Chain Stopper Install

[a64pilot]

I believe Jedi was dragging anchor too which would have the effect of reducing peak loads significantly, I guess maybe an argument could be made that if he had a bigger, better anchor, perhaps the rode would have parted. But you can make any argument, only thing matters is the boat survived, If it's the incident I'm thinking it is.


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[a64pilot]

Is your sprit strong enough?
I grit my teeth thinking about the jarring fetch of that chain in a stopper.
Would a P & S nylon bridle make sense for normal conditions?

I will never anchor except for a lunch stop without a Nylon snubber, I currently use two pieces of 5/8 X 25' three strand and a Mantus hook. I never intend for the stopper to take any load, it is I guess the last ditch, I guess make it as strong as you can in the hope that if you lose your snubber, you don't lose the boat.
I think the bowsprit is incredibly strong, It's laminated wood and solid, I don't what type of wood or number of laminations. I would think the weakest link is where it joins to the hull, I would assume failure mode would be to bust it loose from the hull?
My boat sails like crazy on anchor with just one attachment, using a two rope bridle attached to both bow cleats really seems to tame this sailing

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[thinwater]

Originally Posted by a64pilot

I believe Jedi was dragging anchor too which would have the effect of reducing peak loads significantly, I guess maybe an argument could be made that if he had a bigger, better anchor, perhaps the rode would have parted.

That makes sense. The peak load would have been reduced to something the chain could manage.

But you can make any argument, only thing matters is the boat survived, If it's the incident I'm thinking it is.

I've never understood the logic in this sort of statement. It dismisses the argument because the boat survived, which was not the contested by the argument. I was explaining why the nylon failed, and I explained why the chain did not. There is no conflict. There is a only the problem of too quickly extrapolating the facts of his ordeal to other situations.


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xxxxx

[Paul L]

The other place that a chain stopper like the Lewmar is useful is to stop the snap loads on the windlass when retrieving in rough conditions. You can do some damage with a foot half wind chop and a bouncing bow.

[deblen]

Originally Posted by a64pilot

Is your sprit strong enough?
I grit my teeth thinking about the jarring fetch of that chain in a stopper.
Would a P & S nylon bridle make sense for normal conditions?

I will never anchor except for a lunch stop without a Nylon snubber, I currently use two pieces of 5/8 X 25' three strand and a Mantus hook. I never intend for the stopper to take any load, it is I guess the last ditch, I guess make it as strong as you can in the hope that if you lose your snubber, you don't lose the boat.
I think the bowsprit is incredibly strong, It's laminated wood and solid, I don't what type of wood or number of laminations. I would think the weakest link is where it joins to the hull, I would assume failure mode would be to bust it loose from the hull?
My boat sails like crazy on anchor with just one attachment, using a two rope bridle attached to both bow cleats really seems to tame this sailing

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Sounds sensible to me.
Let's hope you don't have to test everything in 120kts-or anywhere near. If things get that wild,head to shore or head to sea.

[wsmurdoch]

Originally Posted by a64pilot

I'm struggling with figuring a way to drill perfectly straight holes through 8" of material with a hand drill, just a little slant will have the exit holes way off.

While I have never done an 8" thickness, I have done lesser thicknesses by attaching the hardware with double stick tape to a bit of scrap wood as thick as the wood I hoped to drill. I then drilled the holes through the hardware and the scrap wood beneath using a drill press to assure that the holes were both properly spaced and square. I could then use the scrap wood as a jig when I later drilled the real holes with a hand held electric drill. It was easier and more accurate than "eyeball square".

[Panope]

thinwater, I appreciate the additional thoughts regarding the Jedi snubber.

Thank you,

Steve

[Terra Nova]

Originally Posted by wsmurdoch

While I have never done an 8" thickness, I have done lesser thicknesses by attaching the hardware with double stick tape to a bit of scrap wood as thick as the wood I hoped to drill. I then drilled the holes through the hardware and the scrap wood beneath using a drill press to assure that the holes were both properly spaced and square. I could then use the scrap wood as a jig when I later drilled the real holes with a hand held electric drill. It was easier and more accurate than "eyeball square".

