Yet another prop question

[Fergus]

Thinking about changing my 3 blade fixed prop. Are folding props better than feathering? Will they both deliver around 0.5 kn extra? Which are more expensive? How do I figure out the size I need (32', 20hp). Am I to expect some performance deterioration under power?

Sorry if some of these have been asked many times before!

 

[Robin]

Fergus

We inherited a Brunton self pitching and feathering 3-blader with our current boat and it is excellent. We also have as a spare the original folding prop that the previous owners removed to fit the Brunton, so they though it worth the money to change.

I have spoken too with another Sun Legende 41 owner with the same engine as us and we get both better performance and economy under power than he does with a fixed 3 bladed.

Robin

 

[Sans Bateau]

Fergus

Good to meet you at the W/E.

We have a 'cooking' Volvo folder on our 35i. Our friend has the Bruton 3 blader on his 34s, it goes faster at lower revs!

Talking to folding prop people at SIBS, I reckon unless you do a lot of motoring the 2 bladed Bruton would be the way to go, their sales guy told me the 3 bladed came into its own if say motoring hard where a 2 blade may cavitate. The Bruton 2 blade was little more than the Gori 2 blade folder, so I know which one I will go for!

 

[Sailfree]

I have just gone through the same decision loop. Its also aggrevated in my case with the new Yanmar insisting locking gearbox in astern while sailing stresses the gearbox - it also locked the gearbox in astern and had to be started that way before being able to change to neutral.

1. Folding - least resistance of all
-poor power astern
- on most boats worth an extra 1/2 to 3/4 knot when sailing

2. Feathering- slightly more resistance than folding.
- more power astern than even a fixed prop (blades reverse direction for max efficiency). For most boats/engines will stop a boat in astern in its own boat length from 6kts.
- again worth an extra 1/2 to 3/4 kts when sailing

3. Bruntons (forget name) initially need more wellie to get power astern. I was also not keen on the amount of bearings exposed to salt water/marine growth.

I chose a feathering prop. Of these

a) Kiwi prop looked good reasonable price and would be of interest except maximum power handling ability. Plastic blades hence cheapness but for small boats I would have seriously considered them

b) Aquastream interesting as in stainless steel and warranteed for 5 yrs but one of dearest

c) Maxiprop- good but cannot adjust pitch from outside and needs to be assembled and pitch adjusted when installed - quite dear and often better with even dearer larger hub option.

d) Variprop - Can adjust pitch from outside, already assembled can slide on, has a 2,3 or 4 blade option for larger engines. has an internal cushion effect for when going forwards to astern and vice versa. cheaper than the maxiprop & Aquastream

My decision - having checked the market I decided the variprop was technically superior although was tempted with the SS aquaprop meaning no disimilar metals on shaft. I had bought a Variprop before on my previous boat and was happy with it but admit I had done a lot less research then. I finally got a good deal - Variprop can be supplied through a number of suppliers (pm me if you are serious)

Bear in mind my requirement are for heavy use on the charter market, cannot have any idiosyncasies as must be idiot proof (hence Gori prop and Bruntons were out). The advantage of quickly stopping the boat if misjudging a berthing situation was a big plus.

Must add 1st boat had a Volvo folding prop which was replaced 3 times under warrantee. Product IMHO not robust enough for charter market but OK for average owner for a few years. Full marks to Volvo for replacing it FOC but lost money on lost charters though.

Good judgement comes from experience, lots of experience comes from owning charter boats! (apologies to "ETAP_owner" for plagarism)

 

[Robin]

Roger

Just a small comment for clarity about the Brunton Autoprop. We have an earlier version which has exposed S/S bearings on which the blades rotate, ours is now I believe 9 years and many thousands of miles old and although I bought a bearing replacement kit it has not been necessary to do anything other than adjust the existing ones once in the last 7,000mls. The bearings are not part of the prop rotation, only to allow free blade movement in the feathering/pitching mode so not subject to huge wear IMO.

We stop our engine whilst still in forward gear, as is required to make the Brunton feather. We have a Yanmar 4JHE 44hp.

Current Autoprops however have sealed and greased bearings.

Robin

 

[Fergus]

Thanks for the info - the Brunton autoprop seems good - would you classify it as feathering?

 

[ChrisE]

Yup,have one as well and whilst I understand salifree's objections I can't say that I've noticed the need for additional power to go in reverse and I'm not sure what he means by idiosyncracies. Ours sits on the shaft does its job and gets as much maintenance through the season as the old fixed prop ie none.

Now in our second season and with about 3000 miles plus under its belt am still impressed.

 

[Robin]

Yes, each blade moves individually to present the least resistance to flow.

See http://www.autoprop.com/

They are pricey though!

 

[tome]

We inherited a 3 bladed maxprop which certainly gives us an extra 1/2 knot when feathered and is very efficient going astern. We change the anode and re-grease it annually and strip and inspect every couple of years.

It woks well and is a fine piece of engineering.

 

[Sailfree]

Yes it seems that modern gearboxes with fixed props will lock up when sailing and engaging astern to lock the shaft. If you do this with either folding or feathering providing the blades move so there is no stress on the gearbox and it should not lock in astern. I will shortly find out! I do not like the idea of the shaft continuing to rotate while sailing but a necessary evil at present.

I expect to grease the prop every year and change the anode but ideally am looking for one that trouble free if it did say 8000mls per year for 3 to 5 years. If I was buying a car I am also influenced by what minicab driver choose as they learn quickly from experience as well!

My reservations about the bruntons autoprop is that it needs more weelie to go astern, misjudgement by a skipper strange to the boat could seriously reduce the boats length. The ability to stop the boat at 6kts in its own boat length is a great bonus.

 

[Sans Bateau]

[ QUOTE ]
The ability to stop the boat at 6kts in its own boat length is a great bonus.

[/ QUOTE ]

Bloody hell you need disc pads not a prop!

Interesting point going astern with folding prop, it is a bit scarey when you first use one but we have now had three boats with folders but IMHO you soon get used to the way it performs.

 

[bedouin]

[ QUOTE ]

1. Folding - least resistance of all
-poor power astern
- on most boats worth an extra 1/2 to 3/4 knot when sailing


[/ QUOTE ]
As I've posted on similar threads in the past. Not all folding props are equal. My Gori 3 blade folding prop has better performance astern than any other type of prop - fixed, folding or feathering. (Though I think there are now one or two similar designs that will match it).

 

[Sailfree]

To this post and Bedouin.

As I said I aim for the charter market and the problems of engaging overdrive on the Gori puts people off.

Remember my skippers may have no experience of my particular boat and prop so KISS principle applies. Nothing on my boat can have idiosyncacies that require specific experience or knowledge.