by tomodda » Tue Jan 26, 2021 4:26 pm
GL:
Yes, all rigs have tradeoffs, and my "boom downhaul" has the problem that it takes up space at the bottom of the mast, where space is already in short supply/high demand. For what it's worth, I have two "bails" (C-shaped straps) on the lower mast, one right at the tabernacle, one some 3 inches above. The lower bail is actually on the rear pin of the tabernacle itself, so that's where I clawed some space, at the expense of one more thing to do when I'm putting up the mast. The vang is attached to lower bail, and the bitter ends of my boom downhaul go to the upper, as do the bitter ends of my vang cascade. Some creative work with high MWL snap shackles keeps it all compact and rotating efficiently as the boom swings around. The other end of the downhaul (the working end) goes thru a stand-up block on my cuddy roof (that I got on super-sale, $30) and then into a cam cleat at the cuddy lip (another sale, I'm cheap and patient). Historical note - "Bitter End" refers to the fixed end of a running line, which - in wooden ships days - is attached to the "bits", those square wooden brackets you see on old boats. Before you ask, the other end of the running rigging lines gets held by a belaying pin on either a pin rack, attached to a bulkhead, or a "fife rail," freestanding. Nowadays, we use cleats, thank Neptune!
Back to your Cunningham setup, you can easily add a purchase to the line. What I used to have before I went over to a boom downhaul is a line tied to the gooseneck as far back as I could get it, that then went thru the cringle and ended in a small block. Then I had another line coming from somewhere (mast bail or the gooseneck, I forget?) that went thru the block and down to a horn cleat on the boom, up forward. Pull on that line, sweating it against the boom cleat as needed, and I'd get a good bit of tension on the luff, as desired.
As for "dynamic," I seem to remember that when I was using a Cunningham, it was either full on or full off, the purchase was just to help me pull it "on." As you noted, you need to adjust the luff depending on wind speed, it's a tool for flattening the sail. I do adjust the boom downhaul somewhat more finely, basically it's off, 1/2 way, or full on... corresponding to wind strength. Don't know if it makes a real difference, but I don't have reef points, so it's nice having a few "gears" in my mainsail-flattening rig. Likewise, the cleaner foot that you get with a boom downhaul is not really a factor, because most of your drive comes from the upper 1/3 of the sail. In other words, I wouldn't switch from a Cunningham to a Boom Downhaul "just because." I did it to simplify my rigging (one snap shackle, done!) and to free up a cleat on the boom. My next set of sails will definitely have reef points, so I'll need that cleat (slab reefing). But I'm still keeping my boom downhaul, mostly because I've grown to like it and ease of rigging.
Tom
P.S. I think I sunk $150-$200 into 4 snap shackles, even with cruising the online sales. They are a huge time- and space-saver, but you definitely need to spend some money on top quality, no skimping! I like Ronstan, so I got that for all my snap shackles. Yes, there's some cheap chinese stuff out there, $12 snap shackles... no way I'm putting the load of my vang + the load of my halyard on those, even if that load is "only" in the 600-800lb range. Snap shackles need to open when you want them to, and not open when you don't want them to, period. That's worth spending on. Apologies for "preaching to the choir!"