Advice on a shallow swing mooring

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seafox67

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I'm moving onto a new swing mooring this year with my 30ft Westerly Tempest (draft about 1.10m). Navionics charts are showing 1.2 for this area at low tide!

We can get swells of around half a metre during storms so I'm wondering is the trough of the swells lower than the charts 1.2? Will the trough be lower than when the sea state is calm!

This is only my second year on swing moorings so I am wondering if this is a normal margin for moorings close to the shore?

Also, I am with a mooring association who place the mooring at this location. Who would be responsible for any possible damage caused! (Even though they recommended this mooring for my boat, I am guessing is will still be my responsibility!)

Cheers
Paul
 
Only ever had half tide swinging moorings but be wary of boat sitting on exposed anchors or scraping across them when tide turns.
 
I'm on a moorings association mooring at Port Bannatyne. I've just checked, and I'm midway between the 1 and 5 meter contours on the UKHO chart. That squares with my believe that I have about 3m at low spring tides. I draw 1.4 m, and wouldn't want to have any less than 1m clear below me.

There is absolutely no way I would moor a 1.1m deep boat in 1.2m deep water. I'm sure you'd be held responsible since you know the situation. I strongly suggest you ask your MA for a deeper mooring or, if there is room and they're happy with the idea, get whoever services your mooring to move it. When I bought mine it was in only 1m and I had it moved to suit.

By the way, one of the mags had a story a few years back about a proud new owner who smashed his boat to bits in the Thames estuary when he tried to take a route with 20cm charted/calculated under the keel when there were 1m waves around ...
 
Lots of twin keel boats dry out on their moorings, that is said to be one of their advantages. It is likely to be soft mud down there but it is worth poking about at low tide to make sure and asking people who have experience of the spot. You also want to make sure the mooring sinker in well below the surface.

If we binned all drying moorings it would be a sad day. The pick of your moorings will be occupied by the old lags in the club, which is as it should be. As you progress by Buggins turn you will find better spots open up for you, in the fullness of time.

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doug748 said:
Lots of twin keel boats dry out on their moorings, that is said to be one of their advantages. It is likely to be soft mud down there but it is worth poking about at low tide to make sure and asking people who have experience of the spot. You also want to make sure the mooring sinker in well below the surface.

If we binned all drying moorings it would be a sad day. The pick of your moorings will be occupied by the old lags in the club, which is as it should be. As you progress by Buggins turn you will find better spots open up for you, in the fullness of time.

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Click to expand...
Yep, I've got a bilge keel... However, does the boat not get damaged on a drying mooring in a storm or big swell? There must be a point as the tide goes out that the boat is bouncing quite hard off the seabed!!??
 
I don't know the details of your locality, but often places are much more sheltered towards LW. You will also find that a water depth of 1.2 metres, unless in a fairly steep shelving area, cannot support large waves. Take local advice, which will be much more relevant than anything here.
 
Are you able to go there in a dinghy on LW springs and sound it with a pole? Much more accurate than a Navionics chart which may be based on an imperfect survey from decades ago.
 
I don't think touching some mud will do much harm, but a hard sand or shingle bottom could.
Best thing is local knowledge, but it does sound distinctly edgy.
 
When I was on the Exe, sand and mud, I always felt that 2m under the keel at LWS was my limit. While a bilge keel is designed to sit on the bottom the idea of it banging about for an hour or so each day did not appeal.
 
I am moored at Bangor on the Menai straights which dries to mud so you get soft landing,previously at Red Wharf bay there were boats that took a pounding in easterly winds and lost keels.
 
seafox67 said:
Yep, I've got a bilge keel... However, does the boat not get damaged on a drying mooring in a storm or big swell? There must be a point as the tide goes out that the boat is bouncing quite hard off the seabed!!??
Click to expand...
I had a bilge keel Lysander on a tidal mooring for 8 years. Draft is everything. It only drew 18" and as the water level drops, the height that seas can reach drops too and by the time the mean depth is 18" the waves can only be a few inches high and not capable of lifting and dumping the boat. 1.1 metres, more of a possible problem but my guess is that if your mooring association says it's safe, they know what they're talking about. Local knowledge is all. Discuss it with them.
 
You could have storm surges, seiches, and tsunamis, let alone high and low pressure systems which radically alter the available anount of depth. I agree with JD, that's far too shallow a mooring.
 
I used to have a mooring on which my shallow draft long keeler was normally afloat, but sat on the bottom (semi-floating, so still more or less upright) at low water springs. The bottom was soft mud and it wasn't a problem at all. The area was semi-sheltered in a large river (Pin Mill, Suffolk). (I think I had something similar somewhere in the West Country long ago, with a long fin boat, but can't the remember details.)
 
To my mind, it all depends on what the bottom is. My mooring is on thick gloopy mud that the boat floats on at low tide. It's soft enough that it wouldn't matter if I had a fin. it would just sink in. The other extreme is firm sand. I wouldn't regard that as a suitable base for a tidal mooring because, as the boat settled onto the bottom and floats off in a swell, it's nearly as bad as concrete for impact; even a few inches of swell is scary. No one would offer a tidal mooring on rock; if they did, well, hanging's too good.
 
we wintered on a swinging mooring and sank in the mud on low water springs, not a problem. Then moved to our new summer mooring it was a bit shallow and we bumped on hard sand at low water springs - not good at all and moved to deeper mooring next day!
 
I have an update guys... The mooring secretary and I have done more soundings over the last few days and the results show that I would have about 1m under the keel with a rocky/gravel seabed.

This is only my second year using a swing mooring so don't have much experience with moorings, however this is worrying me a bit!! Should I be worried?
 
seafox67 said:
I have an update guys... The mooring secretary and I have done more soundings over the last few days and the results show that I would have about 1m under the keel with a rocky/gravel seabed.

This is only my second year using a swing mooring so don't have much experience with moorings, however this is worrying me a bit!! Should I be worried?
Click to expand...
"I would have about 1m under the keel with a rocky/gravel seabed."

Even assuming that's a minimum of 1 metre at lowest astronomical tide it doesn't leave much a of a margin for the tide falling further in a high pressure area or any kind of sea or storm surge. If you were over soft mud I'd say not much of a problem but I really wouldn't want to be that close to a rock/shingle bottom.
 
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