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Originally Posted by ebizboy
We are about to replace the weight for our mooring as well. It turns that we may have access to an old manhole cover or two and I was wondering if anyone had experience using them as a mooring weight. My guess is that because they are so flat and heavy they would kind of suck themselves to the sandy/muddy bottom and provide a pretty secure weight. Any thoughts?
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You've got an interesting challenge there. If yours is a muddy/sandy bottom, free manhole covers could pay off. Here's what I'd do with "free weight":
Today's manhole covers are made of a really bad mixture of various steels -- including scrap stainless steel, and can be difficult to drill. They may have some existing holes you can use, otherwise, you'll need to "torch" a few holes. If they're older, they could be cast iron --
easy to drill.
First, I'd torch two holes in both -- one in the center -- one offset. I'd run three feet of stainless steel chain through the center hole, and shackle a large stainless steel "stop" of some kind to the "bottom" end.
Check scrap metal yards -- they can't economically recycle/melt stainless steel, so they just wait for someone to buy it. Some big city yards will have stainless chain too. I bought 70' of heavy stainless steel chain at a discount, as it was the "end" of a large reel.
Torch four or more aligned holes for bolts. I'd bolt (with stainless steel bolts) the two covers together, at the shoreline. Add the chain and backup plate.
You could roll the covers to where you want the mooring and, using garden hoses connected together, pump water through the
offset hole and the edges, and sink the covers into the mud/sand as far as you can. With some selective pressing of the covers, you may be able to sink them 6" or more. (That goes for mushroom anchors too -- sink
them). If you can't sink the manhole covers under
your bottom surface, I wouldn't use them as a primary mooring.
Depending on your boat size, wind direction and fetch, they could work out OK. If they get pulled out of the bottom, even a little, I'd abandon the idea. However, the reason I suggested the stainless steel chain is that if you "outgrow" this mooring, you could still chain the manhole covers to a later replacement block -- as a backup.
Alternatively, you could cut the manhole covers into smaller squares, and add them to a concrete-cast mooring block. Adding scrap steel or iron is better than adding rocks to your concrete mix. To start, sink a heavy coarse wire mesh all around the periphery of your block -- supported about 1" from the walls of the mold -- to reinforce the concrete.
You can't have too much weight in a mooring.
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