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Old 02-01-2014, 03:26   #121
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Quote:
Originally Posted by JonJo
Correct me if I'm wrong, again.

But a 10hp engine with a 'sized' prop is said to produce about 100kg of thrust, 20hp 200kg etc. 2 x 20hp 400kg.

We put our load cell on our chain once and measured the thrust, in reverse, 2 x 3 bladed Volvo props (sized for 20hp Volvos). It was very crude and we simply tried it and did not get very sophisticated (we did not not put on a snubber).

Loads at about 2,800 revs 350kg - but the load oscillated. So some of our 350kg might have been momentum. The yacht would move back, to 350kg and then moved forward, then back, then forward - we did not have a sustained 350kg (and 350kg is about the load on a anchor chain at 30/35knots at 7:1 scope for a 38'cat or 45' mono). I would have thought this oscillation greater with a full snubber attached and much of the reverse load 'stored' in the snubber and thus not transferred to the anchor (which is the other reason for not setting with the snubber on).

If you back up with snubber attached the snubber stretches, stores energy, some of the energy is also stored in the catenary - some of this is transferred to the anchor (but not much as its pretty transitory and an anchor takes 'time' to set (see Mantus' videos - its a slow process) but the yacht is not fixed and much will be transferred to the yacht, moving it forward. Consequently the power set with snubber - I have doubts as to effectiveness cf without snubber.

If our anchor does not set at 3:1 (which would be very unusual) we know its a difficult bottom. We might then move, easier if you have no snubber attached and only 25m deployed than 50m deployed. We would rather move, maybe not far, in the hope of finding something better. I'd rather know its difficult, on the 3:1 scope, than assume its a good hold having set at 7:1. One reason a full 50m deployment is not popular, for us, - if we need to move is that with a shallow chain locker we can only retrieve about 30m at a time, then need knock the tower over. I'd rather spend 30 minutes on the bow and get it right.

I have heard of people who set their anchor, put the engine(s) into reverse and drive hard back using a 'power' stop to set the anchor. We have never done this - we set and slowly increase the revs. As mentioned we can tell if the anchor is set from feel of the chain (and looking at transits and later GPS). But if the chain 'rattles' - we have an issue (maybe 5/16th inch chain is more sensitive to feel than 1/2 inch?)

Attaching a bridle on many cats is not difficult - its just a bit fiddly. The main issue is that the hook needs to be applied under the trampoline which usually means one handed (because there is only room to get one hand through whatever small aperture there is (the hook needs to be also released one handed). Consequently the Witchard hook or any hook with a gate is very difficult. But I see many monos with fold over bow rollers (common on Hanses) and chain hook attachment is well forward when the bow roller is folded out and would be best (easiest) done one handed - so any gated chain hook would need 2 hands on some monos.

But with a common 1m draft, with mini keels, having a fathom (2m) of chain between bow roller and hook is easy. In fact for us 2m would not be enough in a decent blow as the snubbers will stretch more than that.

I do not see that our practice is peculiar to a cat, except we have a bridle not a single line. Many bow arrangements with furlers, bow rollers on almost a sprit etc mean attaching a hook is a bit of a balancing act (or in our case lying on the tramp with one hand through a small hole). Hooks with gates seem overly fiddly (and unnecessary) if you have that fathom, or more, of chain providing the attachment. But havng the snubber so long that it touches the seabed seems, also, unnecessary if you have 10m of deck along which you could run the snubber.

Proof tested standard steel chain hooks are cheap and for us work (though we have used identical design AISI 316L stainless and much more expensive hooks).

But here - Snubbers, long, are like hens teeth. So for most it is simply not an issue.

Jonathan
I do it like JonJo. No snubber, and 3:1 scope while setting. Snubber, more scope make it much harder to feel what the anchor is doing in the bottom because of more elasticity/catenary. Gradually increasing revs to work the anchor into the seabed, culminating with a couple of minutes at redline (also blows carbon out of the engine after futzing around at low revs). If the anchor does not set at 3:1, then I move. Maybe there are some situations where it would hold at 5:1 where it wouldn't hold at 3:1, but seems to me that would be rare and marginal, so I prefer to just try a different spot.

Like Erstarzinger, I find transits to be as important as what you feel. Besides transits, I look at the plotter on max zoom. SOG suddenly going to 0.0 is a good sign of anchor setting. Then you can see the hard defined arc of a boat swinging around a well set anchor. The total of all these clues, and also including the feel of the taught chain with no rattling, will give a very clear picture of whether the anchor is solidly set or not. Only after all that, I let out final scope, attach snubber, and make cocktails.
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Old 02-01-2014, 09:13   #122
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Re: Mantus Chain Hook

Wow! All these numbers are making my head spin..Maybe I should have spent more time in math class!!
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Old 02-01-2014, 10:20   #123
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Re: Mantus chain hook

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Originally Posted by Delfin View Post
Starting to understand why you post what you post.

I am listening to the Baylor game so don't take the time to draw a picture, but.....

