Which prop?

[cueball]

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

 

[Daydream believer]

A Brunton is poor for maneuverability. I have one & compared to a fixed it is markedly worse. If i am reversing from the marina fuel berth at , say 2 kts then put it into fwd, the boat will swing through 150 degrees regardless of what i want it to do. I have a very good boat for maneuvers ( short fin, spade rudder saildrive) so get away with it. It has quirks that took me a while to master. Also has a lot of prop wash ( ignore what the bumf says) Also uses more fuel Note --A folding one will pick up less weed. The Brunton pulses in chop.

 

[vyv_cox]

I have had a Bruntons 2 blade Autoprop for well over 20 years. I have none of the problems described by Daydream Believer. It has been excellent since the day I fitted it. My fuel economy, measured over about seven years, could hardly be better.

 

[Gary Fox]

What is the connection between feathering blades and manouevrability?

 

[Tranona]

Darglow Featherstream if going for feathering, or Flexofold if folder. Don't think you will notice much difference in performance either motor or sailing between the two, although reverse stopping might be a bit better with the featherer, although neither will be much different from a fixed 3 blade. changing prop will have little impact on manoeuvrability in tight spots - only a bow thruster will do this for you, although you might experience different amounts of prop walk.

The big advantage of such props are better sailing performance, particularly at low speeds and light airs. In addition Bruntons enables the engine to run at lower speeds for a given power requirements - useful if you do a lot of motoring or motorsailing, but many find the low speed characteristics unhelpful as Daydream believer describes, but this is to an extent boat specific.

 

[penfold]

What is the connection between feathering blades and manouevrability?

A feathering prop will typically have(hull form permitting) the same thrust astern as ahead, whereas with a fixed prop astern thrust is significantly less.

 

[laika]

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?

Yes!

I have a westerly oceanlord with a 40HP yanmar (and no bow thruster) so similar engine and boat size but from the looks of the starlight's keel, mine is a longer fin. I was tempted by pat manley's endorsement of the autoprop saying it tamed his prop walk:
http://www.propelspecialisten.dk/download/testimonials/autoprop/westerly_oceanlord.pdf
..but eventually settled on a maxprop. My experience:
* The max prop didn't tame my prop walk. I have buckets of it. It's simply a "feature" which I've just learned to make the most of (ie per Tranona's commet above, it won't make parking easier).
* The (received wisdom) "feathering delay" when giving a blast of astern has never been an issue for me, but possibly because I never come into a pontoon "hot" unless I really need to
* I'm pretty happy with the motoring and sailing performance of the maxprop over the past 10 years
* I'm *really* happy with the support Darglow have given me over the past 10 years. If I had a new-to-me boat with an unsatisfactory prop I'd be looking to them as suppliers first

 

[[70521]]

A Brunton is poor for maneuverability. I have one & compared to a fixed it is markedly worse. If i am reversing from the marina fuel berth at , say 2 kts then put it into fwd, the boat will swing through 150 degrees regardless of what i want it to do. I have a very good boat for maneuvers ( short fin, spade rudder saildrive) so get away with it. It has quirks that took me a while to master. Also has a lot of prop wash ( ignore what the bumf says) Also uses more fuel ( which i told the MD again today for the 10Th time but he will not have it) Note --A folding one will pick up less weed. The Brunton pulses in chop.

Utter tosh. I have a two bladed folding Brunton prop and the only difference is I now can see some prop wash, the original fixed prop did not kick any up.

 

[tyce]

Well whatever you do don't go for a kiwi. Im less than impressed.

 

[mrangry]

I have just removed a 2 bladed 16" folder from my 44ft yacht with a 50hp Yanmar shaft drive. I was having major issues berthing and basically no power going astern. It transpires I think that the prop was not unfolding when engaging astern. This coupled with the lower reduction in the gearbox when going astern made for comedy berthing and maneuvering in tight quarters.

I have now bought a Darglow featherstream three blade 19" prop. I cannot as yet comment on its performance as I have still to launch the boat

 

[Daydream believer]

Utter tosh. I have a two bladed folding Brunton prop and the only difference is I now can see some prop wash, the original fixed prop did not kick any up.

With due respect but my comments are based on at least 10 years with my Brunton. I have written as I have found so I take exception to suggesting i have written "utter tosh". The "pulsing is not unknown to Brunton- i discussed it with the MD today as I spoke to him about replacing it for a folder. the manouvering was something he warned me about when i bought it & it is a fact that I am more than happy to show others the trick of reversing from Bradwell's fuel berth & doing a 150 degree spin. Any prop whose blade sticks out when sailing is more likely to catch weed when sailing compared to one that is neatly folded away
the fuel consumption is something I took acurate figures for before buying the prop . the prop uses more fuel at 6 kts than my fixed prop did. Bruntons MD did feel that my boat is actually slightly underpowered, thus causing the issue. But it is a standard size for a 31 ft yacht

 

[Tranona]

A feathering prop will typically have(hull form permitting) the same thrust astern as ahead, whereas with a fixed prop astern thrust is significantly less.

