Dyneema or Wire Rope Davit Falls?

[Dockhead]

I replaced my former and much cursed Cooney-Simpson S175 electric davits with smaller manual Simpson (pre Cooney) ones year before last.

They have worked well! Unlike the awful electric ones, with a mechanism which Rube Goldberg's imagination would not have been adequate to come up with, these are totally simple, with really nothing to go wrong. Two brass gears and a pawl, a cable drum, two brass axles in simple bearings installed in the davit body.

Now it's time to replace the wire rope davit falls, which are old and starting to rust and generate meat hooks.

It occurs to me that I flay my fingers regularly on the inevitable meat hooks on these things -- maybe it would be better to go to Dyneema? The new Cooney ones use Dyneema: http://www.cooneymarine.co.uk/PDF/Series-10-Davits.pdf

I get that they are more vulnerable to chafing, but I don't think that should be a big problem -- they will spend 99.9% of their lives wrapped on the lifting drum, and I don't think they touch anything else but the nice nylon pulleys at the davit ends.

Has anyone tried this? Any tips?

[conachair]

Not tried exactly that but I've worked with dyneema a lot, film/tv/theatre stunt work and winches use it a lot these days - marlow D12max sk99. Amazing stuff, I made some short strops out of 5mm which fitted through the fairleads for mooring lines and springs winter before last to see how it would fare - barely any chaff despite a heavy steelboat being severely thrown around in some awful storms in Dartmouth.
One small point is terminating onto the winch drum, any force with no wraps can slowly undo a stopper knot though that shouldn't affect your application.
No reason to ever have any steel wire rope on a drum anymore, unless your wallet is close to empty..

[Hudson Force]

I made a switch from wire rope to Dyneema with my roller furling halyard a few years ago and I'm very pleased with it. My roller furling genoa is the old Schaeffer rig which is separate from the headstay with the long run outside the mast and the same length on the winch and hung coil. I'm using the Endura line with the outer coat over the Dyneema- far easier on the hands and my system is all manual. I'm very pleased with the change.

[JPA Cate]

You're headed in the right direction, mate. Maybe check if you have to change the sheaves for the line. Enjoy.

Ann

[Nauticatarcher]

just go size for size in Dyneema, make sure sheaves are smooth, dont use stopper not on winch end, just splice an Eye and wrap it around winch body and feed other end through, leave three wraps on drum when fully extended, never have to replace it again

[poiu]

Originally Posted by Dockhead

I replaced my former and much cursed Cooney-Simpson S175 electric davits with smaller manual Simpson (pre Cooney) ones year before last.

They have worked well! Unlike the awful electric ones, with a mechanism which Rube Goldberg's imagination would not have been adequate to come up with, these are totally simple, with really nothing to go wrong. Two brass gears and a pawl, a cable drum, two brass axles in simple bearings installed in the davit body.

Now it's time to replace the wire rope davit falls, which are old and starting to rust and generate meat hooks.

It occurs to me that I flay my fingers regularly on the inevitable meat hooks on these things -- maybe it would be better to go to Dyneema? The new Cooney ones use Dyneema: http://www.cooneymarine.co.uk/PDF/Series-10-Davits.pdf

I get that they are more vulnerable to chafing, but I don't think that should be a big problem -- they will spend 99.9% of their lives wrapped on the lifting drum, and I don't think they touch anything else but the nice nylon pulleys at the davit ends.

Has anyone tried this? Any tips?

I did just that 5 years ago for the same reason and more, I got a spiral wrap and tangle in the davits with the wire, it took half a day to fix and unbend the kinks. Horrid stuff. It was a straightforward change to dyneema. A big success. Grab it without fear.

I bought the higher tensile strength (Marlow Dyneema Max) option dyneema rope in the same diameter as the steel wire to give headroom due to UV strength losses and chafe. I also bought a few foot longer than the old wire thinking I would have to regularly redo the end splice because of chafe, but I haven't really needed to shorten it yet. There is a little chafe from the pulley and it probably will be best to shorten it now. The middle section is like new.

There will be some creep going on and now I probably should re-splice the end 4 feet from the drum plus a bit to be safe. That will fix the chafe issue at the same time.

