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Systems:  Mast and Rigging


Chainplates

For the new chainplates, I used a combination of materials.  The headstay used the original bronze stem casting, but for the upper shrouds, I purchased a 4' length of stainless steel bar stock, 1-1/4" wide and 1/4" thick, in order to fabricate my own chainplates.  I also planned to use the stainless steel stock for the backstay chainplate.

For the lower shrouds, I chose heavy-duty bronze deck-mount chainplates from Spartan Marine (#C182), with a listed breaking strength of 10,000 lb.  When backed up beneath with backing plates, and secured with 3/8" fasteners, these chainplates would be more than adequate for the lower shrouds' loading. 


After putting off the project as long as possible, I decided to locate and begin fabrication on the chainplates shortly after the mast arrived.  I waited for the mast so that I could properly locate the chainplates in the deck, even with the spreader tips.  The spreaders were 36" in length, measured off the side of the mast extrusion.

In order to properly drill the first pilot holes, I had to locate the correct placement from inside the boat, so that the slot would end up directly in line with the aft side of the chainplate bulkhead.  I puzzled about how to do this accurately for a time, and eventually placed a strip of wood across the cabin, spanning from one settee locker to another and passing almost directly above the mast step in the bilge.  With this straight, level (for all intents and purposes) stick as a guide, I used a level to transfer the location of the sides of the mast (which I had previously traced onto the mast step before installation), and then measured from that point out along my stick, which brought the tape into the lockers on each side.  Then, with a combination square, I transferred the end of the tape to the bulkhead, which was about 6" forward of where the stick passed through the locker openings.


Next, I drew a plumb line up the bulkhead to the bottom of the deck, indicating the inside edge of the new chainplate.  I repeated this process on each side, and then used a drill with a long 1/4" drill bit to drill pilot holes from the inside, keeping the bit close to the bulkhead and at as minimal an angle as possible (hence the long bit).  After confirming the position of the pilot holes on deck, I marked for a second hole, at the outer edge of the chainplate width, and drilled those.  Then, I connected the holes and created a slot with a jigsaw, working from up on deck.

Next, I prepared the chainplates.  From the 4' length of bar stock, I cut two 12" pieces.  I used an angle grinder with a cutting wheel for these cuts, which worked extremely well.  Then, after checking the fit on deck and fine tuning the slots till the chainplates fit well, I inserted the raw chainplates and held them in place from above with a Vice-Grips at the proper height (allowing for the eventual clevis hole and some clearance), and down below I checked for obstructions that would affect the bolt hole placement.  Forward of the bulkhead, there was a deck beam and a small piece of trim, so I allowed leeway to avoid these installations and then marked the aft side accordingly.

Finally, I marked 4 evenly-spaced holes in the remaining section of the chainplate, and drilled for 3/8" bolts with a slightly oversized bit (25/64").  Until I could confirm how much clearance should remain for the turnbuckle clevis above decks, I left that hole undrilled.

 


I continued my measuring out and marking the locations for the deck-mounted bronze chainplates.   After confirming that they were not located above any obstructions in the cabin or underside of the deck, I predrilled the holes for the mounting bolts.

I also cut the slot in the poop deck to accept the backstay chainplate.  Access from beneath was difficult, and as a result, my first pilothole was located too far away from the existing transom knee.  The hole was easy to fill and repair, and actually helped me locate the actual spot where I should drill, this time from above.  Fortunately, I had not yet painted the nonskid, so the minor repair would be covered invisibly later.

More to come!

 

All photos and text on this site 2002-2009 by Timothy C. Lackey and Lackey Sailing, LLC
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