scottie
Well-Known Member
Definitely look at variable pitch with different setting in ahead and astern
New prop advice
- Thread starter mrangry
- Start date
Elemental
Well-Known Member
I know you said you'd spoken to Darglow, but they came up with a fairly convincing explanation of why a feathering prop is more suited (cf folding) to some hull forms... I fitted a featherstream on my Oceanis 351. Haven't regretted it for an instant. Transformed sailing and marina handling performance.
Laminar Flow
Well-Known Member
The best prop test, IMHO, was the one in Voile magazine; it can be accessed through the Kiwi prop site. Check it out.
Folding (not feathering) props are notoriously poor in reverse, with rare exceptions.
Based on a relative speed of 0.9 kts (square root DWL x 0.9; example: for a DWL of 28' that would be 4.88kts) and in relationship to overall hull drag you can expect to lose in speed:
A locked, fixed 3-blade will cost you 0.8 kts.
The same prop left to spin will reduce your speed by 0.4 kts. Check with your transmission manufacturer to make sure this will not cause damage!
A feathering prop will cause a drop in speed of 0.2kts.
A folding prop will cause a drop in speed of 0.01 kts.
At speeds above 0.9, prop drag, in relationship to overall drag, is less significant.
A fixed 3-blade prop is considered to be the benchmark for prop performance in most tests. It is not as effective in reverse as in forward. 70% is about as efficient as it gets for props on displacement craft; at 50-60% you are already considered to be in the "ball park".
Unless you have a variable pitch system (being able to ajust pitch at the prop is not considered to be a variable pitch prop), props are designed for a relatively narrow speed/load margin.
Feathering props are equally efficient in forward or reverse due to their symmetrical blade profiles; this at a cost in efficiency.
My suggestion would be to enter your boat data in a propeller calculation program such as "Vic-Prop calculator" (google it). It will suggest a suitable (fixed) prop for you boat. You then might be able to find a used one to fit your shaft or even invest in a new one as they are considerably cheaper than any of the folding/feathering types. This would give you the best opportunity to assess the performance and maneuverability of your boat under power in real life terms and at minimal expense.
Folding (not feathering) props are notoriously poor in reverse, with rare exceptions.
Based on a relative speed of 0.9 kts (square root DWL x 0.9; example: for a DWL of 28' that would be 4.88kts) and in relationship to overall hull drag you can expect to lose in speed:
A locked, fixed 3-blade will cost you 0.8 kts.
The same prop left to spin will reduce your speed by 0.4 kts. Check with your transmission manufacturer to make sure this will not cause damage!
A feathering prop will cause a drop in speed of 0.2kts.
A folding prop will cause a drop in speed of 0.01 kts.
At speeds above 0.9, prop drag, in relationship to overall drag, is less significant.
A fixed 3-blade prop is considered to be the benchmark for prop performance in most tests. It is not as effective in reverse as in forward. 70% is about as efficient as it gets for props on displacement craft; at 50-60% you are already considered to be in the "ball park".
Unless you have a variable pitch system (being able to ajust pitch at the prop is not considered to be a variable pitch prop), props are designed for a relatively narrow speed/load margin.
Feathering props are equally efficient in forward or reverse due to their symmetrical blade profiles; this at a cost in efficiency.
My suggestion would be to enter your boat data in a propeller calculation program such as "Vic-Prop calculator" (google it). It will suggest a suitable (fixed) prop for you boat. You then might be able to find a used one to fit your shaft or even invest in a new one as they are considerably cheaper than any of the folding/feathering types. This would give you the best opportunity to assess the performance and maneuverability of your boat under power in real life terms and at minimal expense.
dunedin
Well-Known Member
That’s a very sweeping assertion / opinion. And not sure supported by the views on this thread.
Certainly doesn’t match with my experience on two boats with folding props.
PS. I can motor ahead at 8 knots - I don’t need to go astern at 8 knots, but can stop reliably and reverse reliably as fast as I want to.
Laminar Flow
Well-Known Member
Well, that is not borne out with my experiences with them, relative to others, nor with several prop tests I've read.
