Bruntons Varifold 2B or Flexofold 2B? Do you have experience of either?

[BigCheese338]

Hi all! This is my first post so be gentle!

We own a 30ft, Norfolk Broads, gaff rigged sailing cruiser with GRP hull, fin keel and fitted with a Yanmar 1GM10 in the bows.

The prop is shaft-mounted behind a cutlass bearing half way down the narrow trailing edge of the keel, with the stern tube inside that. The current one is virtually useless astern and if you've sailed on the Broads, you will know how important it is to be able to manoeuvre safely in confined spaces. This is compounded by the keel stalling at relatively high speeds, especially in astern.

Because we often sail in weedy areas, a folding (as opposed to feathering) prop is a must.

The best information I’ve found is in the 2009 YM article, reporting on comparative tests between various folding and feathering props. Along with other research, I’ve concluded the Flexofold 2 blade is probably the best choice. While Bruntons have a good reputation locally with their feathering Autoprop, their Varifold 2 blade came out badly on astern performance during those tests. However, they are now 13 years old and it’s quite possible improvements have been made since, or possibly it was not well matched to the boat / engine.

So, the reason for all this tedium is to ask whether anyone has relatively recent experience of either of these props. I would be most grateful if you could share it with me if so. There is so little independent data with which to make a decision, so any information will be gratefully received.

Thanking you in advance

 

[Tranona]

Welcome to the forum

Good question! - but raises lots of other questions. The simple answer is that the Flexofold 2 blade is probably the best there is - I had one for over 10 years on 2 boats and it performed faultlessly.

The big "however" is that I am not sure that it is suitable for your requirements. You do not have a lot of power to play with (8hp of it is a 1GM10 on a good day) and you need a lot of revs to access that power - particularly important for reverse performance. I assume that is a photo of your boat, in which case you have plenty of space to swing a larger propeller, but to do this you need the 3.2:1 reduction which will allow you to use a 14" prop (or even a 15" 2 blade) compared with a 12 o13" that is common with the 2.2 or 2.6 boxes. To further complicate matters all boxes have a 3:1 reverse ratio so the ideal prop with the lower ratios will not be appropriate in reverse. So if you have one of the lower ratios (which means a higher shaft speed) the pitch will be wrong for reverse hence the poor performance. Just changing to another fixed pitch prop will not change this.

You may well be better off looking at a Featherstream 3 blade which is commonly used with the 1GM in boats like the Shrimpers as you can have different pitch in forward and reverse. If you have a 3.2:1 you can have a larger diameter prop such as I had with a 1GM. This is a 15" JF which is an earlier version of the Featherstream. This performed extremely well on an Eventide 26 in the second photo.

I suggest you give Chris Hares at Darglow (who make the Featherstream and sell FlexoFolds). He is very knowledgeable on these issues and will give you good advice.

 

[Sandy]

Hello and welcome

I have a Bruntons Varifold 2B and have found no difference between that and my original fixed two blade in reversing or going forward.

My primary reason for going to the folding prop was my old one would start spinning at 4.8 knots STW and the noise was driving me insane. The extra speed is a big advantage on long passages as I've gained 12 mn a day just by changing props.

As @Tranona has suggested speak to the manufacturers before purchasing, they are all very knowledgeable.

 

[Bobc]

Personally, I would say that if it's grunt astern and improved maneuverability that you want, get a 3 blade Featherstream.

 

[BigCheese338]

Welcome to the forum

Good question! - but raises lots of other questions. The simple answer is that the Flexofold 2 blade is probably the best there is - I had one for over 10 years on 2 boats and it performed faultlessly.

The big "however" is that I am not sure that it is suitable for your requirements. You do not have a lot of power to play with (8hp of it is a 1GM10 on a good day) and you need a lot of revs to access that power - particularly important for reverse performance. I assume that is a photo of your boat, in which case you have plenty of space to swing a larger propeller, but to do this you need the 3.2:1 reduction which will allow you to use a 14" prop (or even a 15" 2 blade) compared with a 12 o13" that is common with the 2.2 or 2.6 boxes. To further complicate matters all boxes have a 3:1 reverse ratio so the ideal prop with the lower ratios will not be appropriate in reverse. So if you have one of the lower ratios (which means a higher shaft speed) the pitch will be wrong for reverse hence the poor performance. Just changing to another fixed pitch prop will not change this.

You may well be better off looking at a Featherstream 3 blade which is commonly used with the 1GM in boats like the Shrimpers as you can have different pitch in forward and reverse. If you have a 3.2:1 you can have a larger diameter prop such as I had with a 1GM. This is a 15" JF which is an earlier version of the Featherstream. This performed extremely well on an Eventide 26 in the second photo.

