Davit Blocks are Twisting

[zboss]

Hi,

We have a davit system with a triple block set on one side and a double block set on the other side. The side with the double block pulls up the dinghy just fine but the triple block seems to always have a twist to it that only becomes more pronounced when we try and raise the dinghy. Finally, it binds and the lines get mangled.

When I move the blocks by hand, the swivels and the sheaves all seem to spin fine, but when I release them, they just swivel back into the twisted position.

I was thinking that the lines are just old but I don't want to go out and buy more line unnecessarily.

Any ideas?

- z

[Paperbird]

I have the same problem. Comes from the line getting twisted as the dink is lowered. There's enough weight to pull the twists right thru the blocks. Then when raising the dink, the twists jam the blocks.

Couple things that help.

- prevent twists by using a 'figure 8' coil instead of a 'round' coil
- occasionally raise the blocks all the way without the dink, then untwist the line and let it pay out smoothly back down to the water. That will get rid of the twists already in the line

[montenido]

Z,

I just installed davits with the 6:1 blocks on both sides. I had to look up how to thread the rope through and I found a diagram on Harken's website I think. Anyway, unlike the 4:1 set up. 6:1 requires the bottom blocks to be at 90 degrees to the top ones. I'll see if I can find the link for you. It takes a little work, because you have to run all that line through.

Cheers, Bill

[ryon]

Originally Posted by zboss

Hi,

We have a davit system with a triple block set on one side and a double block set on the other side. The side with the double block pulls up the dinghy just fine but the triple block seems to always have a twist to it that only becomes more pronounced when we try and raise the dinghy. Finally, it binds and the lines get mangled.

When I move the blocks by hand, the swivels and the sheaves all seem to spin fine, but when I release them, they just swivel back into the twisted position.

I was thinking that the lines are just old but I don't want to go out and buy more line unnecessarily.

Any ideas?

- z

Has it capsized? This is really common on dinghy blocks, when someone forgets to choke the lower block when handling. Can you draw it up two-blocked correctly?

[Hudson Force]

I would assume that, since the triple block side uses far more line, the amount of twist is increaing as you coil the at lifting. Over time I would expect the same method of coiling the hauled line would produce a twist there too. I am aware of this tendency to develop a twist in my davit lines too. I continue to coil my lines in a manner that puts in a twist, but when I detach my lift lines after lowering my dinghy I always spin the twist back out until I see my blocks hanging aligned in the air. The other option is to raise the line without repeating the coils in the same direction or to produce the "figure eight" coil as suggested above.

[zboss]

Originally Posted by ryon

Has it capsized? This is really common on dinghy blocks, when someone forgets to choke the lower block when handling. Can you draw it up two-blocked correctly?

Yes, the two block comes up just fine.

[ryon]

Originally Posted by zboss

Yes, the two block comes up just fine.

Sorry if you already know this, but two-blocking is when the two blocks come together so that they cannot be hauled any tighter. Do the lines correspond with their mates in the upper and lower blocks? It seems that you've answered that they are fine, but maybe you are referring to the double block being fine as opposed to the treble block and tackle which you are having trouble with? Is this where it binds and the lines get mangled? If so, it's capsized and should be straightened out.

Another twist would be as the blocks separate and the tackle lengthens. The blocks twist on their pendants as the load is lowered until there is so much chafing that they need to be overhauled (the individual lines hauled by hand). But you say it twists as the tackle is hauled, not slacked, so...

Is it the rope itself in the blocks that is twisting? I can imagine that the sheaves could push the lay of a very relaxed rope until it binds. But that should be obvious.

Aha! Maybe I have it. Are you using three-stranded line? All of the smallboat falls I can recall use woven. Maybe that'll do it!

[Sailor Doug]

I have a double a single block on the bow end and a double block on the other. Both lines are lead through sheet stoppers to winches, very easy to lift. After 12 hauls the line is twisting so bad the single block end needs help to go down. Pulling the line out and un twisting it is the only solution I have found. Sure would like a better answer.

[zboss]

Originally Posted by Sailor Doug

I have a double a single block on the bow end and a double block on the other. Both lines are lead through sheet stoppers to winches, very easy to lift. After 12 hauls the line is twisting so bad the single block end needs help to go down. Pulling the line out and un twisting it is the only solution I have found. Sure would like a better answer.

I am wondering if a slippery synthetic line might be better for this type of application.

[zboss]

Originally Posted by ryon

Sorry if you already know this, but two-blocking is when the two blocks come together so that they cannot be hauled any tighter.

no... Did not know that!

Originally Posted by ryon

Do the lines correspond with their mates in the upper and lower blocks? It seems that you've answered that they are fine, but maybe you are referring to the double block being fine as opposed to the treble block and tackle which you are having trouble with?

Yes.. By the time the dinghy gets 1/3 of the way up, the line/blocks on the triple block side are already twisted. I can't lower them without untangling them. I was just on the boat... Should have taken pics.

Originally Posted by ryon

Is this where it binds and the lines get mangled? If so, it's capsized and should be straightened out.

Another twist would be as the blocks separate and the tackle lengthens. The blocks twist on their pendants as the load is lowered until there is so much chafing that they need to be overhauled (the individual lines hauled by hand). But you say it twists as the tackle is hauled, not slacked, so...

Is it the rope itself in the blocks that is twisting? I can imagine that the sheaves could push the lay of a very relaxed rope until it binds. But that should be obvious.

Aha! Maybe I have it. Are you using three-stranded line? All of the smallboat falls I can recall use woven. Maybe that'll do it!

The boat came with the line in the davits. It may very well be... I will look when I get back to the vessel.

[capbillh]

The twist occurs on all my double braided lines including the main sheet so I do a double loop/figure eight that helps.

[RaymondR]

You generally do not need swivels on the blocks used on davits if there are for and aft lifts. Use braided lines and lock the swivels so that the blocks are prevented from turning and allowing the lines to twist.

[Hudson Force]

This photo, though the blocks are partially obscured by the boarding ladder, shows these blocks on swivels.

I think that the line will be able to become twisted with or without the blocks on swivels. The twists originate with the line in your hands as it is raised and coiled. You can either change the method by which you hoist the line or remove the twist each time you lower and detach the dinghy. When I'm standing in my dinghy and the lower block is removed from the dinghy and hanging free, it will not hang in alignment with a twist. It's a quick task to spin the twist out of the line at this time.

[thinwater]

Originally Posted by RaymondR

You generally do not need swivels on the blocks used on davits if there are for and aft lifts. Use braided lines and lock the swivels so that the blocks are prevented from turning and allowing the lines to twist.

Bingo!

One of my personal peves is the number of swivel blocks installed where they are not needed. Sure, they self-align with new line, but in time tangles happen. Sure, you can coil differently and use the correct line, but 80% of the time getting rid of the damn swivel is simpler. I find very few applications where a non-swivel block will not due if possitioned correctly; there is enough swivel inherant in the shackle.