Folding props

[Cardo]

Yes, yes, I'm sure this has been done to death... and back, so let's review!

We have an old but spritely Southerly 105. She's no speed racer and with my lax sail trimming I usually don't go much above 4-5 knots with a decent breeze.

She has a new Beta 35 engine and a large fixed 3 bladed prop.

We are looking to go cruising for a couple of years, specifically down to the Med and potentially across to the Caribbean, depending on how things go. We have a limited budget, so we have to weigh up any expenditure with the benefit we'll receive.

So, would a folding prop be worth considering? Would we notice any difference during extended sailing, potentially crossing the Atlantic?

If you think it may be worth investing in a folding prop, any recommendations as to which type? And I don't suppose you know how much £££ they run for (approx, I appreciate it depends on size, etc.)?

 

[lw395]

Depends how much motoring you intend doing.
If you like to sail as much as possible, then go for folding or feathering.
If you are in the 'gentlemen don't beat up wind' camp, probably no point, so long as you can afford lots of diesel.
Maxprops are god but I think there are more and possibly better choices on the market now.

 

[Teetime]

Folding Props

Hello Cardo. We have just had fitted a Flex-o-Fold folding prop to our Southerly 38. I can only say how pleased I am with it. The boat sails much better indeed noticably so. Even better as far as I am concerned is an increase in speed at a given revs under power. This is sure to be the fact that the new prop recommended by Flex-o-Fold has a greater pitch than the fixed prop fitted by Southerlys. Although the engine will not now reach peak revs it is so much quieter at our usual cruising speed of about 6.5 knots and still has plenty of revs in hand so I dont think the engine can be in any way overstressed. Incidently the Fex-o-Fold came out very well in the Yachting Monthly test of many different props. This would be well worth you reading.

 

[forelle541]

Must agree with Teetime, Flex o Fold has been a great improvment on my Sadler 29. the motoring with the potential saving in diesel is the most noticeable.

 

[Kukri]

I am just going through the same analysis; at the moment I favour a folder rather than a feathering prop because it is so much less likely to catch lobster pot warps etc. I use the engine very little.

 

[Cardo]

Thanks for the replies so far. We motor in and out of harbours, like most people, but the plan is to use the engine as little as possible. Passages will be done when the weather is appropriate and there is some wind. If there's no wind, we'll simply stay put.
I do get the impression a folding prop would be a sensible idea, if we can find the funds for it.
I'll have a look at the Flexofold and see what they say.

 

[Tranona]

There is a lot more to making your choice than discussed so far. You really need to consider what you are trying to achieve. Both folders and featherers will reduce drag and lead to an increase in speed under sail, particularly in light airs when the drag of the prop is a bigger proportion of overall drag. It is difficult to determine in advance what this improvement will be, but it varies little from prop to prop. If you get a not unreasonable 10% increase in speed, say from 5 to 5.5 knots then you average days run could increase from about 120 to just over 130 miles. If you are doing a lot of long distance blue water sailing under sail alone that is a significant achievement.

However, most cruising, particularly in the Med is not under sail alone and you will find you use the motor the majority of the time on passage to keep up reasonable passage averages. Some will be straight motoring, but mostly you will be using the motor to raise speed under sail. Therefore motoring performance, or rather performance while motor sailing becomes more important. The fact that you have a 35hp engine on a not very big boat suggests that motoring will be quite important for you, and you may find a feathering prop, or a selfpitching prop such as a Bruntons more attractive.

In general 2 blade folders are cheapest, but not necessarily appropriate for your use. 3 blade folders give superior motoring performance, but are in the price range where you can also get a 3 blade feathering prop.

You need to seek recommendations from the various suppliers such as Darglow and Bruntons as they have a wealth of experience on how their products perform on different boats.

 

[Seajet]

I had a Carter 30 with a folding 2 blade prop on a saildrive; not the optimum way of transferring power to the water, especially going astern, but I thought it quite adequate.

If going long distances I would fancy a feathering 3 blader but the cost is rather toe-curling.

Hopefully it's a thing of the past, but 2 blade folders should have a toothed cog arrangement meaning both blades deploy equally; I met a chap on a Carter 33 which had simple pivoted unconnected blades, he described only one blade deploying and 'interesting' results requiring a lot of juggling throttle & gearshift !

