Junk Rig Conversion Part 3: The Forward Mast Step and Ring Frame

04 02 2013 Posted by Daniel

With the cabin framing and step largely complete, I moved on to the foremast structures. This work was up in the v-berth area, near the bow, and was thus quite cramped to work in. But I managed quite well to keep the mess and dust largely confined to the forward areas this time, so that made life in the main cabin much more pleasant.

The first step, as usual, was to cut away the headliner and ceiling panels to reveal the hull and deck insides for grinding. I needed to remove the balsa coring from the area immediately around the mast, to reinforce and stiffen the deck for the anticipated forces, and to better transmit and distribute them to the ring frame and other hull structures like the anchor locker bulkhead.

The core came away in messy chips, and took most of a day to remove with a hammer and chisel, working upside down swinging the heavy hammer a few inches from my face. My arms got a fantastic workout that day is the polite euphemism for how I felt afterwards.

With the core removed, I cut away the main plywood panel forming the v-berth, as the structure framing it was in the way of the mast. I’ll rebuild this into proper storage units later. Here is where the mast step is going to go:

Now that all the areas which need new structure are exposed, I ground them down to reveal a solid surface to bond to:

As before, the ring frame is a laminated plywood structure which spans the width of the deck and bonds it to the hull sides. This time, I elected to assemble and shape the laminates as an entire piece, rather than layering them together inside the hull. Since this frame is much more narrow than the mainmast frame, it was much easier to do it this way.

I did the floors in the usual manner:

And glassed the ring frame in place all at once:

The ring frame and floors are both bonded with heavy thickened epoxy and tabbed with two layers of 17 ounce biaxial tape, then covered in 1-2 layers of 10 ounce fiberglass cloth. The deck core was replaced with 3 1/4” layers of quality underlayment plywood which in my area has no voids that I’ve yet noticed and is very durable with an exposure-rated adhesive. It’s also very affordable at $10 a sheet or so. I used about a gallon and a half of epoxy between the frame, fillets, floors, and deck laminations all told, mostly in the fillets.

You may notice that I also took the step of adding tabbing between the deck underside and the anchor locker bulkhead. This is just to give an additional layer of stiffness and support there - the bulkhead itself is not tremendously well attached to the hull but it’s bonded sufficiently to provide a reasonable extra amount of stiffness forward of the mast, which is never a bad thing.

I was able to complete all of this in about four days, as opposed to the two weeks it took me to do the same amount of work in the main cabin, so I felt reasonably accomplished and decided to proceed immediately into the mast steps themselves, as my shipment of Brazilian Ipe had just arrived. Ipe is a tremendously hard and rot-resistant wood and is therefore quite optimal for the mast steps.

For the mainmast, the steps were simple: straight sections, 27” long, of Ipe, laminated to a total width of 14.5 inches, and notched to fit snugly over the floors. I notched the ends using a combination of jigsaw and circular saw, and notched the middle using the jigsaw and a few well-placed drill holes to help the bit turn 90 degrees. The Ipe wood eats through saw blades like nobody’s business, though, and it likes to smoke a bit when you drill it, even if you drill slowly.

The foremast step was a bit more complicated. Because of the rapid taper in the hull that far forward and the rise of the keel at that point the forward floor was significantly higher than the middle and after floors. This required a notch larger than the wood was deep, and thus I needed to get more depth in the wooden step to accommodate that. The way Tad suggested was with a scarf joint, and after some discussion I was able to make a reasonable facsimile of it with a jigsaw. The Ipe doesn’t work very easily, so my joinery work wasn’t perfect, but the epoxy fills the gaps well and actually prefers a bit of a gap to give maximum strength so all in all I hope it worked out. I backed up the adhesive with two heavy bolts running through the scarf on either side just in case, and put the whole assembly in place - it has to weigh at least 25-30 kg! I tied it to the floors with a few 8” heavy lag screws and thickened epoxy, making a fillet as best I could where the notches met the floor.

After getting the floors glued and bolted in place, I turned my attention to the deck again. Specifically, where to cut the opening for the mast and partners. I leveled the boat by eye as best as I could using the waterline as a reference and then used a plumb bob to mark the deck where the mast location was outlined on the step. Drilling through from the inside left me a mark I could use as a reference, and I then measured the circumference and cut from the outside using a jigsaw.

I did encounter a little detail that caused me some frustration… see if you can spot it in this photograph:

I sure hope I put this in the right spot…

Note the color change between the glass work I did (green) and the original deck layup (red). Also note the thickness of the deck and skin at the cutout location.

Tad recommended adding a heavy 3/4” plywood boss / doubler piece right at the partners, both to help straighten out the camber in the deck as well as to add a bit of additional reinforcement right at the high-stress area. I did this for both masts, grinding some of the bottom of the plywood out to match the deck camber and filling the rest with thickened epoxy to transition the stress into the deck. A beveled edge and some fat fillets, a little glass tape and cover the whole thing with cloth. Good to go!

Next week I’ll be taking some metal parts to the welder and hopefully getting the first look at the masts. Stay tuned!