The boom

I dislike clutter on my sailboat, I dislike things being difficult to adjust (important for sailing solo) and mostly, I dislike things being just plain wrong. My boom is a good example. The mailsail outhaul was a series of blocks on the starboard side of the boom. This meant I had to leave the cockpit to get to it and the boom had to be more or less amidships to adjust it. As such, it tends to be set for a flat sail (best for high winds) and so is sub-optimal most of the time. On the port side run a pair of leech reefing lines. (I have two reef points, and two lines per reef point, one line to haul on the luff, one line for the leech). Those leech reef lines run forward down the side of the boom for a bit, then under the boom through a series of bales and then to a block on the mast. This off center path means that the leech is either too tight or too loose, depending on the tack I'm on now and the tack I was on when I reefed. On one tack, this leads to a sail with belly; hardly what you want after reefing. On the other tack, you run the risk of stretching the leech. Fixing the reef lines means running them inside the boom, then bringing them out the bottom of the boom on the center line of the axis of rotation. Fixing the outhaul means running it back to the cockpit along the same (new) path as the reef lines; through the boom, so the outhaul tension does not change with boom angle. I'm not describing a reinvention of the wheel here; all decent boats do this. I buy a new boom with the right end fittings, run some lines; done. Simple enough, except for that "buying" bit. Staring at a few boats in the marina, the solution seems little more complicated than a fancy endcap on the forward end of the boom with a couple of entries for the lines. Fine, buy an endcap. (More buying, it's true, but more palatable than a whole new boom). Unfortunately, these end fittings are all specifically made for a particular boom extrusion and none match my 30 year old extrusion from a long gone BC manufacturer. OK, well, how about modifying my current endcap? (See pic below). Possible, but I would have to be SURE that I did it right, because there's no going back. I was in fact all gung ho until my friend Graham asked innocently enough "you sure about that?", which got me thinking some more and I soon found myself no longer sure at all. (Graham has done that to me more than once .. stopped me before I did something difficult to recover from.) So I stared at the end cap some more and decided that it might be possible to fabricate my own, and this is the (ongoing) story of that attempt. First step was to build a solid model and just look at it for a bit. This was a good excuse to use something called FreeCAD, which is a new parametric based 3D CAD program. It's only in version .14, but works VERY well, and is a whole lot more intuitive than what I'm using now. Currently, I use Vector, which I paid a small fortune for. Vector is quirky enough just drawing something in 2D and darn near impossible to create a 3D model. Every time I want to do some 3D drafting, I have to go back to the tutorials and start all over. What Vector does spectacularly well and extremely easily is generate GCode for machining purposes, once you have a drawing. This alone is worth the (considerable) expense. Hopefully, I'll be able to figure out how to export from FreeCAD and generate code using Vector. For this project, I just drew everything twice. I lucked into a gigantic block of aluminum for exactly the same price as just buying a piece the right size. There's enough metal there to make a second endcap if I made a mistake on the first one. There's even enough, for the next project (a masthead fitting for a new anemometer). A guy would simply have to cut it down to size. The cutting was JUST within the capabilities of my bandsaw, although it did require four cuts after three rotations. For comparison, the part I want to duplicate is on top of the billet. To save milling time, a second cut of the newly cut slab got the block to the approximate size. This was followed by a bunch of trim cuts to get it closer to oval. Three hours later, I was on to the machining. After a few hours on my little milling machine, I'm about half done. I've produced the inner oval (that fits inside the boom), the slightly larger outer oval (that keeps the whole part from disappearing into the extrusion), the cutaway for the sail slug to slide in, the slots for the sheaves and the holes for the shaft. Some time on the lathe produced sheaves out of delrin (that got dirty pretty much instantly) and an aluminum shaft for them to run on.
Here's the endcap with the sheaves installed. Here's the holes bored. I used a ball endmill, so there's almost no sharp corners anywhere to snag or chafe. The few edges that are there will be removed by a subsequent honing process (just as soon as I can find my hone!) 100 0985 Here's endcap with a whole lot of metal milled away to make the ears. Actually, the bandsaw was used to remove most of the material, as sawing is much faster than milling. Once the milling was complete, almost 4 hours was spent filing. Most of the time was used to remove all the machining marks, the rest was spent shaping the inner oval so that it was a nice snug fit inside the boom extrusion. (That's the blue "paint" you see; it's not paint at all, it's machinist's blueing that I didn't clean off completely. It's used to determine where things are tight. Shove the part in, see where the blueing rubs off, file .. paint .. shove .. look, file .. paint .. shove .. look, over and over and over again!) The milling was actually close, but I had to estimate the dimensions, as I had no really good way to measure the existing part. The shape I came up with would have taken a bang with a hammer to get it in, but then I'd never get it out again. Note that since this piece has thicker wings than the original, a new clevis pin was required. Thankfully, I had a length of 3/4" 316 stainless rod around. A few minutes on the lathe and ta-da, shaft. Here's the setup I used to do almost everything. Who has a table in their shop suitable for a 10' boom?
