Dinghy Crane Pulley/Hook

I am not going to re-engineer/design my davit crane which satisfies all my present needs and requirements. I looked at Dyneema cord just to see how it compares to wire rope; gave up, too many numerical conversions. Dymeema is specified as working loads in kilonewtons, wire rope (at least as far as I got) is specified in breaking strength in pounds. Dyneema uses metric system that I wish was universal while the wire rope I found uses the English or Imperial system.

I have no doubt that Dymeema is equal or stronger than wire rope on a weight bases but because I didn't want to spend the time and effort making conversions I doubt it can compare to wire of equal diameter. This is as far as I intend to go on Dyneema use and applications vs wire rope of SS or galvanized steel rope.

foggysail said:

I am not going to re-engineer/design my davit crane which satisfies all my present needs and requirements. I looked at Dyneema cord just to see how it compares to wire rope; gave up, too many numerical conversions. Dymeema is specified as working loads in kilonewtons, wire rope (at least as far as I got) is specified in breaking strength in pounds. Dyneema uses metric system that I wish was universal while the wire rope I found uses the English or Imperial system.

I have no doubt that Dymeema is equal or stronger than wire rope on a weight bases but because I didn't want to spend the time and effort making conversions I doubt it can compare to wire of equal diameter. This is as far as I intend to go on Dyneema use and applications vs wire rope of SS or galvanized steel rope.

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Whatever.

But Dymeema, Spectra, Plasma or whatever is what you'll find being used more and more on newer winches.

And it out performs wire of an equal diameter. By a large margin.

foggysail said:

Capt.Bill-- I wish it was that simple. There is a limited space inside my crane for the winch so a larger drum needed for a line is prohibited. Another problem with line is the larger diameter will require a greater number of wraps on the drum.

The greater the diameter of the pulling drum resulting from wrap buildup changes the pull length/drum turn placing a greater load on the pulling motor. Wenches are popularly rated for the first wrap on the drum and the rating quickly diminishes on each succeeding wrap.

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You don't need a larger diameter line.

It's interesting that you continue to dismiss something without apparently doing any real research into the logical option.

But again, whatever and good luck.

Capt.Bill11 said:

Make your own using an anchor swivel?

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That was my original thought as well.
First impression was what you pictured was likely an anchor...Chain connector w/o the swivel feature made into the block you showed?

BIG ones weigh more...

You haven't said what's wrong with the one shown...
Is it yours or someone else's you want to copy?

This doesn't seem like rocket science...Lots of good suggestions worth pursuing.

If you want / need an EXACT copy just locate a machine shop and have them duplicate it and fork over some boat$ !!
[emoji164] [emoji106]

As Bill said a couple of posts up, you're making a huge mistake here. If you were to poll all of us you'd probably find that we have all converted our SS winch cable to Dyneema as the opportunity arose. The pro's just out weigh the negatives. Do yourself a favor and look at it again.

...I doubt it can compare to wire of equal diameter...

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Everything I have found says that the Dyneema is stronger for the same diameter.

3/16" ss aircraft cable (7x19) has a breaking strength of ~3,600 lbs to 4,200 lbs based on the manufacturers data that I have looked at.

3/16" Dyneema (12 strand) has a minimum breaking strength of ~4,700 lbs to ~6,500 lbs based on the manufacturers data.


The Dyneema is great stuff IMHO.

My wench is not broken and I have no intention to "fix" it. I have too many worthy problems that need attention without seeking additional adventures

You certainly don't need to change from wire to rope. However, when you get to the point when you want to replace the wire due to wear, age, rust etc... then you owe it to yourself to consider dyneema.

This thread does remind me that I should consider replacing the dyneema line on my own winch. The original owner never used the crane on his boat as near as I can tell. So the dyneema line has sat inside the crane for 7 years with very little use. The crane also had a cover during that time so the dyneema was protected from UV.

Steelhead Marine, the maker of my crane, recommends replacing the line every 5-6 years I believe. Probably a good idea even if the crane has only been using a dozen or so times.

dhays said:

...Steelhead Marine, the maker of my crane, recommends replacing the line every 5-6 years I believe...

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Thanks for that. I've been looking for the replacement frequency.

Mike,
This is what my rig looks like, and yes we use Dyneema. Our Dink is close to 700 lbs. so we also added another single block to reduce the work on the winch. Hope it helps.

Not sure it helps much but we used to have one of these on our Selene. After we replaced all the stainless fittings and wires on the boom lift, I tried to find a similar matching block. I did find one. It was made in France but was pretty expensive. We ended up doing similar to what others have suggested. Having had one catastrophic failure of a stainless shackle on the boom lift, I figured it was better to see the components fully if they were used to lift several hundred pounds overhead. The original and the replacement French block enclosed the fittings such that it was not possible to see corrosion at the internal connections.

Bacchus said:

That was my original thought as well.
First impression was what you pictured was likely an anchor...Chain connector w/o the swivel feature made into the block you showed?

BIG ones weigh more...

You haven't said what's wrong with the one shown...
Is it yours or someone else's you want to copy?

This doesn't seem like rocket science...Lots of good suggestions worth pursuing.

If you want / need an EXACT copy just locate a machine shop and have them duplicate it and fork over some boat$ !!
[emoji164] [emoji106]

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It's a friend's. He has the same crane, but a different hook arrangement. I'm going to try to make something up that will be similar. Or I'll use a lighter weight pulley/hook that folks have recommended. Either way, I'm going with dyneema to replace the existing wire.

