Building a Mooring

[Idle]

I have to build my own mooring for summer in the Aegean. The boat is 11,5 meters sailing boat about 7 tons. I want to drop a cement block at about 6 meters depth. Is there a formula to calculate the size/weight of the block or should I go with empirical guessing? A 10 mm chain will come to surface attached to a buoy.

[Stumble]

Idle,

the recomendation would be a 2 ton minimum concrete air weight block. But heavier would be better.

See http://www.ecan.govt.nz/publications...ookletfhmx.pdf for a lot more detail.

The issue is that concrete really isn't all that dense compared to water, so you loose about 1/2 the weight of the block when it's submerged. If you can find an old degreased motor, they also work well.

[capngeo]

You want bullet-proof? Make a triangle!
Whether using concrete, motor blocks, anchors, or helical screws, if room permits I like to place 3 in a triangle about 15 meters to a leg. Then run chain to a central point shackle together, and if you want REAL safety add a kellet. From there using a swivel run a nylon pendant up to your boat with 1.5x the maximum water depth (think storm surge on a full moon) PLUS the elevation from waterline to deck hardware.

BTW, moorings are not build and forget... they require maintenance! I inspect annually and replace all tackle every two years.

[paulf]

I've moored Bouys in rivers, Puget Sound, Norton Sound and the Pacific Ocean.
Scrap railroad wheels are the best!
Paulf

The wheels ability to silt in (cause a negitive pressure) is the thing that holds.

[Idle]

Thank you to all responses. I have a mooring which I use since almost 20 years. The vicinity got quite crowded so I plan to move.
To be honest I was quite surprised when I read the recommendation of 2 tons in Stumble's post comparing what I have at the moment. It is about 500 kg concrete, now fully submerged in sand, with a ground chain of 10 meters 24 mm chain, and 22 mm rope coming to boat. The bay is a quite closed one for summer conditions. There may be gusts up to 35 knots down the hills but almost no waves. That is probably the answer that I had no problem till now.
At looking the details of http://www.ecan.govt.nz/publications...ookletfhmx.pdf
I will definitely take it more seriously.
Once more thanks for all the replies.
Idle

[Uncle Bob]

Originally Posted by paulf

I've moored Bouys in rivers, Puget Sound, Norton Sound and the Pacific Ocean.
Scrap railroad wheels are the best!
Paulf

The wheels ability to silt in (cause a negitive pressure) is the thing that holds.

I will second that, I use a pair of train wheels with a heavy chain, swivel and rope pennant to boat.
Used loco wheels are better.

[Bricky]

The following is a copy from a previous thread.

For our boat, a Seawind 1000 we used an old tractor wheel with wheel weight attached. Not sure on the weight but guessing about 250 to 300 kg. Then 12 mts of heavy 32mm stud link chain, about 150mm long 90mm wide joined via swivel to about 8 mt of 50mm x 12mm.