In a right triangle, if a = .5, b = .372, than c must necessarily = .62. So, a soft shackle made of line that is 50% of .62 inches, a.k.a. 5/16", will fit just fine between the links of 5/16" chain, and have a breaking strength greater than the chain.
A 5/16 Soft Shackle at a .550 finish diameter, may be a bit much to stuff through the 5/16 G4 chain link opening.
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Old 02-01-2014, 10:59   #124
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Re: Mantus chain hook

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Originally Posted by Cotemar View Post
A 5/16 Soft Shackle at a .550 finish diameter, may be a bit much to stuff through the 5/16 G4 chain link opening.
Were a soft shackle not soft as your drawing suggests, quite true. It's not, so it feeds through. Give it a try if reality is your thing. 1/4", better and at 8,000# minimal tensile strength likely plenty strong enough.
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Old 02-01-2014, 11:24   #125
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Re: Mantus chain hook

Quote:
Originally Posted by Delfin View Post
Were a soft shackle not soft as your drawing suggests, quite true. It's not, so it feeds through. Give it a try if reality is your thing. 1/4", better and at 8,000# minimal tensile strength likely plenty strong enough.
I do know that a 3/16" soft shackle doesn't fit 1/4" G4 chain; I have to go to 1/8", which is cutting it a little thin. As Cotemar explained, G4 chain is tight between the links.
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Old 02-01-2014, 11:47   #126
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Re: Mantus chain hook

Quote:
Originally Posted by Delfin View Post
Were a soft shackle not soft as your drawing suggests, quite true. It's not, so it feeds through. Give it a try if reality is your thing. 1/4", better and at 8,000# minimal tensile strength likely plenty strong enough.
I had tried putting a 1/4 Soft Shackle and a 5/16 Soft Shackle through a 5/16 G4 chain this summer with no luck, But if you say it works I will dig up my piece of 5/16 G4 chain tonight and see if I can give it another go on the 1/4 and 5/16 Soft Shackles.
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Old 02-01-2014, 12:10   #127
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Re: Mantus chain hook

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Originally Posted by thinwater View Post
I do know that a 3/16" soft shackle doesn't fit 1/4" G4 chain; I have to go to 1/8", which is cutting it a little thin. As Cotemar explained, G4 chain is tight between the links.
You can jump up one size on your Soft Shackle from 1/8 to a
5/32" Amsteel line diameter, (.156) which has a 4,000 lbs tensile strength and a .300 finish dia.
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Old 02-01-2014, 13:28   #128
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Re: Mantus chain hook

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Originally Posted by thinwater View Post
I do know that a 3/16" soft shackle doesn't fit 1/4" G4 chain; I have to go to 1/8", which is cutting it a little thin. As Cotemar explained, G4 chain is tight between the links.
Yes, I think the limitation is that the soft shackle shouldn't exceed the diameter of the links, which would still give it greater strength than the chain. The shackle's profile is nominally that of a rectangle - 1 x in one dimension and 2 x in the other. So the fact that you can't shove the darn thing through the link opening on the x axis doesn't prevent you from rotating it and inserting it on the y access or even diagonally, which is wider. Further, they're soft, so they mush down. I'm holding in my hot little hand a 3/8" Plasma shackle that at the loop, smushes down pretty well so it should fit through a 3/8" chain. Not saying it isn't tight, but if one were concerned that the soft shackle would be a weak link, it needn't be.
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Old 02-01-2014, 15:02   #129
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Re: Mantus Chain Hook

My thought is that while I probably can stuff a soft shackle in the G4 space, at that point there are easier ways. No big deal. Looks slick for other chain.

I do love my soft shackles on my genoa clew, though.
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Old 02-01-2014, 16:01   #130
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Re: Mantus Chain Hook

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Originally Posted by thinwater View Post
My thought is that while I probably can stuff a soft shackle in the G4 space, at that point there are easier ways. No big deal. Looks slick for other chain.

I do love my soft shackles on my genoa clew, though.
Sensible. I'm trying to go for the strongest attachment point to the chain I can get, because I wonder about chafe of the shackle. Other than that, the stretchy part of my snubber is light enough to stretch around 4', at which point I want either the chain to take over, or if I am expecting a serious blow, another larger diameter snub line that will absorb energy before the chain is engaged.
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Old 02-01-2014, 19:39   #131
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Re: Mantus Chain Hook

So with soft shackles, how much does the knot (the weak link) effect the working load?
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Old 02-01-2014, 20:14   #132
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Re: Mantus Chain Hook

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So with soft shackles, how much does the knot (the weak link) effect the working load?
It is hard to know exactly . . . But the theoretical strength is 400% of the cord strength and the best anyone seems to have measured in a finished shackle is 200%, and it always breaks at the knot, so probably the knot weakens it by about half. . . . And that is consistent with the testing showing the "good" knots in general cut dyneema line strength about in half .
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Old 02-01-2014, 22:43   #133
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Re: Mantus Chain Hook

I asked this question over on the "soft shackle thread" but got no response.

Can a extra long soft shackle be "doubled up" by looping through two (or more) chain links?

Steve
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Old 03-01-2014, 00:57   #134
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Re: Mantus Chain Hook

estarzinger that is what always was the rule when I climbed. Ropes kind of important once in a while. Guess no method is fail safe. How about a prussic knot? I dock friend swears by them? Anyone used those?
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Old 03-01-2014, 05:51   #135
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Re: Mantus Chain Hook

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I asked this question over on the "soft shackle thread" but got no response.

Can a extra long soft shackle be "doubled up" by looping through two (or more) chain links?

Steve
You don't gain any strength by just running the soft shackle up or down thru multiple chain links. But if you mean to loop it multiple times back and forth between the snubber and chain links (like a lashing) you do gain strength (actually quite a bit, more than linear, because the diamond knot is the weak point and it is only on one loop)
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