TMH--

I feel your pain, but the solution isn't Lowe's light snapshakles (unless you really yearn for a very dubious "wrestle" with a mast that's gone overboard).  CLC has some nice ones that will bear the load and they're not that much more expensive than the cheap ones.

As to the "tight as a banjo string" instruction, there was a time when I was equally fanatical about rigging a boat.  Age has resolved that problem mostly, while also allowing for a touch of rationality to creep into some of the stuff I do.  Many years ago I raced internationally aboard a very competitive 44' custom built sloop (D2 design).  We looked at every part of that boat to coax as much speed out of her as we could find.  And yes, we "tuned" our shrouds right down to the ounce.  Now, think about this:  You're going to be sailing a flat bottomed, homebuilt dory with a tiny daggerboard, a barndoor rudder, and, for all practical purposes, a loosefooted mainsail all of which weighs in at maybe 130 pounds.  No matter what you do to that vessel you're not going to be race-competitive with anything, except, perhaps, another NE Dory.  Worry about keeping the mast stepped properly at around the right angle and stoutly stayed -- the nylon stretch encountered over a couple of hours in a 10 knot wind be dammed -- and go have a good time.  That's what this boat is for.  Enjoy it.   

I assume we are talking about the NE dory with the sloop rig here?  This rig would appear to be derived from the "traditional" alpha beachcomber dories from around 1900, on which see Howard Chapelle, et al.  The difficulty with any sort of sloop rig in a hull like this is getting and keeping sufficient tension on the forestay so that the jib will set well, especially close-hauled.  If the forestay is too slack, increasing wind will cause the luff of the jib to sag, introducing more belly into the shape of the sail just when less is wanted.  Absent any standing or running backstays, this rig relies on such tension as you can get on the forestay by giving some "drift" aft to the shrouds.  The reason for the relatively small jibs in this rig, by modern standards, is that there's a limit to how effective this can be without the whole business becoming more like a grand piano than a banjo, a fairly low-tech stringed instrument.  A wise sailmaker, knowing that low forestay tension is expected, can compensate for this somewhat by anticipating a certain amount of sag, but there's an early limit to what can be accomplished that way.

So, yes, if your shrouds aren't "tight as banjo string" by the time you're ready to hoist sail, your jib will start to look more like a bedsheet on a broomstick as it breezes on, and you will feel like Lester Flatt trying to play "Foggy Mountain Breakdown" on a washtub bass fiddle as you try to coax the baggy business upwind.  The trick is how to do this in such a way as (1) be quick to set up and (2) not cost a fortune.

What to do?  You may already be on the path of righteousness with the lashings on the shrouds as you described.  I think Phil Bolger would like that concept, in principle, but he'd probably urge you to accomplish that with maybe half a dozen passes of 1/8" low-stretch (polyester) braided line, either directly between the attachment points (padeyes?) and whatever is on the end of the shrouds (thimbles eyespliced or swaged in?).  Add smooth shackles to attachment points and the ends of the shrouds if that helps the things to lay better and shortens the distance between the end of the shrouds and the attachment points.  Half a dozen passes (secured with a couple of half-hitches around all parts) each side should be enough purchase to get sufficient tension, and can be easily cast off when it's time to strike the rig without removing any hardware and without having to introduce snap shackles or other such hardware.  Once the forestay length it adjusted to allow the desired mast rake, setting up the shrouds each time will likely be less trouble than fooling with turnbuckles and such.

Pelican hooks and turnbuckles would be another, albeit more expensive, way to go.  The pelican hooks would allow you to set up and take down quickly without having to fool with major adjustments of the turnbuckles each time.  You might have to shorten the wires to compensate for the extra length, though.

Thinking about all this sort of business was a lot of what prompted us to choose the balanced lug rig over the gunter sloop for our Passagemaker Dinghy.  Couldn't be happier.  We have found that, given a well-cut sail (Douglas Fowler's as supplied by CLC are excellent) and proper attention to setting it correctly, the rig is much more weatherly than its undeserved reputation for poor upwind performance might suggest.

.....Michael Scheibeck

   Thank you all. You've helped frame the problem space better. I'm certainly not going to fixate on minute increments of adjustment since, as I've experienced just playing around trying to set it up three or four times, there can be a lot of variation to deal with each time (with the 1/8 twisted rope approach). Like MountainSailor says, this is not a precision instrument anyway. 

I went out and bought turnbuckles today and a bow shackle or three. I think my goal is a) to not spend more time rigging it up than it takes me to drive to my local reservoire and de-trailer. That's about 17 minutes. Same for de-rigging. b) to have my set up such 75 % of the placement is taken care of just by having pre-set loops or eye straps in place, shackles and turnbuckles in the right place and I never have to look up and say "hey that's crooked" or "swaying wildly" or "damn it, the mast is about to rip the mast step out of the boat because it fell too quickly during set up and I couldnt catch it.

Another 10-15% of adjustment should lie in a few easy twists of the turnbuckles (I will ignore remaining 10%... I wanna get on the water) and c) the only reason to have sore forearms is because I was trying to hold the mainsheet on a gloriously windy day and not because I was wrestling with shrouds and the forestay on the boat ramp. Mine hurt today and I didn't even get out of the driveway.

Michael, I've never heard of a pelican hook until today. Must investigate. :) Christmas is coming.

A pelican hook sorta acts like a snap shackle, except the opening end is extra long and acts like a lever to apply tension as it closes.  See here for some various types:

http://www.suncorstainless.com/pelican-hook-w-slide

The type which are held closed by a slide obviously work best if the hook is in a down position all the time.  The type with the quick-release like a snap shackle work in any orientation.

Perhaps the most common use of these is to make an opening in lifelines so that tension is easily reapplied when closing the open section.  Here's a series of photos showing a pelican hook in action that way:

https://captnmike.com/2014/06/23/pelican-hooks/

As you can see, substantial leverage is possible.  Archimedes would love it.

I've seen folks who trailered daysailers with fractional rigs (think Interlakes, Windmills, Blue Jays, etc. without backstays where the forestay tension was dependent on the aft-leading shrouds) use these to speed up set up and take down without having to readjust things much once all was in place.  If there is room between the foredeck and the tack of the jib, a single one on the lower end of the forestay may be sufficient, with the strouds attahed while slack (before raising the mast if stepped on deck), perhaps using twist locking shackles like so:

https://www.fisheriessupply.com/wichard-key-pin-shackles-1433

...or maybe a variation on this using a knurled nob and a spring to do the twisting and locking.

Once the mast is raised and pressed forward to take up the slack in the shrouds, the forestay can be quickly attached by hooking the long end of the open pelican hook through the attachment point on the stem of foredeck, applying tension to all three members as the lever is brought into a closed position.

Since the NE Dory mast is stepped through partners, you might need pelican hooks on all three wires to make this work.  As I said, quick, effective, but maybe not cheap.

.....Michael