Mooring block question
 

How much should a mooring block for a 10'x10' swim float weigh?

It depends where you will place it. In a calm bay 75-100lbs x 2 would be fine. Out in the chop and wind you may need double that.

Check the bottom where you are, too.
 

You can't make your block too heavy. Blocks weigh just half of their above-water weight when submerged. If your float is moored at a nominally windward shore, you should add still more weight.

Winnipesaukee's lee shores tend to be sandy or, in recent years, muddy. (Due the oversized-boat wakes of the past decade). Soft bottoms will "hold" the block better.

Rocky bottoms offer a poor surface. In a strong wind (like last Saturday's 52-MPH-in-gusts -- thanks Don), your float could repeatedly jerk the block across a rocky bottom into deep water -- and end up floating off somebody else's shore!

Use more chain than you think it needs. If the chain or shackles are left submerged over winter, inspect the steel parts every third season. These waters eat steel. (And aren't too friendly to stainless, either).

If you elect to prepare a poured concrete block, I'd suggest molding a hole through it, or using an oversized stainless steel eye bolt. (I use a huge stainless plate which penetrates the block, so it is exposed for the shackle attachment on either side of the block).

My community-lakefront neighbors on the windward shore use 4-by-4-by-4 granite blocks for their middle-sized boats. At first I thought that was overkill.

Maybe not.

My raft is constantly exposed to NW winds, including pretty strong wave action at times. Not anything like you'd get on, say, the North side of Rattlesnake though. My block is about 2X2X2, sitting on a sandy bottom in about 8 feet of water and is more than adequate. You really don't need the same amount of weight as a boat since the raft weighs so much less and doesn't produce nearly the same up and down forces on the mooring.

I strongly endorse the idea of running a piece of maybe 3 inch PVC through your mold to give you something to feed the chain through, as opposed to using an eye-bolt. The latter, unless very over-sized and stainless, will rust away over the years leaving you a rather useless block of concrete on the bottom of the lake eventually. Prior owners did the latter and I will soon (this year?) need to replace the block.

Thanks for the input. I like the PCV pipe idea, I had not thought of that.

You can take the PVC idea one more step. Use two pieces of PVC at different angles. Perhaps one piece side to side and one up and down. This way you can get your chain through the block no matter how it is situated on the bottom.