Which folding/feathering prop? ...

[Bobc]

I used to have a 1985 First 345, and fitted a 2-blade Maxprop to it.

I can't remember what size I had. 17" sounds about right. Call the guys at Darglow and ask for their suggestion.

Better to go on the bigger side, as you can always step the pitch down if you find that you're over-propped.

Over the original fixed 3-blader, we got quite a good speed increase under sail, and a reduction in prop walk astern.

 

[Elemental]

As yet, the project remains a research job. I ended up replacing other parts (anchor/ anchor roller), new genoa and some other internal upgrades.

Maybe next winter...

 

[ianj99]

I looked through all the options and choose a Kiwi prop. Very happy with the prop and delighted by the support from them.

+1.
The 17" Kiwi prop looks a bit 'lost' on my 10T long keeled steel ketch but it's much better than the fixed blader. In particular, the greater reverse pitch means I can actually stop.

Its dead easy to fine tune the pitch using a 4mm Allen (hex) key and this came into it's own after I fitted a larger engine 2years ago, as I just tweaked the screws 1/4 turn to make the most of the extra engine torque, giving more speed for the same revs.

Yes, support from Vecta Marine in the UK is superb.

 

[NFCN]

Having had a fixed bladed LH prop then a RH prop when I re-engined, both of which were a pain in terms of too much prop walk, it was a delight to use the Gori 3 blade folder I have on my new yacht. Powerful ahead when motoring, there is just enough prop walk when needed and if you go gently in astern very little when you don't. They do require maintenance but I am very pleased with mine.

 

[frankcilo]

I own a sun odyssey 33i with 21hp engine. I had a 3-bladed propeller blade with which I could take all 3600 engine speeds with a 7.5-knot nozzle speed even with a slightly dirty hull. I decided to install a propeller that would give me more sailing speed, and after so many studies I was undecided between Autoprop and Ewol. Eventually I chose Ewol because I was afraid that Autoprop was too complicated. I first mounted a Ewol with a diameter of 15.5, but I was not satisfied, too much cavitation and a little push, then I asked to replace it with a 17 ", paying the difference (Ewol's owner claimed I was the first customer complaining) , Things have improved, but I continue to make half a knot less the maximum speed and when the weather conditions deteriorated, the propeller did not push well, I tried to adjust the pace in all ways, but nothing to do! After a year , I decide to go to Autoprop, and then here's my full test, starting from a test with fairly dirty hull (but with log 100% cleaned and fixed), I did not want to clean it before the test. First tested the Ewol to make a comparison at the same conditions, and at 2500 rpm it took 5.5 knots of speed while clutch could not exceed 6 knots at 3000/3200 rpm (the pitch is set to take 3200 rpm).
Mounted the Autoprop without even using a bottle, all in apnea, I immediately sailed to start the test, the sea in the meantime began to increase due to the intense libeccio, graft the gear and feel a tougher tap than the Ewol, I understand from various subsequent tests that he does not always do so, depends on how the blades are all set apart. Start to accelerate and all smooth without vibration, the acceleration is progressive and, giving the handle, up to 3600 rpm with a speed of 6.5 knots. At 2500 rpm (maximum torque and cruising speeds) the speed stops at 6 knots, rewinds to the handle and rises to 6.6 to 3400 rpm this time, indicating that the propeller has had to reduce the pitch for more favorable marine conditions at that time (and the tenth most node testifies).
Here's the video of this first comparison: https://youtu.be/RJSj2vInJFQ

I clean the hull well, which was really dirty, and text the Autoprop, the current is around the node, so I try at various angles to get a real result, and this time I solved the gps problem that did not work before: speed the maximum reached 7.6 of log and 7.8 of the current with crossover current, the maximum number of engine speed this time is 3200 rpm, a sign that the clean hull really brakes less and the propeller does not need to take all the engine speed (but I do not rule out that it will take them when there are unfavorable sea conditions); The hull speed is still reached smoothly!
Here's the video of the latter test:
https://youtu.be/bRImZ4hOFhs

Finally I sailed it, I was curious to see how the blades were to be oriented, and I tested that even by turning the engine off in neutral, the propeller stops rotating and the blades are pointing to the flag, however, making it unnecessary to engage the march. No visual turbulence at 7 knots the speeds, so I would say this test too good!

