Repair of bobstay minimising rig disruption

[Petronella]

We need to repair Petronella's forward bobstay connection. This will mean taking the bobstay off where it meets the underside of the pulpit.

The question is how to do this with as little disturbance to the recently tuned rig as possible bearing in mind this is a wooden mast and that there is a lot of tension on the bobstay?

We have two forestays right next to each other, one with furler, the other unused. Two corresponding backstays. Also an inner forestay with running backstays. At present she is out of the water.

One suggestion is to weight the pulpit down with anchor and chain and then tighten inner forestay and its running backstays. Then loosen main backstays taking some tension off the bobstay and finally unscrew the bobstay bottlescrew. Will this work? Are there any inherent problems with this approach? Is there a better way? The less we have to mess about with the rig the better but the main objective is to not crack or bring the mast down.

Thanks

 

[jerrytug]

The tension is in the bobstay at the moment.
You want to maintain that tension while you remove the bobstay.
I'm taking it she is a cutter-headed ketch.

Can't you put on a temporary bobstay in parallel to the one being repaired? Then take up the tension and carry on.

However: If you needed to work on the stem fitting that would not be possible. You then might be thinking about dangling weights etc, but you might just heave the whole boat down by the bows! The tension in the bobstay would be ten times the weight of the anchor, at a guess.

But anything else apart fron the stem fitting, you could rig a temporary bobstay I would have thought. Let us know what you do, cheers Jerry
PS
My approach would be the one to avoid dicking about with re-adjusting everything again, since you mention you don't want to.
Also, work out a way to mark exactly the height/angle of the pulpit, to get it back the same as it was.

Has she a triatic? Have you a Loos gauge?

 

[Wooden Boat Fittings]

I'd be thinking of rigging a rope bobstay alongside the existing one and tensioning it with a tackle until the wire bobstay loses its twang, when it can be released -- which is more or less what Jerry suggests.

How does the bobstay come to meet the underside of the pulpit -- do you have a dolphin-striker? If so, perhaps you can fit a permanent bobstay-plate further down the stem to take the tackle, and leave it there for possible future use after you'e finished.

Photos would be really useful....

Mike

 

[William_H]

I would suggest you mark the place of the turnscrews of both the back stay and forestays. Take the tension off the back stay then the forestays then the bobstay. Bit by bit would be best. The mast should be n problem with no sails on it and the pullpit should be able to support itself. I think if you try to remove the bobstay with tension on the rig you are setting yourself up for possible dissaster. I don't think rig tension adjustment is so critical as to risk removing bobstay without taking tension off. good luck olewill

 

[Petronella]

Bobstay Photos

Photos would be really useful....

Mike

As requested.

View attachment 41618

View attachment 41619

It will not be easy to ease the tension on the furling forestay as the bottlescrew is up inside the furling gear. Also note this is not a flimsy pulpit!

Thanks J

 

[sarabande]

perhaps a re-design of the bobstay is called for ?

You are putting enormous tension on the system by having such narrow angles, and it is pulling the outer end of the platform back into the boat when it should be pulling the end downwards to oppose the tensions in the forestays.

A look at some design pages on dolphin strikers or "martingales" will show you the techy reasons why a change would be beneficial and lead to less extreme loads in the chain. There are very good engineering reasons why a short triangulating stay or striker has been built into ships and recreational yachts for many many years. And you have a really solid frame to sustain it.

 

[Wooden Boat Fittings]

Ah. Thanks for the pictures, John -- they make a world of difference. That 'pulpit' as you call it is what I would call a fancy bowsprit. So where your bobstay is fastened on the stem was where I was recommending you fasten a temporary bobstay, with tackle, to take the load off the main bobstay while you work on things. (This assumes that the bobstay plate on the stem is okay.) The outer end of the temporary bobstay looks as though it could be fastened around the last stanchion on the (real) pulpit (the 'fence' around the bowsprit) without any problems.

What your temporary bobstay has to do is to balance the tension in the outer forestay. While a dolphin-striker would cerrtainly change the angle of attack of the bobstay for the better, I have seen plenty of hulls where the bobstay was on the same angle yours is without presenting any problems. The bowsprit looks as if it might have rust in its outer end, but at the moment it's carrying the loads okay. A temporary bobstay might damage the bowsprit when you tension it, but if you go at things carefully I can't see why. If you rig a temporary bobstay and tension it until (and only until) the outer forestay slackens off just a whisker, then I reckon you should be good to go.

The alternative is to detune the rig first, do whatever repairs are needed, then tune it again later, but I understand why you would prefer not to do that and I think the temporary bobstay might save the day for you. On the other hand, if the bowsprit has got rust in it and needs replacing, then clearly this won't work and the outer forestay has to be removed while you replace the bowsprit.

Note that in traditional sailing rigs the bobstay was considered the most important piece of standing rigging. If that went then you could get a chain reaction between bobstay, forestay, foremast, triiatic stay, main mast.... Horrible -- the whole rig could collapse. So I guess you should makle your own decision about 'risk vs reward' in this instance.

Mike

 

[Petronella]

Many thanks guys. I will think about these options and let you know how it goes. The welder is coming on Tuesday so it will have to be off by then!

 

[Wooden Boat Fittings]

Sorry John, this is wrong --

If you rig a temporary bobstay and tension it until (and only until) the outer forestay slackens off just a whisker, then I reckon you should be good to go.

What I meant was, "Tension the temporary bobstay until the original bobstay slackens off" -- not, of course, the outer forestay.

And good luck for Tuesday.

Mike

 

[SamSalter]

Why not move the boat (it's on the hard I believe) so you have some solid structure forward of the bow.
Use your jib halyard(s) attached to this fixed structure to take the tension off the forestay(s).
Sam

 

[john_morris_uk]

This all sounds very complicated for no good reason....

I guess that its been sorted by now, but the far simpler solution would be to either measure the rig tension or just mark where all the bottle screws are and take the load off the forestay. The mast won't fall down with the inner forestay still attached and there's no need to wind it up to compensate. The bits of rigging to slacken off are the backstays and the forestay. Bob's your uncle - that will mean there's no load on the bob-stay.

PS I agree with Tim, a 'dolphin striker' (in modern slang) would be a much nicer method of providing tension to the end of the 'pulpit'. Just because the current system works, doesn't mean that its good practice.

 

[Petronella]

OK - it's all done!

Running backstays and their inner forestay tightened.
Plumbob dropped from bowsprit end to just touch ground (to ensure accurate re-assemly).
Backstay positions marked.
Backstays eased (21 full turns) to take tension off forestays. No visible bend to mast top but tension taken off forestays.
Bobstay now loose but bottlescrew siezed.
Weight taken off bottlescrew by leading lines from forward end of bobstay chain to windlass over front of bowsprit.
Pin knocked out at bottlescrew/shackle join.
Windlass lines eased.

BOBSTAY REMOVED, MAST STILL INTACT!

Thanks to all contributors.

PS - Joshuas have to my knowledge never had a dolphin striker so we'll build it as before but with strengthened forward bobstay tang and all galvanised (no stainless shackles) parts. There is no rust in the aft tang or the tubing that the forward (corroded) tang is attached to so we look good to go.