Ridiculousness

Nonsensical.  Unnecessary.  Misguided.  

These are the words that come to mind having completed my carbon slat bench backs.  While this whole project might meet that description, the curved, foam-cored, carbon slats that I molded one at a time are are pure ridiculousness.

Let's start with some history.

After 15 year break from sailboat racing, there were two things that sucked me back into the fold, the Melges 24, and a 30 footer built by the great Erik Jesperson.  Anybody that's paid attention knows the boat I'm talking about.  Myrrh is a bewitching wooden box of a craft.  Absolutely lethal in light air, and able to get on the step and rip off the wind, she exudes a disarming warmth below decks.

Hinged along the top, her wood grate backs flip up for gear storage and down for seating.  Better yet, they can be secured in the full upright position, to reveal a full width mattress for sleeping.  I've heard this design concept appears here and there, but for me this was fresh and so I set off to copy it, but with my own spin.

I wanted my slats to be clear coated carbon, and worse yet, I wanted them to be light and curved to match the flow of my interior.  I puzzled quite awhile on how I might accomplish making a banana-shaped mold without any true Z-control on the CNC.  It finally occurred to me that I might be able to machine a flat MDF mold then just assemble each plank on a rocker table.  Take a look at the process.

Here shows the mold sets.  After machining, I coated each with several layers of West Systems 105/207 and sanded between coats.  For the final coat, as you can see in the background, I added white pigment which helped me gauge my sanding depth.  Adding a few coats of wax, I went ahead and bagged a test plank.  

First came the skins.  Since the resultant planks are curved, I knew the lengths of the two halves would not match when bagged to the rocker table.  To combat the problem, I added a buildup of layers to the plank ends to have something to sand back against for the final true-up.

Then came pre-shaped cores which I formed up on the router table.

I then used the CNC to skin the two halves flat.  A couple of boards to act as rails and a flat plank bolted to the router shoe work too, but since I know my router table is reasonably true, I just used it to surface the parts down to the splitting plane.

I had a little rocker table left over from making the benches themselves, but the curve was a little shallow, so I increased the curvature by staking battens on the sides and backfilling with Bondo.  Collin Taylor told me dispatch a series of blobs on pre-metered Bondo and catalyst on my pallet.  The idea is to mix one blob and use it off before stirring up the next one.  Of course, I didn't follow this solid advice and I found myself in Bondo hell, as if you have any reasonable volume on the go, the stuff kicks practically faster than you can mix it.  The upside, you can get right to sanding without much waiting.

To join the halves, first I primed the joint with neat resin, plus black pigment to keep track of my progress.  After priming, I mixed some thickened goo and glued up the parting plane with a notched trowel.

The first one out of the mold ended up being too bendy, so I added a layer of 0/90 as a secondary step.  My goal was a flex similar in general terms to a snow ski.  That seemed about right to get the bench to flex and contour slightly to the human form.  I experimented with adding a red pinstripe at the joiner line on this first prototype by using a slot cutter on the router table, and then filling her up with red tinted bog.  I thought it looked cool, but Jacque told me that I was headed for something unbelievably tacky.  

With the proof of concept plank finished, tacky or not, it was time to churn out 10 of them, 5 shorter, and 5 slightly longer.  The first three were fun.  The next seven were painful.  With a healthy dose of adult ADHD, I find I'm pretty OK at R&D, but just terrible when put into a repetitive role.  Honestly, after three slats, I was in too deep, and I just ground them out in my own private little hate mission.  

With planks fabricated, it was on to repeated hot coats to try to kill pinholes.  I used some scrap cardboard honeycomb with finishing nails for kickstands applied several coats of resin to both sides, sanding each time.

The wood uprights were milled on the Autometrix and I went ahead and mounted spring-loaded barrel bolts by bonding in stainless inserts from McMaster.  On the port side, these will key with a hold in the main bulk, and a second hold on the side of the kitchen island.  For the starboard side, I will once again key into the main bulkhead at the forward end, but haven't really worked out what's going to happen at the back.  

Here is a look at the bench backs in rough position.  In this picture, you can see the door-skin"L" that I used to copy my kitchen chair geometry back into the boat.

After more hot coating and sanding, I finally felt like it was time for some clear.  I bought paint and got psyched, but in the end, I chickened out and had the fabulous team at Betts Boats hose them in some Awlgrip LP.