Here's the video: https://youtu.be/9If_zQHSW8Q

In maneuver the evolutionary effect seemed to have disappeared, but in reality there is still fortunately, less but there is and for me it's a good thing because in the maneuvers it can be useful.

For long motor transfers just place the throttle lever to the maximum torque speed to get the best ratio between fuel consumption and boat speed without creating unburned deposits that will ruin the engine, the rest will think Autoprop to adjust the continuous pitch if the sea conditions should vary, making you always achieve the highest speed!

This is really the propeller that everyone should have on their own cruise ship

 

[Elemental]

As the OP - I thought I'd update this thread with an update.

Boat: Beneteau Oceanis 351 (1993)
Engine: VP2003

After much deliberation, I decided to buy a Darglow Featherstream. Darglow couldn't have been more helpful and spent ages answering my questions. I fitted it myself and took the boat out for a spin a couple of weeks ago.

Here's how I found it...

Marina manoeuvring
Prop walk is hugely reduced (as Darglow predicted). Previously starboard prop walk was very pronounced. There is still a slight walk - but it's barely noticeable. Reversing into the berth after the trial did not require the normal large pre-turn to starboard in anticipation of the prop-walk.
Subjectively, I'd say that engine RPM pick-up is a little slower than previously, but there's not much in it and whether that equates to a delay in power coming on would be even harder to quantify as I suspect the prop is more efficient in reverse.
Motoring in open water
The engine does not reach the same max RPM as before. The old prop would permit around 3100/3200 rpm whilst on our sea trial we were maxed out at a tiny amount less than 3000rpm. There's a definite spot at the top of the throttle action that produces no increase in revs which wasn't there before.
However, I didn't sense any reduction in speed through the water (which was flat). I didn't get the chance to try in any kind of swell/turbulence. We reached 7.2kt as before.
Sailing performance
At the risk of sounding corny, Seaspray feels like a transformed boat. Acceleration in gusts is noticeably better. I mean "really better"... We've made a few changes over the years and performance had increased steadily. This prop has made the single biggest increase of all the changes we've made. Whilst pointing high, the increase in boat speed approached an additional knot in 12kt true. And the silence was deafening (especially below) due to the absence of a spinning prop...

It would be fair to say that I'm very happy with the new prop...

The usual comments about having no relationship with Darglow other than as a customer apply.

 

[Laminar Flow]

I have a Brunton auto prop on a Hanse 311
downside
Does not drive the boat well in chop as the chop stops the boat, the prop re pitches & the boat takes a while to get going again & by the time it does the next bit of chop hits it so I have to rev quite hard & this uses fuel- This is the really bad bit about it
Uses more fuel - so I tend not to motor more than 6 kts & get 1.8 litre /hour( against old prop using 1.6litr) 6.4kts uses 2.3 ltr per hour )
Drives the boat slightly faster ( if water flat) if I want -I can get 7 kts in canals against 6.7kts before at max revs
Just as much "initial" prop wash as my old fixed prop- but one gets to learn how to use it to good effect. ie if boat hardly moving a good hard rev then cut the revs will turn the boat 30 degrees before it goes forward much. A gentle increase in revs will not do this
Still prone to hook the odd pot
upside
Half a knot at 6kts extra speed when sailing
Fantastic assistance when motor sailing. I can just have the engine on a fast tick over & it will give the boat a significant push
if one is doing, say, 3 knots then with a fixed prop one has to motor at a speed that is faster to get any push but with the Brunton a fast tickover will add a knot easily
In some ways this last item outweighs most of the downside

Thank you for the detailed post, Daydream. I have been considering a feathering prop for our boat in our quest for improved performance.

