Bridle Chafing on Bobstay

[rebel heart]

Originally Posted by Guy

I know it's kind of lame to use the L&L show as an example but they do have some stuff figured out and they seem to be believable to most everyone. I have used the same set-up as they do and the only chafe I get anywhere on the snubber is a tiny bit at the block on the Cranse Iron. I think that could be cured with a block that swivels a little better than the one I use, because the chafe is on the block cheaks. If you use 5/8 line for example, it takes a good sized block to not rub a little when the pull is off to the side. There is no other way to completly avoid chafe even if we are talking about running your snubber through a Hawse Pipe because you still need chafe protection there.

I've thought about going with their approach but I sort of like having everything in reach of the deck and not having ground tackle gear dangling from way up on the bowsprit. My first attempt was just putting a block under the bowsprit, I might experiment with moving it out further and further.

[Kettlewell]

Here's what my set up looks like with the snubber pulled up on deck and cleated off. As I said before, this is very quiet, almost no chafe, requires less chain out in tight anchorages, and the lower angle of pull seems to make the boat ride better in high winds.

[model 10]

Thanks Rebelheart for the correct name "Cut Water" fitting.
Seems like you hear stuff like , "almost no chafe", "hardley ever", "my boat doesn't move around", etc., a lot when talking about snubbers..

[barnakiel]

Originally Posted by rebel heart

(...) More relevantly though, I know a guy who ripped his cutwater fitting out when making the snubber fast to it. If you add your own fitting that's fair enough, but using an existing rig point designed for one type of load and then using it for another can result in some problems.

+1

Off course.

Not a part of the bobstay fitting; a separate eye, backed, in strong SS like material.

b.

[model 10]

Originally Posted by barnakiel

+1

Off course.

Not a part of the bobstay fitting; a separate eye, backed, in strong SS like material.

b.

But the pull on a snubber would be in the same direction as the bob stay pull, if you use a block at the Cranse Iron. If your snubber could pull out your Cut Water fitting, it was not strong enough anyway.

[rebel heart]

Originally Posted by Guy

But the pull on a snubber would be in the same direction as the bob stay pull, if you use a block at the Cranse Iron. If your snubber could pull out your Cut Water fitting, it was not strong enough anyway.

The block is kind of interesting because it's obviously not absorbing 100% of the load otherwise the line would be slack aft of it. Maybe it's 50%; I'm sure it depends on the angles.

But the downward / outward pull on the cranse iron would also be absorbed by the forestay which then connects to everything else, all the way back to the stern chainplates. How much is really happening to the bobstay I'm not so sure. If anything I think it's compressing the bobstay.

Either way any scenario you calculate is a lot different loading than "make the cutwater fitting terminate the ground tackle".

[model 10]

Some of what you say has always been the argument against this setup and I think Brian Toss addressed them pretty well.

[rebel heart]

Originally Posted by Guy

Some of what you say has always been the argument against this setup and I think Brian Toss addressed them pretty well.

I've got Rigger's Apprentice on my Kindle, do you know where he talks about it? I'm still experimenting with it all and don't claim to have all the answers. Interested in reading up on it.

Fundamentally though if I jump down on my bowsprit the backstay will come under tension, and if I just yank on the cutwater fitting it loads the bolts holding that plate on. I don't see how the rig is involved at all.

[Kettlewell]

I don't see how the rig is involved at all.

Pulling downwards on the bowsprit does put increased compression on the mast, though in the real world the bowsprit seems to fold before the mast does. My gut feeling would be that anchoring from the bowsprit in normal conditions up to maybe gale force, without wave action, would be OK, but when things get worse I would want to take the load off of the bowsprit. That seems to be what most people with sprits do too.

[Bash]

Originally Posted by Bash

Yes. Often the bobstay tang has a hole at the bottom through which a shackle can be fitted. That shackle becomes the attachment point for the snubber. It's not difficult to use if you're handy with a boathook. The only downside is that you're limited to 6-8' of snubber.

Here's a link to a photo that shows the sort of system I'd described: http://hackingfamily.com/images/BobstayTang3_CM.jpg

[rebel heart]

Originally Posted by Kettlewell

Pulling downwards on the bowsprit does put increased compression on the mast, though in the real world the bowsprit seems to fold before the mast does. My gut feeling would be that anchoring from the bowsprit in normal conditions up to maybe gale force, without wave action, would be OK, but when things get worse I would want to take the load off of the bowsprit. That seems to be what most people with sprits do too.

I know the pardey's run a block right at the tip of their bowsprit and have weathered some crazy stuff in that, but they're also a very light displacement boat and again the angles matter a lot. Their bowsprit isn't standing 5' over the water (or more) like a lot of boats do.

That's sort of why I have my block hanging closer to the stem fitting. It's 8"x8" mahogany that's maybe 12" from the stem fitting. The rig loading seems inconsequential at that point and I can't even imagine what kind of sheer load it would take to rip that much wood in half.

[Kettlewell]

You can read some of what the Pardeys say about this in the Capable Cruiser around page 112-113.

[Hudson Force]

[QUOTE=rebel heart;1253420]................Fundamentally though if I jump down on my bowsprit the backstay will come under tension..............QUOTE]

I favor the "unibody" distribution of stresses thoughout the entire frame that includes the rig and hull. As you stress the bobstay and see the tension increased on the backstay; I see my added shrouds from my mizzen to my dinghy davits carrying the stress across my tiactic to my forestay. In the dance, partners establish a frame that leads the clasped hands from hip and torso through the tango with the same distribution of stress. The drawn bow and arrow has the same stability. There are limits when stress can hog a deck or strain fittings, but I'm in favor of the full distribution of tension across the rig and through the hull. There's great strength in this circle.

[rebel heart]

Originally Posted by CaptForce

I favor the "unibody" distribution of stresses thoughout the entire frame that includes the rig and hull. As you stress the bobstay and see the tension increased on the backstay; I see my added shrouds from my mizzen to my dinghy davits carrying the stress across my tiactic to my forestay. In the dance, partners establish a frame that leads the clasped hands from hip and torso through the tango with the same distribution of stress. The drawn bow and arrow has the same stability. There are limits when stress can hog a deck or strain fittings, but I'm in favor of the full distribution of tension across the rig and through the hull. There's great strength in this circle.

I think that's part of the idea of putting a block on the bowsprit. At minimum it will absorb a decent percentage (maybe half?) of the force, which then goes back to the rig. The sampson posts and heavy deck cleats are there to do their thing as well, but it's nice chopping the load down and spreading it across things that are actually designed for that.

Someone could put a cutwater (or otherwise fitting down there) plate on so strong that it would literally rip the bow off before parting, but I think 90% of the boats I've seen with tackle down there have no idea what the size and health of the hardware is.

[model 10]

Originally Posted by Kettlewell

You can read some of what the Pardeys say about this in the Capable Cruiser around page 112-113.

I was probably talking out my ass. It was the Pardey's who wrote about this and Toss just just refers to their set up as an example of something he likes. I have no library handy to check.
Seems like if you have a proper bow sprit and rig it would handle the loads whatever the conditions were like. I know I would never change the snubber set up we have for any storm. It is really chafe free. I suppose you would add additional snubbers in a bad situation but they would probably chafe if they came under load for very long.