Darglow feathering propeller

[Rikds]

Thinking of changing my 2 blade folding prop on my old 34ft yacht with a 20hp Beta engine for a Darglow 3 blade feathering prop.
Has anyone had experience of these props?

 

[jamie N]

Yes. Superb prop, and 1st class support from Darglow.

 

[Tranona]

Yes. Had 2 of them. Latest one on my Golden Hind 31 with Beta 30.

What boat do you have and what size and type is your current prop. As important is what do you feel is lacking in your current setup and what improvement are you looking for.

 

[Rikds]

Yes. Had 2 of them. Latest one on my Golden Hind 31 with Beta 30.

What boat do you have and what size and type is your current prop. As important is what do you feel is lacking in your current setup and what improvement are you looking for.

Boat's an S&S 34. Hate to say I've no idea of the prop spec but it's been on the boat for at least 30 years! Since long before I bought her.
Lacks stopping power in reverse is sometimes an issue. Just feel that better performance is possible.

 

[jwfrary]

Darglow are nice to deal with and the props are well made. Silky smooth bits of kit.

A feathering prop always had blade sticking out when your sailing which for me is more oppertunity for catching a line, but they are better under power. Horse for courses

 

[Poecheng]

They certainly give you stopping power.

 

[Tranona]

Boat's an S&S 34. Hate to say I've no idea of the prop spec but it's been on the boat for at least 30 years! Since long before I bought her.
Lacks stopping power in reverse is sometimes an issue. Just feel that better performance is possible.

You are on the limit for 20hp. You should just get displacement speed of just over 6.5knots. I suspect the propeller you have is pretty useless if it is 30 years old. A good modern 2 blade folder such as a Flexofold will be as good as a fixed blade prop in both forward and reverse. However another limitation you have (if you have the mid mounted engine) is probably the size of propeller you can swing because of its location just behind the keel and close to the hull. I expect you have a 2:1 reduction which also limits the diameter of the propeller to 13 or maybe 14". Good motoring performance was probably not even on the list of of priorities, never mind high up, when the boat was designed!

Where a Featherstream will help is first you will get increased blade area with 3 blades, but without any drag penalty and second you can set a different pitch in reverse to get better low speed thrust. Ideally the boat would be better with a 15" 3 blade, but first you would need to change the gearbox ratio to the optional 2.65:1 and second suspect you would run into tip clearance problems with the hull.

I notice that some boats have fitted 30hp engines (a bit OTT!) which need a larger propeller (16" usually) so maybe the tip clearance is not an issue - difficult to tell looking at the profile drawings and photos.

Anyway you have what you have and suggest you talk to Chris Hares at Darglow for his advice as to the best way to go. He has done 4 props for me over the years and knows his stuff. The photo is the latest. 17" on a Beta 30 with a PRM 2.5:1 reduction box.

 

[Rikds]

You are on the limit for 20hp. You should just get displacement speed of just over 6.5knots. I suspect the propeller you have is pretty useless if it is 30 years old. A good modern 2 blade folder such as a Flexofold will be as good as a fixed blade prop in both forward and reverse. However another limitation you have (if you have the mid mounted engine) is probably the size of propeller you can swing because of its location just behind the keel and close to the hull. I expect you have a 2:1 reduction which also limits the diameter of the propeller to 13 or maybe 14". Good motoring performance was probably not even on the list of of priorities, never mind high up, when the boat was designed!

Where a Featherstream will help is first you will get increased blade area with 3 blades, but without any drag penalty and second you can set a different pitch in reverse to get better low speed thrust. Ideally the boat would be better with a 15" 3 blade, but first you would need to change the gearbox ratio to the optional 2.65:1 and second suspect you would run into tip clearance problems with the hull.

I notice that some boats have fitted 30hp engines (a bit OTT!) which need a larger propeller (16" usually) so maybe the tip clearance is not an issue - difficult to tell looking at the profile drawings and photos.

Anyway you have what you have and suggest you talk to Chris Hares at Darglow for his advice as to the best way to go. He has done 4 props for me over the years and knows his stuff. The photo is the latest. 17" on a Beta 30 with a PRM 2.5:1 reduction box.

