Installed a helix mooring anchor last weekend... - Page 5 - SailNet Community
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post #41 of 72 Old 02-11-2010
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another update

we have had several significant storms here... many with gusts of 60 knots plus...
Tuesday night we had a front come through... sustained 30-40 knott winds with gusts of 60 knots plus recorded.

mooring is still sound and in perfect position....

we had a house boat moored near me break loose three times recently and drag all over the place. He has a small >30 foot houseboat on aluminum pontoons... not much mass, but still broke a 50 lb danforth loose three times now.
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post #42 of 72 Old 02-11-2010
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However, no one has discussed the fact that the force is not pull-out...

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Originally Posted by YARDPRO View Post
my boat in a 65 knot wind will put 1100 lbs of force on an anchor...
a single 10" helix is rated at over 3000 lbs pullout force.

using the multiple (3) mooring system, the load will be distributed to two screws. giving about 6K of pullout force required.
It is in shear. Scope still matters.

Also, when an anchor is placed that deeply into a material like firm clay, it cannot simply pull out; it must pull out a large cone shaped section. If the anchor is 5' in, this cone will weigh nearly a ton, not counting the friction effect.

We really need a soil engineer to weigh in on this, as we are not experts in this area. I am a chemical engineer and have only studied this application in construction.

(when asked how he reached the starting holds on a difficult rock climbing problem that clearly favored taller climbers - he was perhaps 5'5")

"Well, I just climb up to them."

by Joe Brown, English rock climber




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post #43 of 72 Old 02-12-2010
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I don't think that doubling up on the helix anchors gives you twice the holding power, depending on how you rig the bridle. With a fixed length of chain to each eye, you're only going to be loading one helix anchor at a time, in almost all circumstances, just like with two regular anchors.

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post #44 of 72 Old 03-12-2011
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Can anybody give me some guidance on how to calculate what the minimum pullout force of a system should be for a given boat. Mine is a Bristol29.9.

The original displacement was 8650lb. I would like to install a system that will securely anchor my boat in a protected bayou, but it is the Emerald Coast area of FL, so prone to hurricanes, although a storm surge is more frequent in this area (Panama City).
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post #45 of 72 Old 03-12-2011
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Didn't want to hijack the thread though, but I am interested in the helix system. I will post this on a new thread also.
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post #46 of 72 Old 03-13-2011
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Quote:
Originally Posted by AdamLein View Post
I don't think that doubling up on the helix anchors gives you twice the holding power, depending on how you rig the bridle. With a fixed length of chain to each eye, you're only going to be loading one helix anchor at a time, in almost all circumstances, just like with two regular anchors.
I concur, so consideration of a sliding pennant, or some sort of bridal, could be of some logic, but an interesting physics issue. Continuous equal distribution of the load is the challenge.

Funny but true, over here on the West Coast, it seems Helical Mooring is largely unknown. I've been studying this subject now -and the industrial construction applications that spawned it- for a couple weeks now. Very, very interesting.

Anyone like to update this thread with their more current Helical Anchor/mooring experiences?
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post #47 of 72 Old 06-06-2011
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equal pulls

Scurvysailor wrote: I concur, so consideration of a sliding pennant, or some sort of bridal, could be of some logic, but an interesting physics issue. Continuous equal distribution of the load is the challenge.

You would need 2 anchors to have equal pulling in two directions, 3 for 3 directions...ect. What hasn't been mentioned is something to keep the helix shaft from being pulled sideways when it's in a strain as the scope of the rode will try to pull it out sideways, not straight up. House trailer helixs use a side plate to take the lateral strain. For a marine helix, a 12" diameter steel pipe cap about 12" long welded near the top of the shaft might work. It would turn as the helix turns and would hinder lateral movement of the shaft.
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post #48 of 72 Old 07-21-2011
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Great Post! Thanks to the original poster for taking the trouble to take the photos and provide the detailed instructions.

I am researching how to place a Helix for my 23.5' Hunter sailboat in about 10ft of water on the northern Chesapeake Bay. My problem is that I don't have any help and would like advice on how this could be done by one person. I don't mind getting wet because the water is about 80 degrees right now. The location is only about 30 feet off the beach so I could easily walk/swim out.

Do you think I could use the ingenious PVC pipe method and turn it while floating in the water in my PFD, or would I need the traction of standing on the bottom? On some days the tide goes out so far that I could probably stand on the bottom and a snorkel would reach the surface. I am a certified diver but don't have any gear any more. Would it be smarter to rent gear and do it from below? I'm trying to keep costs and complexity to a minimum. Am I crazy?
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post #49 of 72 Old 07-21-2011
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Tri Anchor

Read in Chapman's that 3 anchors 120 degrees apart was way superior to massive mushroom anchors.
That proved itself correct when I used 3 Delta's which held my 4000# 25' Cape Dory 25 in an infamous nor'easter that devastated much of the Chesapeake several years back.

It follows therefore that 3 helix's at 120 degrees apart connected with chain would always have at least 2 of them holding regardless of the wind direction.

That would be my approach for anything short of a major hurricane.

Dick
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post #50 of 72 Old 07-21-2011
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Reef, you will not be able to install the mooring by simply swimming as you won't be able to exert enough force if the bottom is any good. You either need good traction on the bottom (note- I have personally never installed one in deep enough water that I have had to suit up and dive) or you need to have a boat very firmly anchored in place to work from. If you have a way to extend the shaft of the helix so that it is long enough to be reached from above the water's surface, this works decently well but you do need to spend some time getting the anchor lines adjusted right (or you need to rent a spud barge). Anytime you do this, you should make sure that the soil is appropriate for the anchor type.

Flybyknight, putting 3 helix anchors at 120 degrees apart is very different than putting 3 danforths or similar in the same arrangement. In this arrangement, each anchor has to be able to independently take all of the load from the boat (imagine 1 anchor being directly upwind, the other two won't do anything). A helix makes a great boat anchor not only because of its holding power but because it doesn't need to reset or rotate if the direction of pull changes. If you take the examples of danforths, 3 anchors is necessary so that the anchors always see a relatively straight line pull. There is way more to the 3 anchor arrangement than most people realize, the lengths of chain are very critical to really minimize the load. The arrangement does work quite well but a lot of people install them improperly because they don't understand the important of the geometry.

It is possible to rig up a load sharing arrangement between multiple anchor points so that they will have relatively equal loading independent of wind direction but this is not standard to my knowledge. The problem is that you need to allow for moving parts which tend not to work well over long periods of time underwater. The way that most systems are setup, in most wind directions, one anchor will be doing all of the work and the other one will simply be there for backup.
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