Dyneema for lifting the keel?

[ash2020]

My Hunter Medina has a lifting keel, weighing in at 300lb. At the moment it has a steel wire and winch for lifting. However, when the keel is down the bottom pulley and shackle are in the water leading to the wire being quite corroded. I could disconnect the shackle each time I lower the keel but as it's underwater it's a bit fiddly. If I were to replace the wire with maybe 8mm Dyneema, would it mind being submerged all the time? Does it deteriorate? And would an eye splice be strong enough?

 

[Chiara’s slave]

My Hunter Medina has a lifting keel, weighing in at 300lb. At the moment it has a steel wire and winch for lifting. However, when the keel is down the bottom pulley and shackle are in the water leading to the wire being quite corroded. I could disconnect the shackle each time I lower the keel but as it's underwater it's a bit fiddly. If I were to replace the wire with maybe 8mm Dyneema, would it mind being submerged all the time? Does it deteriorate? And would an eye splice be strong enough?

Admittedly our ‘keel’ weighs only 35kg, and it’s the downhaul that takes all the strain, drag, and the occasional touch on the bottom. But ours has dyneema downhaul and uphaul, with eye splices. No deterioration, and a properly executed eye splice retains at least 80% of the strength of the line. 8mm dyneema, you could hoist your boat, and probably your car too, into the air simultaneously. If your eye splice retained 20% it would be adequate

 

[ridgy]

I have a lifting keel, 1000kg and am planning to replace the current steel cable with dyneema over the winter:

ropelocker.co.uk - Synthetic Winch Rope Dyneema/HMPE

 

[Chiara’s slave]

I have a lifting keel, 1000kg and am planning to replace the current steel cable with dyneema over the winter:

ropelocker.co.uk - Synthetic Winch Rope Dyneema/HMPE

That stuff is about mid range for strength. Adequate as safety line for elephants and small to medium whales. Very suitable for your purpose.

 

[Poecheng]

My Southerly 38's keel apparently weighs 1700kg (not including the cast ballast plate) and is lifted by a Spectra line - looks about 20mm to me.

I would have thought an 8mm dyneema line would be able to lift your boat !. Cannot see how it can be harmed by water and you could check it all the time anyway and cheap and easy to replace. I doubt you would ever need to do it though.

 

[ash2020]

I have a lifting keel, 1000kg and am planning to replace the current steel cable with dyneema over the winter:

ropelocker.co.uk - Synthetic Winch Rope Dyneema/HMPE

Thanks for the link. I'll probably use 6mm and I can use spare bits to make soft shackles, which I'm a recent convert to, I love'em.

 

[ash2020]

My Southerly 38's keel apparently weighs 1700kg (not including the cast ballast plate) and is lifted by a Spectra line - looks about 20mm to me.

I would have thought an 8mm dyneema line would be able to lift your boat !. Cannot see how it can be harmed by water and you could check it all the time anyway and cheap and easy to replace. I doubt you would ever need to do it though.

Yeah, much too big. I'll use 6mm. Only because it's easy to handle.

 

[ash2020]

Admittedly our ‘keel’ weighs only 35kg, and it’s the downhaul that takes all the strain, drag, and the occasional touch on the bottom. But ours has dyneema downhaul and uphaul, with eye splices. No deterioration, and a properly executed eye splice retains at least 80% of the strength of the line. 8mm dyneema, you could hoist your boat, and probably your car too, into the air simultaneously. If your eye splice retained 20% it would be adequate

I hope I can do a better eye splice than that!

 

[Poecheng]

Yeah, much too big. I'll use 6mm. Only because it's easy to handle.

I don't think it will be too big, as in too imposing, it is just that it is incredibly strong.
Depends what space you have and whether you might ever have to use your hands. I have a halyard split with 8mm and 6mm 'tail' and the 6mm would be very thin to handle under pressure without a winch.
However, if you ever needed to pull hard on either with your hands, there is the Karver Jaws thing, which is very well made: KJH - Karver systems

 

[Chiara’s slave]

My Southerly 38's keel apparently weighs 1700kg (not including the cast ballast plate) and is lifted by a Spectra line - looks about 20mm to me.

I would have thought an 8mm dyneema line would be able to lift your boat !. Cannot see how it can be harmed by water and you could check it all the time anyway and cheap and easy to replace. I doubt you would ever need to do it though.