 

[vyv_cox]

I suspect that the claims made for the increase in sailing speed are somewhat exaggerated. It is not something that it is possible to measure and most owners will want to persuade themselves that the money they spent has been of benefit. I replaced a fixed two-blade with a two blade Autoprop, with which I have been very pleased for many years. I have my doubts that any worthwhile increase in sailing speed was realised, not more than tenths of a knot for certain.

 

[Conachair]

Thanks for the replies so far. We motor in and out of harbours, like most people, but the plan is to use the engine as little as possible. Passages will be done when the weather is appropriate and there is some wind. If there's no wind, we'll simply stay put.
I do get the impression a folding prop would be a sensible idea, if we can find the funds for it.
I'll have a look at the Flexofold and see what they say.

I´ll heading the same route for the next big cruise. Not had any experience of folding/feathering props but having spent some time out there anything which will gain some speed in light airs will be very welcome. I would find it quite difficult to justify the cost down to and in the Med. (From what I´ve heard of the Med anyway). But Atlantic it can win over. Plus the added bonus of worrying slightly less about picking up a fishing net, though your prop looks quite safe.

 

[lw395]

......Even better as far as I am concerned is an increase in speed at a given revs under power. This is sure to be the fact that the new prop recommended by Flex-o-Fold has a greater pitch than the fixed prop fitted by Southerlys. Although the engine will not now reach peak revs it is so much quieter at our usual cruising speed of about 6.5 knots .......

This sounds like a classic over-pitching to me?
If the engine won't reach max revs in calm water, you are not going to get full power from the engine.
Moreover, when the seas get up a bit, the engine will struggle.
If you are aground, the engine will develop very much less thrust than with a prop that allows it to hit full power.
But that compromise may be right for some people on some boats.

Re the drag of a fixed prop, I think it is worth about half a knot of boatspeed as a rough guide, for a typical conventionally sized 3 blader on a typical modern hull form. Assuming sailing upwind, flattish seas, not reefing weather. There are drag curves in the textbooks you can work it out from.
IMHO half a knot is a big difference, I fully respect others have more time on their hands.
On a trip from Yarmouth to Dartmouth, that would be the difference in getting to the pub in time for a couple of pints, or not.

 

[cliff]

Before jumping in have a look at these feathering props

 

[Sans Bateau]

Flexofold for me every time. From when I reverse out of my berth to my return when a good blast of throttle is applied to stop the forward motion, reverse is dammed good. Forward isnt bad either.

 

[Seajet]

Flexofold for me every time. From when I reverse out of my berth to my return when a good blast of throttle is applied to stop the forward motion, reverse is dammed good. Forward isnt bad either.

Galadriel,

I always think relying on a big burst of astern power on arrival is always going to end in tears one day; the prop falling off, cables parting etc !

However as I think I know where you keep your boat, slightly radical moves may be required and you're hardly a novice.

Vyv Cox,

I do believe there is a significant speed improvement under sail when fitting a folding / feathering prop.

On my boat - I realise the drag involves the well aperture along with the prop - I get well over a knot more speed when stowing the engine and fitting the fairing plug.

With folding props there is also the rather important bonus that it's unlikely to catch weed or lobster pot markers; my Dad once had the fixed 3 blade prop of his Centaur pick up a bunch of weed so that she'd hardly move, I tried to shut off my imagination about sea toilets when diving underneath in E.Cowes marina & being in the 'mud'...

Talking of lobster pot markers, I'd like to meet the clown who's laid black and dark blue buoys right on the bee-line between Chichester bar beacon and the Dolphin...

 

[vyv_cox]

Any improvement must be dependent upon what is replacing what. In my case I replaced a fairly narrow two bladed fixed prop with a two bladed Autoprop. The difference in sailing speed was not enormous. No doubt if I had replaced a fixed three blade with a folder I would have seen a far bigger difference.

I would also assume that the underwater profile of the boat must be significant - a beamy long keeled motor sailer would presumably react differently to such a change than a slippery fin keel racer.