Laysula
Well-Known Member
Try turning around outside the marina and reverse in. Go into your berth astern and use a touch of forwards to stop you. If things go wrong you can always motor forwards out of the marina and try again.
Pye_End
Well-Known Member
The other way round eg possibly 2.2:1 ahead and 3:1 in reverse - ie. it is a reduction not a multiplication.
Don't understand why Yanmar don't go the same fixed reduction in both directions like so many others do.
So, you need more revs in reverse to get the same prop speed, but additionally a 2 blade rather than a 3 blade giving a lack of grip on top of the loss in rpm. Is the folder a fixed pitch? If so perhaps this explains the comments from Darglow.
KompetentKrew
Well-Known Member
From Yachting Monthly's 2009 Ultimate Propeller Test:
Links:
Mine is a 3-blade folding prop, which I'm quite happy with on a boat about the size of yours, @mrangry. Seems to go ok in reverse - hard enough to crack the tiller if one is careless! I think it's the Brunton's Variprop, but I'm not sure.
Links:
Mine is a 3-blade folding prop, which I'm quite happy with on a boat about the size of yours, @mrangry. Seems to go ok in reverse - hard enough to crack the tiller if one is careless! I think it's the Brunton's Variprop, but I'm not sure.
KompetentKrew
Well-Known Member
Weird, their website claims they have supplied a "drag reducing" prop for a Beneteau Oceanis 440 at least once before.
I trust you've checked in all the lockers and under all the berths to see if you can find the original fixed prop? It's natural to think that a folding prop must be "better" but I think a fixed prop would be a vast improvement, if your current one leaves you unable to reverse!
jwfrary
Well-Known Member
I was impressed with the darglow props, good engineering and machine work, fitted one to a Sadler 32 and it performed very well. 3 bladed feathering
laika
Well-Known Member
I could be misunderstanding but I believe this list includes boats they've supplied featherstreams for as well as flexofolds. "Folder not suitable" doesn't necessarily imply "feathering not suitable".
I have a maxprop and have found Darglow's aftersales support so good that next time round I'd be inclined to choose supplier before product. Not sure whether they still distribute maxprop in the U.K. though as they're no longer mentioned on the web site but iirc the featherstreams were cheaper anyway.
Pye_End
Well-Known Member
Might have a different engine/gearbox? Mind you, just because they have put one on doesn't mean Darglow thought it was the best solution perhaps.
Daydream believer
Well-Known Member
I would not have another feathering prop. My autoprop is poor in choppy water . It is poor in reverse when one changes from forward to reverse & the first time I did it the boat swung through 180 degrees because of the prop wash. I have learned to live with that & i wonder if the Op has actually persevered with his prop. At first I really struggled with my Brunton, but now I do not give it much thought, as its "quirks" are second nature. I now have little problem but it is harder than with a fixed blade
I would rather have a folder because the feathering one picks up masses of weed & nets & every year I get endless trouble with a fouled prop. I would get similar with a fixed blade but at least it used to work enough to help me limp into a marina. The feathering prop gets disabled completely.
If the saildrive is not locked it spins & causes as much drag as a fixed bladed prop. So check saildrive manufacturer allows prop locking.
I would rather have a folder because the feathering one picks up masses of weed & nets & every year I get endless trouble with a fouled prop. I would get similar with a fixed blade but at least it used to work enough to help me limp into a marina. The feathering prop gets disabled completely.
If the saildrive is not locked it spins & causes as much drag as a fixed bladed prop. So check saildrive manufacturer allows prop locking.
dunedin
Well-Known Member
Thanks KomeptentKrew for that very informative data. Certainly confirms why I am very happy with my Flexofold 3 blade. Very efficient drive thrust, near zero drag when sailing, minimal prop walk and plenty enough tug in reverse to power into any wind and reverse at 3 knots or so (can go faster in reverse, but then risk of rudder blade slamming over dangerously).
Unlike some I don’t tend to come into berths at 6 knots and try to stop dead very often (one day the gear cable will have parted and you won’t find reverse anyway).
