Mooring risers

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advscot

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www.adventure-scotland.com
Hello. I currently use 10m of 8mm galvanised chain as a riser on my swinging mooring. This is attached to the mid point between two opposing spade anchors linked by much heavier chain. On annual inspection the ground tackle seems to be good as new but the riser chain only lasts around 3 years before corrosion demands replacement. MOst of the corrosion occurs within a meter of the surface - presumably where the water is moe oxygenated. Does anyone have experience of using a rope riser instead of chain? - perhaps with the addition of a substantial sinker weight attached to the rope to help reduce snatch?
 
I've never been an advocate of rope for a riser - others may have different experience and opinions, of course. Three years is not that bad for a chain riser, certainly not here in the South, and certainly better than I'd expect with a rope. For anything more than a large dinghy, I'd have thought 8mm chain rather light but as you say it's the top end that corrodes in the oxygenated water. You might consider an old method witha long rope from the chain riser to a pickup buoy so when unoccupied the riser chain is lowered to the seabed, to be hauled up when you return.

Rob.
 
I'm on a swinging mooring and use a similar arrangement and size of chain. Mine dries out and I find the chain lasts quite a few years before replacement is necessary. There is some stuff called anchorsteel or something that has very good strength and no corrosion problems (it's some sophisticated rope used in Scottish salmon farms). You could also consider dispensing with the big buoy and having the rope strop and pickup buoy attached directly to the top of the riser so that it drops to the bottom when your not there. This might reduce corrosion and saves the cost of a big mooring buoy.
 
Polysteel is the name.

http://www.ebay.co.uk/sch/i.html?_f...A0.H0.Xpolysteel.TRS0&_nkw=polysteel&_sacat=0

It floats, is UV resistant. And is quite difficult to splice. I have used a set for mooring ropes for about a year. No complaints. If you soak it in Patio Magic, weeds and critters are disinclined to take up residence.

I looked at rope risers a couple of months ago. The view of a very competent rope manufacturer is that polyester is more flexible and easier to work, and a riser could be made with an armoured (HMPE) braid to resist UV and abrasion. There would be substantial savings in weight, and inspection of the cover would therefore be easier and enable DIY checking of the condition.
 
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My mooring was laid by a professional company and they used a rope riser for my 10t ketch and all year round use. Its only the shackles and thimbles that need occasional replacement.

A nearby mooring using a chain riser was in a bad state even though it had not been used for some years. The top 2metres were worst affected. I would never consider a chain riser.
 
3 strand nylon onto some heavy chain and concrete block. Used for 6m rib and still good nearly 9 years. Will probably be going to sail boat soon and intend to use nylon again for a 4.5 tonne boat. Doesn't dry out.
 
ianj99 said:
My mooring was laid by a professional company and they used a rope riser for my 10t ketch and all year round use. Its only the shackles and thimbles that need occasional replacement.

A nearby mooring using a chain riser was in a bad state even though it had not been used for some years. The top 2metres were worst affected. I would never consider a chain riser.
Click to expand...

Rope is common practice on the East Coast
 
As the above posts show, there are a huge number of possible variations on this. One of the better ways of choosing is to see what everyone else in your area does. Whereabouts are you (othe than Aviemore, obviously)?

8mm sounds absolutely titchy- OK as an anchor chain but I'm surprised at people using it as a permanent mooring riser.

My own boat is on a 19mm chain riser, supported by a big fish farm buoy, and with a swivel part way down. I can pull the swivel on deck at low springs, by using a succession of rope strops led back to the windlass. It's a bit tedious but costs nothing so I check the swivel a couple of times a season in this way.

Gaelforce will sell you a mooring using a rope riser, and plenty of fishing boats live on these all year round. Generally multiplait polysteel or seasteel- as mentioned upthread, this is an improved grade of polypropylene.
I use the 32mm version as my strop, and didn't consider it particularly hard to splice. When I next need to change my riser, I am considering using polysteel instead of chain, for the upper half above the swivel. This part takes no wear from the seabed but is in a more oxygenated environment.

@Sarabande, that's a great tip about patio magic, I must give it a go. How long does the effect last?
 
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