Friday, September 13, 2013

Installing a Chain Stopper

A while back I installed a Lewmar chain stopper on the foredeck to make anchoring a bit easier. It was a simple job to fashion a mounting block out of teak, make a backing plate out of apitong and bolt it all together. The job was done in a day. Then I went out and anchored and discovered that if I left it as is, the stopper would soon knock all the galvanizing off the chain. This is a standard flapper type chain stopper, rated at 5,000 lb SWL and sized for 5/16 chain. I had used this unit on my last boat, which had 1/4" chain and a vertical capstan windlass, and it worked well. The problem is that there is barely enough clearance in the stopper for the chain to pass through, and only if it is perfectly aligned and set at an angle that matches the angle of the chain as it passes from the windlass to the roller. On top of that, the deck in that area is only about half an inch thick. It is made of a fairly heavy fiberglass laminate and a bit of wood core.  This isn't really enough structure to simply throughbolt the stopper to, so I added a carbon fiber top plate and a larger wood backing plate to bring it up to snuff. The photos below outline the process.


First I measured the amount of crown in the deck forward of the anchor locker. It's nearly flat but I wanted the edges of the top plate to fit tightly to the deck so I created a bit of extra curvature in the mold, which is made of a piece of old 1/4" Starboard.

Paper pattern with pre-cut carbon fiber

I took a template off the deck and drew the shape in AutoCad. I wanted the top plate to be fairly large so I could attach it to the deck with several widely spaced fasteners to spread the loads out as much as possible. The rectangular shape is the outline of the teak mounting block.

Laminating the carbon fiber
I used four layers of Vectorply C-LT2200 carbon fiber cloth for the laminate. This fabric is made of carbon fiber bundles aligned along the 0 degree and 90 degree axes of the roll and stitched together. This architecture is stronger than traditional woven fabric. The four layers amounted to about 88 ounces/sq yd of material for a total thickness of about 3/16" when it was finished.

Second layer is rotated 45 degrees 

I oriented the first and fourth layers so the fibers run at 0 and 90 degrees to the centerline of the boat and rotated the second and third 45 degrees to provide strength in all directions. I used WEST systems resin which works really well for hand laminating projects.

Finishing the top plate

After the plate was laminated and cured, I glued another copy of the paper pattern to it so I could precisely locate all the holes. It was a simple matter to drill and countersink them exactly where they need to be.

Top plate ready for finish sanding and paint

Check fitting the hardware

Finished part installed

I made a backing plate out of 1" thick apitong that extends out to the bulwarks to help spread the loads as much as possible. The 10" cleat allows for a snubber to be run out over the port bow roller. I found that if I take a turn around the roller with the snubber, it won't jump off if it when the boat swings at anchor.

Chain and snubber geometry works
It took a couple of tries to get the alignment and angle of the stopper to match up perfectly with the chain. It would have been nice to have a larger stopper, but there was just enough clearance between the shank of the anchor and the hatch for this smaller unit.

55 LB Rocna just fits

1 comment:

  1. You do such a nice job of describing your projects and adding photos. Looks like this came out great. Best of luck on moving on board and starting your trek south! Pam and Carl s/v ExTerra