Unlike some I don’t tend to come into berths at 6 knots and try to stop dead very often (one day the gear cable will have parted and you won’t find reverse anyway).
KompetentKrew
Well-Known Member
Ah! That must be it! I overlooked the distinction.
laika
Well-Known Member
That's interesting: When I was researching props 10 years ago I came across a testimonial from PBO's Pat Manley about the autoprop on his oceanlord which talks about much reduced prop walk and better performance in choppy seas:
http://www.propelspecialisten.dk/download/testimonials/autoprop/westerly_oceanlord.pdf
Maybe it works better on a long shaft than your saildrive?
The variable pitch autoprop might have different quirks to other feathering props. The delay in power delivery when going from forward to astern which received wisdom says is an issue with feathering props hasn't been an issue for my maxprop but I can't discount the possibility that I've subconsciously built that into how short my short turns can be. I certainly haven't suffered from picking up excessive amounts of nets and weed.
Laminar Flow
Well-Known Member
Our Dutch friend had both a Brunton Autoprop and a Maxprop for his Southerly.
As I was quite taken with the idea of the Autoprop as an ideal motorsailer prop, he quickly burst my bubble: In his opinion the Brunton was quite useless for maneuvering in port or in locks, both of which are a staple part of Dutch cruising; the Maxprop excelled in that respect, while the Brunton, according to his estimate, was "ok" for open water.
Kwik Decision
Well-Known Member
The Brunton's Autoprop is very different from a normal feathering prop - it is designed to "self pitch", and therefore be more efficient when motor sailing, which none of the normal feathering props do. I did a lot of research on the subject of props 6 yrs ago, when we got our old Sadler 29 re-engined. Brunton's Autoprops are like marmite, with some users loving them, and some hating them. They were also about the most expensive option I looked at. For these two reasons, I discounted it, but as noted above was very happy with the Featherstream I bought.
Stemar
Well-Known Member
I've sailed on a Dufour 385 with a Kiwi and it was predictable and manageable astern, and good under power. I've also sailed on a Starlight with a Brunton 3-blade which behaved immaculately, but I have a friend with a Brunton on his Rival, and he'd has a lot of problems.
I had a two-blade prop on Jissel (tubby bilge keeler) and she was a nightmare astern. Kick to port then the bow blew off downwind - except when I relied on it, when she'd do something imaginative just to mess me around. I changed to a smaller diameter 3-blade fixed prop and, while it's slowed me down under sail, the boat's a little more manageable, but still not great.
I had a two-blade prop on Jissel (tubby bilge keeler) and she was a nightmare astern. Kick to port then the bow blew off downwind - except when I relied on it, when she'd do something imaginative just to mess me around. I changed to a smaller diameter 3-blade fixed prop and, while it's slowed me down under sail, the boat's a little more manageable, but still not great.
Daydream believer
Well-Known Member
I have a totally different experience experience to P Manley. propwash under power is greater & it is tiring holding the tiller. Especially once a bit of fouling gets on the hull from the equally useless coppercoat. When the boat hits a 1 metre chop as one might get in the Thames estuary the boat stops & the prop goes to zero pitch then gradually pitches up to start driving again. But by the time the boat gets moving it hits the next wave & stops again. One can see the prop "pulsing" when one looks over the stern. Fuel consumption at 6Kts has increased from 1.6litres per hour to 2 litres. Manouverability is not so good & in locks ( I have done over 300 lock passages- 50% SH) one has to really watch prop wash when one wants to stop. It can, however, be really useful when one gets used to it & if it is working in the direction one wants. ie approaching a wall & kicking hard in reverse for a second can pull the stern in tight. Similar for marina parking. But if the opposite way one has to start gently reversing well in advance, slow down the approach & stop the boat on the ropes whilst hoping the wind will not push one off the wall at the same time.
Motoring speed is no different to fixed, except for motor sailing when it is brilliant. In tickover it will add to sailing speed because it pitches to suit & give drive.. Unlike a fixed prop that has to motor faster than sailing speed to have any effect. Sailing only speed is better, saving about .6kt at 6kts which is significant & well worth having a different prop to a fixed one.