A Dutch friend of ours had a Brunton, then a Maxprop on his Southerly. For maneuvering in port or locks (a lot of those in NL) he felt that the Brunton was significantly inferior to either the fixed or the Maxprop. His thoughts were that the Brunton's only advantage, if any, was in long distance motoring or motorsailing. In conclusion, he could not recommend a Brunton.

As far as resistance is concerned: a folder has quite a bit less parasitic drag than a feathering prop; a fixed prop allowed to spin freely has about half the resistance over a fixed one. Our PRM box permitts us to let the prop spin without damage. Realistically, a feathering prop might gain us an extra 0.25Kts under sail. We are still struggling with that cost/benefit ratio. Any thoughts?

 

[Elemental]

As far as resistance is concerned: a folder has quite a bit less parasitic drag than a feathering prop; a fixed prop allowed to spin freely has about half the resistance over a fixed one. Our PRM box permitts us to let the prop spin without damage. Realistically, a feathering prop might gain us an extra 0.25Kts under sail. We are still struggling with that cost/benefit ratio. Any thoughts?

From my limited testing, I'd say that the featherstream affords me more than 0.25Kt over the spinning fixed blade. There is, undoubtedly, a risk of rose-tinted glasses syndrome, but that's how it seems. All boats will behave differently of course.

 

[Daydream believer]

We are still struggling with that cost/benefit ratio. Any thoughts?

I have been a friend of Brunton's MD for years, so got a significant price reduction. Hence, I have no idea of what costs are & how they compare

 

[Laminar Flow]

From my limited testing, I'd say that the featherstream affords me more than 0.25Kt over the spinning fixed blade. There is, undoubtedly, a risk of rose-tinted glasses syndrome, but that's how it seems. All boats will behave differently of course.

Thank you for that, Sea_Spray.

I just looked up some tables regarding loss of speed and increase in resistance for folders, feathering & two blade spinning and three blade spinning. (Donat, Motorsegler, Delius Klasing)

My boat has a 28.2' waterline; looking at "relative" speeds of 0.55 (2.93kts) and 0.9 (4.78kts, average boat speed) and "hullspeed" 1.35 (7.2kts)

The graph shows a fairly consistent loss in speed for a folder of 1%,
in my case a loss of: 0.0023kts at 2.93kts, 0.0478kts at 4.78kts, 0.0072 at hullspeed. (all pretty much negligible)

For feathering and spinning two blades the losses are at:
RS 0.55 6.3% or 0.18kts
RS 0.9 4% or 0.19kts
RS 1.35 2% or 0.14kts

For spinning three blades the losses are at:
RS 0.55 11% or 0.32kts
RS 0.9 8% or 0.38kts
RS 1.35 4% or 0.29kts

I do not have the room to swing a folder with their, across the board, excellent values, though these do not take into account things like exposed shafts and struts.

So my losses with a fixed, spinning prop over a feathering prop amount to:
RS 0.55 0.14kts
RS 0.9 0.19kts
RS 1.35 0.15kts

See my dilemma or am I wrong? Thousands in hard cash for less than 0.2 of a knot? Trust me, I sail our girl hard and try and squeeze every last bit out of her, but the cost/benefit equation doesn't quite add up for me. Corrections welcome

 

[Greemble]

See my dilemma or am I wrong? Thousands in hard cash for less than 0.2 of a knot? Trust me, I sail our girl hard and try and squeeze every last bit out of her, but the cost/benefit equation doesn't quite add up for me. Corrections welcome

Not a correction, but extra variables for the equation.
Fishing nets, stray lines & ropes and the occasional badly (un)marked lobster pot catching onto your prop?

Not so much with the feathering prop, but a folding prop isn't likely to pick any of these up as you're sailing along.

Of course, there's the extra maintenance that comes with the moving parts against the possibility of snagging a rope - or fitting a rope cutter.

 

[Laminar Flow]

Not a correction, but extra variables for the equation.
Fishing nets, stray lines & ropes and the occasional badly (un)marked lobster pot catching onto your prop?

Not so much with the feathering prop, but a folding prop isn't likely to pick any of these up as you're sailing along.