Crusty Chief said:

Mike,

This is what my rig looks like, and yes we use Dyneema. Our Dink is close to 700 lbs. so we also added another single block to reduce the work on the winch. Hope it helps.

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Thanks Chief. I will probably end up with something that looks very similar.

Someone pointed out that adding a block (pulley) doubles the time required to lift the dinghy. Do you find that to be a problem? Is the benefit of reducing the work on the winch worth the cost?

MikeM said:

Thanks Chief. I will probably end up with something that looks very similar.

Someone pointed out that adding a block (pulley) doubles the time required to lift the dinghy. Do you find that to be a problem? Is the benefit of reducing the work on the winch worth the cost?

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It takes a few more seconds to deploy or recover. The winches dont have to work as hard, and the snatch load is less stressful on the boom rigging. We picked up the 2 blocks from Columbia Marine in Portland, they were almost new and about 25% of the cost of new ones.

When we installed these, the New Dyneema and rebuilt the winches, I also incorporated small remote control devices from the 4 wheel community. All of these made Launching and recovering the dink so much safer and easier.

Crusty Chief said:

It takes a few more seconds to deploy or recover. The winches dont have to work as hard, and the snatch load is less stressful on the boom rigging. We picked up the 2 blocks from Columbia Marine in Portland, they were almost new and about 25% of the cost of new ones.



When we installed these, the New Dyneema and rebuilt the winches, I also incorporated small remote control devices from the 4 wheel community. All of these made Launching and recovering the dink so much safer and easier.

Click to expand...

[emoji106]

MikeM said:

Thanks Chief. I will probably end up with something that looks very similar.

Someone pointed out that adding a block (pulley) doubles the time required to lift the dinghy. Do you find that to be a problem? Is the benefit of reducing the work on the winch worth the cost?

Click to expand...

If you are adding a block, you may want to check to be sure the crane will handle the extra length of winch line required.

dhays said:

If you are adding a block, you may want to check to be sure the crane will handle the extra length of winch line required.

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We used it all last season and it worked great. The Dyneema line takes up less space on the drum then the Cable. Another ++ for Dyneema.

If you add a pulley, the lifting speed will be halved. This is not a big deal, but is not desirable in a rolly anchorage. We lift 12 feet (25-30 seconds I think). Sometimes we have to wait for a wake to pass us so that we have calmer water during a a lift. If you double the lift time, you will have more chance for the dinghy to swing into something.

We switched to Dynema 3 years ago. It is terrific and we found we do not need the head ache ball on the cable. The weight of the hook is sufficient to let the cable pay out.

Dyneema is simple to splice Just be sure to use the double Brummel lock splice. There are other splices but they are not as secure.

Do not try to tie knots in dyneema it is too slippery. You must splice it but it is simple and actually qqite fun.

tadhana said:

If you add a pulley, the lifting speed will be halved. This is not a big deal, but is not desirable in a rolly anchorage. We lift 12 feet (25-30 seconds I think). Sometimes we have to wait for a wake to pass us so that we have calmer water during a a lift. If you double the lift time, you will have more chance for the dinghy to swing into something.



We switched to Dynema 3 years ago. It is terrific and we found we do not need the head ache ball on the cable. The weight of the hook is sufficient to let the cable pay out.



Dyneema is simple to splice Just be sure to use the double Brummel lock splice. There are other splices but they are not as secure.



Do not try to tie knots in dyneema it is too slippery. You must splice it but it is simple and actually qqite fun.

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Tom, How do you secure the Dyneema to the drum?

Mike, I wish I could take it apart and take a picture, that might be easier than describing it. I'll do my best to describe it as well as I can remember it. It has been a few years now since I did it. Your drum may be different. The hoist manufacturer has two cautions. First, spool no more line onto the hoist than is necessary. If you have too much line. as the spool gets larger the hoist motor looses mechanical advantage. But, be sure when the cable is fully out there are at least 4 turns remaining on the drum. So we spliced the hook on the cable and fitted the cable to the crane to be sure we had the length of rope required.

I used electrical shrink tubing. The core of the hoist drum has a 5/16 hole . To dead end the cable it is passed through the hole. I installed the cable and pulled 8" past where it needed it to end. To provide chafe protection where the cable passed through the hole in the central core, I put a 3 or 4" section of shrink wrap tubing over the 3/16 dyneema to provide chafe protection leaving about a 4" tail . I tied a figure 8 knot in the rope, I put a 1-2" length of 1/4 shrink tube on the tail of the tail after the knot and heated it to shrink it and glue it to the rope so that the knot could not slide off the end. Then I slid the 4" section of shrink tubing snug against the knot and heated it to glue it into place. Then I put a 1" piece of larger shrink tubing onto the knot and shrank it to lock the knot. Then I pulled the cable so that the knot was snug inside the center of the drum. Where the cable contacted the hole in the drum, it was now protected from chafe by the shrink tubing.

Mike, as a bit of background and perspective. Our hoist motor came from Atkins and Hoyle. They told us it was a Rule Industries boat trailer winch. Our dinghy is a 130# rib with a 9.9hp 4 stroke. I would imagine the total boat, engine, gear weight is 250-275#. We cruise full time, and with a dog, so the hoist gets a lot of use. Over the past 7 full years of cruising with this rig, I would guess the dinghy has gone up and down 500+/- times.