Which prop?

cueball said:
Afternoon all, it’s time to buy a new prop. I have a late bowman built Starlight39. I think the advantage of a feathering 3 blade, (no bow thruster) giving more manoeuvrability in a tight Marina is tempting me towards a brunton, or max prop, haven’t ruled out a folder yet. Engine is a 40hp yanmar. Any experience from the forum?
Thanks
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If manouverability under engine (especially for stopping or in reverse) is important to you, then buy a Featherstream.

I have a 50 (with no bow thruster) and moved from a fixed 3 blade to a Featherstream 3 blade a couple of years ago. I got the same performance when motoring forward, gained about 1kt when sailing, but the biggest difference was in stopping, reversing and maneuvering in marinas. I can now stop the boat in half the distance that I used to, and without the stern sliding sideways. If I put it in reverse on tickover, I still get some sideways walk, but if I stick it into reverse and give it a blast of throttle for a couple of seconds instead, it just goes straight backwards with no propwalk at all.
 
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Laminar Flow said:
I still am struggling as to the benefit of a feathering prop, at least for us
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The primary reason for my purchase of a folding prop was the lack of prop noise. At 4.8 knots the action of water over the old prop caused it to rotate and make a noise for hour after hour after hour! I really did not fancy listening to that as I headed down to the Azores next summer.

One huge side affect is I now get up to hull speed, 7 knots, at the bottom of a F4 rather than a top. By my calculations an extra 24 nm/per 24 hours.
 
Bobc said:
If manouverability under engine (especially for stopping or in reverse) is important to you, then buy a Featherstream.

I have a 50 (with no bow thruster) and moved from a fixed 3 blade to a Featherstream 3 blade a couple of years ago. I got the same performance when motoring forward, gained about 1kt when sailing, but the biggest difference was in stopping, reversing and maneuvering in marinas. I can now stop the boat in half the distance that I used to, and without the stern sliding sideways. If I put it in reverse on tickover, I still get some sideways walk, but if I stick it into reverse and give it a blast of throttle for a couple of seconds instead, it just goes straight backwards with no propwalk at all.
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Thanks for recommendation of a featherstream, it's on my preferred list, wanted someone to confirm that they are as good as I think. My research has narrowed it down to a 2 horse race between Brunton autoprop and darglow fetherstream, you have given me great advise in the past, thank you again.
 
cueball said:
Interesting comments, the reason I was considering bruntons was I have one from another vessel which I can get a £500 discount as part exchange, but I will contact darglow and compare pricing. I also bought a second hand gori 2 blade folder which has the incorrect taper so I will also sell that if anyone has a need.
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I assume that you do know that the Brunton you buy needs to be the correct pitch for your boat
 
Daydream believer said:
I assume that you do know that the Brunton you buy needs to be the correct pitch for your boat
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Hi Daydream believer, yes I’m aware, I have the spec sheet with all measurements needed, Including engine and gearbox details. I think I’m leaning toward a feather stream than a bruntons, your account of the brunton has put the feather stream ahead, along with bobc advise
 
cueball said:
Afternoon all, it’s time to buy a new prop. I have a late bowman built Starlight39. I think the advantage of a feathering 3 blade, (no bow thruster) giving more manoeuvrability in a tight Marina is tempting me towards a brunton, or max prop, haven’t ruled out a folder yet. Engine is a 40hp yanmar. Any experience from the forum?
Thanks
Click to expand...

I've had a Darglow Featherstream on my previous boat for over 10 years.
When I bought my current boat, a Featherstream was top of my shopping list.
I would thoroughly recommend it.

Less drag when sailing.
Performance in reverse is very good - instant 'grip'.
Both were older boats with a mind of their own when reversing, however with the Featherstream I can perform a 180 on a sixpence even in confined spaces.
And I would also like to add that the people at Darglow are a pleasure to deal with.
 
Just a note of caution on "before & after" effects of prop performance. A lot of this is very subjective and often the prop that came with the boat was not optimal in the first place.

Furthermore, optimal prop loading occurs only in a very narrow range of boat speed, RPM, displacement and sea state. This loading will, particularly on a cruising boat, be continuously changing. The only exception to this is a variable pitch prop such as a Hundested system.

In a displacement craft a prop efficiency of 70% is about as good as it gets; at 50% a prop is already considered to be in the ball park. This to indicate the range of uncertainty or of potential improvement, depending how you would like to look at it. Even the pros do not always get it right; admittedly, the variance of the input factors can be rather considerable. Ideally, one would test a number of different props to get it right; a process rarely engaged in.