Of course, there's the extra maintenance that comes with the moving parts against the possibility of snagging a rope - or fitting a rope cutter.

Agree, but we have a long keel and the only lines we ever caught have been our own, please don't ask ....

Another point of course is prop efficiency.
Max efficiency for displacement hulls at 100% RPM:

Fixed prop; 55-70%
Feathering, 40-55%
Folder, 30-40% (newer models claim up to 50%)

At 50% engine load the best fixed blade delivers a mere 15% of available power. The best prop would be a variable pitch, unfortunately such systems are prohibitively expensive. Any other prop has a relatively small range of optimum performance; a reason why motorsailing does not really make much sense, economically speaking (says he with a motorsailer).

 

[ithet]

Re prop walk and feathering props, which has been mentioned on this thread. Can someone explain why a feathering propeller would be expected to have different prop walk than a fixed prop of similar diameter, pitch and blade number - assuming the blade action is working correctly in forwards and reverse? I can understand there could be a reduction with a folder where the blades might not be fully deployed in reverse.

I have a Maxprop on a Oceanis 331. There is pronounced prop walk in reverse, but also full thrust. The Maxprop was fitted by the previous owner but the walk is much as I would expect (and have experienced) from a fixed prop.

 

[Homer J]

My experience with a Brunton’s prop follows. It works really well when the whole of the hull and prop are first cleaned giving me over 7 kn forward. However when the prop and the hull gets slightly dirty then the prop does not spin fast enough andunburned fuel is released into the exhaust which means having to reduce revs This year I may under pitch the props slightly from the Brentons recommendation. I’ve had it checked twice and it is at the recommended pitch but I think this is a little bit too much.

i still get some prop walk which is sometimes a hindrance and sometimes a bonus.

I hope this helps somebody.

 

[Norman_E]

Don't assume a feathering prop will cure your prop walk. Pat Manley (I presume the technical writer rather than someone with the same name) wrote a testimonial for the autoprop which Bruntons published saying that the autoprop eliminated prop walk on his Oceanlord (long fin with shaft). That may be true of the variable pitch autoprop but it certainly isn't the case with the (feathering) Maxprop I have on my Oceanlord. It's certainly effective at reducing drag when sailing, but I still have loads of prop walk.

Which just goes to show that not all boats behave the same. I had pronounced prop walk to port going astern in my Jeanneau 45.2 when it had a 3 blade fixed prop. I chose a 3 blade MaxProp an inch bigger in diameter because the boat was originally under propped for the more powerful than standard engine, and prop walk has substantially reduced.

 

[Old Bumbulum]

My Featherstream is being fitted (I hope) at the moment.
The last thing I want to do is eliminate prop walk. At present I have too much, but it is very useful for manoeuvering a long-keel boat and I'd hate to be without some.

 

[Elemental]

Re prop walk and feathering props, which has been mentioned on this thread. Can someone explain why a feathering propeller would be expected to have different prop walk than a fixed prop of similar diameter, pitch and blade number

Prop walk is caused by water being propelled sideways when the prop is spinning in reverse. Because the prop is mounted at an angle (with a shaft-mounted prop) the side vector from the top of the prop interacts with the hull differently from the lower part of the prop - and the resulting flows over the hull result in an asymmetric set of forces and the stern moves sideways. Saildrives generally suffer from it less because they're mounted horizontally. Now, fixed blade props don't have flat blades, they're curved in such a way as to be much more efficient (powerful) in forward than reverse and this makes them less efficient in reverse. As a result, the sideways vector from the prop is more pronounced in reverse (which is one reason you don't experience prop-walk in forward gear). Feathering props have flat blades. This makes them slightly less efficient in forward propulsion, but they are equally efficient for reverse. Because they're not curved they're more efficient in reverse than a fixed blade and therefore prop-walk is also reduced. For my boat, the effect is dramatic. I still have some prop-walk available if I use high revs (which IMHO is a good thing) but at low/moderate revs it's negligible.

Leastways, that's my understanding of it.