This is a Helix Anchor (Click on pictures to enlarge)
Once fully driven into the bottom type of helix is has been tested at over 3,000 pounds holding power (depending on bottom consistency.) There is no other anchor that comes anywhere close to it as far as power versus weight or cost (under $100.) Most likely something else will fail long before this anchor begins to pull out; usually the pendant or deck cleet.
Notice the heavy eye that allows a steel pipe to be placed through it to turn the helix to screw it into the bottom.
This part that acts as the threads to bore it into the bottom formed from a steel plate that is bent just enough to allow it to bite into the bottom as it is turned.
A mooring is only as strong as the weakest part so each item must be selected carefully. The helix anchor is certainly a good start if you have the right bottom for it.
Here are the components I use for our moorings in Half Moon Bay in 20 feet of water:
- 15 foot New England Mooring Pendants - West Marine Item# 8003642
- 18" Sur-Moor T3C Mooring Buoys - West Marine Item# 127896
- 2.5" T3C Mooring Collar - West Marine Item# 288590
- 25 feet of 1/2" inch chain (upper chain - should be as long as depth of water plus tide max height)
- 5/8" Jaw and Eye swivel - West Marine Item# 480038
- 12 feet of 5/8" inch chain (lower chain at least half the depth of water)
- 3 - 5/8" inch shackles - West Marine Item# 173346
- 1 round shaft Helix anchor - http://www.helixmooringsystems.com/
- Monel Seizing Wire - West Marine Item# 4488789
The only difficulty in putting in the mooring is installing the helix. It can be done by a single diver with support from a boat on the surface. Be sure that you have an experienced diver who is use to working in zero visibility that will result from the hard work of installing the helix. Here are the steps I follow:
1. On shore (close to the water) fully assemble all mooring components together as follows:
- Pass 1/2 chain through buoy,
- Insert mooring collar into top of buoy,
- Attach pendant to chain on top of buoy with 5/8 shackle and seize pin with monel wire,
- Attach jaw and eye swivel to 1/2 chain using the eye on the swivel and seize pin in place with monel wire, (note: do not use the cotter pin that came with the swivel; they tend to fail quickly.)
- Attach 5/8 inch chain to eye of swivel using 5/8 inch shackle and seize pin with monel wire,
- Attech lower end of 5/8 inch chain to top of helix with 5/8 inch shackle to insure that the shackle fits over eye of the helix; have the diver practice attaching the chain to the helix so that he can do it by feel on the bottom.
- Detach the helix and leave the shackle attached to the chain with pin hand tight so that it will not fall out; attach 3 feet of monel wire to the shackle (so the diver will have it handy).
- Attach 1/2 gallon plastic milk carton to bottom end of 5/8 inch chain to help the diver locate and move it once the chain is on the bottom.
- Prepare the following tools for the diver: wire cutter, wrench to tighten shackle, 5 foot 3/4 inch steel pipe to turn helix.
2. Take the tools and the helix anchor to the boat and attach a 1/2 inch line to the helix eye. Attach a tow line from the boat to the pendant on the mooring and walk the mooring out into the water so that the buoy is floating.
3. Tow the mooring out and anchor the boat over the desired location.
4. Lower the helix into the water until it hits bottom (you may want to attach a small float to the line such as 1/2 gallon milk carton to help the diver move it and keep the helix standing vertical while the diver works with it.)
5. The diver should enter the water and then be handed the 5 foot steel pipe. He should proceed to the bottom and begin searching for a suitable spot to install the helix which is free of surrounding obstacles that may foul the chain as it swings around the helix.
6. Once a suitable location is found the diver should begin probing the bottom looking for a soft spot. Any rocks or hard pan in the bottom will prevent the helix from being driven all the way flush with the bottom. Normally if you can drive the 5 foot pipe into the bottom all the way using its weight then the helix will have no problem going in. Keep in mind that you may have to try several locations with the helix before you succeed in installing it.
7. Installing the helix is simple. Just stand up the helix and place the pipe through the eye and start turning the helix doing your best to keep it vertical. Take your time and watch you air supply, since it is hard work it is easy to over-breath your regulator and exhaust yourself so work slowly. It can help to have a second diver at this point since you can work together to turn it. You should be done in about 15 minutes or less depending on the bottom consistency. (Make sure that the top of the helix is still connected to a line to the boat so that you do not lose it after it is flush with the bottom; the silt will tend to cover the eye as it settles.)
8. Return to the boat with 5 foot pipe and take wire cutter and wrench (should be attached to diver with tether.)
9. Locate and attach the end of the 5/8" chain to the helix eye with the 5/8 shackle and seize the shackle pin in place with the monel wire and your done.
I will be installing another one this fall, so I will add some picture then so you can see what I am talking about.
Some Observations on Moorings and Anchoring
After maintaining moorings for the last 6 years and regularly observing their performance both from below in the water and above from the boats during heavy weather I am extremely impressed with the mooring buoys ability to absorb shock. I consider the mooring buoy the single most important element in absorbing shock; the short pendant and heavy chain can almost be complete ignored since they quickly reach their limit becoming bar tight without the buoy. Considering they would have to resist several tons of boat surging against the extremely short 2 to 1 scope they provide it is easy to see how much stress would be on the system without a buoy.
Given I know that the 18 inch buoys we use only have a limited buoyancy of 100 pounds, with 50% of that being used to support the chain. This leaves approximately 50 pounds lift to absorb shock, which seems far too little to make much difference. However in practice the buoy has an amazing ability to pull the boat forward as the waves lifts it imparting some forward momentum to the boat as it encounters the same wave. At this same time the buoy is now in the trough giving slack allowing the boat to stop and back up as it encounters the wave without transferring any load to the mooring system. Now the next wave arrives starting the process over again with the buoy lifting and pulling the boat forward.
This wonderful behavior can be confirmed by simply taking hold of the mooring pendant from the bow of a moored boat and feeling the load, which even in winds of thirty knots and is far less than what would be experienced if the buoy were not there.
Given this it would seem extremely wise to include a buoy in any heavy weather anchoring situation since it should provide the same benefits allowing a much shorter scope on the anchor to hold the boat in place. Considering most crowded anchorages force short scopes to be used this becomes even more important. It should be kept in mind that the buoyancy provided by the buoy should not be excessive otherwise it will not properly submerge in the larger waves and then softly pull the boat forward. An overly large buoy will act much as the boats bow does and transfer most of the load to the anchor as it rises too quickly on every wave. A 12 inch buoy when used with a line rode should provide the needed lift for boats up to 30 feet and an 18 inch buoy should be good for boats to 40 feet. Try it the next time you anchor in a rough location with limited protection from waves.