Here's a 3rd possibility stolen right from what CLC did for the Rhode Runner:

They left the deck as a large piece of wood, but routed grooves that are filled with black material (maybe graphite/epoxy mix?) to make it look caulked. CLC uses a CNC machine, but a hand router and straightedge should also work fine.

This method has the advantage of preserving the integrity of the decking and not having as many openings for possible water intrusion.

I also built a schooner 14 years ago. It was an 18-foot scaled-down version of Bolger's single-handed schooner converted from plywood on frame to monocoque stitch-and-glue. I used the puzzle-jointed plywood from CLC to build up the long pieces of plywood I needed.

The quality of the wood and the appearance of the puzzle joints let me leave the boat unpainted. You might want to consider that. But, even if you're going to be painting it, the puzzle joints are a good solution for joining plywood into large sheets.

Have fun with your build,

Laszlo

  Oh wow.  another Bolger schooner.  I'm doing a scaled up about 15% larger light schooner.  Basically, maxing out my available building space.  I used the puzzle pieces for the sides like you did.  Because of the size, it is a mixture of frame and stitch and glue.  It was kind of a puzzle figuring out which was best at a given location.   Interesting deck idea.  That is kind of what I was looking for.  Hmm.

   The "stripes" in the deck of the Rhode Runner are dark wood (mahogany or walnut or similar) about 1/4 x 1/4" laid into routed grooves routed into the deck panel, then sanded flat/flush with the surface of the panel (and then glassed over).  When I built my RR, after joining the panels down the centerline (there is a backing board underneath the deck along this seam) I routed an extra groove right down the joint seam and added a center stripe of wood - the kit came with enough extra that I was able to have a full length piece of the (I think) walnut left over based on carefull layout of the shorter pieces to minimize scrap. Thus, my deck shows no seam joint (which would be under the cleat in the picture above) - there I have another stripe on the deck.

On a "traditional" teak deck of a sailboat, the grooves between the boards are filled with black polysulfide caulk. It is gunned into the grooves, excess scraped flat, and then sanded after curing/drying. 

I think this would work for the application discussed above.  Just put up a fence along the deck (clamp on a long board) to guide a hand router, set the depth at a shallow/half-depth of the panel, and route in some grooves.  Fill them with polysulfide or wood, and off you go. Sanding effort has to be limited when sanding on a plywood panel as compared to a 3/4" thick teak deck.  I'm not sure how caulk would behave if the intent is to glass over the whole deck - maybe the caulk flexibility would be an issue and that might be why CLC uses wood strips.  Something to consider - either way, is either dark wood or caulk set into grooves.  Both easier than joining multiple panels.

Good info, Bubblehead. I bet CLC would sell just the mahogany strips. I would not epoxy or glass over polysulfide compound. That'd be asking for adhesion issues.

Laszlo

 Hmm, what about filing the groove with epoxy that is colored black with something like coal dust?  Sort of like old fashion paint.

  How thick are the mahogany strips?

   I think the strips provided with the kit were about 1/4" thick (maybe a little thinnner) x by 1/4" wide. Much thinner and they'd be tough to handle without breaking. I can't remember the thickness of the deck plywood, but I think the pre-routed grooves were slightly less than half (maybe about 1/3) the depth of the plywood. The strips are quite "proud" when epoxied in, then they get planed/sanded down to level with the deck. CLC reps will have the details.

Colored epoxy would certainly work. Even wood flour mixed in could provide some contrast, but wouldn't be as dark.  I've used alcohol based stain to color epoxy/wood flour mix for filets to get them to match surrounding stained wood. (I also add cellofill to lighten the color of "standard" wood flour filet material to better match unstained okume when I filet in visible areas.) I'm sure jacobean or dark walnut or some other dark color could get the mix dark enough. Using epoxy (as opposed to wood strips) will necessitate a conscientious use of a scraper to smooth things before the epoxy is fully cured, and a good, hard, fair sanding board for final smoothing to prevent the stripes from being raised higher than surrounding deck. Glassing over the deck will help fair things out, too. Even slight ridges will be visually very evident on a flat deck. 

>> Hmm, what about filing the groove with epoxy that is colored black with something like coal dust?  Sort of like old fashion paint.

Epoxy/graphite mixture is exactly that. In the schooner rigging picture above, the bottom of the boat has been coated with the stuff so you can see the color.

There are multiple considerations for the depth of the grooves. Keep in mind that plywood gets its strength from its thickness and the number of plies with criss-crossing grains. Cutting the grooves weakens the wood. The grooves also act as force concentrators. The way you get around these problems is with the choice of filler material.

The mahogany strips are a really good choice because they have many of the same physical characteristics of the plywood - weight, thermal coefficient of expansion, hardness, density, etc. Filling the grooves with wood restores many of the same properties that are lost by routing them.

A custom colored mix of wood flour and epoxy as suggested by Bubblehead makes an artificial wood substitute with similar properties to wood. The biggest difference is the lack of long grain which reduces its ability to resist tension compared to wood. A layer of glass on the deck will take care of it.

Epoxy/graphite mix is not as good as wood but can be made to work. The issues are that it's harder, denser and more brittle than wood. It has a different thermal coefficient of expansion. As such, it will still act as a force concentrator even if the groove is completely filled. The lack of grain means that it won't help with the required tensile strength, though glassing the deck will take care of that problem.

Epoxy/graphite can still be used cosmetically, though. Just skipping the grooves completely and using the epoxy/graphite as black paint will avoid many of the problems. Just be sure to carefully tape the boundaries. You'll also need to put on a topcoat of epoxy and sand or just glass and fair the deck if you don't want the slight ridges. Note that epoxy/graphite is 100% compatible with epoxy and means that you don't have to worry about topcoats and glass adhesion.

Another cosmetic approach is to use a very dark alcohol-based wood stain to make the lines. Getting sharp lines with stain can be a pain, but hspira has covered how to do that somewhere in these threads.

Finally, if you're going for a traditional caulked wooden deck look, don't forget to use satin finish varnish instead of glossy. And if you're going to be walking on the deck use some kind of non-skid additive.

In closing, I'd recommend epoxy/graphite if you don't want to route grooves and mahogany strips or colored wood putty if you do.

Good luck,

Laszlo