New Coaming Boards and Boxes

[Salty Dawg]

My Coaming Boards are beginning to give up the ghost and i'm considering replacing the boards and rebuilding the storage boxes with star board (less maintenance). Anyone out there in Ericson Land have any suggestions...any pitfalls to watch for?

Thanks

The Dawg:thepaw:

 

[tenders]

Boy, that wood looks lousy when it's left to peel, doesn't it! I finished this a few months ago. This was my first major "wood"working project and it turned out well if I may say so myself.

I bought an entire 4x8 sheet of dolphin grey 3/4" Starboard. This is enough for two coaming boards, a set of hatchboards, and plenty of extra--I'm thinking about handrails now. I think it cost $280. That's a lot but the fact that you NEVER have to refinish it makes a huge difference over a 20+ year expected horizon.

I used a table saw, handsaw, drill press, and router to cut everything out. The hard parts for me were (1) properly placing the coaming box cutouts and (2) properly placing all the screws with nice-looking plugs.

You have to drill everything 1/8" oversize to accommodate expansion of the Starboard, which is more significant than for wood. So, 1/4" screws require 3/8" holes. 5/8" washers (countersunk) require 3/4" holes, which require 3/4" plugs. That's a big plug and there are 30+ screws per side. Maybe you don't need so many screws...but I used them.

You have to rip very thin slices of Starboard (1/16") and use the plug cutter with the slices "upside down" to make yourself a plug with the correct textured finish on the outside.

 

[NateHanson]

I'd expect the starboard expands along it's length the same as it does along it's width, right? (unlike wood, which has no significant movement in the direction of the grain).

According to the manufacturer, Starboard has the following Coefficient of Thermal Expansion : 1/32" / foot / 40 degrees F. So, if you have an 80 degree seasonal swing as we do up here, then I'd be very worried about it buckling over it's length when used as coaming. If you have a 7' cockpit coaming, it should expand 1/2" beyond it's winter dimension. If this stuff gets heated in the sun to 120 degrees (ever had trouble walking on deck in bare feet?) then it could expand nearly 3/4" along it's length. That means you'd need 3/8" slack on either side of your screw to allow for the movement, assuming you're building it at the middle of the expected temp range.

If you want to keep the movement even on both ends, don't leave any slack in the center holes, and increase the size of the screw slots as you go towards each end. Also, leave enough room at each end so the coaming can grow without running into something.

All these assumptions are based on the CTE, and I don't know if that's really true in the real world, but I'd be concerned about that.

Wood needs attention occasionally, but hey, it doesn't move along it's length, and it won't bend in the sun. Personally I'd slap on two coats of cetol each season, but I can understand others wanting to cut down on maintenance.

 

[tenders]

A risk I suppose, but tons and tons of modern exterior marine joinery uses Starboard and products like it in conjunction with fiberglass. I asked about this on the King Plastic website and the response was that 1/8" oversize holes would keep it together.

I'd guess my boat's annual temperature exposure ranges from 15 degrees in the cold of winter to 120 degrees in the sun of a summer day...we'll see in a year or so.

 

[Salty Dawg]

Thanks for the insight.....Worst case: It doesn't work well and I re-install the teak.

Thanks again

The Dawg:thepaw:

 

[wurzner]

I've used starboard for backing material on thru hulls with good success. I would not use it for hand rails though. My neighbor did this and after a fair amount of cost and little time (1 year), there are all kinds of crack in it. It looks good from a few feet, but I question the strength of it in a very critical application.

shaun

 

[Loren Beach]

Going with the Grain

One feature about molded resin products is that they are seldom reinforced with long fibers, like a matrix of resin and cloth/roving for instance... or your teak handrail with it's grain structure.
And that "grain" is what holds it together when you point load it with hundreds of pounds of falling human scrambling to stay on board.
That's why those inexpensive "resin chairs" that we buy in bunches for our YC outside deck have to be thrown away when they start cracking/breaking after a few years due to UV damage.
Some plastics are much stronger than others, like nylon. And some are more resistant to UV, but cost more.
Cost alone would preclude building hand rails out of FRP, and with the constant rise in price per board foot for teak, the polished SS option is looking better and better...

Ahhh, speaking of SS hand rails, if Kim were only still lurking here, to lecture me about "turning to the dark side!"


Since cockpit coaming boards was the subject that started this... How about simply making the new ones out of half inch cedar (for coring) with a couple of layers of 9 oz cloth and epoxy wrapped around 'em? Fair the surface and lay on a couple coats of epoxy/LPU paint.

Loren