Kato Davit Hoist Block -Line Lashing

[jefndeb]

Hello,

I was thinking to replace the davit hoist line with a new set and I noticed this is how they connected it to the end block.

Is this a good way to do the new line as well or is there something better.

Thanks for your suggestions...

[Off Trail]

I have the same davits. Love the davits but don't like this attachment method.. however the forces are pretty small here. I think they're trying to allow a very close "chock-a-block" hoist and not wanting the long tail of an eye splice.

There are more expert knot folks than me here, but FWIW if replacing I would use a buntline or halyard hitch.

[tkeithlu]

You could substitute a bowline or even two half hitches (AKA a clove hitch on a rope). I'm hoping that the double seizure they've used was done with nylon cord. The seizures have the advantage of very little loss of stength due to the knot and of fitting neatly into a very small space. They have the disadvantage of not being the strongest method around.

[Breaking Waves]

Originally Posted by jefndeb

Is this a good way to do the new line as well or is there something better.

That is a neat and compact way to do it, and it looks like it has held up just fine, so certainly no problem to just do it again. BTW if you redo this method, there are (obviously) two whippings in series - jfyi the one closer to the tail end (away from the eye) takes a lot more load than the one right next to the eye. So you want to the one next to the tail end first, make it big and strong and tight and perfect, then do the one nearer the eye second and ofc do as good a job as you can but it might be a little harder to get perfect.

Sewing the eye could be (if done well) stronger and equally neat and compact.

A knot would be quickly a bit less work but bulkier.

net net, it does not look like there is much load on this connection, so really any of the options are just fine and it is more of an aesthetic choice. If this was a high load application and it had to be short then sewing would likely (if well done) be the preferred approach.

[Nicholson58]

The cover is a bit fuzzy but intact. Why change? The splice see no more load than the end you pull and it does not look stressed.

[s/v Jedi]

Originally Posted by jefndeb

Hello,

I was thinking to replace the davit hoist line with a new set and I noticed this is how they connected it to the end block.

Is this a good way to do the new line as well or is there something better.

Thanks for your suggestions...

These are two stitched seizings and it is the best way for this application. The only failures I’ve seen on these is when the thread fails due to UV deterioration.

[Clivevon]

To the OP, the double seizings look to have done their job well. They look to me like a pair of shear lashings - you would need to bury or stitch the start & finish clove hitches for security. You could improve on the setup by using a thimble in the loop (to avoid chafe & increase the radius of the loop) & by wrapping some rubber self amalgamating tape over the lashings to protect them against UV. If it was me I would leave the end of the rope exposed so I could see if the lashing was ever slipping.

On a wider point, someone said that using the lashings avoided the loss of strength caused by a knot. I am wondering if that is true - doesn't seem so to me because the rope is still bent tightly around the shackle pin, so it still has uneven stresses across its width which are what weakens the rope. I was interested to find these sites:
https://www.sciencefocus.com/science...weaken-a-rope/ & also https://www.edelrid.de/en/knowledge-...s-by-knots.php

Can't see why the same issue wouldn't apply to an eye splice also. Seems to me the safe assumption is that any tight bend in a rope is going to reduce its strength by say 50% & allow a correspondingly suitable safe margin.

[adjo]

I would be more concerned about the SS pins in the block than the line.
The staining is significant.

[BillKny]

I have done the same kind of attachment in a lot of permenent attachment points, with the only exception that I take one half hitch, and then a single lashing.

Under low loads the lashing keeps everything connected, and when the loads rise, the half hitch takes most of the load. Never had one of these fail, even in slippery high tech line with very high loads where knots can be difficult to keep together.

I know it offends some crusty salts, but it is effective and very functional, and very compact, which is sometimes very important. Knots in some places, lashings in others, and splices in yet others. It Depends. It ALWAYS Depends.

[jefndeb]

Thanks for all the comments, do you think this was a wax based thread used?

[s/v Jedi]

Originally Posted by jefndeb

Thanks for all the comments, do you think this was a wax based thread used?

Hard to tell after so much time, but I think it wasn’t. I use waxed polyester thread in V346 gauge or one of the colorful equivalents from Marlow.

About old salts not liking this: they should because this is old school and time proven.

[s/v Jedi]

Originally Posted by jefndeb

Thanks for all the comments, do you think this was a wax based thread used?

Actually, taking a close look, it looks the same as the strands of the outer braided cover, so they may have used that…

[BillKny]

Originally Posted by s/v Jedi

Hard to tell after so much time, but I think it wasn’t. I use waxed polyester thread in V346 gauge or one of the colorful equivalents from Marlow.

About old salts not liking this: they should because this is old school and time proven.

I very specifically avoided saying that “old salts” were offended by lashings! The only adjective I used was “crusty.”

Specifically the ones thinking about how they spent a month learning to tie a bowline, and now, damn it, everybody should use one, everywhere!

[Kd9truck]

Originally Posted by Clivevon

To the OP, the double seizings look to have done their job well. They look to me like a pair of shear lashings - you would need to bury or stitch the start & finish clove hitches for security. You could improve on the setup by using a thimble in the loop (to avoid chafe & increase the radius of the loop) & by wrapping some rubber self amalgamating tape over the lashings to protect them against UV. If it was me I would leave the end of the rope exposed so I could see if the lashing was ever slipping.

On a wider point, someone said that using the lashings avoided the loss of strength caused by a knot. I am wondering if that is true - doesn't seem so to me because the rope is still bent tightly around the shackle pin, so it still has uneven stresses across its width which are what weakens the rope. I was interested to find these sites:
https://www.sciencefocus.com/science...weaken-a-rope/ & also https://www.edelrid.de/en/knowledge-...s-by-knots.php

Can't see why the same issue wouldn't apply to an eye splice also. Seems to me the safe assumption is that any tight bend in a rope is going to reduce its strength by say 50% & allow a correspondingly suitable safe margin.

Great point! I believe the pulley reduces the load by half, the pulleys size is meant to distribute the load forces evenly across its radius. So a knot in any system becomes its weakest point, how ever lashing done correctly distributes the load along the length of rope and it’s strength is determined by the type and length of lashing.
Given the same task, as a rule of thumb, I would sew though the sides of the rope to incorporate both the sheath and the core then lash the length to cover the buried portion (if it’s that type of line).
I worked as a supervisor testing rope among other things in the 2nd largest fire service municipality in the world we regularly tested rope on a digitally calibrated machine that exerted forces up to 15,000. PSI. Cheers