Originally Posted by a64pilot

I need a type of drill guide to pull this off, and a very long bit. I think it's only realistic to first drill the bowsprit, then the backing plate. Odds of me getting perfectly straight holes over that distance are not good, and I do not want to Wallow out the holes to make it work.
I'll start with small pilot holes to see if I can pull it off, they are easier to fill
I can't mount to the deck and if nothing else I would think it difficult to strengthen the deck to the point that you couldn't just pull a big hole in the deck. The bowsprit is solid and I assume stupid strong compared to the deck. I have several feet of 316 SS all thread where I did the windlass install. I dislike all thread though as it's weak, but I guess it ought to be strong enough. I understand about protecting the wood, I had thought seal it with very very thin slow set epoxy, then after that dries for a week or so bed the stopper with 5200...

Through bolting with backing plate is the only sensible method of mounting.

Ws has described one way to make a jig to keep your drill bit running straight and square; a thick block which has been accurately pre-drilled, square, on a drill press. No need to make the backing plate later. No need for pilot holes. And no need for slow-setting and no need to wait a week for epoxy to dry; WEST dries in hours. Also 316 allthread should be no weaker than 316 bolts of similar grade.

12" drill bits are readily available in common sizes. Don't make the holes any more oversize than absolutely necessary; you don't want any subsequent movement when under extreme loading. Clamp the jig on top and a piece of scrap wood against the bottom of the sprit to prevent chipping the holes when they break through.

If the footprint of the chain stopper is small, consider mounting a larger "adapter" plate, also of 316, so that the stopper mounting is maximized and does not crush the wooden sprit. Like size for backing plate.

[UNCIVILIZED]

For those who want it, some of the story of S/V Jedi's hurricane survival story is can be found here SetSail FPB » Blog Archive » Interview with Hurricane Ivan Survivors
As well as in a few locations on CF.
And there's lots more info to be found on Setsail.com as well. Such as via a search on anchoring in hurricanes SetSail FPB » Search Results » hurricane anchoring

Also, there’s a lot on mounting chain stoppers, & designing one’s anchor retention system in this thread http://www.cruisersforum.com/forums/...ns-164988.html


Some thoughts & questions about the Lewmar stopper.
- It would be wise to contact them in order to get the strength specs on it. Especially on the pin which holds the stopper’s gate, particularly as it has a threaded hole machined into it’s center for a bolt that positions the gate. So that the hole will weaken what may or may not be a sufficiently strong pivot pin.
From there, the strength of the gate should be questioned, including it’s attachment method.

- Both the WLL, & the BL of all of the components of the unit are needed, as well as how such tests were conducted, & by whom. Plus how often a unit is pulled at random from the assembly line & tested to failure, how, by whom, what the results are… With tests to include; static loadings, cyclical loadings, veering loads, etc. Tests on individual components, mounting methods, etc.

- One thing which jumps out at me is the bolt size used to secure this chain stopper. If you do the math for the strength of four ¼” 304/306 bolts in tension, their strongest holding mode. They’re not sufficiently strong to withstand the BL of 8mm G40/43 chain, even when the bolts are sharing the load equally. Which, in such a mounting setup, under extremely high loadings, they won’t be doing.
So that’s an early failure right there.

- Since the stopper is designed for ¼” bolts, then odds are, it’s not designed for anywhere near the loads which you’re speaking of. Nor probably, even those generated by 8mm G40/43 chain at/near it’s maximum. Which is all the more reason to query them.

And if you’re feeling paranoid, there are plenty of Non-Destructive Tests (NDT) which you can do on a stopper, and it’s fasteners) to examine their integrity. Much as is done on Rod Rigging, & other critical components on the mast, & elsewhere. And this is definitely a critical system.


With regards to drilling mounting holes through the sprit.
Were it me, I would contact IP directly. As odds are a load mapping science went into the layup of your sprit. And drilling it in the wrong place(s) could sever some critical structures in it’s makeup. Thus destroying more integrity than would seem obvious to the eye. And create a “tear/break here” point or stress riser.
So speak to IP first. And also ask them what other owners have done, & for their recommendations.

You might also inquire about bonding some G10 tubes in place for the bolts, to act as structural compression sleeves. Which also aid in adding back some strength lost in drilling through the sprit. Given G10's strength vs. that of the boat's laminate. And so that the G10 prevents any water from entering into the wood layers in the sprit as well.

Ditto on talking over the possibility of bonding a G10 backing plate onto the underside of the sprit. In order to add more strength to it, especially in the area which it may be slightly weakened by the bolt holes.