Tranona many thanks that's great advice. She is mid engined and your comments and advice are much appreciated. More research to be done.
At 2000 RPM I get 4.5 - 5 KTS in flat water.

 

[Bobc]

I changed from a 3 blade fixed to a 3 blade Featherstream and the difference in stopping power and close-quarters grunt was really noticeable.

Worth every penny.

 

[Tintin]

Just make sure you use lock tight on the anode, unlike the engineer that installed mine, which now has pink spots on the prob hub body

 

[jaminb]

I have one. Can’t comment on performance as I have never used anything else but prop walk to port in reverse is very useful. its mechanical operation out of the water is a thing of beauty, the way it feathers and alters pitch in forwards and aft. Second the lok tight mine fell off. I need to find so clean water and have an inspection to see if the replacement is still there.

One other thing I found at the start of this season the boat pulled violently to starboard under power. I assume i had been a little to liberal with the ludicrously expensive grease or anti fouling and the blades werent opening fully.

 

[KREW2]

I put a Beta 25 in my Westerly Storm, and bought a Darglow Featherstream. I let them work out what spec was needed. I was disappointed with the top speed compared to my old Volvo 2002 with a fixed two blade prop. A quick phone call to Darglow solved the problem, they sent me a new cassette to alter the pitch, which I fitted on my next liftout.

 

[DanTribe]

A fixed 3 blade prop on my UFO 31 caused dramatic prop walk in reverse. Changing to a Darglow 3 blade feathering prop reduced that a lot and cleaned up the turbulent wake. Much less rudder vibration when sailing.
Darglow were very helpful even when answering idiot questions.
Mine came with a preset pitch cassette which can be changed if the pitch is wrong. Never needed to.

 

[lustyd]

Just make sure you use lock tight on the anode, unlike the engineer that installed mine, which now has pink spots on the prob hub body

The guy at Darglow laughed when I asked about Locktite for anode bolts on my Maxprop. The sheer quantity of grease present makes Locktite almost useless. Torque ought to be sufficient.

 

[Tranona]

Tranona many thanks that's great advice. She is mid engined and your comments and advice are much appreciated. More research to be done.
At 2000 RPM I get 4.5 - 5 KTS in flat water.

That is about right speed for those revs. The optimum revs for cruising should be a bit higher, in the range 2200-2400 which should get speed closer to 5.5knots in flat water. Worth making a series of runs in flat water at 200rpm increments from 1800 up to maximum which should be in the region of 3400- 3600 and plotting speed against revs. This will help in determining whether your current prop is the "correct" size. The problem with many older folding props is that they lack blade area and shape and while they perform OK at lower speeds in flat water they lose out in adverse conditions such as against wind and waves as well as being poor in reverse. You may find this useful background in understanding the ins and outs of the subject.

Folding and feathering propeller test

 

[Babylon]

I've had a Featherstream for 12 years. Superb piece of kit. Anode never fallen off, just use suitable waterproof thread-locker.

A tip the guy from Darglow gave me: if you want the decent kick from prop-wash to help spin the boat then give plenty of revs, but if you want to track astern in a straight line (especially with a long-keeler like mine) then just ease the revs on very gently and there'll be no sideways kick.

 

[B27]

I've recently changed my prop from 3 blade fixed to 2 blade folding.
I had to compromise a bit, choosing the best prop which came up on ebay.
I bought Dave Gerr's book on props, which helped, and worked on the basis that I could alway chop a bit off the blades.

One of the constraints I had is the prop is closer than ideal to the hull, because the new prob is bigger diameter.
This supposedly influences vibration and prop walk.
But how much so may depend on how flat the hull is, there a s skeg, how close is the rudder and maybe some subtleties of prop design?
Also the folding prop gains 20mm of clearance because the long hub puts the prop further aft.

Perfromance astern does not seem too bad.
Motoring ahead, any changes are small, maybe it gives a little more speed in flat water at low RPM, flat out speed and 2500RPM speed seem about the same, fuel consumption seems OK.
Sailing, it's a world better.

The point I'm rambling towards is that there's a multiway compromise between pitch, diameter, blade area, hull clearance, different prop blade designs etc etc.
To go for the 'recommended best' in all boxes, I would have needed a differen gearbox ratio, but none were on ebay this winter or spring!