Bahamian Mooring

SloopJonB · #1 (**permalink**) 10-06-2011

I am seeking opinions on using a Bahamian mooring instead of a conventional huge block of concrete for a summer mooring for a 43', 11 ton boat.

What I have in mind is using two BIG anchors - 150# each or so, linked by chain with a chain shackled from the middle of the span rising to a buoy. The proposed mooring spot is reasonably sheltered but the wind CAN blow and the seas can reach maybe two feet.

My reasons for wanting to do it this way are twofold - I don't want place an essentially permanent lump there and I would like to do it myself, not requiring a barge, crane etc. and the purchase of the aforementioned lump.

I figure I can pick up a couple of decent big anchors for less than the lump would cost and they are retrievable relatively easily when the time comes.

Thoughts?

Gene T · #2 (**permalink**) 10-06-2011

First thing that comes to mind is are you planning to set the anchors, or just drop them in place. Also anchors need scope to work properly. Are you planning to use the appropriate scope? It would certainly work if set and using proper scope.

Gene

klem · #3 (**permalink**) 10-06-2011

I would advise against using a bahamian mooring setup as a permanent mooring. If the wind blows perpendicular to how the anchors are laid out, you can end up with very high loads on the anchors unless you have left a lot of slack in their chains and then you end up with changing directions of pull.

If you are set on doing a multiple anchor setup, a 3 point setup works well if setup properly. Getting the ratio of chain in the legs to chain in the leader from the legs to the ball right is very important. Additionally, getting the correct amount of slack in the chains is key. Believe it or not, you need some slack or you will greatly increase the loads on the anchors because they will be reacting against each other. Also, you need to have a good way of attaching everything that will not twist up. When properly done, this provides excellent holding power but when improperly done, loads can be greatly magnified or direction of pull on the anchors can change a lot. I would highly recommend drawing out free body diagrams and figuring out how much load is on each point for given geometries if you decide to go this way. Doing this will help a lot in figuring out what the geometry should be.

What is the bottom where you are? If you have sufficient tide and the bottom is decent, you can move an appropriate size mushroom or pyramid with your boat as long as you are careful. By driving the gear down to the low tide line and then coming over it with just a little tide left to do the final lifting, you can use the boat's buoyancy to pick it up. Just be careful to rig it so that you can lower it in control down to the bottom.

Windborn · #4 (**permalink**) 10-07-2011

Can you use screws?

Our mooring consists of 5 screws linked with heavy chain. A 20' chain connected to the screw's chain has two 3/4" pendants that come up to the boat. We've survived hurricane hits with this setup.

klem · #5 (**permalink**) 10-07-2011

Windborn,

Out of curiosity, do you have a wave of equalizing the load on your screws? I am not a fan of most multiple anchor moorings because there is not load equalization and you can pull out each anchor one by one. There are ways obviously to deal with this but I have rarely seen it effectively done.

SloopJonB · #6 (**permalink**) 10-07-2011

Quote:

Originally Posted by Gene T

First thing that comes to mind is are you planning to set the anchors, or just drop them in place. Also anchors need scope to work properly. Are you planning to use the appropriate scope? It would certainly work if set and using proper scope.

Gene

I had thought to set them, one at a time, facing each other with a length of chain equal to proper scope across. I figured the pull from a near vertical chain in the middle would have a vector that would try to pull them together rather than up (basically).

The bottom is is mostly rock and shale. I had planned to have a diver check the set of them prior to use.

JimsCAL · #7 (**permalink**) 10-07-2011

I think Bene505 uses a multi[ple anchor system to moor his boat at Montauk. You might PM to get his experiences.

MastUndSchotbruch · #8 (**permalink**) 10-07-2011

Quote:

Originally Posted by Windborn

Can you use screws?

Our mooring consists of 5 screws linked with heavy chain. A 20' chain connected to the screw's chain has two 3/4" pendants that come up to the boat. We've survived hurricane hits with this setup.

Can you be more specific? Helix anchors (TM) or something else? How did you get them in? What kind of situation (bottom, exposure, boat size)?

Thanks for any information on this. I am considering getting a mooring set-up for a hurricane situation.

paulk · #9 (**permalink**) 10-07-2011

Our harbor uses helix anchors for strings of 6 or more boats. In the recent Hurricane/Tropical Storm Irene, the main concern was not that they would pull out, but that boats would be held down by their anchors and sunk when the water rose over their gunwales. We're talking 30 to 40 foot cruising keelboats - not daysailers. Crews went around lengthening the mooring lines to accommodate the extra four feet or so of water we got at high tide that day, and nothing happened.

Faster · #10 (**permalink**) 10-07-2011

With your center-chain pull I wonder if you wouldn't have some very high loads on the system if you ended up pulling hard at 90 degrees to axis of the two anchors.. (similar to how a crosswind in a stern/shore tie situation can put heavy loads on the hook)

btw.. where are you going to try this??