Rigging Question -- Friction Device

[Dockhead]

I am rigging a tackle to raise my heavy transom platform in lieu of troublesome hydraulics, consisting of a low friction ring at one outside corner of the platform, a through-deck block (to lead the line through the transom behind the platform, and a through deck bush (to lead the line on up through the rail).

I would like to include some kind of friction device so that the platform can't fall sharply. There are all kinds of friction devices for climbers, but you have to hold those. Is there one which can be fixed mounted? Any tips?

[Suijin]

You might consider fabricating something similar to your basic boom brake along the run of the line...basically a takeoff on old school belaying gear. You could have it made out of stainless and welded to the rail or mounted somewhere along the run. Would basically be the top 3/4 of one of these:



This design gives you two "tension" settings depending on how you run the line. Benefits of this approach are no moving parts and easy and quick to remove the line from the device with the line still run.

[Kenomac]

Why not just fix the hydaulics? Or are you looking for more of an emergency fix when the hydraulics fail.

[Dockhead]

Originally Posted by Kenomac

Why not just fix the hydaulics? Or are you looking for more of an emergency fix when the hydraulics fail.

I just didn't like the hydraulics. It's overkill and inelegant, and completely unnecessary. First few years I had this boat this system vied for top place on the repair list along with the horrible electric davits I used to have. I was constantly fixing them while the crew had a great time in different exotic places

Part of the problem is just that the system was badly engineered. I could have re-engineered it -- stronger mounts, stops to prevent the rams from being overextended, etc. -- but why bother. Hang on -- I did do that, and I have the re-engineered parts on board, but before installing them, I realized that it's just simply stupid to open and close your transom platform with such a complex system, when a simple tackle will do it much more simply, elegantly, cheaply, and reliably. I have actually just been using a rope for the last few years, which works more or less OK, but a double purchase tackle led properly through the transom (partially copied from the Moody 49) will be just so much nicer.

[Dockhead]

Originally Posted by Suijin

You might consider fabricating something similar to your basic boom brake along the run of the line...basically a takeoff on old school belaying gear. You could have it made out of stainless and welded to the rail or mounted somewhere along the run. Would basically be the top 3/4 of one of these:



This design gives you two "tension" settings depending on how you run the line. Benefits of this approach are no moving parts and easy and quick to remove the line from the device with the line still run.

Thanks; that may be a hot tip. Trying now to visualize how they work . . .

[conachair]

Sketch of the system might help. One possible option could be to have a locking ratchet block as the final block before diverting down to a pair of willing hands, still need to pay the rope out, let go it will go bang, but the slightly serrated sheave acts as a brake so you can lower substantial loads under control.

[thinwater]

What type of line? Naked Dyneema, I assume, since you are using LFRs.

I've tested that devise as a boom brake and was not very impressed. I've used figure 8s uncountable thousands of times climbing. It would not be my choice for this.

Why not just use a cleat? With a few round turns, they are quite good at easing lines under tension, easy to adjust, and with the option of locking it off. Compact, fixed mounting. Pick a nice rounded design. Remember that cleating naked Dyneema requires a LOT of turns, so the cleat must be over sized a little.

[RaymondR]

Originally Posted by thinwater

Why not just use a cleat? With a few round turns, they are quite good at easing lines under tension, easy to adjust, and with the option of locking it off. Compact, fixed mounting. Pick a nice rounded design. Remember that cleating naked Dyneema requires a LOT of turns, so the cleat must be over sized a little.

Rope clutch and cleat are a good combination, the rope clutch is handy when you are hauling it up, the cleat safties it and allows you to ease it back down gently.

[thinwater]

The critical factor is rope-type.

Dockhead, help us out.

[Dockhead]

Originally Posted by thinwater

The critical factor is rope-type.

Dockhead, help us out.

8mm poly double braid. For comfortable handling.

I want the friction device to prevent the platform's accidentally being dropped. It's heavy, and that could break the holding mechanism.

[conachair]

Originally Posted by Dockhead

8mm poly double braid. For comfortable handling.

I want the friction device to prevent the platform's accidentally being dropped. It's heavy, and that could break the holding mechanism.

You can get commercial fixed rate descenders designed for rope rescue. https://www.heightec.com/product/rot...ion-descender/

[thinwater]

Originally Posted by Dockhead

8mm poly double braid. For comfortable handling.

I want the friction device to prevent the platform's accidentally being dropped. It's heavy, and that could break the holding mechanism.

I'm still thinking a horn cleat would be simple and reliable. Is if it is lifted by a tackle, a ratchet block should do. If it's a winch, the winch drum, of course.

Polyester DB is not going to run through LFR easily if there are 180 degree bends, and the rings need to be big.

[Dockhead]

Originally Posted by thinwater

I'm still thinking a horn cleat would be simple and reliable. Is if it is lifted by a tackle, a ratchet block should do. If it's a winch, the winch drum, of course.

Polyester DB is not going to run through LFR easily if there are 180 degree bends, and the rings need to be big.

A horn cleat is fine of course - provided the rope is actually on it. But we don't kneel to lower the platform. I'm just looking for a bit of safety against breaking it.

I've never used a ratchet block - maybe that would do it? A descender wouldn't work, would it? I think you have to hold on to it, no? What I would like would be something which could be fixed under the rail (or possibly above) which would impart a constant amount of friction on the line so that it couldn't run out suddenly if someone let it go. Does such a thing exist?

[TeddyDiver]

How about a simple spring or bungee to carry most of the weight?

[Dockhead]

Originally Posted by TeddyDiver

How about a simple spring or bungee to carry most of the weight?

Yes, I thought of putting a heavy spring at the anchor point of the line, and I will probably do that in any case. It's certainly at least a partial solution to the problem if the line has a good stop on it (stopper knot where it goes through the rail) exactly adjusted, and if the spring is heavy enough.

But a little friction on the line would be really nice -- so that you could just let the line go and nothing bad would happen -- the platform would just smoothly go down.