Zing
Well-Known Member
Oops, quite right. I'm jumping to the obvious conclusion, but my assumption as you say is not based on fact.
Stainless steel anchor chain
- Thread starter Magnum
- Start date
Zing
Well-Known Member
But your picture shows it unfitted. Have they gone and fitted it before you had the chance to agree the mod with them? That would have been foolish. Then again, if it is unfitted, such an explanation for the price would be deeply troubling. Also, the stem does not look to be attached to the chain channel, so to remove the stem doesn't make sense either as it shouldn't be necessary to do so.
Magnum
RIP
The factory would not allow the chain stopper to be fitted to the stem head, prior to it being fitted.
MapisM
Well-Known Member
But in practice, this makes the whole channel concurrent in withstanding the chain longitudinal load, doesn't it?
Ok, I guess you could argue that the stopper bolts shouldn't work in shear stress, and I would agree in principle, but I can't imagine a scenario where the chain pull could be enough to break them through shear stress...!
Mind, I'm not saying that a backing plate is pointless - simply that the stopper alone doesn't make it so much more compelling, if it isn't already there.
MapisM
Well-Known Member
Just tell them to deliver the boat without fitting the stem head. And ask a discount for that, in the process!
Neeves
Well-Known Member
This is all a bit abstract as I have no idea of the layup of the deck round the channel into which the stopper fits. But if the bolts are to pass right through the channel and deck into the locker (with nuts on the inside) then it seems so simple to add a decent backing plate. Now it might be the layup is such that it needs no backing plate - but in the absence of confirmation - Its simply cutting a rectangle, drilling 4 holes and bolting into the roof of the locker (with a bit of Sika thrown in). For all I know its a foam/glass deck - and then a backing plate is not an option - its essential.
Its easier for me as I could go and make one now, except it would be noisy and its 10pm here. But I have the stainless, angle grinder, rather large bench drill, drill bits, cutting oil - so, as they say - I'd just do it! and it would not occur to me not to add the backing plate - being so simple.
Portofino
Well-Known Member
If the stem thing has to come off ( although in your earlier pic it was was not fitted ) for more holes, then why not ask them to weld it on .
It's looks like a nice coincidental fit anyhow .
The weak link in a massive horizontal force will be the pin anyhow .
One pin Vs 4X SS bolts -with /without backing plate .
How ever if welded then the horizontal pull will transfer to the stem thingy -it's normal bolts which I suspect looking at the pic Dia size and number 4? -seem a bit light .
If its a cored deck here -most likely then an extra 4holes + backing plate or even large spread washers will be beneficial as a said the exsisting attachment of the stem thingy looks a little light -cos as it stands the windlass suppose to take the forces.
Returning to sq1 --how about a simple chain hook on a short mooring line to one or both mooring cleats we cab see in the pic .
I know it means somebody has to up n the bow -even a female can undo the line --a few fig 8,s -- let it slacken off before unhooking ,you don,t have to send a gorilla .
The same line + chain hook also comes in handy if you ( likely on your proposed del - tour with a big boat ) end up in a visiting mooring whereby you are loo long for the rope on the bow and end up pulling chain up -so,s not to have it scrapping on the new gelcoat /teak .
It think it would be neater if welded but then the whole "stem" thingy would need bigger holes for bigger bolts and a beefier backing plate ---if you think the cored top side can take the strain before the pin # in extremis .
But it main function is at normal anchorages to take the strain off windlass in normal to moderate winds -read force s
It's looks like a nice coincidental fit anyhow .
The weak link in a massive horizontal force will be the pin anyhow .
One pin Vs 4X SS bolts -with /without backing plate .
How ever if welded then the horizontal pull will transfer to the stem thingy -it's normal bolts which I suspect looking at the pic Dia size and number 4? -seem a bit light .
If its a cored deck here -most likely then an extra 4holes + backing plate or even large spread washers will be beneficial as a said the exsisting attachment of the stem thingy looks a little light -cos as it stands the windlass suppose to take the forces.
Returning to sq1 --how about a simple chain hook on a short mooring line to one or both mooring cleats we cab see in the pic .
I know it means somebody has to up n the bow -even a female can undo the line --a few fig 8,s -- let it slacken off before unhooking ,you don,t have to send a gorilla .
The same line + chain hook also comes in handy if you ( likely on your proposed del - tour with a big boat ) end up in a visiting mooring whereby you are loo long for the rope on the bow and end up pulling chain up -so,s not to have it scrapping on the new gelcoat /teak .
It think it would be neater if welded but then the whole "stem" thingy would need bigger holes for bigger bolts and a beefier backing plate ---if you think the cored top side can take the strain before the pin # in extremis .
But it main function is at normal anchorages to take the strain off windlass in normal to moderate winds -read force s
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jfm
Well-Known Member
@hurricane, I struggling to digest that they're M16. Surely they're M10 or 12
@mapism, in general there should be no shear loads at all on the bolts. The correct assembly is to have the bolts in tension only, and the shear forces are then taken entirely by the friction created thereby. Of course in a mushy deck it won't work like that in practice, but if this is solid deck not sandwich with a decent backing plate (ie decent area, and stiff, hence use ali) you will get this "no shear load on the bolts" effect
@mapism, in general there should be no shear loads at all on the bolts. The correct assembly is to have the bolts in tension only, and the shear forces are then taken entirely by the friction created thereby. Of course in a mushy deck it won't work like that in practice, but if this is solid deck not sandwich with a decent backing plate (ie decent area, and stiff, hence use ali) you will get this "no shear load on the bolts" effect
Portofino
Well-Known Member
Ah did not see this -sorry -if it was me I would drop it -and -try the simple chain hook + cleat idea .