One of the biggest problems I had was in the rope (and wire) jumping off the sheaves and jamming tight down the sides. A frequent and very frustrating repair. I had machined stainless sheaves, much wider to fill in the gap and to have a much deeper groove. The rope never pulls out nor jams now, a huge improvement.

I welded the head of a socket bolt to the centre of the crank handle and now can use an electric drill to power them. With my heavy 230kg dinghy it is a big help. For yours, maybe less so.

I also rebuilt the internal gearbox with new tougher high end stainless gears and sealed ball bearings. I had a big wear problem. That reduced wear, friction and improved solidity.

[Dockhead]

Originally Posted by poiu

I did just that 5 years ago for the same reason and more, I got a spiral wrap and tangle in the davits with the wire, it took half a day to fix and unbend the kinks. Horrid stuff. It was a straightforward change to dyneema. A big success. Grab it without fear.

I bought the higher tensile strength (Marlow Dyneema Max) option dyneema rope in the same diameter as the steel wire to give headroom due to UV strength losses and chafe. I also bought a few foot longer than the old wire thinking I would have to regularly redo the end splice because of chafe, but I haven't really needed to shorten it yet. There is a little chafe from the pulley and it probably will be best to shorten it now. The middle section is like new.

There will be some creep going on and now I probably should re-splice the end 4 feet from the drum plus a bit to be safe. That will fix the chafe issue at the same time.

One of the biggest problems I had was in the rope (and wire) jumping off the sheaves and jamming tight down the sides. A frequent and very frustrating repair. I had machined stainless sheaves, much wider to fill in the gap and to have a much deeper groove. The rope never pulls out nor jams now, a huge improvement.

I welded the head of a socket bolt to the centre of the crank handle and now can use an electric drill to power them. With my heavy 230kg dinghy it is a big help. For yours, maybe less so.

I also rebuilt the internal gearbox with new tougher high end stainless gears and sealed ball bearings. I had a big wear problem. That reduced wear, friction and improved solidity.

Thanks; very useful comments! And thanks to others as well. I think that's a clear case for Dyneema and that's what I'm going to do


I had davits similar to yours (except electric) and I gave up on them. The Rube Goldberg gearboxes, clutches which didn't clutch -- truly an engineering horror show.

The new ones are much better, but they have one big flaw -- the fall jumping off the drum and getting wound up on the axle. I don't quite know what to do about that, but I am loathe to invest all the time and money you have with machining new sheaves etc. etc. Maybe I will just put some long screws in to catch the rope before it gets into the works.

Other than that, they are beautifully simple and foolproof and that's the way they should be. I don't want to spend my time maintaining and repairing davits -- there are plenty of other things to do around the boat.


As to the dinghy -- this is thread drift, but I am absolutely loving the lighter dinghy. It eliminates by dependency on the davits. I can get the dink single handed (!) up on to the foredeck, and I can deflate and stow it before ocean passages. It is far less stress on the davits when I'm using those, even if I leave the engine on. It's not as seaworthy or capacious as the old one (Avon Rover 340), but it's a RIB and it's acceptable for my purposes.

[poiu]

Originally Posted by Dockhead

The new ones are much better, but they have one big flaw -- the fall jumping off the drum and getting wound up on the axle. I don't quite know what to do about that, but I am loathe to invest all the time and money you have with machining new sheaves etc. etc. Maybe I will just put some long screws in to catch the rope before it gets into the works.

I'm sure you know that they are meant to be used with weights on the ends to maintain tension on the rope at all times. It is the lack of tension that can cause the rope to bounce out. I have a plate in the middle of the spool, which also helps do that job, though the rope looks like it can get around the sides if unlucky. It hasn't happened to me yet. I'm sure some bolts there would work fine too as you suggest.

I have thrown away the tensioning weights as part of a boat diet. I think they are a crazy dangerous wrecking ball and find I can manage fine without them by pulling gently on the rope on the rare occasion it goes slack. I have Wichard snap hooks on the ends (a perfect product for attaching the dinghy by the way), which is plenty enough weight.

