Mooring advice

[claymore]

I need to organise the purchase and laying of 3 moorings in tidal water. I'm going to use the heftiest chain that the budget will cover and try to get an upper limit of around 12-15 tons. If I was anchoring in windy conditions I would probably go for 5 times the depth rather than 3 so is this a reasonable formula to use or should I be going for more chain. Additionally - what size chain from the ground tackle up to the swivel should I consider? I think 12 mm should be ok from the swivel to the bouy.

 

[kds]

You also need to consider the nature of the bottom. We have deep mud and so a sinker (car or lorry tyre full of concrete) beds itself in after a week or so. If the mud is hard, we have to dig it in. The riser to the bouy would be on a scope of less than 3/1 at spring highs.
Ken

 

[jerryat]

Hi Claymore,

For our club moorings on the River Tamar we use extremely heavy ex-ferry chain around 8' (2.4m) long set into the circular concrete blocks. To this is shackled 19mm chain up to the underside of a 'riser' to the main buoy, the length determined by whether the mooring is for the drying, mid-depth or deep water line.

On the deep line the 19mm stuff is about 30 feet long and ends in a very heavy duty swivel. To this swivel is shackled a nylon/polyester 'riser' circa 4 feet long the top of which is shackled to the under side of the buoy. This latter is to hold the chain lower in the water and reduce its exposure to the most aerated water.

The pick-up line(s) are also taken from the swivel to the boat via a smaller pick-up buoy. So, on my mooring for example, in a max water depth of circa 22 feet, the total length from block to surface level is aprox. 42-45 feet.

The Tamar is very tidal with spring rates where we are, running at up to 2.5+ knots at springs. The depth (on my mooring) varies between 5 foot and circa 22 feet at springs.

Touching wood, but during the 28 years I've been on our moorings, I can't remember one that has dragged. About three other moorings in the area have, but I don't know their construction. Don't know if this is of any help to you, but hope so. /forums/images/graemlins/smile.gif

 

[longjohnsilver]

Are you using ground chain or a sinker? Whichever I would be looking at a riser of no more than 1.5 x max depth otherwise your mooring will be wandering all over the place.

As for the size of the riser you'll need to take into account the weight of the chain on the buoy. I've used 3/4" stud link on my mooring, max height about 10 meters, which is one hell of a weight, and I've got a large buoy with about 4kts or so of tide on a big spring.

My best tip is to find a shackle which is a very snug fit in the eye of the buoy, should last for many years if you do, then you only need to worry about the connecting shackles. Buy the best you can find.

 

[Miker]

John
I can't offer any advice but am wondering where you will be putting them. Piel island? I thought that the club already had some there, not that I have ever located them.
Best wishes
Mike

 

[claymore]

Hi Mike
Yes - Piel. The others have gone!!
Investigation seems to suggest that the previous ones were not up to spec. Ribble and Glasson have got some decent moorings and, I'm sure you will agree, B&F are spending a lot of money providing safety boats for training and the dinghy racing - the offshore fleet, whilst not the most active at present is by far the largest and so I feel it is essential that we maintain good moorings at Piel otherwise we are in danger of sending a very negative message to this section of the Club.
We are going over there again on the August Bank Holiday and I sincerely hope you will be able to join us.

 

[capt_courageous]

Hi
These are the minimum chain sizes recommended by Minehead HB. Mixed units again.

30 footer - riser 12.5 mm pick up 9.5 mm

35 footer - riser 19 mm pick up 11 mm

Our old club had DIY swinging moorings in Southampton Water - pretty exposed. The swivels were usually the main things that failed. We used the heaviest ground chain we could handle. I ended up buying a pair of really big Danforths since the bottom was mud and the water to deep to do any digging in. As John says do not overdo the riser length.

 

[Marmalade]

We use (Marconi SC) two anchors - in line with the tidal stream on a ground chain (mine is over 100ft) with a riser to the buoy from the centre. The buoy should be buoyant enough to lift the centre of the bridle (ground chain) off the seabed to create a catenary and should be afloat at high tide - this determines the length of your riser (scope).

 

[Ecosse120]

These are the mooring regulations for the Harwich Harbour Authority (East Coast). May give you an idea:

http://www.hha.co.uk/default.asp?section=leisure/moorings&page=notes