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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #11  
Old 10-24-2009
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Whether it is a genuine mushroom or the train wheel you propose to use, either one requires time to settle in before its holding power is established. 10 days is not enough, even in the soft mud found in the Chesapeake. A safer bet would likely be around 60 days.

How do I know? I set a 200# mushroom in the protected waters of Galesville 2 - 3 weeks prior hurricane Isabel. With no where else to leave my boat, I decided I had better add some holding power before the surge. I pulled the chain up to the lower swivel and attached four more anchors - 2 per leg Bahamian style. I figured if the mushroom broke free at least it would act like a 200# sentinel. Given how hard it was to break the anchors free and remove them after the storm -- even with trip lines and floats already in place -- I'm pretty certain the mushroom moved a bit.

Last year, five years after Isabel, I had a diver go down and check on things. He told me little more than the mushrooms' ring at the stock end was showing - perfect. And, for the record, this mooring holds a 30' 5500# catamaran.
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Old 10-24-2009
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I'd point out that concrete is a lousy material for moorings...since they tend to sit on the bottom and depend almost entirely on their mass for their holding ability, and that concrete loses a lot of its mass when submersed in water.

Normal concrete has a density of about 2300 kg/m^3. Water has a density of about 1000 kg/m^3... so a 2300 kg concrete anchor only has 1300 kg of holding power, or about 56% of its actual mass.

Steel, like the train wheel above, has a density of about 7700 kg/m3... and retains about 87% of its above water mass when submersed... Mushroom anchors, and probably train wheels, also bury rather than sitting on the bottom, and have greatly increased holding power as a result. A typical mushroom anchor will have about EIGHT times its actual weight in holding power once set.

A 300 lb. mushroom anchor will hold to about 2400 lbs... based on the eight times estimate... and a concrete anchor that would provide an equivalent amount of holding power would weigh about 4300 lbs... Good luck trying to get an anchor that heavy into place.
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  #13  
Old 10-24-2009
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Quote:
Originally Posted by sailingdog View Post
I'd point out that concrete is a lousy material for moorings . . . a concrete anchor that would provide an equivalent amount of holding power would weigh about 4300 lbs
Hey Dog

Except, where we are mooring, in a small bay, on a lake, with soft mud in the bottom, for us, in our location, they work great. So - I guess it is all relative.

At Saint Andrews, NB - concrete blocks are all they use. But again, in a small shallow bay, totally surrounded, small channel in and out, no long fetch, no huge waves, works perfect. They don't put a bar in the concrete, they put a piece of 4 inch black plastic pipe through the middle and slide logging chain (or an equivalent large linked chain) through the plastic pipe. Every so many years, they replace the chain - makes replacing the chain really easy.

Cheers

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Rik, I thought concrete came in a bag. I agree with S.D., concrete does not make a very good mooring anchor. I built a new bowsprit , jibboom, and billet knee on a schooner that was moored to 850-900 lbs. of the stuff. It drug down to the Conch House dock where it tore the bow off. I'm sure that the shape had something to do with it as well. Anything that relies solely on weight for it's holding power is not my idea of a good anchor and I would certainly not want an anchor made from a material that loses weight when it hits the water.[not even for my concrete boat]
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I just noticed that there are two Atomic 4 mooring anchors available in the Seattle area on another thread.
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Old 10-26-2009
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Quote:
Originally Posted by xsboats View Post
Rik, I thought concrete came in a bag. I agree with S.D., concrete does not make a very good mooring anchor. I built a new bowsprit , jibboom, and billet knee on a schooner that was moored to 850-900 lbs. of the stuff. It drug down to the Conch House dock where it tore the bow off. I'm sure that the shape had something to do with it as well. Anything that relies solely on weight for it's holding power is not my idea of a good anchor and I would certainly not want an anchor made from a material that loses weight when it hits the water.[not even for my concrete boat]
I agree. Concrete is not a good mooring anchor. I've seen them drag. I have moorings in a protected anchorage and used 600 lb steel mushroom anchors with 1 " bottom chain and 1/2" top chain. I also use polydyne mooring pendants. Most people around here use cheap poly rope. A mooring is not a place to try to save money. Look at what you have invested at the end of the pendant.
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Old 10-26-2009
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I agree. Concrete is not a good mooring anchor. I've seen them drag.
It's certainly not the best mooring material but you can design an adequate system keeping in mind the properties of the material you're working with. Washington State park buoys were based on two concrete blocks tied together with large chain, the bouncer block and the primary block. The state appears to be switching to a helix set up for their new moorings though.
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Train Wheels

the use of train wheels and crain weights is a fairly common practice in Lake Michigan. I would go with as much weight as possible just to be safe. Critical factor is how you connect the mooring chain and the ability to periodically inspect the entire chain for wear. Likely that it will get burried in the muck making inspection difficult but essential. My chain broke this year right where it fastended to the mooring. When I bought it a couple of years ago, the chain had been replaced, but not the section around my weight which was in the harbor muck. So ability to isnpect is important.
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Old 10-27-2009
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I have to ask: whether it be old engines, concrete blocks or train axils, how does one go about placing the mooring? Do you hire some kind of work boat or something to drop it where you want it? Just curious.
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I moved a mafia block with a 28' sailboat. I think it weighed in between 1,000 and 2,000 lbs. Dumped it on the beach at low tide. Attached a line to it with a float on each end. Floated over the block on an incoming tide and attached each end to the primary winches. Waited for the tide to life the block off the bottom and then motored it out to my mooring site.
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