Recommended Mooring Block weight?

Discussion in 'All Things Boats & Boating' started by SpiritWolf15x, Aug 11, 2010.

  1. SpiritWolf15x
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    SpiritWolf15x Senior Member

    Hello everyone, I have a 7 tonne boat I'm needing to build a mooring block for. What I am wondering is how heavy do I make said block and what do I attach the mooring ball to said block with (ie: Heavy rope, chain, rope and chain, ect...)?

    Any and all input is greatly appreciated.

    -Wolf
     
  2. waikikin
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    waikikin Senior Member

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

    I made a block to the scheme on this site, its probably the best I've seen online, you've gotta find out whats been used with success localy, a mooring contractor from around where you come from would be best, for mine a mate with a crane truck & an employer with a worthy barge dropped it for me, it's no joke & easy to get hurt without the right gear. Regards from Jeff.:cool:
     
  3. SpiritWolf15x
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    SpiritWolf15x Senior Member


    Shoot, I need something that weighs upwards to a tonne?! I was hoping this would be something for along the lines of 150-200 lbs, something I could could bring down with a car and move into place with my 16' speed boat.
     
  4. anthony goodson
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    anthony goodson Senior Member

    You haven't included any detail of the ground ,or tidal conditions in your question.Without these, an accurate answer is impossible. Mud ,shingle, sand, stone, rock, dries out at low tide ? etc
     
  5. alan white
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    alan white Senior Member

    Always ask the locals what to do. My guess is a rocky bottom would require a 3000 lb granite block for your boat. A mud bottom is easy. Use a mushroom mooring of 150-250 lbs (every supplier of mushroom anchors has a weight guide).
     
  6. gonzo
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    gonzo Senior Member

    If you use iron, the rule is 15% of the displacement of the boat. With cement or other less dense materials, you got to add to compensate accordingly.
     
  7. CDK
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    CDK retired engineer

    Materials: stainless steel bar, welded to the reinforcement in the concrete, heavy ss shackle and a spliced line with a metal eye insert. Once in place you don't want to go there anymore for repairs.

    The size totally depends on the bottom. On flat rock the block or slab is always too small, in sand or mud you need a cube because it digs in better than a slab. Like Alan said, ask the locals.

    With some rope and empty jerrycans you can move any weight in the water.
     
  8. peter radclyffe
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    peter radclyffe Senior Member

    an old engine
     
  9. Submarine Tom

    Submarine Tom Previous Member

    I second Alan White, a mushroom anchor as it's probably silt/mud/sand.

    If it's rock, have a diver put in a rock anchor, or three, and chain them together to centre (drill, epoxy etc.)

    You'll have to service it every two to three years due to corrosion.

    -Tom
     
  10. WestVanHan
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    WestVanHan Not a Senior Member

    My 'water access only" cabin came with mooring.

    I dove it to find a Detroit 12v71 with a rod sticking out of the block sitting on the bottom.

    3200 pounds-cheap,totally degrease it and you're done.
     
  11. Petros
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    Petros Senior Member

    you had better check local permitting requirements. I know here in Washington state you can get a petty large fine if you do not permit your mooring anchor. There are a number of simple but important requirements for the sake of protecting the sea floor from damage caused by dragging a chain around on the bottom, and to prevent it from becoming a navigation hazard. IT is not that any of the requirements are difficult, it is just they have good reason, with long experience with it, for having them done a certain way.

    For a really large vessel I think the simplest thing to do is install a large helical or auger type anchor if you have a sandy bottom. Only weighs about 50 lbs, but it must be installed by rotating it down deep into the bottom. they can hold up to 10,000 lbs or more, depending on the size. It can be installed by hand from a floating platform with a long ratchet type handle, or with air compressor driven handle.

    Here is a company that makes these anchors specifically for mooring boats, but there are many other types that can be adapted to work for you:

    http://www.helixmooring.com/
     
  12. anthony goodson
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    anthony goodson Senior Member

    Or a new Chinese one
     
  13. anthony goodson
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    anthony goodson Senior Member

    Here we use an old large truck tyre ,placed on a board with the beads wedged apart ,then filled with concrete ,an iron bar is cast in it with a hole in the centre of the concrete to attach a swivel. A loop is taken in the riser chain and another much smaller tyre acts as a snubber. This is the economy version but it works ,partly because you never have to lift or drag the tyre ,you can roll it. Our moorings dry out ,but I liked CDK's idea of jerrycans if yours doesn't.Tyres suck down very well in mud and once covered ,corrosion only occurs on the riser where there is oxygen in the water.
     
  14. CDK
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    CDK retired engineer

    Anthony, when I came here 16 years ago and needed a mooring, there was an enormous concrete slab on the pier. A fisherman made it years before but abandoned it because he knew he'd never get it in the right place.
    So the locals grinned and said yes, you can have it if you think you can move it.....

    12 jerrycans did the job.
     

  15. jonr
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    jonr Senior Member

    Be sure to calculate that concrete loses 1/2 of its weight under water.

    It would be interesting if you could pour a mooring in place - picture a large plastic bag on the bottom with a tube leading to the surface. Just inflate the bag with concrete and then stick a piece of rebar down the tube.

    An auger is probably hard to beat from a weight standpoint.
     
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