Anyone have experience (or engineering advice) on fabricating helix / screw anchors? - SailNet Community

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Old 05-10-2011
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Anyone have experience (or engineering advice) on fabricating helix / screw anchors?

Hi folks,

I am considering using a couple / few Helix / Screw style anchors to hold my floating dock in place.

For a couple of reasons ( need to do this in next couple of weeks, no local availability of Pre-made, and cost) I am condiering welding up my own out of some heavy duty galvanized pipe, and flat stock cut / welded to form the conical screws.

I would have to grind off the galvanized coating where I weld, but, as this part would be buried several feet in the deep sand and mud, I would think it would be good for several years.

I think I would walk up to about my waist, at low tide, and have a friend help me turn them into the bottom, prehaps using a 10' piece of pipe / rod , horizontally, to turn it in. I could have this go through a slot or hoop at the top of the anchor, to drive it in.

Any thoughts would be appreciated.
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Old 05-10-2011
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Absent knowing anything about your bottom conditions, any advise you might recieve on this subject hereinabouts is pure speculation. You might be screwiong into nothing more than Jello or screwing into dense sandy clay or better. It does make a difference.

FWIW...
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Old 05-10-2011
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Could you maybe use something like these dock augers?
Overton's® > Stationary Dock Hardware - Leg Pipe Sand Auger - Mooring & Dock > Docks & Hardware > Stationary Docks & Hardware :
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tidal river, sand/rocky bottom, I believe. Will have to check further,

I think I need something more robust than the dock auger in the link.

Thanks.
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Old 05-11-2011
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Based on how this member did it, sounds like you're in pretty good shape.

From an engineering standpoint, there are a few things to consider. The anchor will hold better with a larger diameter pipe, but it will be much harder to install. The distance between threads you use will also affect this-a smaller distance between threads will make it harder to install, but it will hold better. Also, the more threads you use the harder to install, but the more holding power.

It also might be advantageous to create a triangle at the beginning of your flat stock to make a gradual thread, as in your typical drywall screw.

Hope this helps, let us know how it goes!
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Old 05-12-2011
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Thanks for the engineering advice. I did read that member's posts, and that was the catalyst for getting me thinking in this direction.

I would think that a tapered start would make the entry easier as well, without sacrifing much holding power.

I will try to drive a stake or rod a few feet into the ground at low tide this weekend, to see how much sand/rock there might be above what could be larger rock or bolders.
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Old 05-12-2011
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sounds like the perfect application for old, unused, or discarded post hole drill bits.... Jus sayin..
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Old 05-12-2011
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The same guys that make the Spade (Sea tech) make a helicoidal anchor, the screw anchor. Probably they are available in the US through the Spade distributor.

Anyway you have here lot's of information. The best is in French but you have also lot's of images.

Catalogue - Ancre ŕ vis SKREW pour vos mouillages forains - Sea Tech and Fun - Spade - (Version JPG)

Sail-World.com : The Skrew Anchor

Boat anchor - SPADE - Sea Tech and Fun - Spade

New generation of permanent anchors Skrew at the METS, Sea Tech & Fun Europe sarl

Home page - Ancre Spade Sword Skrew - Ancres haute performance -
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Old 05-14-2011
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Old 05-25-2011
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Thanks Gary. The AB Chance website had lots of info, drawings, etc.
Looks like their ground / earth screw anchors, which come in a couple of different models / sizes, are re-branded as the Helix anchor (for Marine use), at least that is where the website link takes you, after clicking on mooring anchors.
Anyway, after looking at their design, I welded up a similar anchor to their round stock screw anchor, using a 15" disk.

It took a couple of attempts, standing in a couple of feet of very cold water, at low tide, but I did get it to go over halfway in, before running out of steam. I should be able to finish turning it in this weekend. The ground / bottom there varies between rocky to somewhat sandy, near shore.
The one I built was about 6 ft high, and I feel it will have lots of holding power, if I can get it to go all the way in. I used a 6ft bar to turn it in.

When I find out where the local power companies buy their similar anchors, I may buy one of two, if the price is reasonable, and add a couple more for security.
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