Chain Stopper Install

[a64pilot]

OK stupid question.
I have a Lewmar chain stopper for 5/16" chain to install on my bowsprit. I believe it has holes for four bolts, I'd guess 1/4", but I don't have it here to look at.
My bowsprit is I think about 8" thick and glass over wood I'm sure. Do I need to drill through the thing and install the chainstopper with bolts and a backing plate? I know that would be preferable, but for starters I don't know where to get 9" SS bolts, and 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.
Would 6" lag bolts be sufficient? It's my understanding that a chainstopper is a back up at most anyway? I currently do not have one and to be honest don't really understand their purpose.

[Paul L]

Here's a shear calculator that supports lag screws. Not sure how you'd apply it in this case.
https://courses.cit.cornell.edu/arch...rs/example9.1/
I do not consider the chain stopper as a back up. If you anchor often enough you will at some point snap a snubber.
Could you mount the stopper closer to the windlass and through the deck?

[noelex 77]

Originally Posted by a64pilot

OK stupid question.
I have a Lewmar chain stopper for 5/16" chain to install on my bowsprit. I believe it has holes for four bolts, I'd guess 1/4", but I don't have it here to look at.
My bowsprit is I think about 8" thick and glass over wood I'm sure. Do I need to drill through the thing and install the chainstopper with bolts and a backing plate? I know that would be preferable, but for starters I don't know where to get 9" SS bolts, and I'm struggling with figuring a way to drill perfectly straight holes through 8" of material with a hand drill

Cruising boats are subject to much higher loads than the typical weekend marina hopping boat and the gear needs to reflect this.

The chain stopper should be (ideally) stronger than the chain. The chain stopper will be mostly be in shear, but this requirement is still difficult to meet in fibreglass boat. I think it is worth getting as close as possible, especially in boat made for long distance sailing like the IP.

5/16 G4 chain has a SWL of 3900 lbs and a break load of 11,700 lbs. For G7 it would be 4700 and 18800 lbs. This latter number is close to the displacement of the boat!

So I would through-bolt with a backing plate.

Stainless steel all thread with nylock nuts on both ends will solve the length issue. If you use a set square while drilling you can get very close to perpendicular to the foredeck. An assistant is helpful as are frequent pauses to compare the horizontal and vertical alignment. If you pre install the backing plate so you also drill though the plate it does not matter anyway. If you are little off perpendicular no one will notice if on the underside the bolts are slightly irregular. With some care they should be very close.

You also need to protect the wood core from water intrusion. The West manual provides the best advice.

[Steve Bean]

How about drilling through the bowsprit first, and then marking the backing plate?

[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.
I am paranoid about water intrusion, fear of that is what kept me from buying a boat with cores.

I will ideally go with G70 5/16" chain, when its time to replace.


So the stopper is meant to hold the boat in the event of a snapped snubber? I figured nothing would hold if you lost the snubber as you then have no give, and the snatch loads would have to be enormous?

Has anyone stretched G40 chain with an anchor?

[Thumbs Up]

Just over drill the holes except for the tip, no need to through bolt the bowsprit, you can bed the chain stopper and the bolts in fiber reinforced, thickened epoxy in one operation. Mask everything off beforehand. The tip of a 1/4" x 5-6" machine bolt should thread tightly into the bottom of the hole so that you can snug them up. The over drilled part should be at least 3/4". It is mostly shear load so buy bolts with a shoulder (not threaded all the way to the head).

[a64pilot]

Interesting thought, basically similar to an insert?


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[thinwater]

Originally Posted by Thumbs Up

Just over drill the holes except for the tip, no need to through bolt the bowsprit, you can bed the chain stopper and the bolts in fiber reinforced, thickened epoxy in one operation. Mask everything off beforehand. The tip of a 1/4" x 5-6" machine bolt should thread tightly into the bottom of the hole so that you can snug them up. The over drilled part should be at least 3/4". It is mostly shear load so buy bolts with a shoulder (not threaded all the way to the head).

Is this stronger than a lag bolt and why? An interesting idea, I've threaded plenty of stuff into GRP, but I'm not sure why it is better in this case. Lag bolts are pretty well understood.

I'm also wonder how you would ever remove it... though why would you.

[Dockhead]

Originally Posted by Paul L

. . .I do not consider the chain stopper as a back up. If you anchor often enough you will at some point snap a snubber.. .

Absolutely right. The chain stopper is the primary link between boat and ground tackle. It needs to be as strong as the chain or there is no point in having that chain. The snubber is a shock absorber and not designed for this purpose.

[noelex 77]

Originally Posted by a64pilot

So the stopper is meant to hold the boat in the event of a snapped snubber? I figured nothing would hold if you lost the snubber as you then have no give, and the snatch loads would have to be enormous?

Some elasticity in the anchoring system is important, but snubbers do break.

The holding power of anchors in the comprehensive 2006 test showed many 15Kg anchors had in excess of 5000lbs holding capacity on occasions. (The test was stopped at 5000 lbs). This is for a constant pull.