I suggest you give Chris Hares at Darglow (who make the Featherstream and sell FlexoFolds). He is very knowledgeable on these issues and will give you good advice.

Many thanks Tranona, there's a great deal to think about there! I may be able to swap my 2.62 'box for a 3.2, which would obviously mean it would spin faster astern, which I would guess is ideal.
I'm sticking with folding for two reasons. First, ever since first lockdown, the weed on the Broads seems to have gained an upper hand over its management regime and we often find ourselves sailing through patches of it. I anticipate a feathering prop is much more likely to become fouled with it than a folding. When I mean fouled, I'm talking masses of the stuff! See the press photo of a small yacht (not ours). The second reason is cost. We took om Bewitched July last year and at 25 years old and GRP (the previous one was wooden and 97 years old), we expected minimal maintenance. How wrong we were! The costs are well into 5 figures now, so the price of the feathering props is simply out of reach.
I will certainly take your advice and call Chris

 

[BigCheese338]

Hello and welcome

I have a Bruntons Varifold 2B and have found no difference between that and my original fixed two blade in reversing or going forward.

My primary reason for going to the folding prop was my old one would start spinning at 4.8 knots STW and the noise was driving me insane. The extra speed is a big advantage on long passages as I've gained 12 mn a day just by changing props.

As @Tranona has suggested speak to the manufacturers before purchasing, they are all very knowledgeable.

Many thanks for your response Sandy. In fact the existing prop is also folding, but being a graduate engineer with a decent knowledge of fluid mechanics, it didn't take me long to see the design is sadly lacking. See pic. I'm surprised it works astern at all presenting that blunt leading edge. For the record, the logo belongs to the Italian company Eliche Radice. Looking at their website, it appears the design has not changed in the intervening quarter century. I'd give it 2/10 overall and 1/10 astern

 

[BigCheese338]

Personally, I would say that if it's grunt astern and improved maneuverability that you want, get a 3 blade Featherstream.

Thank BOBC. See my reply to Tranona above

 

[BigCheese338]

Personally, I would say that if it's grunt astern and improved maneuverability that you want, get a 3 blade Featherstream.

Thanks Bobc but see my reply to Tranona above

 

[bignick]

Many thanks Tranona, there's a great deal to think about there! I may be able to swap my 2.62 'box for a 3.2, which would obviously mean it would spin faster astern, which I would guess is ideal.

The gearbox ratio you quoted is a reduction ratio, so a higher ratio (3,2) means the prop will spin slower.

 

[Tranona]

Many thanks Tranona, there's a great deal to think about there! I may be able to swap my 2.62 'box for a 3.2, which would obviously mean it would spin faster astern, which I would guess is ideal.
I'm sticking with folding for two reasons. First, ever since first lockdown, the weed on the Broads seems to have gained an upper hand over its management regime and we often find ourselves sailing through patches of it. I anticipate a feathering prop is much more likely to become fouled with it than a folding. When I mean fouled, I'm talking masses of the stuff! See the press photo of a small yacht (not ours). The second reason is cost. We took om Bewitched July last year and at 25 years old and GRP (the previous one was wooden and 97 years old), we expected minimal maintenance. How wrong we were! The costs are well into 5 figures now, so the price of the feathering props is simply out of reach.
I will certainly take your advice and call Chris

As bignick says a larger reduction ratio means a slower turning shaft. With a 2.62:1 shaft speed is 1374rpm forward and with a 3.22:1 it is 1118rpm. With either box the reverse is 3.06 giving a shaft speed of 1176rpm. The lower shaft speed allows you to run a larger diameter flatter pitch prop.

I thought it was a Radice which as you say is a very old design and the FlexoFold is in a different league to that. The one I had was a 16*11 2 blade in a saildrive in a Bavaria and the reverse performance was at least equal to the fixed 2 blade. However that was with 30hp. With the meagre horsepower you have you really do need a 3 blade propeller to get the most out of it.

Moving to a 3.22 and a better propeller will be an improvement, particularly as the fixed pitch will be more closely matched in reverse . A rough and ready calculation suggests you should be able to run a 15*9 2 blade with a 3.22, but only a 13*8 with a 2.62. That gives you an idea how far out the prop is in reverse with a 2.62 (13*8 instead of 15*9). looks like your Radice might be a 14*8 - can you get the full 3600 engine rpm with this?