[conachair]

Originally Posted by Dockhead

The new ones are much better, but they have one big flaw -- the fall jumping off the drum and getting wound up on the axle. I don't quite know what to do about that, but I am loathe to invest all the time and money you have with machining new sheaves etc. etc. Maybe I will just put some long screws in to catch the rope before it gets into the works.
.

Theatre pulleys/winch drums commonly have cable keeps fitted, say an M10 bolt with an oversize piece of seamless tube which can be adjusted so it just clears the sheave before tightening the bolt - might work if your cheekplates are big enough?

[barnakiel]

But I think if you forego the weights, a spectra cable could fly high and away in any reasonable wind. On many bigger boats the distance from the davit to the dinghy is at least 10'.

So you may still need these weights on a Spectra wire.

b.

[conachair]

Originally Posted by barnakiel

But I think if you forego the weights, a spectra cable could fly high and away in any reasonable wind. On many bigger boats the distance from the davit to the dinghy is at least 10'.

So you may still need these weights on a Spectra wire.

b.

2t swl shackle & boathook might be enough to do it. Dyneema doesn't have the spring like steel wire rope (esp stainless) has so you don't need all that weight to keep it on the drum.

Thinking about it more, before messing about with fitting cable keeps it would be worth trying it , with no spring the dyneema might sit on the drum fine without making a bid for freedom like steel wire rope does on a drum.

[poiu]

Originally Posted by barnakiel

But I think if you forego the weights, a spectra cable could fly high and away in any reasonable wind. On many bigger boats the distance from the davit to the dinghy is at least 10'.

So you may still need these weights on a Spectra wire.

b.

It is indeed about 10' to my davits and a couple of snap hooks control the dyneema rope very well even in strong wind. The wrecking ball weights that are normally used is total overkill and kill being the operative word. I think those heavy weights may be mainly needed to control stainless rope from tangling inside the davit mechanism. Dyneema is better behaved, so doesn't need the weights.

[Glacier Crews]

Talked with Nick Jackson just last week about this very thing. He said, "do not replace the wire unless you replace all the rollers. It's like pulling a piece of silk cloth across the sidewalk. The wire has caused numerous small abrasions on the rollers and every single one, even the ones you do not see or feel, will cut and abraide."

just shared information.

[poiu]

Originally Posted by Glacier Crews

Talked with Nick Jackson just last week about this very thing. He said, "do not replace the wire unless you replace all the rollers. It's like pulling a piece of silk cloth across the sidewalk. The wire has caused numerous small abrasions on the rollers and every single one, even the ones you do not see or feel, will cut and abraide."

just shared information.

There are no metal rollers in the Simpson davits and no parts will need replacing, but it is a good point to check for parts that could have got damaged and burred. That is just the flange of the drum. It is bronze and can be easily buffed smooth.

[Neziak]

Originally Posted by Dockhead

Thanks; very useful comments! And thanks to others as well. I think that's a clear case for Dyneema and that's what I'm going to do


I had davits similar to yours (except electric) and I gave up on them. The Rube Goldberg gearboxes, clutches which didn't clutch -- truly an engineering horror show.

The new ones are much better, but they have one big flaw -- the fall jumping off the drum and getting wound up on the axle. I don't quite know what to do about that, but I am loathe to invest all the time and money you have with machining new sheaves etc. etc. Maybe I will just put some long screws in to catch the rope before it gets into the works.

Other than that, they are beautifully simple and foolproof and that's the way they should be. I don't want to spend my time maintaining and repairing davits -- there are plenty of other things to do around the boat.


As to the dinghy -- this is thread drift, but I am absolutely loving the lighter dinghy. It eliminates by dependency on the davits. I can get the dink single handed (!) up on to the foredeck, and I can deflate and stow it before ocean passages. It is far less stress on the davits when I'm using those, even if I leave the engine on. It's not as seaworthy or capacious as the old one (Avon Rover 340), but it's a RIB and it's acceptable for my purposes.

Did you change the wire to dyneema in the end? If so, can you share your experience and what modifications you ended up making. I have a pair of Simpson S225 manual davits and thinking of doing the same.