 

[Tranona]

Galadriel,

I always think relying on a big burst of astern power on arrival is always going to end in tears one day; the prop falling off, cables parting etc !

However as I think I know where you keep your boat, slightly radical moves may be required and you're hardly a novice.

Vyv Cox,

I do believe there is a significant speed improvement under sail when fitting a folding / feathering prop.

On my boat - I realise the drag involves the well aperture along with the prop - I get well over a knot more speed when stowing the engine and fitting the fairing plug.

With folding props there is also the rather important bonus that it's unlikely to catch weed or lobster pot markers; my Dad once had the fixed 3 blade prop of his Centaur pick up a bunch of weed so that she'd hardly move, I tried to shut off my imagination about sea toilets when diving underneath in E.Cowes marina & being in the 'mud'...

Talking of lobster pot markers, I'd like to meet the clown who's laid black and dark blue buoys right on the bee-line between Chichester bar beacon and the Dolphin...

It is more likely the fairing plug that gives most improvement. The difference now I have a folder instead of the fixed two blade on my Bavaria is in fractions of a knot. It is really difficult to establish consistent figures unless you have long term data on days run under sail. However, I was experimenting last week crossing Bournemouth Bay and typically speed rose by .3-.4 of a knot when locking the prop so the blades fold - with a speed under sail of 5+. You can tell the difference - but not earth shattering. That was of course in between dodging the black and blue (and white or tiny orange) pot buoys. My fisherman contacts tell me that the blue ones are whelk pots rather than crab pots!

Not convinced folding or feathering props are really better at avoiding snagging lines when you are sailing - most of the incidents are under motor when the water and debris is drawn into the rotating prop.

Good reverse is essential if you have a big heavy boat and tight berth. My folder is as good in terms of thrust as the fixed. However, if I was back in the Med where reliable reversing is arguably even more important I might stick with fixed and suffer the slightly poorer light airs sailing performance - but that is why Mr Volvo makes such good engines!

 

[Woodlouse]

I'd recommend the Darglow Featherstream props. Reliable, simple and fantastic customer service. I believe they are one of the more reasonably priced as well.

 

[Seajet]

Tranona,

I've always thought I was lucky in a way, that my first engine had no reverse; one does get used to being very conscious of how much way is on !

I apply this to larger boats too; I am not saying I'm some super hero, just it's my choice not to rely on a big handful of reverse in normal conditions, also I like to make a quiet entrance; at least there may be less people watching if I cock it up !

I and several others have tried modified fairing plugs in the Anderson, where the engine leg was a close fit in a small shaped aperture with flexible seals, a bit like a centreboard slot but tighter fit if you see what I mean.

There was still a significant improvement when taking that lot out and fitting the normal well plug; several A22's have various inboards, they are noticeably slower, and it's not weight as my boat has tons of junk ( which I vow every Autumn not to carry ) and the inboard equipped boats have been empty !

 

[Tranona]

Maybe you should come and try your hand getting my Bavaria in and out of my berth singlehanded! Or even more exciting when I get my Eventide back up and running.

The thing with drag as Vyv pointed out is that it depends on what you are replacing with what - and in your case you are removing a gearbox and prop plus drag from the hole in the bottom, whereas I am just folding two blades away - the hub and drive unit is still there. In other words the reduction in overall drag is very small. Would be different if I had a 38 which came as standard with a whopping 3 bladed prop and I changed to a 3 blade folder.

That is why I always say that, although you can generalise about the benefits of particular props you can only get to the specifics if you know what the boat is and what the owner is looking for. Even then there is often no clearcut choice, or rather similar results could be achieved with different props. I would prefer a 3 blade feathering on my boat (as on my Eventide), but Featherstreams are not available for saildrives and the others are way out of my price range. The FlexoFold is, however a good compromise as it performs just like the fixed under motor but has that little edge under sail.

 

[cmedsailor]

I would prefer a 3 blade feathering on my boat (as on my Eventide), but Featherstreams are not available for saildrives and the others are way out of my price range. The FlexoFold is, however a good compromise as it performs just like the fixed under motor but has that little edge under sail.

What if you were getting a 3blade Flexofold instead of the 2 blades? Would you still prefer the Featherstream? Prices are very similar.