That is not always the case as many gearboxes have a different reduction ratio in astern which gives more thrust at low revs.

 

[Gary Fox]

A feathering prop will typically have(hull form permitting) the same thrust astern as ahead, whereas with a fixed prop astern thrust is significantly less.

I've never had a feathering prop, but this statement seems rather mysterious.
My fixed blade props (one is shiney, so it's pictured) have visibly slightly assymetric camber and blade shape, but the thrust is not 'significantly less' in astern gear, obviously it will be a little less efficient, but not much, certainly not enough to notice.
Do feathering props have symmetrical blade cross-sections and shapes, unbiased to either forward or reverse gear? Or is there another method by which they achieve equal thrust in either direction?

 

[[70521]]

With due respect but my comments are based on at least 10 years with my Brunton. I have written as I have found so I take exception to suggesting i have written "utter tosh". The "pulsing is not unknown to Brunton- i discussed it with the MD today as I spoke to him about replacing it for a folder. the manouvering was something he warned me about when i bought it & it is a fact that I am more than happy to show others the trick of reversing from Bradwell's fuel berth & doing a 150 degree spin. Any prop whose blade sticks out when sailing is more likely to catch weed when sailing compared to one that is neatly folded away
the fuel consumption is something I took acurate figures for before buying the prop . the prop uses more fuel at 6 kts than my fixed prop did. Bruntons MD did feel that my boat is actually slightly underpowered, thus causing the issue. But it is a standard size for a 31 ft yacht

Forgive me, I come from a long line of Clydeside engineers and we have a reputation for being blunt.

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?

This is not intended as confrontational, but you are clearly unhappy with your current prop. I would have been on the phone long ago.

 

[cueball]

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.

 

[penfold]

That is not always the case as many gearboxes have a different reduction ratio in astern which gives more thrust at low revs.

That's a product of the gearbox though, not the prop.

I've never had a feathering prop, but this statement seems rather mysterious.
My fixed blade props (one is shiney, so it's pictured) have visibly slightly assymetric camber and blade shape, but the thrust is not 'significantly less' in astern gear, obviously it will be a little less efficient, but not much, certainly not enough to notice.
Do feathering props have symmetrical blade cross-sections and shapes, unbiased to either forward or reverse gear? Or is there another method by which they achieve equal thrust in either direction?

As per the bold basically; swings and roundabouts, it loses a little efficiency when driving ahead.

 

[franksingleton]

Not all hull shape/prop configuration are suitable for the Brunton. I do not know details except that they will advise if that is the case.

 

[franksingleton]

We have had a Brunton on our HR34 for nearly 20 years and never met anyone not totally satisfied With one. Our impression was that, compared to a fixed prop, we got a little better speed under sail and better permanent under power. On one occasion, coming down river fro m Seville, we were slowly passing another HR34, 10 years younger with an S-drive, ours is a straight shaft, and a Volvo 2030, we have the older 2003. Our friend asked how many revs we had, we said about 1,700 - 1,800. And you? 2,200, he said. His prop was a Volvo folding prop. The comparison was interesting and confirmed our impression of the Brunton.
Going astern in a close quarters situation, you have to be careful because it can be alarmingly quick. With our long prop shaft, we do get appreciable prop walk, comparable with our old fixed prop, as I recollect.
We do not motor hard and do not normally go if it means a long motor-sail. We have not had to replace bearings even after many years and many thousands of miles. There is no noticeable play when we check the prop out of the water. Left to themselves, each blade gently rotates under gravity.
I do not get a retainer from Brunton!

 

[Laminar Flow]

Forgive me, I come from a long line of Clydeside engineers and we have a reputation for being blunt.

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?

This is not intended as confrontational, but you are clearly unhappy with your current prop. I would have been on the phone long ago.

Just to add: Day Dreamer's experience is congruent with that of our Dutch friend who had both a Brunton and a Max prop on his Southerly. In his Opinion the Brunton was much poorer for maneuvering than either a fixed or the Max. He was quite emphatic about this as I had thought that perhaps a Brunton would be a good idea for our boat.

 

[Laminar Flow]

I still am struggling as to the benefit of a feathering prop, at least for us:

A fixed and locked three blade will cause a loss in speed (at a relative speed of 0.9) of 0.8 kts.

The same prop if left to spin (providing the gear box permits) will cause a drop of 0.4 kts.

A feathering prop will reduce this to 0.2 kts.

A folder will cause a loss of speed of a mere 1%.

As speed picks up resistance caused by the prop has less and less impact on speed.


Our PRM gear box allows us to let the prop spin. As we do not have enough room to swing a folder the only have the option is a feathering type.
I'm not sure a gain of 0.2kts over our existing setup is worth the expense or the sacrifice of the reliability and performance of a fixed prop.