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post #61 of Old 11-04-2012
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Re: Installed a helix mooring anchor last weekend...

Harry Tams,

I googled the anchor/mooring system that you mentioned and here is my take on it. These helix anchors are pretty small meaning that the holding power per helix is going to be pretty low. In a relatively hard bottom, this would be okay for a smaller boat but not a larger one. The trick with helix anchors is that you need to match them to the bottom. The professional installers will often take a sample from the bottom to analyze so that they can estimate the holding power from the different size helix's. Also, the stated weight is pretty light which makes me think that these are lightly constructed. It is quite possible that they are plenty strong to resist bending, my concern would be the reduction in strength related to corrosion because thin pieces lose a greater percentage of their strength for the same amount of corrosion.

Regarding the Octopus mooring system, I really dislike mooring systems where multiple anchors are put together to increase the holding power of the system. The problem is that until you have 5 or greater anchors in a star pattern, there are directions of loading where a single anchor will take all of the loading. If the force on this single anchor is too great, then it will pull out and the next anchor in line will be shock loaded with all of the load and likely pull out. Therefore, every anchor needs to be sized to carry the entire load so there is no need for multiple. There are ways to load equalize in all directions but I am unaware of any that I would trust for a permanent mooring because they are prone to chafe, fouling and sticking. The major advantage of setting multiple anchors in a star pattern is that the direction of loading does not change so that you can use anchors like danforths. Since the helix is symetrical about its vertical axis, the direction of pull does not matter.

In the right circumstances, I feel that a well engineered helix install is one of the best mooring systems possible. However, I feel that a single helix should be used which means that it must be pretty large for a reasonably sized boat.
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