Home-made chain stopper

[noelex]

That is a nice bow roller and the chainstopper should be a great addition.

I tried making my own chainstopper many years ago, but eventually gave up and used a commercial model,. I suspect yours is going to be much better.

 

[Neeves]

Thank you for the feedback.

The risk of the 6mm stopper plate bending under heavy load is certainly a concern. I am however a bit reluctant to increase the general thickness of the plate, as I fear that might impair the stopper's ability to grip and release the chain. (The gap between two horisontal links is limited and the geometry changes quickly as the stopper plate lifts).
If beefing up the plate to resist bending is necessary, I suppose the best way would be to ask the welder to put a reinforcing piece of steel (like a ridge) across the upper part.
The welded on links that connect the plate to the pivot point will, as mentioned, be made thicker, maybe 4mm. (There is not so much force on them, as the load from the locked chain is more or less at right angles to the plate).
Here are some further data for assessment of the loads involved:
The chain is standard 8mm, the unsupported span between the cheeks of the bow fitting is 50mm and the boat has a displacement of 4 tons.

Yes, indeed rubber doorstops. They keep the shank of the anchor central in the fitting when parked and (I believe) reduce some noise.

I appreciate that the distance between the links prohibits use of a plate too thick. I made a bridle plate for my snubber/bridle and had the exact same problem. The locking plate itself can be made, as thick as you want - all you need to do is cut a rebate either side of the slot to accomodate the distance between the links. If you look at modern chain hooks - they had the same issue and their rebate is shaped to accept the crown - I don't know what you call such a rebate (a reverse bullnose?) so a concave rather than convex rebate. If you are skilled you can do it with an angle grinder (and file + grinding wheel). You don't need to remove much as you remove from both sides (so added together its a similar amount). I imagine you could do it with a Dremel, but I don't have a Dremel, so don't know) and do most of my work with an angle grinder, grinding wheel, files and rasps.

I started off making my bridle plate from Bis 80 (800 MPa steel - as used in anchor shanks) I then dropped back (?) to Duplex stainless - which might be an option if you don't fancy making the rebate.

Now, if you want to be really clever. I suggested opening the bottom, entry, of the slot to make the chain 'drop', its really the plate that drops (but I am in Oz ) into the slot in more easily (I would still do this). I was thinking of a simple or slightly curved 'V'. If you make the actual entry to the 'v' shank sized (slightly) bigger then the gate can drop onto the top of the shank and stop it wobbling in a seaway. Maybe if you rebate the slot (in bigger plate) that would answer my idea and the enlarged rebate would sit and hold the top of the shank. This doubles up on your door stops, a clever idea. I cannot see, or cannot determine what it is made from, but if the anchor wobbles at sea and the roller itself is a polymer you will wear the roller.

I have to wonder why you have 8mm chain on a 4t yacht - but better leave that conundrum to later for when you need new chain (which looks a long way off - your chain looks good! So unless you have bottomless pockets, stick with the overly heavy 8mm

All you need now is to replace that anchor

Tongue removed from cheek

Take care, stay safe

Jonathan

 

[GHA]

The risk of the 6mm stopper plate bending under heavy load is certainly a concern.

For your boat good chance 6mm flat bar would probably be fine, though your fabricator would know much better than anyone here (including me ) - lots of different areas of experience on these forums but structural engineering isn't one of them..
For piece of mind you could get a piece of flat bar welded on edge from top to bottom each side just outside where the chain links go to reduce the cantilever.

 

[Neeves]

The gap between the two horizontal links (for 8mm chain), the vertical link is in the slot, is 8mm (I think I have that right). This may be a bit tight if you try to release under tension. This will be more of an issue as the plate lifts and maybe you can emphasise the suggestion at the slot entry - and there might be no need to carry it right up the slot.