This might also be a good idea to do on deck too, underneath of the chain stopper, perhaps in conjunction with a stainless plate under the stopper & other high load hardware. Such as deck cleats, padeyes, possibly the windlass, etc. And they too should be through bolted to substantial solid laminates, with substantial backing plates & load spreaders.
Pretty much the whole foredeck should be a monolithic solid, with some frames & ribs supporting it’s underside. With tie rods added as needed, in order to spread out the load to sub-frames & ribs in the hull/stem’keel.

The other thing to keep In mind, is that it’s only prudent to plan for having a chain stopper on your #2 anchor as well. Whether you mount a stopper on deck there now or not. The reasoning for such being explained here http://www.cruisersforum.com/forums/...ml#post2106033


I know that also, I’d surely appreciate it if someone were to compile a list of links on this subject & post them here. Ditto on an address list of the posts in which S/V Jedi has written about heavy weather anchoring, given their successes & history.
Interesting stuff. Which I hope that no one needs to test in anger.


PS: There are jigs which you can both purchase or make, that attach to hand drills so as to facilitate the drilling of holes which are fully perpendicular to a surface. Or at any other desired angle. So they're essentially built in drilling jigs, that convert a hand drill into a light duty portable drill press.

The caveat is that as the depth of hole to be drilled increases, so does the propensity of the drill bit to wander off center while drilling. Being best mitigated by using sharp, cool, drill bits. And allowing the cutting edges to do the work, while using only light pressure on the drill.

The bottom line is that drilling a hole this deep & of such a small diameter, is almost aking to drilling a shaft hole, or for rudder bearings.

[UNCIVILIZED]

Originally Posted by Terra Nova

Through bolting with backing plate is the only sensible method of mounting.

Ws has described one way to make a jig to keep your drill bit running straight and square; a thick block which has been accurately pre-drilled, square, on a drill press.

Over the course of drilling an 8" hole for the chainstopper, the holes in a pre-drilled block made out of anything but a very hard steel will become hogged out. And in addition, in the course of drilling through 8" of bowsprit, the tip of the drill bit is bound to wander to some degree. How much is a function of techniques, tools used, & materials. But it's almost unavoidable. Especially when using such a thin bit over so great a distance.
So the backing plate will need to be drilled in place/mated to the holes in the sprit, in this instance.
No need to make the backing plate later. No need for pilot holes. And no need for slow-setting and no need to wait a week for epoxy to dry; WEST dries in hours. Also 316 allthread should be no weaker than 316 bolts of similar grade.

All thread is definitively not as strong as bolts of the same diameter. The engineering formulas for calculating materials strengths show as much when calculating the properties of threaded steel vs. non-threaded. Notched (threaded) steel being significantly weaker, as well as being prone to cracking at the threads. Much as are chainplates where they're bent or drilled.

12" drill bits are readily available in common sizes. Don't make the holes any more oversize than absolutely necessary; you don't want any subsequent movement when under extreme loading.Clamp the jig on top and a piece of scrap wood against the bottom of the sprit to prevent chipping the holes when they break through.

All very true.

If the footprint of the chain stopper is small, consider mounting a larger "adapter" plate, also of 316, so that the stopper mounting is maximized and does not crush the wooden sprit. Like size for backing plate.

The above is a pretty decent idea. And there are lots of ways to even take it a step or two further.

[thinwater]

^^ Interesting.

First, nothing Lewmar makes is based on G43, IMHO. If you look at the size rope they use with the chain on windlasses, particularly in the larger sizes, it is far too weak to use with G43. Therefore, I'm guessing the stopper was designed around BBB. That gets the 4 x 1/4" bolts close (I could not find a bolt spec from Lewmar), although probably not quite there.

Actually, I think the above statement holds for all windlass makers; they claim to fit G43 and even G70, but they don't recommend the matching rope size. Sneaky IMHO.

[UNCIVILIZED]

For bolt strength I just use the cross sectional area of the bolt x 85,000psi for common boat grade stainless. With it's yield strength (where it deforms) being 40-50% of that.
If you want to calculate for the threaded part of a bolt, multiply by 0.85. And again, that's for a bolt in tension, not sheer.
Here are some #s on stainless MatWeb - The Online Materials Information Resource

Also, I hadn't thought about what standard of chain & rope Lewmar bases it's products around. Though your findings don't surprise me. Sadly. As I've almost always been universally underwhelmed by their products.

