private memo and I will see if I still have it somewhere. Could make pics and forward them for your enjoyment.

There is at least one prop that adjusts its pitch (is it pitch?) to the revs - you get more push from it when you go slow, less (per turn) as you go faster. CREAM when motor sailing. But heard one negative comment on this one. It did not click in, but could have been a plastic bag or anything else. (Make - Burton, Brunton or anything like).

b.

[Ex-Calif]

We had a standard folding prop on our saildrive. We switched to a maxprop 2-blade feathering and it was the best upgrade we ever did. The folding prop compromises forward speed and reverse performance. The feathering prop is like have a fixed prop in terms of performance.

Regarding the beat frequency of a 2-blade behind the keel I think that would be a legitimate concern.

OTOH - There are a couple of things that I think you splurge on. The prop system is one of them. Given a choice I would put the choices in this order -

- Feathering
- Fixed
- Folding

[DHHong Kong]

We had two x two blade folding props on our cat with shaft drives and skegs and could not get the 40HP Yanmars over 2000 RPM due to excessive vibration caused by the two blade props hitting the shadow or turbulence behind the skegs each time they came around to the vertical. Changed them for three blade Seahawk Autostream feathering props and now very smooth right up to the 3000 RPM max.
I know ours is a cat but the shaft/skeg combo did not work with the folders.
Good luck!!