You must have tried this with the plywood 'mock up' and its why you mention (and I quote) ' and the geometry changes quickly as the stopper plate lifts' (endquote). Even with 6mm plate I'd be inclined to bevel the edges, my reverse bull nose, or even simply chamfer each edge of the slot (front and back) to 45 degrees to give you more room. Bevelling the edges of the slot or a reverse bull nose is not going to impact strength. You can make a 45 degree edge to the slot relatively easily with an angle grinder and grinding disc. The plate can be made with a cutting disc (which you must know as you have made the hinge already)

I assume you will be using some form of snubber with the chain lock as back up. Snubbers fail, we have had 2 fail (in 20 years) and when they fail your back up needs to be man enough to take the snatch loads until you sort something else out (replacement snubber, we carry a complete spare bridle). I went for belt and braces with my bridle plate which was designed to be as strong as the shackles in the original design (the shackles were later discarded) and had it tested, with chain in the slot and retained by the two snubbers - to check its integrity. The snubbers fail first and its also stronger than the chain. So it is over engineered - but for a small part I don't mind. Knowing that a Witchard hook failed (though I assume by simply bending) in use crystallises ones mind.

On snubber failure - there was no sign at all of abrasion of the failed snubbers, neither of them. The failure was an internal weakening but they both failed where they 'rubbed' on a bob stay (we have now removed that point of failure).

Jonathan

 

[noelex]

I have just been to the bow and measured our chainstopper. This is a commercial Muir product. The paw (the part that moves) is made from a mixture of 12mm and 9mm stainless steel (or it may be chrome plated bronze) that has been welded together at about a 70° angle. There is a 9mm triangular shaped gusset reinforcing the join and toe piece.

It is a beefy bit of hardware, but this is for a 50 foot boat with heavy duty anchoring gear.

 

[BabaYaga]

Thank you all for the further input.

The locking plate itself can be made, as thick as you want - all you need to do is cut a rebate either side of the slot to accomodate the distance between the links.

Now, if you want to be really clever. I suggested opening the bottom, entry, of the slot to make the chain 'drop', its really the plate that drops (but I am in Oz ) into the slot in more easily (I would still do this). I was thinking of a simple or slightly curved 'V'. If you make the actual entry to the 'v' shank sized (slightly) bigger then the gate can drop onto the top of the shank and stop it wobbling in a seaway.

I see your point, that the plate can be made thicker, provided that I make some adjustments of the angles around the slot. I will consider this, maybe use 8mm plate, which I am quite sure will not bend from the forces involved.

The second idea – I have already thought about something of that kind, but decided it is probably over complicating things (and the rubber door stops work really well...).

Regarding the suggestion to widen the entry of the slot, I might do this if it proves necessary. My trials with the mock-up indicate it is not, probably because there is a slot already in the roller(s), which means that when I haul in the chain it comes off the wheel with the links perfectly horisontal/vertical.

 

[Kukri]

Claud Worth, “Yacht Cruising”, 1912.

 

[Neeves]

View attachment 117179
Claud Worth, “Yacht Cruising”, 1912.

It is very difficult to develop something that was not common place (or known about) 100 years ago. I find myself (and others) reinventing the wheel

Thanks.

You have much better library than me - I'm envious.

Jonathan

 

[Barnacle Bill]

Just saw this thread come up again - I've now tried it out for real, and it's excellent. Instead of hauling hand over hand, you use both hands: lean back to get a length of chain in: relax and change your grip: and go again. It's a real help, and will be particularly useful hauling the dead weight of chain plus anchor from a bit of depth.

 

[Neeves]

Just saw this thread come up again - I've now tried it out for real, and it's excellent. Instead of hauling hand over hand, you use both hands: lean back to get a length of chain in: relax and change your grip: and go again. It's a real help, and will be particularly useful hauling the dead weight of chain plus anchor from a bit of depth.

And so much cheaper than a gym subscription.

So now I do have to ask - why 8mm chain?

Don't tell me 'because its there!'

In any event - well done.

I do find it useful when the OP raises a question, they receive advice, weight the advise up, act on it

and then tell us how the 'question' developed and worked out.

So thanks for the last chapter!

Jonathan

 

[Countess of Camaret]

Such an elegantly simple solution! Though there's concerns, worst case scenarios of 'up n down' bar tight chain and pitching bow ... yes you've got options to unload the stopper ... and SO many advantages! I went a 5 month summer always anchoring, W Brittany, with windlass out for repair, 11 ton, 37ft, and weighing anchor by hand, few time per week, solo. I coped, yes, but often moved on well ahead of any threat, wind, swell, to be sure I could cope. After that, I promised I would sort out a chain stopper, essential back up. Windlass will some day let you down, different ways, battery, switches, worn brushes, corroded electrics. Chain stopper... it's always there, ready ... and snatching in a few feet every time bow dips, so much easier, and no risk of mashed fingers when load comes back on!!!