mooring block?

Niander

Niander

Well-Known Member
Joined
25 Jun 2003
Messages
2,090
Location
YORKSHIRE
Visit site
Im starting to make mine
1 tonne of balast and this lot
what i want to know is how many bags of cement do i need?
or what mix is recomended?
and will that chain be strong enough?...:)
cheers
 
Last edited:
That is a serious piece of ground chain you have there - I think it should certainly be strong enough!
It is not very long though - what are you planning on attaching to it?
Is there some more chain of similar size for 'on the bottom', and then a lighter riser chain?
And just being nosy, what sort of bottom will this mooring block be living in, and what depth of water?
(And what size of vessel?)
 
What are the dimensions of the mould please, and the average diameter of the links ?

Concrete under water has a density of between 1000 and 1400 kg/cumeter, so it's not as heavy as you might think. The scrap will help, but should be well encased in the mould to avoid exposure to water.
 
I made one similar.

I made a similar mooring some years ago. I made a circular 5' diameter steel mould approx 1' high with a steel base and filled with about a ton of granite chips (granolithic mixture) I think I used about 5 cwt of cement and heaved in some PVA mixture. Took about 4 weeks to harden up. Before I cast the concrete, I welded in a 1" diameter loop onto which I attached a 1" link chain of about 20 feet then dropped down to 1/2" chain for the riser.

Held my Westerly Pentland off the old Largs Sailing club in some real stormy weather. Only problem were shackles coming loose even though I had moused them.

To get the completed mooring down the slipway, I cast the mooring on a heavy wooden pallet. At low tide, I and a friend went down to the slipway at low time (4AM !!!!!!) and trundled the mooring down on a pallet truck to meet its new environment. The workboat came in at 10 AM and picked up the float and dropped the mooring.

J.
 
Last edited:
Is it possible to cast a pipe into the block, so that a chain can be fed through and shackled to form a loop? The idea would be that you could change out the chain as required, rather than abandoning the block when the cast-in chain rusted.
 
Personally I would not use concrete. In time it will break up. Best to use granite, also double up on the ground chain, two lengths side by side. The exra weight is less likely to cause snatching on the block.
 
Almost identical to my own. I lined the fish bin with poly and fired in a 5:1 concrete mix and the old swords. I had the block lifted with a forklift and placed on the ramp of a very convenient vessel off which it was launched into position in 6m of water. I have 20m of 1 1/4" chain which does not appear to have been pulled straight in the 6 years its been in place. I dive it occassionally and have only replaced one shackle at the buoy in this time. Your chain appears to be the bridles of a dredge beam which probably has had a bit of a hammering but looks pretty substantial and with the bonus of the large masterlinks. I am in a very sheltered location and this will probably be the primary factors in whether your mooring meets your requirements.
 
I say again...

....invest a fiver to learn what the top professionals do to avoid doing it twice - after the boat has gone walkabout!

Here are a couple of ideas, from the horses' mouths:

Use high-strength construction concrete mix - 1/2" to dust, vibro'd, no local salty sand, no salty water, no metal or rubble 'inclusions' - and that means those rusty lumps of metal, which will continue to rust, and eventually crack your concrete block severally. If you must use steel, get a couple of old railway wagon wheels.

If you have a question mark about weight, make sure it's completely buried. Or go bigger. Many Scottish West Coast operators are upgrading toward 2 tons, when opportunity presents.

Granite is good. There's lots about near Luing.

Your 'thresher chain' looks fine. Make up a riser from 'medium-link' chain and join it on with either a tested, certified BIG lifting shackle, where the pin is not less than the same diameter as the chain, or make up a long-welded pear-shaped end-link on your riser chain to pass the standing part through. That makes a form of cow hitch, is cheap and strong, and misses out on the costly lifting shackle.

Any shackles used should be certified 'Lifting Grade' and not the cheap-and-cheerful and unreliable, untested 'Commercial/Farming Grade' that many chandlers are so keen to flog to us. Any swivels should be 'fully forged', and Cosalt provide superb and reliable s/s ones in 19mm that have stood the test of time, dozens of times.

Countersink the shackle pin holes to remove any sharp edges, and fit 2 or more black Ty-Wrap cable ties to prevent unscrewing when the threads start to corrode.

