Folders, featherers and fixed

[TQA]

OK Thinking of buying a prop. My 44ft cruising boat a lightish 70s IOR hull with a cruising interior, 3/4 keel and skeg hung rudder has a Perkins 154 with a hydraulic gearbox driving an 18 x 17 three blade fixed prop. I am overpropped by many peoples standards 6 knts at 1600 rpm with WO rpm being 2000. The prop is showing signs of dezincification with pink blotches and some nibbling on the edges. .

I am lucky enough to be out in the Caribbean where the trades blow so rarely use the engine other than a few minutes at either end of the day. I plan my passages at 6 knts and mostly do better. Beam reaching between the islands at 7.5 to 8.5 knts is the norm on a good day.

I have no interest in racing.

I can get a good used similar 3 blader for about 400 to 500 US delivered down here in Grenada.

I have been recomended to use the Brunton Autoprop which seems to be about $4000 US however the benefit of better drive under power is not required as I sail most of the time.

So maybe a simple folder would suit?

A Gori 3 blade folder is also about $4000 US

A Gori 2 blade folder is about 1500 US

A Martec is even less at about $1000

So should I go for a 2 blade folder. I can live with the poor performance in revese which I only use to set the anchor. Will I need a shaft brake?

I saw this

I think that there is a solution to your problem. When shutting down the engine whilst sailing, briefly put it in reverse at idle speed. This spins the prop backwards. Then shut down the engine. The motion of the boat will try to spin the prop forwards. During the time when the rotation is stopped, the blades will fold, and then there is nothing to spin your shaft as you sail along.

Will this work?

Finaly what sort of speed gain will I get?

 

[Woodlouse]

OK Thinking of buying a prop. My 44ft cruising boat a lightish 70s IOR hull with a cruising interior, 3/4 keel and skeg hung rudder has a Perkins 154 with a hydraulic gearbox driving an 18 x 17 three blade fixed prop. I am overpropped by many peoples standards 6 knts at 1600 rpm with WO rpm being 2000. The prop is showing signs of dezincification with pink blotches and some nibbling on the edges. .

I am lucky enough to be out in the Caribbean where the trades blow so rarely use the engine other than a few minutes at either end of the day. I plan my passages at 6 knts and mostly do better. Beam reaching between the islands at 7.5 to 8.5 knts is the norm on a good day.

I have no interest in racing.

I can get a good used similar 3 blader for about 400 to 500 US delivered down here in Grenada.

I have been recomended to use the Brunton Autoprop which seems to be about $4000 US however the benefit of better drive under power is not required as I sail most of the time.

So maybe a simple folder would suit?

A Gori 3 blade folder is also about $4000 US

A Gori 2 blade folder is about 1500 US

A Martec is even less at about $1000

So should I go for a 2 blade folder. I can live with the poor performance in revese which I only use to set the anchor. Will I need a shaft brake?

I saw this



Will this work?

Finaly what sort of speed gain will I get?

Have a look at the Darglow Featherstreams. They're a fair bit cheaper than the Variprops and Maxprops, but I'm afraid I couldn't give you the price in dollars. They're very simple in their construction and you don't need a shaft brake, which I believe is necessary for a variprop.

I reckon I get about half a knot or more on average with a feathering prop.

 

[Tranona]

So should I go for a 2 blade folder. I can live with the poor performance in revese which I only use to set the anchor. Will I need a shaft brake?

I saw this



Will this work?

Finaly what sort of speed gain will I get?

Yes, Putting in reverse is a sure way of making sure the blades close. You can then go back into neutral so the gearbox is not turning and the blades should stay shut. You won't need a shaft brake. You will need to check you have enough clearance to the skeg when the blades are folded, otherwise a featherer such as the Featherstream is an option. The Martec is a very crude device as the blades are not geared. You maybe do better buying in Europe as most of the folding props are made there. An Autoprop is perhaps not the most suitable for your use as its main benefit is self pitching which is very good for motorsailing.

You will see a significant improvement in sailing speed in light airs, probably between .5 and 1 knot compared with your very draggy fixed 3 blade. If you get the right pitch you will see a rise in engine revs but not necessarily an increase in fuel consumption as the power requirement will be the same.

 

[alahol2]

This is the most comprehensive comparison I've seen... http://www.flexofold.com/upload_dir/docs/Test_YachtingMonthly_low.pdf
My Flexofold 2 blade will start to spin if I don't put the gearbox in reverse when sailing. If not in gear, even if the prop is initially folded, a good bump from a wave can be enough to open it and get it spinning. It's just possible you could need a shaft brake.

 

[michael_w]

No noticeable delay with my three bladed MaxProp. Extra maintenance pretty minimal. Grease gun and maybe an anode.