How ever sometime down the line (excuse the pun ) if the boat is out being AF,d and the yard seems a bit engineer like ask them to revisit the issue -fitting a chain stopper .
Arie d Boom in La Rague are such a yard .Saw them fit stabs on aRiva ego 68 recently --nothing phases them .
Labour is €65 / hr charged out + tax
MapisM
Well-Known Member
I get that, but it wasn't my main point.
Don't you agree that as long as the stopper is bolted above the roller channel, they become concurrent in resisting any load?
And if the whole bow roller assembly as it is (with or without the backing plate - I still didn't understand how the OEM setup is like) can withstand the heavy lateral snatch loads that can occur when the boat swings badly, don't you think that "a fortiori" it must withstand the longitudinal chain pull?
Again, I'm not saying that the backing plate is a bad idea - far from it.
Just wondering if and why the stopper per se can make it more necessary.
MapisM
Well-Known Member
You know what, I sort of agree.
Let's face it, there are two possible anchoring scenarios, in practice:
1) you drop the hook in glorious weather for having a swim/lunch/whatever before heading back to the marina.
In this case, the winch is more than enough to take the chain load without the need to use any stopper.
2) you drop the hook for overnighting, and/or in windy conditions.
In this case, you want to use a snubber anyway, whether you have a stopper or not, to avoid getting the chain constantly pulling and grinding on the bow roller sides.
Bottom line, the stopper is more useful in theory than in practice, imho.
Hurricane
Well-Known Member
I did check before posting so I checked again.
Yep - M16 - 100mm long to go through the deck.
I also remember getting an allen key socket attachment for my socket set - because I didn't have any allen keys that big.
It maybe over engineering on Lewmar's part but I think I read somewhere that they specify the chain stopper's breaking strain as one and a half times the breaking strain of the chain.
jfm
Well-Known Member
Magnum
RIP
I have decided against removing the stem head from its channel. As well as bolted it is likely to be Sikaflexed in position and I can only imagine how difficult it would be to remove and what damage might be caused in the process. The factory did not fit it with removal in mind.
So drilling in-situ is the only acceptable solution, with a backing plate.
So drilling in-situ is the only acceptable solution, with a backing plate.
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Neeves
Well-Known Member
I've never used a chain stopper - but I would have thought there was still chance for the chain to rattle on the bow roller and cause annoyance (though I vaguely recall someone said sound insulation were good). If there is noise you will still need a snubber (which part negates the stopper. I wonder how the option of a simple chain hook stacks up - to be applied to the chain in the channel, so on deck. You will still need a strong point to which to attach the cordage or chain to which the hook is attached - but it might be simpler instlltion than drilling through the stainless channel. I'm thinking of a centrally located horn cleat or padeye to which you could attach a short length of appropriately sized chain with a simple claw on the end.
MapisM
Well-Known Member
In another thread, maybe? I can't find it in this one...
I would have thought that the grp mould was sized to allow the ss channel to sit "comfortably" inside it, hence relying on the bolts for strength.
But maybe you are right, and the ss channel is actually "forced" inside the mould - hard to tell from the pics...
MapisM
Well-Known Member
You bet.
The stopper makes zero difference in terms of grinding against the bow roller sides, as I already said in previous posts.
Mind, the same goes for a chain hook to be attached on deck in the channel: you still need an external snubber if you want to get rid of the chain rattle on the bow roller - no way around that.
Hence my conclusion in the last line of post #311, when all is said and done...
Neeves
Well-Known Member
Yes - I was not trying to be original - I was agreeing with you and surprised your comment sank like a lead balloon!
A couple of snubbers (bridle), and a chain hook on deck attached to a strong point (not the windlass) seems one solution (and beats drilling though the stainless channel. The hook can also secure the anchor at sea. Its also, on a smaller scale, exactly what we do (though our strong point was 'built in')
D
Deleted User YDKXO
Guest
Yup a stopper and a snubber are 2 different things. As you know we only use the stopper to protect the winch when going astern to set the anchor. We find that the Rocna can set very hard very quickly and 40t of boat going astern at that point can put a large shock load on the winch if there is no stopper. But in order to stop the chain grinding on the bow roller and in our case putting large lateral loads on the bow roller assembly, we use a snubber although in quiet weather we wouldn't use it
Zing
Well-Known Member
In most leisure boats the snubber is primarily there to act as a spring, to reduce peak loads on the anchor and boat. With really light boats using using chain in shallow water (no catenary) it is essential equipment. The shock loads can pull the anchor out or spill your beer. It is a useful function in heavy boats too. It also silences the chain noise. I put the snubber on before setting the anchor. It is much nicer to the boat if you stop suddenly.
For the spring to work well the snubber has to be springy and that will mean it will be thin and will fail well below the holding limit of the anchor and chain, so in strong conditions something else is needed to stop the windlass being pulled out of the deck or to prevent the chain back-winding out. That is where a second heavier snubber can help, or a wrap of chain around a cleat or best of all, a nice tidy chain stopper.
The chain stopper is not the thing to hold your anchor to the bow tightly. A claw with tensioner for example would be ideal for that job.
For the spring to work well the snubber has to be springy and that will mean it will be thin and will fail well below the holding limit of the anchor and chain, so in strong conditions something else is needed to stop the windlass being pulled out of the deck or to prevent the chain back-winding out. That is where a second heavier snubber can help, or a wrap of chain around a cleat or best of all, a nice tidy chain stopper.
The chain stopper is not the thing to hold your anchor to the bow tightly. A claw with tensioner for example would be ideal for that job.
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