On resistance: a feathering/folding prop will have less impact on performance at higher speeds. Not because resistance does not increase with speed, but because the resistance of the prop becomes less significant compared to the overall resistance of the hull at higher speed. Most noticeable gains with a folding/feathering prop will be at lower speeds.

Example in relative speed (sqr root DWL x factor): My boat, at a relative speed of 0.9 (this being the average speed for displacement sailing yachts 4.78 kts on my boat) has a resistance of 54kg, at 6 kts it is 92kg and at hull speed (1.34 relative speed) it is 205 kg.
Speed loss for a spinning fixed 3-blade would be 8%, 6% and 4% consecutively.
 
Sandy said:
The primary reason for my purchase of a folding prop was the lack of prop noise. At 4.8 knots the action of water over the old prop caused it to rotate and make a noise for hour after hour after hour! I really did not fancy listening to that as I headed down to the Azores next summer.
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I must say the noise from our spinning prop is barely noticeable and once we have any kind of way on it simply disappears into the fold of the regular sea clatter.
Of course I could just be going deaf in my old age; my wife has voiced her suspicions in this regard.
 
Laminar Flow said:
I must say the noise from our spinning prop is barely noticeable and once we have any kind of way on it simply disappears into the fold of the regular sea clatter.
Of course I could just be going deaf in my old age; my wife has voiced her suspicions in this regard.
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Like Sandy, one of the main reasons I changed to a feathering prop to stop the prop spin. Drove me nuts. Any other benefits are a bonus, chief of which is the stopping power of my (Kiwi) prop. Is it possible for a feathering prop to have more stopping power than a fixed 3-blade, or is just my imagination?
 
fredrussell said:
Like Sandy, one of the main reasons I changed to a feathering prop to stop the prop spin. Drove me nuts. Any other benefits are a bonus, chief of which is the stopping power of my (Kiwi) prop. Is it possible for a feathering prop to have more stopping power than a fixed 3-blade, or is just my imagination?
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The Kiwi prop has a very steep (non adjustable) pitch in reverse which is why you get such good stopping, assuming the blades are swivelling freely. On some boats this is negative particularly with small horsepower as the steep pitch limits revs and speed. This can be a downside if for example you need to reverse to exit a marina berth that is a long way from the entrance.
 
Laminar Flow said:
I must say the noise from our spinning prop is barely noticeable and once we have any kind of way on it simply disappears into the fold of the regular sea clatter.
Of course I could just be going deaf in my old age; my wife has voiced her suspicions in this regard.
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Suggest that is a function of the underwater shape of your boat. Very different if you have a modern flat bottom boat with the prop just a small distance from the hull as in many P bracket installations, or particularly if you have a saildrive when not only do you get the noise from the prop, but also the gear train.. avoided by have a folding or feathering prop which you stop spinning by engaging reverse as the engine stops and then putting back into neutral (as advised in the Volvo manual)
 
Tranona said:
The Kiwi prop has a very steep (non adjustable) pitch in reverse which is why you get such good stopping, assuming the blades are swivelling freely. On some boats this is negative particularly with small horsepower as the steep pitch limits revs and speed. This can be a downside if for example you need to reverse to exit a marina berth that is a long way from the entrance.
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Ah, that makes sense. I have plenty of power fortunately - 27hp in 31ft, 3 tonne boat.
 
My boat and engine were too big for a featherstream, so I fitted a Maxprop, which was brilliant. Darglow supplied it and were equally brilliant. I suggest talking to them, and would choose a feathering prop over a folder for good propulsion forward and astern.
 
Sandy said:
One individual's experience does not constitute scientific/engineering fact, that is how I read your posting. If 10, or 100 or 1000 Brunton prop owners had issues with their product I am more than convinced they would be re-engineering the product. However, in the leisure sailing world we are faced with the combination of different hull shapes, engines and skippers which make each individual vessel practically unique.

On reading the above I am quietly scratching my head. You have had issues with the prop for at least 10 years, have a blade that is pulsing for some of the time, have accurate fuel consumption figures and are in contact with the MD why have you not addressed the issue years ago?
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FWIW My own experience with a Brunton Autoprop was much the same as Day Dreamers. As others have commented, much seems to depend on specific hull shape and other variables. Undoubtedly a well engineered product with a great theory underpinning it, but in practice it does not always perform as advertised.
 
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