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Old 10-06-2019, 11:47   #1
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Chocks. If a 1:1 D/d ratio is the BEAR minimum for thimbles...

... and 5:1 for pulleys, why is the bend radius on the typical chock >0.3? Some are just plain line-cutters.


Why not more like this ?



One downside, of course, is that the line must be threaded, but the increase in security would be worth it in many cases. Certainly for any mooring application.





No answer, just starting a discussion.
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Old 10-06-2019, 12:52   #2
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Re: Chocks. If a 1:1 D/d ratio is the BEAR minimum for thimbles...

Good point. Small radii reduce the breaking strength of the line and increase chafe, a bad combination.
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Old 10-06-2019, 16:06   #3
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Re: Chocks. If a 1:1 D/d ratio is the BEAR minimum for thimbles...

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Good point. Small radii reduce the breaking strength of the line and increase chafe, a bad combination.

Hurricane season is coming, and the lines always break either at the chock or where they rub on the dock. Chafing gear helps a lot, but it's a bandaide to a problem. The Boot Key marina was filled with boats with chafed pendants.
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Old 10-06-2019, 16:21   #4
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Re: Chocks. If a 1:1 D/d ratio is the BEAR minimum for thimbles...

I hear ya Thin. Add to that a really poor lead to the crappy cleat location or not enough of them.
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Old 10-06-2019, 16:41   #5
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Re: Chocks. If a 1:1 D/d ratio is the BEAR minimum for thimbles...

somewhat related . . .

https://www.samsonrope.com/docs/defa...rsn=6693131b_2

basic points - large radius more important than rollers, and surface smoothness very important
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Old 10-06-2019, 18:33   #6
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Re: Chocks. If a 1:1 D/d ratio is the BEAR minimum for thimbles...

This cat just showed up in my backyard and it stopped me to have a look.
The first pic is the bow line that goes to a fixed point up there. Iím going to assume they have this tied like this and just drag it out when required. The second was midship.
Interesting and like the concept.
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Old 10-06-2019, 18:45   #7
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Re: Chocks. If a 1:1 D/d ratio is the BEAR minimum for thimbles...

Notice that because the load is not aligned with the cleat a horn had been snapped off.
Fairleads serve a purpose.
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Old 10-06-2019, 18:50   #8
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Chocks. If a 1:1 D/d ratio is the BEAR minimum for thimbles...

Moonbeam has closed chocks at the bow. Polished stainless. About 1.5Ē-2Ē radius. The fact that they are closed is a mixed blessing. Very secure, but sometimes a nuisance to pull mooring lines through.
The midship and stern chocks are closed as well. The transom fairleads are open. Thatís super convenient for Dinghy painters. Click image for larger version

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Old 11-06-2019, 04:50   #9
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Re: Chocks. If a 1:1 D/d ratio is the BEAR minimum for thimbles...

Good bend radius and open(ing) tops are not mutually exclusive, at all.

You can make chocks with tops which are normally closed, but open (with a bolt or pin) to take line in and out.

And you can make chocks with 'open' tops, but which still trap loaded lines. You just split the top and carry the two pieces past each other, so you have to turn the line to get it out.
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Old 11-06-2019, 04:58   #10
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Re: Chocks. If a 1:1 D/d ratio is the BEAR minimum for thimbles...

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Moonbeam has closed chocks at the bow...
Beautiful boat!
I do, however, like to see the cleats mounted very close to the chocks/fairleads. This minimizes the "sawing" movement on the line.
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Old 11-06-2019, 05:13   #11
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Re: Chocks. If a 1:1 D/d ratio is the BEAR minimum for thimbles...

^^ Location is a another important factor.


  • Closer is better. the shorter the distance, the less heating and chafe can be caused by stretch under load.
  • Smaller angle. Chaffing increases exponentially with the angle, because pressure, tension reduction across the fitting, and flexing all increase. But you can't always foresee the angle, except for anchoring and bridle loads.
I've seen boats with no chocks at all; they locate the cleats so that the line runs across a smooth deck in any required direction. I suspect many boats would be better served by a smooth rail.


My PDQ has bow chocks that are well positioned for anchoring with a bridle. The rest of the cleats are without chocks but just have a clean run, which works fine. The bow cleats do not use chocks when docked to a bulkhead, which is fine.
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Old 11-06-2019, 08:30   #12
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Re: Chocks. If a 1:1 D/d ratio is the BEAR minimum for thimbles...

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Beautiful boat!
I do, however, like to see the cleats mounted very close to the chocks/fairleads. This minimizes the "sawing" movement on the line.


Thank you.
I agree entirely re location of the cleats. Stern and midship are close to the cleats. Iíve got a couple of heavy dyneema pennants to help reduce the stretch at the bow. There is also a Samson post as part of the bow vent that helps as well.
Not as convenient as a cleat though.
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