Daydream believer
Well-Known Member
Tension is not the same as shear force
Tying up to the shrouds - is it acceptable?
- Thread starter MissFitz
- Start date
Tension is not the same as shear force
Stemar
Well-Known Member
I think I'd be very concerned if my chainplates couldn't handle normal mooring loads on a small boat where the're likely to be simple u-bolts with backing plates - not dissimilar to how a cleat is fixed.
However, the alternative is always to go the other way - take your springs from the aft cleat to a midway cleat on the pontoon and on to the bow. Better still, use two lines and have springs the length of the boat
However, the alternative is always to go the other way - take your springs from the aft cleat to a midway cleat on the pontoon and on to the bow. Better still, use two lines and have springs the length of the boat
RichardS
N/A
This is what happens when one's cleat is ripped out by a storm surge:
Now let's consider what happens when one's chainplate is similarly afflicted ....... :ambivalence:
Richard
flaming
Well-Known Member
In any boat that you can pull around in its berth by hand you will have no problems running mooring lines to the shrouds. Been doing that for years on race boats of all sizes. Just try and get the warp to sit at the bottom and not directly onto the wire.
If you really were expecting conditions where the cleat of a big MOBO could be ripped out of the deck, then maybe do something different, but in normal use in a normally sheltered marina - no problem,
AntarcticPilot
Well-Known Member
I think it depends on what stresses you're applying to the mooring lines. I use a midships spring to go onto my berth, and if I misjudge it and am going a bit too fast as we enter the berth, the spring puts a large load on the cleat - it's stopping several tons of boat in a few inches! I have midships cleats bolted securely to an aluminium toerail that is part of the deck-hull join, so I don't have any concerns; the stress is in any case in the "strong" direction of the fixing. I'd be very worried about putting that sort of stress on my chain plates, which, while amply strong in the direction of the load on the shrouds, are not supported sideways in any particular way. It would probably be OK, but probably isn't certainly!
However, once moored, I wouldn't expect the stresses on springs to be that great; I'd expect the main stresses to be on the forward and aft lines, which presumably have good solid cleats.
However, once moored, I wouldn't expect the stresses on springs to be that great; I'd expect the main stresses to be on the forward and aft lines, which presumably have good solid cleats.
johnalison
Well-Known Member
I think that is optimistic. I don't think the OP was particularly asking about using the shroud/plate for a mooring spring so much as an occasional aid to arrival and departure, when the line will often be taking the whole load, though this need not be high.
Buck Turgidson
Well-Known Member
Pencil and paper. Draw force vectors. Think about load path. Fit a cleat.
MissFitz
Well-Known Member
I was mainly asking about using shrouds for a mooring spring, which is what I do at the moment. I was also interested in views on using them for berthing as it would be really handy, but I haven't tried it yet.
Looks as though the jury is out on the use for springs, so I'll probably keep doing that & keep my fingers crossed (I don't have side deck winches, so it really is the easiest option by a long way). But it also sounds as though using them for berthing might not be such a good plan - guess I'll just have to work on my parking technique & train my crew to stop the boat if it goes wrong. Thanks for all the input guys, really interesting & helpful.
Lon nan Gruagach
Well-Known Member
Would you ever berth by sailing forwards up to a wall with a tyre as a buffer.. misjudge it and your bow will be stopping the boat in a few inches too...
Bang on the money!
JumbleDuck
Well-Known Member
We can do the sums. 5,000kg of boat slowing from 1m/s to 0 in 0.1m. F = ma = mv2/2s = 5,000 x 12 / 0.2 = 25kN = 2.6 tons-force, which is roughly the breaking strength of 10mm braided polyester or 6mm 1x19 stainless.
The OP's boat only weighs a ton, so would only take 5kN to stop from the same speed over the same distance. That's a lot less than the breaking strength of 6mm braided - you're practically at bootlace territory
I'm not sure what a diagram of vectors and loads is going to show. Tying onto the shrouds and significant distance up them will increase the tension a lot, but tying onto the chainplates should be just fine.
aslabend
Well-Known Member
coo, how fast do some of you come into a berth?
I'm usually almost stationary by the time I hop off and only occasionally need to use a rope amidships as a temporary line to quickly hold the boat while i sort other lines out. Still rig one most times I arrive or leave a berth just because they are handy
I'm usually almost stationary by the time I hop off and only occasionally need to use a rope amidships as a temporary line to quickly hold the boat while i sort other lines out. Still rig one most times I arrive or leave a berth just because they are handy
JumbleDuck
Well-Known Member
One wonders. A helpful fellow yachtsman this summer who came across in a marina to take my lines and looked very bemused when I said "we'll just stop" an reply to his query about which line to stop us with. From reading magazine articles it seems that using the ropes to stop is standard practice in some places.
aquaplane
Well-Known Member
I keep looking at my side decks trying to work out where to fit midships cleats, I can't decide on a good place.
Outside the guard wires would just be odd. On the side deck would be intrusive.
I don't use the shrouds though.
Outside the guard wires would just be odd. On the side deck would be intrusive.
I don't use the shrouds though.
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Kelpie
Well-Known Member
My first boat was an Albin Vega and didn't answer the helm if you were under 2kt. I got into the bad habit of screaming into berths fairly quickly as a result.
I've been trying to unlearn this as the new boat is about 6t and I'm going to end up dislocating an arm one day...
AntarcticPilot
Well-Known Member
Problem with my boat is that at very low speeds I lose steerage. I tend to be doing 1-2 m/s in neutral when the bow passes the end of the pontoon. The propwalk in reverse throws me off the pontoon, so I try not to use reverse heavily - a gentle drag rather than slamming on the brakes. There's also not much space between me and my neighbour! So your worked example above mimics very closely what I usually do, these days. My displacement is about 5000kg + all the gubbins on board! I can halt her with reverse, but tend to lose control if I have to do so - which happens when my wife misses picking up the spring! Allowing the midships spring to take the way off her has two advantages 1) I can keep steerage all the way in and b) the spring places her exactly where I want her in relation to the pontoon.
All this isn't helped by the fact that the throttle isn't conveniently positioned on my tiller steered boat; to operate it I have to bend right down into the cockpit, losing all visibility outside the well of the cockpit. I can operate it with my foot for the approach, but large positive movements need more "hands on" operation.
MissFitz
Well-Known Member
I'm sure/hope that once I've had a bit of practice I will be able to do that. But in the meantime.........
Lucky Duck
Well-Known Member
Does the boat actually 'weigh' 5 tonnes in this situation? I can reliatively easily move my boat of a similar weight by hand but my car weighing a lot less, not a chance!
JumbleDuck
Well-Known Member
What you need is a small person who loves operating engines!
I too have to come in at a reasonable speed to have control, but I'm perhaps lucky that the engine will stop her very nicely, particularly when coming in port side to.
JumbleDuck
Well-Known Member
Rolling resistance of tyres is much higher than skin friction drag (the only sort that matters) on a slow-moving boat. If you drive your car into a swimming pool you'll find it can be quite easily pushed around until it sinks.
AntarcticPilot
Well-Known Member
In this case it's the mass of the boat that matters, surely. The force required to stop a 6 tonne boat moving at 1 m/s is exactly the same as the force required to stop a wheeled vehicle weighing the same. Of course, that force may be partly provided by either skin friction or rolling friction, but the total force required is the same.