This is more than the SWL of even G7 5/16 chain.

The chain stopper is only a small component and (if possible) it is worth trying to design a system where this is not the weak link.

[Panope]

The following is copied from a CF thread from about three years ago. CF member S/V Jedi (Nick) was describing the aftermath of his boat's survival of a hurricane (unattended, I believe).

Originally Posted by Panope:

Nick,

When Jedi rode out its hurricane, what sort of snubber was in place and did it survive the chafe?

Jedi responded:

Thanks, Steve
We had a 3/4" nylon 3-strand snubber which broke with the expensive (hook) end missing. The piece still attached to the boat was molten where it broke. This indicates internal chafing: the fibers rubbing against each other generating heat with imminent failure.

The only way to survive that kind of load (120 knot sustained wind with 140 knot gusts) is to have steel where it counts. Strong chain with chain stopper is what saved us (a Maxwell 3/8" chain stopper). You need strong deck reinforcement where the stopper is mounted, like a partial bulkhead with stringer if possible.
Another method is to create a short snubber from steel wire, that attaches to a strong cleat and is short enough to stay on deck. A chain stopper is obviously the way to go but not always possible.

[a64pilot]

OK, got it, stopper must be Hell for strong.
I'll have to get a good look at this thing, initial impression was the gate part would be weaker than the chain. Maybe not.


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[Thumbs Up]

Is this stronger than a lag bolt and why? An interesting idea, I've threaded plenty of stuff into GRP, but I'm not sure why it is better in this case. Lag bolts are pretty well understood.

I'm also wonder how you would ever remove it... though why would you.

The basic method is outlined here:WEST SYSTEM | Use Guides - Bonding Hardware
a machine bolt is stronger than a lag bolt of a given shank size. The extra coarse threads on the lag bolt reduce the amount of metal on the shank. Lag bolts break where the thread meets the shank. You only want the tip of the bolt to thread into wood as sort of a clamping aid. To remove, apply heat or coat the bolt with wax beforehand.

[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

[thinwater]

Originally Posted by Panope

The following is copied from a CF thread from about three years ago. CF member S/V Jedi (Nick) was describing the aftermath of his boat's survival of a hurricane (unattended, I believe).

Originally Posted by Panope:

Nick,

When Jedi rode out its hurricane, what sort of snubber was in place and did it survive the chafe?

Jedi responded:

Thanks, Steve
We had a 3/4" nylon 3-strand snubber which broke with the expensive (hook) end missing. The piece still attached to the boat was molten where it broke. This indicates internal chafing: the fibers rubbing against each other generating heat with imminent failure.

The only way to survive that kind of load (120 knot sustained wind with 140 knot gusts) is to have steel where it counts. Strong chain with chain stopper is what saved us (a Maxwell 3/8" chain stopper). You need strong deck reinforcement where the stopper is mounted, like a partial bulkhead with stringer if possible.
Another method is to create a short snubber from steel wire, that attaches to a strong cleat and is short enough to stay on deck. A chain stopper is obviously the way to go but not always possible.

Let's take a closer look at those conclusions. I'm sure he felt that way, but perhaps the facts are not exactly what they seem.

Boat: Sundeer 64. Big boat.
Approximate load with 8-15' snubber at 60 knots on 34' cat (measured): 3300 pounds. Scary. There were waves.
Wind load only, 60kt, 34' cat: 885 pounds (about 1400 for Sundeer)
Expected wind load only on Sundeer at 120 knots: 5600 pounds.
Expected peak at 120 knots for Sundeer: >10000 pounds.
Breaking strength 3/4" nylon: 16,700 pounds, safe working load about 2000 pounds at most.
ABYC mooring design load (based on 60-80 knots): 6000 pounds.

So depending on which numbers we like, the loads were almost certainly 8000-10000 pounds. Personally, I have doubts that the wind was 120 knots at the actual location or the chain would not have survived either. Perhaps it was at altitude.

But the reason the rope failed is because it was probably too short and certainly was dramatically, laughably undersized for the task. At BS 16,200, the chain was well beyond its SWL, but not too far since chain can work closer to the limit without rapid fatigue. IF the wind was 120 knots, he was very lucky.

The other problem with rope is that as the diameter >5/8 inch heat dissipation is a problem. Smaller lines for smaller boats, heating is almost impossible, but big lines can't dissipate.

So the lesson does not logically hold for smaller boats. Where a 3/4" line failed for the Sundeer, a 5/8" line, at least 20 feet long, faced with no more than 80 knots of wind, should last the OP a very long time. For him, 3/4" would survive 120 knots because the loads would be only 1/2 and it would not heat. At 80 knots only about 2000 pounds for the OP and within the working load, without heating, of 5/8" line. And I know for a fact that many sailors have used 1/2" snubbers around the world on 40' boats.

I'm just sayin' that the meaning of facts is not always obvious. Short snubbers (at least 20' is needed to absorb the energy and reduce impact loading--any shorter, the strain goes up and the snubber fails) and too small snubbers fail. Obviously.