[deblen]

Originally Posted by deblen

1/4" x 9" bolts = 1/4" SS rod with SS nut peened --on the bottom of sprit,--with flat washer.
Nyloc nuts on top.
Drill holes 9/32" to save beating rod bolt thru.
You can make a plywood jig to keep drill square to top surface of sprit.
Basically a vertical V that drill rides in-Google it.
Buy an electricians long twist drill bit
Chamfer the top of holes a bit & bed with butyl tape.

Above IMHO

Is your sprit strong enough?
I grit my teeth thinking about the jarring fetch of that chain in a stopper.
Would a P & S nylon bridle make sense for normal conditions?

Len

I'm not a structural engineer,but I have drilled perpendicular holes with a good power hand drill using simple jigs.
This video shows one type of jig of which I spoke,only I used scrap plywood to make the V.

https://www.youtube.com/watch?v=PtayvNvIa6E

I'm not a materials engineer either,but OP "thought" the mounting holes were 1/4" in the chain stopper that he ordered, & we've all accepted that premise. If you feel he needs a stronger model,please advise him.

I'm not aware of 316 SS bolts in 1/4" x 9" being available. I don't know of any viable substitute other than threaded rod,but I do know threaded rod has been regularly used in boatbuilding for 200? yrs-good enough for me.

My chain stopper is thru bolted to deck with backing,but I have a rope rode, with 20ft of chain at anchor end ,so it is only used to hold the anchor from self launching.I'm not knowledgeable about using a chain stopper to hold my boat in a hurricane (or at all)-but it makes sense to me that you would want one as strong as mooring cleat(s),if you are going to use it as one. What other way can you mount a chain stopper besides in sheer??

What other methods are available to "tie" a chain directly to your GRP boat? I'm not talking about the bridle,but the chain itself,when the bridle parts.

Anything bolted thru GRP that has sheer loading on it will eventually elongate the holes in GRP. It would seem to me that a "glassed on ridge" of some kind,for the stopper to butt against,would help prevent this movement. Drill the holes first though,while you have a flat surface for your jig. That is why I suggested a drill bit 1/64" or so larger than bolt/rod.
Make it easier on yourself' driving the rod/bolts up thru.

I agree a backing plate should be used on the bottom.
I don't believe you will be able to drill 8" without some wander of a 1/4" bit.
Accept that & if anyone dinghys under your sprit to criticize,drop your anchor on them
I would drill the backing plate for 4 RH self drilling screws,screw it to bottom of sprit & drill down from the top-all the way thru or at least enough to dimple the backing plate,so it can be un-screwed & drilled.

Yes-check with mfgr about sprit strength & internal structure if possible.
There are a zillion IP's out.Someone must have one with a stopper on it.

If a hole doesn't work out-it can be plugged-sometimes hardly noticeable

Finally-I don't know the story of Jedi-must read it-but I'm glad the force was with him. Not many boats would survive anchoring in 100+ knots for very long. Glad he made it & damn glad I wasn't aboard

Len

Edit: One of these portable drill presses are great aboard a boat,if you can find one.
I used mine regularly for drilling thru steel & aluminum x-trees on comm. fish boats.
Makes drilling a one handed operation,applies more force to the bit than you can generate by pushing on a drill & gives some control over things.
http://www.ebay.com/itm/VINTAGE-CRAF...EAAOSwkl5Xdn7U


Here is one that would work for OP's project http://www.ebay.com/itm/Vintage-Craf...wAAOSwtnpXk-FI

[Snowpetrel]

Uncivil. You also need to consider the bearing stress of whatever it's bolted into, and the tear out strength of the rear bolts and deck as well.

For metal bolts shear strength is approximately 50-60% of tensile for the shear plane. In this case they are in single shear, but friction between the fitting and the deck and any glue/sealant makes a big difference to the shear loads, as does torque values for the bolts, and the tensile loads.

For me I'd rather just have a very strong spectra strop from the chain back to the Samson post. It can be cut if need be, and the Samson post should be one of the strongest parts of the boat.

[Jim Cate]

No one has questioned this, but are you sure that the mounting bolts are only 1/4 inch? Seems far too small to me for this item.

Jim