Appreciate your reluctance to go to a 3 blade, but while the performance in forward may be little different, it will give you far better reverse, simply because of the greater blade area and the ability to match the pitch exactly. Not convinced it would be any worse in weed as the blades present only a narrow area to the waterflow - and balls of weed such as in your photo will catch both the keel and the rudder. (Memories of hours of testing "weedless" propellers on Seagull outboards in the thick Canadian pondweed in the River Frome. The reality was that even with the old fan props the motor was more often stopped by the weed balling up around the leg than actually around the prop). Cost is of course an issue - but the added benefits are there forever!

Just to whet your appetite this is the prop that Chris made for my latest project, a Golden Hind 31 - bigger sister of the Eventide.

 

[BigCheese338]

The gearbox ratio you quoted is a reduction ratio, so a higher ratio (3,2) means the prop will spin slower.

Thanks bignick
I didn't explain myself well. I meant faster astern than ahead, which, with a folding, must be a good thing, right?

 

[BigCheese338]

As bignick says a larger reduction ratio means a slower turning shaft. With a 2.62:1 shaft speed is 1374rpm forward and with a 3.22:1 it is 1118rpm. With either box the reverse is 3.06 giving a shaft speed of 1176rpm. The lower shaft speed allows you to run a larger diameter flatter pitch prop.

I thought it was a Radice which as you say is a very old design and the FlexoFold is in a different league to that. The one I had was a 16*11 2 blade in a saildrive in a Bavaria and the reverse performance was at least equal to the fixed 2 blade. However that was with 30hp. With the meagre horsepower you have you really do need a 3 blade propeller to get the most out of it.

Moving to a 3.22 and a better propeller will be an improvement, particularly as the fixed pitch will be more closely matched in reverse . A rough and ready calculation suggests you should be able to run a 15*9 2 blade with a 3.22, but only a 13*8 with a 2.62. That gives you an idea how far out the prop is in reverse with a 2.62 (13*8 instead of 15*9). looks like your Radice might be a 14*8 - can you get the full 3600 engine rpm with this?

Appreciate your reluctance to go to a 3 blade, but while the performance in forward may be little different, it will give you far better reverse, simply because of the greater blade area and the ability to match the pitch exactly. Not convinced it would be any worse in weed as the blades present only a narrow area to the waterflow - and balls of weed such as in your photo will catch both the keel and the rudder. (Memories of hours of testing "weedless" propellers on Seagull outboards in the thick Canadian pondweed in the River Frome. The reality was that even with the old fan props the motor was more often stopped by the weed balling up around the leg than actually around the prop). Cost is of course an issue - but the added benefits are there forever!

Just to whet your appetite this is the prop that Chris made for my latest project, a Golden Hind 31 - bigger sister of the Eventide.View attachment 145734

How could you nail that on the bottom of a boat and hide it underwater? It should be framed and hung above the fireplace!

Seriously, I'm certain it's under-propped. I don't have a tacho (yet) but I'm convinced the engine is nudging the governor at full power! At lower throttle settings, the engine gets very busy while the speeds are still pedestrian, only speeding up towards full power. On the Broads, we're nearly always motoring on flat, often sheltered water (mostly in speed limits), so we can get away with a lot less power than at sea. Our last boat was 32ft + 7ft bowsprit, weighed 3.5t and we had a 6HP 4 stroke outboard as an auxiliary.

I hear everything you say, but she has been bleeding us dry over the 15 months we've had her and, being retired, I have considered leaving as is for that reason. Until I just couldn't get her docked stern on in a stiff headwind a month ago. And I can forget it in a crosswind. I've accepted we're just going to have to accept a compromise, not least because I'm permanently cringing , awaiting the next expensive thing to break!

 

[Tranona]

Yes, no doubt it will look horrible when it comes out next May after 7 months in the water. However I keep the prop off the Eventide in my study and admire from time to time - as much for its physical beauty as for the memories of the enjoyable work developing it first for the Yanmar and later for a Nanni 14. Pity it is so specific as would love to find somebody who could use it. It would work well on your boat for forward, but would be hopeless in reverse because it is pitched for a 2:1 reduction.

While a tacho is useful, you can sort of tell when a 1GM is hitting its full 3600rpm by the noise!. You have not mentioned what speed you get in forward, but I would expect something close to 5.5knots in flat water - and you would need full revs to achieve this with the correct size prop. I think you have to be realistic about performance in reverse. Even allowing for the poor blade shape of your current prop the lack of power at lower rpm and the type of underwater configuration you have will always be a challenge, not just getting the boat to move but making it go where you want it to go.