Anchor design

why they're generally not interested in certifying anchors much under 100 kg??
I was searching a normative for the nautical mooring to dimensionate a block anchor (deadweight anchor) but i found nothing..
anyone of you can help me??

 

Perhaps google MOORING BLOCKS ...not anchors. Sometime ago I read a good article on mooring block guidlenes for harbours...try googling

 

Jacckko,

Societies almost never certify an anchor of this size since the expense would be prohibitive. An anchor may be certified as to type (design), but not the actual anchor.

Dead weight anchors really are pretty terrible. Certainly if you get one large enough it would work, but the cost for a deadweight block probably exceedes the cost of a designed anchor by orders of magnitude. Remember that concrete is almost useless since it looses about half of its weight underwater to boyance, so a deadweight mooring of 2000lbs then displaces around 1000lbs of water. This means you really need to go to metal to stay within a reasonable size, which only looses around 20% of its weight to displacement.

As for a holding power chart... It would heavily depend on the shape of the mass. A flat plate for instance would have more bottom friction than a globe.

 

I remember seeing quite a bit of data on mushrooms (anchors) and moring blocks which considered bottom structure and whether or not they were set well and I think it was published in a catalog that was selling components for permanent moorings.

 

do you think it can be interesting to make an intensive research on block anchor to create a guidelines for nautical moorings??
it can be seen as a scientifical work?

 

The attributes of a good anchor are that

1) It hold bottom in all and any condition.

2) It is easy to retrive as Anchors get expensive if you only get to use them once.

3) It must be light to handle

4) It must store conviently

5) It must deploy instantaniouly almost by majic

6) It must be low cost.

Being that the Ocean is the same everywhere I would say that the Best anchor is made of old Railroad Truck wheels with 2 inch chain welded thru the whole.

 

do you think it can be interesting to make an intensive research on block anchor to create a guidelines for nautical moorings??
it can be seen as a scientifical work?

 

No, simply wait for someone to reply that knows how much weight it takes to hold how much boat in how much wind and surge. Wait for Richard, in other words. It will be a simple answer, not worth a "scientific work".

 

Moorings for small yachts seldom exceed 2 tons because of the difficulty in physically manhandling them. When more holding power is needed 2 ton blocks are laid out in a grid pattern.

Some general yacht info here. New york Port Authority also published a rather complete set of data for ship moorings. Google it

http://www.ecan.govt.nz/publications/General/MooringBookletfhmx.pdf

 

When I worked a buoy tender here with the Coast Guard, we used three huge blocks triangulated on the sea floor and chained to the mooring line in the centre.

If I were setting up a secure mooring for a pleasure boat here, I would use the biggest mushroom anchor I could handle placed in sand/mud/silt with lots of heavy chain and a big bloody orange ball.

-Tom

 

Always best to check with local authorities. Here its illegal to lay any non standard mooring system down.. Very .Heavy chains and mooring block patterns are the official route. I see they are, at this moment, fabricating some jumbo cement mooring blocks...perhaps ten tons...have no idea how they will handle them. Obviously some kind of barge crane industrial gear.

 

"Obviously some kind of barge crane industrial gear."

Not necessarily, they may simple float them.

-Tom

 

Yah..I guess they could float them. Be intersting to see how they handle them. Normally they are using 2ton blocks handled with a small purpose built mooring service barge.

Oh and be carefull with mushroom anchors. Very poor holding if they are not burried. They seat them locally with a steel pipe lashed to the mushroom. The pipe is attached to a gas powered waterpump and you waterjet the mushroom into the sand or mud.

 

The last deadweight anchor I put in around here was about 2 tonns but instead of a square or trapezoid we used a 12" plate about 4'X4' It was unweildy as heck, but after a month it sank more than 6 foot into the soft river bottom mud we have, and I doubt it could be lifted without unburying it. However if you took that same anchor to say Jamaica where the bottom is 2" of sand covering coral I doubt it would hold much at all. It would just slide along the bottom.

This is the problem with trying to design the same anchor for use in all bottoms. You really need to address each bottom individually and design a system around what you are trying to bite into. Though the new helical screw in anchors seem to work great in everything but soft river mud.

 

"Oh and be carefull with mushroom anchors. Very poor holding if they are not burried."

Ya, that's a given, and the whole principle most anchors work on, especially mushrooms. It's a common misconception about anchoring that they'll just mysteriously hold if you simply drop them on the bottom.

-Tom