Wednesday, January 02, 2013

Finally the hull is turned over!

I didn't realize it has been so long since I updated my current boat building.  When I went to my local lumber store(last summer) to buy planking stock, I noticed that they had some beautiful African mahogany for not-much-more than the cost of cypress.  It also came in sizes more amenable to re-sawing with less potential waste, so I went for it.  My wife has pretty much blessed the project, saying, "Don't go cheap; get whatever is best."  She liked my last boat and the compliments it gets (here in Colorado boat-building is quite rare, so almost anything impresses the onlookers), so she fully supports my current project.

At home I used a bandsaw to slice and re-slice the mahogany into strips of about 5.5 mm. thick by 3 inches wide with assorted lengths so that I could stagger the plank junctions.  A bandsaw leaves some roughness and thickness variation in the planks which I corrected with a planer.  Planks were laid out on the rosin paper patterns, which I had used to outline-shape the plywood sheathing, and numbered in sequence for placement on the hull.  Then the task was to tack the planks in place on the hull with temporary staples after coating the hull and plank underside with a thin layer of slightly-thickened epoxy.  Mahogany is heavier, denser, stiffer than cypress.  I discovered that the staples I had used for the cypress on my previous boat were not quite strong enough to penetrate and hold the mahogany in place on the ply sheathing, but I switched to using brads (airgun, pad under the head for easy removal later) where necessary and got the job done.  I was glad that I hadn't made the planks any thicker.

 Next is (of course) a preliminary sanding to get rid of any resin blebs and  planking variations.  I used an orbital sander with a canister to collect the fine mahogany dust, as well as a long board.  Then came a layer of fiberglass cloth (8 oz. on the bottom, 6 oz. on topsides) and five coats of epoxy resin to completely bury the cloth.  Did I mention that sanding is my least favorite task?  The bottom wasn't too difficult because the surface is almost horizontal and I was able to use filler to achieve the correct non-slumping mix of resin.  So the resin coat came out fairly even.  But the plan was to finish the topsides clear to show the underlying mahogany grain.  This meant that I was working on a somewhat vertical surface and could use no fillers.  Even when the epoxy coats were quite thin, runs could happen easily and show up after you thought you were finished and had walked away.  Those tiny little brad holes that I thought would cover easily didn't always fill like I had hoped.  So I sanded and re-coated several more times.  I used the fine mahogany sanding dust (from the sander canister) as a filler to a limited extent.  The color match was perfect, but the particles weren't uniform enough to create a true smooth layer.  I should have used a flour sifter.  Lessons:  1.  Avoid clear finish on the vertical hull surfaces.  2.  Fill every imperfection, no matter how tiny, before applying epoxy.  3.  When creating your own wood flour, use a fine sifter to get uniform particle size.

With the winter holidays coming up, it was time to paint the bottom and let it thoroughly dry for several weeks before turning the hull over.  I washed the epoxy to get rid of any wax, lightly sanded, then cleaned the bottom again and let it dry.  The paint went down beautifully in a nice even coat.  Then I waited for it to dry.  We went away for Thanksgiving, and when we came back the bottom was still tacky.  That paint never did dry on the hull; it dried on the mixing paddle and in the application pan, but not on the hull.  So I scraped and sanded to take all the non-completely hardened paint off.  I had heard that with epoxy, you didn't need a primer.  Well, now I put down a primer coat, then paint from a fresh can.  And it dried nicely.  I use a laser to mark my intended waterline.  I designed the hull; I know its displacement; only a few minutes for me to mark three points along the side of the hull and then connect them with a laser and tape it with painters tape.  I am sure I will come back to this task for a touch-up and plan to add a boot stripe.

Last night, with Christmas and New Years past and the decorations put away, my wife and I turned the hull over.  First I constructed a sling; when the hull was supported from overhead, I released it from the building strongback.  Then the hull was rotated in its sling and lowered down unto a cradle I had constructed.  Now comes more enjoyable and creative steps in building.  I have learned to start from the bottom.  Do those things which are most difficult to access before covering over with decking, seating, and other surface coverings.  Next week is the Denver boat show.  It is not too early to start looking at outboard motors; debating between 60 and 75 hp.