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Old 10-02-2013, 05:36   #1
F51
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Bobstay lower attachment

I am having to replace the lower fitting that attaches the bobstay to the stem near the waterline. I am having a new fitting welded up at a local shop. I need advice on attaching the new fitting. The old bolts are SS 1/2" Whitworth. I cannot find replacements, so I will be going with 1/2-13 NC bolts. I plan to run a 1/2-13 tap into the holes so the bolts will thread into the fiberglass. This is not ideal, but there is no access possible to the original British Whitworth backing nuts without cutting into the hull. I am thinking to epoxy the bolts in place for added strength/security of the fitting. At my age, I do not expect to ever have to deal with removal in the future--it will be somebody else's problem. Has anyone else had to deal with this problem? Thanks.
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Old 10-02-2013, 07:04   #2
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Re: Bobstay lower attachment

I think you are asking for a major catastrophic failure if you don't thread these fasteners into a backing plate or bedded fasteners....

Try these guys for your bolts : British Tools & Fasteners, LLC

Or at the very least... slightly drill out the holes in the hull AND bedded whitworth nuts and tap with 9/16" NC
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Old 10-02-2013, 09:51   #3
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Re: Bobstay lower attachment

Well, I tried the website above, and they don't have any stainless 1/2 -12 BSW bolts in 3" length. If I can find the bolts that is probably the best solution. Anybody got a source for 3" SS Bolts?
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Old 10-02-2013, 10:03   #4
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Re: Bobstay lower attachment

make sure your backing plate is sturdy enough to support the rig of the boat, as that is what that fitting does... have fun..
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Old 10-02-2013, 10:23   #5
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Re: Bobstay lower attachment

Bolts won't stay in fiberglass. You'd be better off to just drill through the whole mess and make another backing plate in the inside and screw it together with nuts. Your mast coming down pretty much ruins the day.
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Old 10-02-2013, 12:50   #6
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Re: Bobstay lower attachment

If you haven't made up your new bobstay fitting here's one I have for sale. It was made up for a Cascade 42. I don't know what boat you are making yours for or where you are located but this one could go in a flat rate box to anywhere in U S for about $15. Cost of the fitting was $200 for me but I'd sell it for $180. Never used, never installed. Looks great.
kind regards,
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Old 10-02-2013, 12:59   #7
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Re: Bobstay lower attachment

I just found out that you are working on a Formosa 51. Great design!

The reason for the two holes is this bobstay fitting is so that you can use the bottom one for mooring or anchor snubber. It has bolts nuts and washers and backing plate included.

If you would like I can send more specifications.

kind regards,
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Old 10-02-2013, 13:19   #8
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Re: Bobstay lower attachment

It is a backing plate in our case - three bolts: - one under the attachment point and two more one at each end of the plate.

I would not trust screws+epoxy.

b.
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Old 10-02-2013, 13:30   #9
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Re: Bobstay lower attachment

I agree with the other posts. Bigger is always better. Drill out oversize and run longer bolts clear through to a new backer.

If you wish to "involve" the old plate then re-tap the old embedded plate or nuts (its probably an embedded tapped plate). Use long bolts and thread them to the boat interior. Bed a plate with clearance holes inside the boat and use washers and nuts. I would use a mess of 5200.
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Old 11-02-2013, 18:38   #10
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Re: Bobstay lower attachment

Almost any thread into something metal would work better than a thread into fiberglass, even a cross thread! If it does not fall off glue would do nothing more than keep water out, hopefully.
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Old 11-02-2013, 19:13   #11
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Re: Bobstay lower attachment

I believe the bobstay is the most highly stressed rigging point on the boat.. Concur with every one else that just threading into fiberglass is a recipe for disaster.

My old Westsail 32 had a plate on each side of the hull with the bobstay eye pinned between. The plates were through bolted into the hull. Has worked for 40 years and tens of thousands of cruising miles. If you are going to use a fitting like SkiprJohn pictured, just drill through the backing plate and use long enough bolts to through bolt to the inside of the hull with another backing plate inside.

Had an anchor snubber that attached to the lower hole in the bobstay fitting
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Old 11-02-2013, 19:14   #12
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Re: Bobstay lower attachment

Any even fair machine shop should be able to make any type of bolt you might need with any thread needed ! Just a thought from an old machinst who trys to fix eveything himself LOL
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Old 11-02-2013, 19:20   #13
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Re: Bobstay lower attachment

FWIW,

Here in Oz 1/2-12 is a BSB standard thread and commonly available. Just about any fastener vendor will be able to supply the bolts that you need.

It is interesting to note that BSB and NC threads are all the same (for common boating sizes) except for 1/2 inch diameters. Dunno why they picked that one to differ on... can't be much theoretical difference between a pitch of 12 and 13. Can be a bugger on a boat with "mixed ancestry" and NC, BSB and metric scattered about.

Cheers,

Jim
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Old 12-02-2013, 17:54   #14
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Re: Bobstay lower attachment

I agree with all that has been said, and add this bit of advice, Check the clevis pin on the lower bobstay attach point more often than any other spot on your rigging. That little bugger goes in and out of the water a 100 times a day even at anchor and is subject to more corrosion than just about anything else on your boat. I helped a fellow check his rig before a passage and everything was fine, but that lower clevis pin was almost half way corroded thru. Kind of scary!!!!_____Grant.
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