Dyneema rigging on bowsprit

[roland stockham]

Hi all. Got my new boat and one off the first jobs is fitting a bowsprit. Looking to use synthetic cord instead of wire and thinking about the chain plates. The boat is a custom built in epoxy ply so need to protect against water ingress the same as you would with balsa cores. Any one done this and did you use conventional chain plates or come up with a novel solution better suited to Dyneema?

[Pauls]

Hi Roland,

I assume you're familiar with the various ways to terminate dyneema, ranging from a heavy duty thimble to the various terminations made by Colligo. You can design your chainplates to work with whatever you choose for the terminators.

An important point with your chainplates is to have the load spread out across enough surface area that the wood fibers are not crushed. A bobstay is the most heavily loaded piece of rigging on a boat. Forest Products Laboratories provides accurate, engineering grade data on woods. I would suggest you look up their data on the woods you'll be using to support your chainplates. Take their data and then apply a decent safety factor, I'd suggest 2. I believe you'll find that you will need a decent sized backing plate to support the load from your bobstay. And that backing plate should be thick enough to be quite stiff, otherwise the load will just be concentrated close to bolts passing thru the stem.

Chainplates are typically designed to take 1.5X the breaking strength of the wire they hold. Dyneema is oversized as regards strength, it is sized to control stretch. I'd size chainplates to 1.5x the breaking strength of the wire that would be used if your bobstay was wire.

[Bowdrie]

Originally Posted by roland stockham

Hi all. Got my new boat and one off the first jobs is fitting a bowsprit. Looking to use synthetic cord instead of wire and thinking about the chain plates. The boat is a custom built in epoxy ply so need to protect against water ingress the same as you would with balsa cores. Any one done this and did you use conventional chain plates or come up with a novel solution better suited to Dyneema?

Hold on a minute. Is some terminology mixed up?
Is the boat supposed to have a bowsprit?
What do you mean by "chainplates"?
Are they to attach the standing rigging of the mast to the hull or do you mean the fitting on the stem that the bobstay attaches to that goes to the bowsprit?

[The Yacht Rigger]

In the past we've done a carbon tube mounted through the bow athwartship, with nicely faired edges, so you can either splice directly through it, do a luggage loop, or use a soft shackle to attach the bobstay.

[Benz]

Originally Posted by The Yacht Rigger

In the past we've done a carbon tube mounted through the bow athwartship, with nicely faired edges, so you can either splice directly through it, do a luggage loop, or use a soft shackle to attach the bobstay.

+1
I've done the same with fiberglass tube rather than carbon, because, well, poverty.

[s/v Jedi]

I agree with the pipe going through the hull. I would reinforce between the pipe and the point of the bow with a vertical piece epoxied into the point of the bow to spread load. Now you can use this attachment for moorings, anchor snubber or even towing too.

For fiberglass heavy duty pipe, Centek sells this for exhaust systems.

[Orion Jim]

Photo’s?

[The Yacht Rigger]

Originally Posted by Benz

+1
I've done the same with fiberglass tube rather than carbon, because, well, poverty.

Yeah Glass works just as well! I can't remember the boat, but tha partcular client just really wanted carbon.

[s/v Jedi]

Originally Posted by Orion Jim

Photo’s?

Here is a photo of a finished installation.

From sailinganarchy: https://forums.sailinganarchy.com/th...nstall.234939/

[s/v Jedi]

So when it’s finished, you only see a hole.