And make pd sure that whatever you intend to use as boat ropes - chain is better than rope -are well able to cope with the inevitable swift chafe on stemhead fairleads when a real 'hooly' hits.

Make sure that your boat ropes secure directly to the riser chain, and not to some feeble ring on top of your net float. Think 'weak links'....

I'm not usually so emphatic, but here's the source of all this certainty....


IMG-1.jpg



:cool:
 
Last edited:
Instead of using a homemade sodding great big concrete block, you could consider using a much less heavy mooring anchor that will probably have considerably more holding power than a block.
Some interesting mooring anchors here - also scrap railway wheels :
http://www.boatgeardirect.co.uk/id17.html

Gaelforce Marine took over Seaboard mooring anchors 12 years ago, but they dont make much mention about these anchors on their website - these are the ones that the RNLI (used to?) use for their lifeboat moorings.
They do mention the Sea Claw anchors though - http://www.gaelforcemarine.co.uk/Anchors-and-Mooring/Anchors/SC12-Seaclaw/
You could probably buy a Sea Claw heavy enough to use for a mooring for the same cost as a lunch hook anchor from Rocna or Fortress......... :)
 
Just a thought. Out here in the med the local fishermen make up the mooring block out of a HUGE tractor type tyre filled with heavy mix concrete. They have a tube through the middle and put the chain through it. The bigger boats use two of these in tandem.

Good luck

Peter
 
Bajansailor said:
Instead of using a homemade sodding great big concrete block, you could consider using a much less heavy mooring anchor that will probably have considerably more holding power than a block.
Some interesting mooring anchors here - also scrap railway wheels :
http://www.boatgeardirect.co.uk/id17.html
I used 1.5 ton concrete sinkers cos the "sodding" theives steel mushroom and big CQR mooring anchors. I had a 300 lb mushroom stolen from the Gareloch so cast my own.

J
Click to expand...
Click to expand...
 
Last edited:
I have always used a 1:2:3 mix for general concrete
That is 3 measures ballast (10mm to nothing)
2 measures sharp sand
1 measure cement
Added to the mixer in that order
so if you have one ton of premixed sand and ballast you will need 200kg of cement = 8 x 25kg bags
 
I had a 300 lb mushroom stolen from the Gareloch so cast my own.
got any pics of doing that?..would be interesting

Hmm think ill stick to casting concrete...:)
but if i worked at a foundry...then maybe

8 x 25kg bags
sounds about right!
 
that link to

http://www.boatgeardirect.co.uk/id17.html

has an interesting line about steel wheels.

"Scrap railway wheels make excellent mooring sinkers and unlike concrete they do not lose weight when submerged."


Not only do they suspend chain moorings, but also the laws of physics. What would Mr Archimedes say ? :)
 
Pics of my concrete morring

Niander said:
I had a 300 lb mushroom stolen from the Gareloch so cast my own.
got any pics of doing that?..would be interesting
Click to expand...

Managed to dumb down the resolution of a couple of pics of my mooring. 1st shows the concrete having been poured with the 1" steel eye which was a 7' steel rod bent into a loop and welded to the base. Sides were 1/4" and base was 3/8".

I made my mooring circular as I was paranoid about the chain being caught up on a square mooring sinker.

2nd pic shows the ground chain which was at least 1" with big end links. Riser chain was 1/2" and at low water i could (using deck winch) lift the end of the ground chain to the surface to renew shackles and swivels.

Even with all of that I nearly lost the boat due to a the thread on a heavy duty shackle on the riser eroding. All that was holding it was the mousing wire. Wondered if the problem was electrolytic and should I have used a Zinc Anode on the mooring.

One point is that once I had pourded the concrete, I covered it in plastic and went down to the slipway every three or four days to keep the concrete wet to stop it cracking or drying too quick. (just a bit more paranoia)
 
Last edited:
slate is structurally weak. Not a good idea unless you grind it up to dust, even then its density is only about 1300kg / metrecubed.
 
Last edited:
You must log in or register to reply here.

Other threads that may be of interest

R
Leisure batteries, how to fit? Help!
Replies
10
Views
605
Skipper Felice
Skipper Felice

Share this page

Top