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Old 09-09-2012, 08:54   #1
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Stem Ball Fittings on Isomat Rig

Hello folks -

I have a 47' steel cutter, recently purchased. During the purchase survey, the surveyor noted that the fit on the shrouds at the top of the mast was incorrect. his pictures indeed show that for 3 of the 4 wires terminating at the top of the mast (the forestay and both cap shrouds); there was a significant gap (i'd estimate it at 1/8" or so) around the back side of the ball where it seated in the cones on the fitting. This compared to a much smaller gap (~1/16" by eye) around the back side of the backstay stem ball fitting.

It is an original (1990 vintage) Isomat spar and fittings.

My question is - which is correct?

I realize there needs to be some clearance to allow the fittings to pivot slightly when under load or deflection... but the large gaps do seem a little excessive. What concerns me is that if the fit is wrong, then there is simply a line contact around the ball on the receiving cone; not proper distributed contact over a larger surface (resulting in high stresses on the line contact situation).

Is it perhaps possible that both are correct? the backstay is in fact a rigid stemball fitting that is a male clevis on the other side - goes straight into a tri-plate for a split backstay; whereas the shrouds and forestay are of course swages on the end of wires.

any crack riggers out there willing to comment?

thanks-

bg
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Old 09-09-2012, 12:31   #2
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Re: Stem Ball Fittings on Isomat Rig

Sending a rigger aloft for a first hand look is a small investment and can pay huge dividends. There may be some associated stress cracks. This isn't something that can be satisfactorily resolved over the internet IMHO.
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Old 09-09-2012, 18:24   #3
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Re: Stem Ball Fittings on Isomat Rig

thanks for the reply. The rig is down on trestles next to the boat, so inspection is easy. I have a good guy looking at it, but he is not necessarily a very experienced rigger. Anyone have suggestions for an experienced rigger in or around Tarpon Springs/Tampa/St. Pete's, FLA?

I will post pics of the spacing and fit tomorrow when I get back to work (where the pictures are).

also - I'm wondering about having to replace all of the standing rig. the wire and fittings are 20 years old, but the boat spent the vast majority of it's life either sitting alongside a dock up a fresh water river, or tied to a marina berth in the keys. it has had very few actual sailing cycles on the rig - maybe a dozen actual 'trips' in it's entire life. total cycles are going to be very, very low on this rig; as is exposure to salt spray. I know this for a fact, from the previous owner's sailing trips, his sailing style and and work schedules.

so - given the above, what can one do to thoroughly inspect the rigging in some way to be able to confidently pronounce it fit for more service? dye penetrant and meticulous visual examination? the top ends are all swaged, bottom ends are all Norsemans. the turnbuckles are all ok, and the Norsemans show little to no signs of corrosion. it would be easy enough to open them up and replace cones etc. but I'm wondering if that might even be unnecessary.

replacing it all is a pricey proposal, however we will be going blue water when we go (spring 2013). I'd rather NOT have the sticky thing and all the other hard bits fall on us.

thanks-

bg
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Old 09-09-2012, 20:39   #4
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Re: Stem Ball Fittings on Isomat Rig

Can you post the pictures so we can understand it better?

I wouldn't go cruising with a 20yr old rig regardless of previous use. Rigging doesn't cost that much - especially since you already have the Norseman terminators on one end and the turnbuckles are likely to be good to go. So you need some good wire and a few stem ball fittings and swages for them. Lots cheaper than a dismasting anyway, and probably not much more than a proper dye test by an expert rigger.

Mark
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Old 10-09-2012, 05:40   #5
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Re: Stem Ball Fittings on Isomat Rig

You might ask Rig-Right
Phone: (001) 401-739-1140
FAX: (001) 401-739-1149
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Old 10-09-2012, 07:32   #6
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Re: Stem Ball Fittings on Isomat Rig

Thanks for the replies. Here are two pics of the top of the mast, taken by the surveyor. One shows the side shrouds and the gap around the stem ball there; and the other shows the backstay (going to a tri-plate for a split backstay), with a much smaller gap around that stem ball.

See my concern? which is right? both? neither?

Thanks-

bg
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Old 10-09-2012, 08:03   #7
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Re: Stem Ball Fittings on Isomat Rig

I would ask this on Brion Toss's "Spar Talk" forum. You'll need to register.
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Old 10-09-2012, 11:14   #8
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Re: Stem Ball Fittings on Isomat Rig

NSBoatman,

It's far easier to replace the rigging and fully inspect the mast with it sitting on stands than it will be later with the rig stepped. I don't know your cruising plans but it's almost always cheaper and easier to get things done while you're in the US than "down island" or especially on the other side of the Atlantic.

This falls into the category of "penny-wise and pound foolish." Even if the boat hasn't been sailed a lot, it's still been exposed to salt air. And if the rig was left a bit loose it might have suffered from some shock load stresses. Many insurance companies won't even insure a boat for offshore use if it has old rigging.

If you can't afford to do it properly now, how will you be able to afford it later when you're out cruising?

My idea of being properly prepared for cruising is having the basics covered. Keep water out of the boat, rig in the boat, and crew onboard. You can certainly cruise safely without a bunch of gadgets but the rig and sails are really the most critical components. My advice to anyone who can't afford to look after those items properly is to downsize into a boat they can better afford.
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Old 11-09-2012, 07:20   #9
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Re: Stem Ball Fittings on Isomat Rig

Is the concern that the stemball head does not completely "fill" the fitting cup around the top rim? It is most important that the head ball contact area in the cup is continuous and does not have point-loaded areas. This may or may not mean that the fitting cup is "filled" completely at the top. I would suspect that it would not be, so that the correct fit is ensured on the ball body and not just the top of the fitting is in contact.

Get a professional rigger to look at it and give an opinion if you have concern.

Mark
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Old 13-09-2012, 20:01   #10
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Re: Stem Ball Fittings on Isomat Rig

Thanks all for your input. turns out that the wire in the Norseman fittings on the bottom is showing heavy corrosion inside the fittings anyway... so it's all gotta be replaced. still - I haven't found a definitive answer regarding the fit between the balls and the sockets - yes it makes sense that there should be nice even contact over as large an area on the ball as possible, but no information on how to measure whether what's there is correct or not. I will be consulting a few more professional riggers...

best-

bg
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Old 15-09-2012, 14:05   #11
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Re: Stem Ball Fittings on Isomat Rig

The back stay is fine the uppers are missing the second cup.
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