At 1700kg you have a winch, or other mechanism for lifting? I’d have thought that 8mm would be enough for you too. Well inside the SWL.

 

[ash2020]

I don't think it will be too big, as in too imposing, it is just that it is incredibly strong.
Depends what space you have and whether you might ever have to use your hands. I have a halyard split with 8mm and 6mm 'tail' and the 6mm would be very thin to handle under pressure without a winch.
However, if you ever needed to pull hard on either with your hands, there is the Karver Jaws thing, which is very well made: KJH - Karver systems

It has a winch and a 3:1 pulley system. I could never do anything to it by hand. I loved the Karver Jaws - until I saw the price!

 

[langstonelayabout]

I changed from stainless and galvanised steel wire to Dyneema on my E-Boat years ago. It proved to be a great success
The E-Boat has a 300kg keel and I changed from wire to 6mm Dyneema line. If I went back to a lift keel boat this is one of the forest improvements that I would make. 100%!recommended.

 

[ash2020]

I changed from stainless and galvanised steel wire to Dyneema on my E-Boat years ago. It proved to be a great success
The E-Boat has a 300kg keel and I changed from wire to 6mm Dyneema line. If I went back to a lift keel boat this is one of the forest improvements that I would make. 100%!recommended.

Thanks for that. It will be one of my first winter jobs.

 

[thinwater]

Thanks for the link. I'll probably use 6mm and I can use spare bits to make soft shackles, which I'm a recent convert to, I love'em.

The only downside is chafe. Dyneema is not very resistant to sharp metal, no matter what you may hear. You mentioned corrosion. Make VERY sure there are no rough edges on pulleys or guides. A steel thimble, of course. I do not think you'll like a soft shackle on a sharp/worn eye at the keel end. It will wear.

I'm not anti-Dyneema or anti-soft shackle. I use pleanty of both. But I have learned to follow the rules.

 

[Poecheng]

At 1700kg you have a winch, or other mechanism for lifting? I’d have thought that 8mm would be enough for you too. Well inside the SWL.

Massive electro-hydraulic ram rather than a winch.
TBH, I read what you had put about 8mm dyneema for lifting my keel and thought you were crackers as I know what is actually used for the keel raising mechanism and how small 8mm feels on this boat when I swapped out the jib halyard this year.
I have just checked the breaking strain of 8mm and it is over 5,000kg !!! I am sure that, as a swing keel (that can if needs be swing back and then drop down), its engineering factors in shock loads but Marlow 18mm SK78 has a minumum break load of 31,000kg. I knew this stuff was strong but the entire boat is only about 10t so one 18mm dyneema could lift a couple of Southerly 38s without breaking into a sweat? Bizarre stuff

 

[William_H]

I have fitted dyneema to my trailer winch just 4mm pulls the whole boat up on to trailer no problem in lieu of 5mm galvanised wire. 8mm would be huge for keel unless it is 8mm with polyester cover. So go for bare dyneema. ole'will

 

[Ian_Edwards]

As per Poecheng, my Southerly 46RS has a Dyneema pennant to lift the keel.
2,500kg using hydraulic ram and electro hydraulic pump.
The way the system is designed, the ram works with a 2:1 disadvantage. This is to give sufficient stroke to raise the keel, which is about 2.5m long.
The draft of the boat is 3.3m with the keel down, about 0.8m with the keel up. the mechanical disadvantage means the rope is loaded to 5,000kg plus friction.
It's a massive and expensive dyneema rope.
The system doesn't use splices or shackles. The dyneema is wrapped 3 times around a big SS bar, and the tail clamped between a substantial flat bar and a solid base which is bolted to the hull. A bit agricultural but it works and is easy to adjust.
To answer the original question, yes, you can use dyneema to raise a lifting keel, it's commonly used on bigger boats, and it doesn't rot.

However, there are 2 problems; it may be difficult to in incorporating a splice, you need a long buried section to get the strength in the splice, which may give problems with any turning blocks (because the rope is thicker), and, although Dyneema doesn't stretch that much, it does "settle in", when first put under load. This happens when the air is squeezed out between the stand of dyneema, and the rope turns from something flexible into a solid rod of high density polyurethane.