I'd second the idea about concrete. It has very low density and unless
it is buried very deeply is less likely to provide as much holding power.

An alternative approach might be to use something very heavy as a center
weight such as a car engine block but to then add a few additional
anchors around it.

I helped a friend do this with his mooring a few years back and it seems
to have worked very well. We dropped an engine into the mud, having
first threaded several heavy chain loops threw it and welded them in
place. Each loop attached to a singe very large turnbuckle to which the
mooring chain was attached.

What made it someone different was that we added three small danforth
anchors in a star pattern radiating out from it, each on about 10' of
chain. We dug a trough for each of these and tensioned them so that the
anchors were completely set and then covered them over.

The block provided weight and the anchors provided lateral resistance.
Seems to have worked fine.

Hope this helps.

Robb


Dennis Pogson wrote:
Depending on the aggregate in the mix, concrete is just about the worst
substance you can use. A stone aggregate will barely hold a 35-footer unless
the weight is dug in about 12 feet down in heavy mud. How are you going to
do this? I saw a newly-laid slab of concrete "hopped across" the bay by a
Nicholoson 32 in a force 6 some years ago. If you use iron or steel
aggregate, then you increase the weight per unit volume slightly, but it's
still too light for storm conditions.

Train wheels are far-and-away the best moorings, next to a couple of large
(and expensive) mushrooms with 30 metres of 1" link chain between 'em.