As you can see, a nice fit. I've also drilled and tapped for some mounting bolts. (I'm going to screw this together rather than pop rivet it, so it's easier to take apart if required.) But just after having done this, I got a bad feeling. My bimini was purposely designed to get VERY close to the end of the boom, so as to maximize coverage. But with this new fitting, the boom would be an inch longer, and I wasn't sure I had an inch! And as the bimini was removed, there was no good way to find out. So ... Nothing to do but cut an inch off. This was the first task that was irreversible. Everything up until now could be undone, but cutting is a WHOLE lot easier than welding, especially when the material is aluminum! I carefully leveled the bandsaw, then carefully leveled the boom, then carefully ensured that the boom was flush to the bandsaw table. (Detecting a pattern here?) Two deep breaths, then started to cut. And after cutting, still a nice fit. Three threaded holes on each side, countersunk smooth, and one more at the bottom for good measure. Dissimilar metal corrosion is something I take great pains to avoid. For the padeyes, I have some wonderful adhesive backed kapton. (Kapton is to plastic film as kevlar is to straw, insanely strong and completely impervious to all chemical attacks from anything.) For the cheek blocks though, the kapton wouldn't do. The blocks are not flat on the bottom, but do in fact have a bit of a radius. This helps them sit (more) flush on a curved surface, but also means that they would sit on four points on a flat surface. These four points could puncture the kapton, so a different solution was called for. I have some very thick mylar film from a printed circuit board house. This stuff is also very tough. I cut out some gaskets and punched the mounting holes. Should be fine. Here's an inlet for a reefing line. To remove any chance of chafe, I've mounted a fairlead inside the boom. To fasten it, I simply tapped the fairlead Because I'm using stainless fasteners, there is the chance of dissimilar metal corrosion. I've therefore installed titanium sacrificial washers between the stainless bolts and the aluminum boom.
The plates are mounted with pressed in nuts, as I try to avoid pop rivets whenever I can. While light, pop rivets make disassembly for inspection or repair difficult. There is a chance of dissimilar metal corrosion here too, but I'll be using Locktite thread locking compound on the "nuts". This will prevent the corrosion as well as hold things in place. As stated above, I don't like pop rivets, I prefer nuts and bolts. But the nuts present a problem when fastening things down a long boom. Even if a guy is able to somehow get things assembled, he'll never be able to take them apart because he'll never be able to convince himself to take them apart, the memory of the assembly being just too painful. So I drilled and tapped some plates for the cheek blocks and padeyes. They both have an extra hole that will keep the plates in place even if the device above is removed. The big holes are just to save weight. The left plate is for the most forward check block. The bevel will act as a bit of a fairlead, as the reef line from the aft inlet will pass over this plate and could rub. Here things are shown assembled (although not yet clean and tidy). Why the angle on the inlet plates? Because I wanted the fairest possible angle lead from the block to the inlet. A 3/8" diameter length of drill rod helped visualize the angle. Things installed. Now to trim the kapton and blow away the dust. It's now 2018 and sadly, time and UV have taken their toll on the sheaves in the turning blocks. I should probably have done this in 2015 with all the other mods but ...
So, back to Al's standard repair. New sheaves made from Delrin should last forever. It's a fairly simple matter to turn them up on the lathe. The secret is to grind a tool just the right shape to plunge into the blank. Some aluminum bushings in the middle, a barrel bolt on the bottom, BHCS on the top and tada, repaired. Since the boom was off the boat, I decided to fix something that again, was not actually broken. The bales were held in place by a standard hex head nut and bolt. These have, of course, six "hard" edges and hard edges just won't do. Time for more barrel nuts with their nice smooth surface. Here's the various pieces. Barrel nuts and ready rod replace the hex nut and bolts. I added some nylon washers to separate the stainless steel bales from the aluminum boom. I just have a thing about dissimilar metal corrosion. One small problem is that ready rod has a rough surface, so I cut some PEX pipe to just the right length to fit inside the boom. Mind you, getting that piece of PEX into position 6 feet down the inside of the boom was going to be a problem. Here's the fix, a holder made of plywood. It held the pex securely enough to not slip off but would let go with a solid tug. One last fix. I was convinced by .. someone .. that single sided slab reefing was better than conventional slab reefing in terms of kindness to the sail; conventional slab reefing just scrunches the sail up between the reefing lines. Single sided reefing allows the excess sail to fall nicely to one side. Single sided slab reefing should also improve the sail shape when reefed. In the top half of this pic, you see all the lines running down the same side of the sail. The bottom half shows the other "clean" side. I left the unused pad eyes on the boom, just in case I change my mind about this. Here's the various bits and pieces used to turn conventional slab reefing into single sided slab reefing. I made some loops out of Amsteel and then attached them to some low friction Ronstan "Ropeglide" rings. The rings that are apparently made out of brass are in fact stainless steel; a quirk of the lighting makes them look gold. These rings are slightly larger in diameter than the existing cringles and are about as neat a solution as can be had.
Here's a closeup. I used high quality whipping to hold the slides to the loop, and lots of it. Since the forces involved are small, this should hold just fine.