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Old 08-02-2013, 06:01 AM   #57
AusCan
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City: Adelaide
Vessel Name: Kokanee
Vessel Model: Cuddles 30 Pilot House Motor Sailer
Join Date: Jul 2012
Posts: 3,218
Quote:
Originally Posted by manyboats View Post
I'm quoting Peter as I think his response to my theory is most revealing, accurate and well thought out.

Peter wrote;
" whether the rode is nylon or chain, you just have the pull of the boat transmitted straight to the anchor, and the composition of the rode is almost irrelevant"
It is not "irrelevant" because the chain pulls very strongly at both ends of the rode. The pull on the boat can only be proportional to the wind or current. But the pull on the anchor end of the rode limits the holding power of the anchor as it's already preloaded. Then the pull of the boat must be added to the chain induced load. The sum total is greater than what it eould be w a light rode.

Peter wrote;
"by definition must include the effort/tension required to lift the rode off the seabed, so one can subtract that from the ultimate force of the pull, meaning the net force the boat can exert is the total force minus the force to straighten the rode...which relates directly to its weight...you do the math, as you US guys say...

No Peter you need to ADD the force that is the pull on the anchor from the weight of the chain. Is there any information/argument that can show me that shows this is not true?
Good arguments - You had me questioning my conclusions for a while. I had to simplify things to get my head around it.

For simplicity, let's say the wind & current are pushing the boat and creating a pull of 10 pounds on the chain at the bow of the boat, but due to gravity and friction have yet to transfer a pulling force on the anchor.

Wind increases and the pull on the bow is 50 lbs. At this point the chain is partly off the bottom and just begins pulling a force on the anchor. Pull on the anchor is 1 pound.

Wind increases more, and the pull on the bow is 100 pounds. The chain is fully off the bottom. The pulling force on the anchor would be less than 100 pounds. How much less would be dependant on the overall average slope of the chain. I'm sure there is an equation to calculate the difference but my math isn't that good.
With all nylon rode, 100 pounds at the bow would equate to much closer to 100 lbs at the anchor.

I can give you proof without math.
Take a 4 foot length of chain and stretch it out between two hands (or fish scales if you want accuracy). Holding both ends level; there is equal pull on both ends. Move one end higher than the other; you will feel more weight pulling from that end, and the lower end will decrease. More angle = more difference. Doesn't matter if the chain is slack or tight, same result.

This equates to less pull on the anchor with chain. A small difference in shallow water, but a bigger difference in deep water. Heavier chain = more difference. Does this prove that an all chain rode holds better? Not necessarily, but it is an argument in favour. Lots of other variables out there.
The extra weight on the bow could do some harm.
(I wouldn't want to put an end to this argument)
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