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Old 08-12-2010, 10:16   #1
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Moving to External Chainplates

Hi, I have a 35' endurance cruising sailboat that had 4 internal glassed in chainplates I am going to move them to the external hullside. Mast is 42Ft . Making the chainplates out of 2in * 1/4in 316 SS flat bar. Trying to figure out:
1) How long they should be ?
2) How many securing points (bolts) ?
3) size of bolts (1/2in - 3/4in) ?

Any help appreciated
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Old 08-12-2010, 10:32   #2
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The idea of the multiple bolts is pretty much to distribute the shear loads over a larger surface area, any more then 3 bolts per plate is probably overkill (especially as you will likely build up the thickness quite a bit)...

Four would be ok (and commonly seen) but more then that and you are just making more failure points. (stress cracks are likely to start at the bolt holes.

The size of the bolts is more a product of the surface in shear then the shear strength of the bolts... 9/16" stainless carriage bolts would seem appropriate to me.

Something between 12 - 14" long should be fine. That would provide reasonable spacing between the bolts.

The biggest issue (in my mind) is that the angle they are placed matches the angle of the shrouds as closely as possible... that and the angle of the bents where it comes over the rail lines up as closely as possible. You might be tempted to get around this with extra toggles.. avoid that if you can, the potential for stress cracks will go down significantly if your angles are correct.
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Old 08-12-2010, 12:35   #3
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Quote:
Originally Posted by s/v 'Faith' View Post
... The biggest issue (in my mind) is that the angle they are placed matches the angle of the shrouds as closely as possible... that and the angle of the bents where it comes over the rail lines up as closely as possible. You might be tempted to get around this with extra toggles.. avoid that if you can, the potential for stress cracks will go down significantly if your angles are correct.
Indeed.
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Old 08-12-2010, 12:45   #4
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don't forget to take into account how this will affect your foresail sheeting angle. If your genoa track is mounted on the caprail, you're going to lose a few degrees on a beat.
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Old 08-12-2010, 12:50   #5
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Another factor that you need to consider is the strength of the hull at the points where you intend to attach the new chainplates. If the hull is cored, I would have some serious concerns; even if it is not, I would think that on virtually any boat, substantial reinforcement will nevertheless be in order. Indeed, even if your boat is steel (as I recall, some Endurance 35's were built out of that material), you will need to ensure that the chainplates are attached to not only the hull plating, but also some vertical framing; in fact, if the verticles are not attached to the hull itself (often they are attached only to horizontal stringers that are attached to the hull plating), I would fear whether there would be sufficient strength.

Put another way, why are considering moving the chainplates outboard? Inboard chainplates will provide narrower sheeting angles and improve performance upwind. If the original chainplates have deteriorated to the point that they need replacement, just understand that very few boats have been engineered so as to allow simple through-bolting of new chainplates on the topsides of the hull.

Brad
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Old 08-12-2010, 15:50   #6
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Thanks for the replies, great info.
The boat is solid fiberglass, I believe about 1/2 in at the gunnels.
The boat is a cutter, and the track was mounted aft of the stern most chainplate. The original chain plates were mild steel imbedded in fiberglass bolted thru the deck to SS deck plates. The wire connection to the chainplates topside was right beside the caprail. See attacment, pics of before deconstruction
So thinking of instead of grinding all this **** out of the hull just move them outside. I had also been talking to another Endurance owner who was complaining of leaks coming thru the chainplates, so thinking I was killing two birds with one stone
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