NormanS
Well-Known Member
The trouble with having the swivel at the top of the riser, is that there is all the weight of the riser hanging on it, so it doesn't want to turn.
More on moorings .... swivel or not ....rope or chain.....?
- Thread starter iainzxr
- Start date
GrahamM376
Well-Known Member
Ours rests on the sand at LW springs but is off bottom most of the time. It's overkill strength wise in being 8 tons SWL which gives a breaking strain in excess of 24 tons but, that means it has a lot of meat around the swivel to wear away over time so will last many years.
Neeves
Well-Known Member
The ideal mooring, to us, has minimal weight when you lift to attach to the bow. Lifting chain, swivels, shackles, bigger buoys should not be necessary. It should be easy - as easy is usually safe.
Jonathan
Jonathan
lw395
Well-Known Member
A nice sentiment, I don't entirely disagree, but I've seen this methodology tried in our mooring area. The result was a very rough ride for the boat.
A mooring that can be trusted in a blow tends to involve fairly heavy gear, if you don't have the luxury of a very well sheltered mooring spot.
A very good point about 'thinking safe' when it comes to handling the mooring though!
vyv_cox
Well-Known Member
It depends on exactly what is meant by 'mooring'. Ours and most (all?) others on Menai Strait need heavy chain to cope with the exposed location aligned with the prevailing wind and tides up to four knots. Our mooring had two admiralty pattern anchors weighing around 50 kg each, one inch ground chain from each in a bridle, a heavy welded joint at the junction, a swivel with a 3/4 inch riser to a large buoy that carried the weight of the riser. A pick-up buoy on light rope attached to 1/2 inch chain was attached beneath the buoy, the chain being attached to the boat when moored.
In more sheltered moorings it is quite common to have a single weight, concrete or iron, with a relatively light, short chain, then rope attached to a much smaller buoy. Many of the visitor moorings at Greek tavernas are like this, although there are some of the former design.
Neeves
Well-Known Member
See Post #15. I think our concrete and steel work sitting on the seabed is quite adequate for anything that is thrown at us. the 1" floating line that connects this steel work to the yacht is all we need to pick up (we do not need a buoy to support the mooring line - it does that itself). Our marker buoy floats and maybe weighs 500gms. All we do is lift the floating line, 10m of it, we do not need to lift any steelwork. Needing a large floating buoy to support the mooring line does not seem quite right as that means the mooring line itself is heavy and you inevitably need to take on some of the weight of the large buoy. But tides for us are simply insignificant and if we get one 50 knot event a year - that would be unusual, strong wind is typically 35 knots with only small seas, just enough to splash the deck..
Jonathan
Jonathan
afterpegassus
Well-Known Member
If the riser is supported with a dahn type buoy ie, the riser coming through the center, then there is no downward load on the swivel.
This is my arrangement, in my particular location, and works very well for me.
NormanS
Well-Known Member
Presumably you have a swivel on the top of the buoy. That takes care of any potential twist between the boat and the buoy, but doesn't address any twisting in the riser.
Capt Popeye
Well-Known Member
Humm, suggest that he load value of any swivel is checked before choosing / using it, quite often the load value is surprisingly low compared to the size of the swivel.
Hardware items supplied for some activities, like cranes or lifting systems do have the load values stated with the sales info.
Hardware items supplied for some activities, like cranes or lifting systems do have the load values stated with the sales info.
lw395
Well-Known Member
I'vr found no problems with the riser twisting on a mooring which gets spun twice a day, we had a swivel above and below the buoy. Swivels on the seabed seem to be very unreliable in Portsmouth Harbour. Likewise the kind of swivel you get built into the bottom of a buoy. Maybe the load of a heavy riser does not help, maybe they are just not great engineering.
There can be an issue if the pendant is long, the boat winds up the bouy instead of rotating the swivel, but we found a short, tight pendant gave a far better motion for the boat in wind-over-tide and worked well with a swivel in it. Also keeps the buoy under the bow and off the gelcoat.
At least a swivel under the buoy can be accessed by tipping the buoy over at low tide. One above the buoy can be lubricated. I used motorcycle chain wax from an aerosol for this. Then covered the swivel with half an old fender.
But moorings must be adapted to what works for boat x in location z IMHO.
Neeves
Well-Known Member
+1
The best idea is to cast around your local mooring field, most of which have been honed over generations, and find out what works best and maybe tweak with some of the ideas here.
Jonathan
afterpegassus
Well-Known Member
......scratching my head now Norman.
You only really need one swivel in the system - to counter rotations between boat and riser. Surely if the boat is free to rotate to the swivel, then the riser can also rotate against the swivel if required?
My swivel is above water so I can conveniently keep an eye on it and only have one shackle under water to worry about. The objective was a secure mooring with minimal maintenance (because I do it myself) and i think I have achieved that.
The very minor downside is the surface buoy rubbing against the hull.
vyv_cox
Well-Known Member
Which is why I posted as I did re Menai Strait. AFAIK every one is as I described. This is a very tough location for moorings, conditions are sometimes bad enough to prevent people from getting ashore from their boats.
