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| LUNA's Hull on Launch Day |
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| T32x8 LUNA.. Note the eaves (mid-deck overhangs) and larger windows. |
Phil Bolger developed the Advanced Sharpie hull type, a descendant of traditional East Coast sharpies. It's distinguished from them by rectangular sections, bottom raised well clear of the water at the ends, and matched side and bottom curves (seen in profile and plan view, respectively).
Matching curves equalizes pressure on both sides of the right angle chine, reducing drag from turbulent cross-flow along its length. To match the curves without a long overhang at the bow (whose exposed bottom is prone to pound, it is clipped to the distinctive bow transom.
The high ends mean a short waterline, when upright, for nimble tacking. Heeled, the sailing waterline lengthens to almost full length, raising hull-speed accordingly.
Rectangular sections maximize form stability and reserve buoyancy, and simplify construction greatly. Chine logs are bent in gentle curves (no steaming or beveling), and all vertical lines are straight (no curves). Longitudinal components must be lofted or spiled (their curve transferred from the hull), but only once for any given area. Thus, a set of shelves in the salon, say, all have the same, longitudinal curve against the hull, rather than a different curve at each height.
BRILLIANT!
We followed Phil's lead and designed LUNA for ply dimensions (vs. the trailer and slip constraints the AS29 was designed for). We used a simplified interior inspired by British Pilot Cutter layouts, blaspheming by adding a dinette. Junk Rig, outboard rudder, off-centerboards (leeboards prevented from winging on the windward tack). Went together relatively fast and cheap, and we lived happily aboard for 13 years.
Alas, we didn't insulate and overballasted (and/or under displaced). Probably would have lived with it, but wanted to check out TriloBoats. SLACKTIDE (our current T26x7) proved the concept to our satisfaction. On the drawing board, now, is LUNA, recast along TriloBoat lines.
TriloBoats carry AS construction savings to the bitter end. Rectilinear as possible, excepting only the ends, to let the hull slide forward. The cabins, especially, are designed to be fully rectilinear, so interiors may be installed square and true.
Where a sharpie (or any curved boat) carves displacement and volume with every curve, box barges stubbornly hang on to every cubic centimeter. Thus, on the same overall dimensions, a TriLOBOaTomized LUNA has half again the displacement (13500lbs vs 8300lbs).
I expect we'll lose some speed... rockered bottoms are said to be easier to drive, and I believe it. The long, barge dead-flat combined with right angle chines makes them slower turning. But SLACKTIDE has met our sailing needs with room to spare, so these are compromises we accept.
One could build an AB (Advanced Barge), by pinching in at the bow and stern to match bottom, end-curves. This would help keep transoms clear of the water when heeled, and eliminate that pesky cross-flow. I'm sure that it would improve performance. But each time, we talk ourselves out of it... the construction savings, bountiful deck-space and interior volume advantages make our cost/benefit analyses favor the simpler approach.
If we ever get to the point of building again, it'll likely be this design - LUNA's more ample sister.
SIP construction, lumber framed with selective tape 'n' glue, copper plated, Dynel/resin decks... maybe even resin saturated ply walls for easy maintenance in our golden years.
In the sweet bye 'm bye...
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| LUNA's Rig and Layout... will repeat in T32x8 LUNA with more elbow room. |
What is the best way to attach the copper plate to the hull? If I recall correctly you've had difficulty with adhesives not holding between copper and plywood, and with sea water soaking into the plywood through screw holes.
ReplyDeleteHave you found the longitudinally-adjustable off-center boards on SLACKTIDE to be useful? It seems they go against your mantra of simplification.
John
Hi John,
DeleteRE Attaching Copper Plate (Not the BEST way, necessarily, but experiments in progress):
Gluing with PU (3M5200 and SikaFlex) worked fine until contact with salt-water, then rather dramatic failure. Some glues (latexes in particular) caution against "contact with yellow metals". Never seen that for PUs, but...? We wiped down with acetone to remove oils... maybe should have fresh water rinsed? Still, terrific adhesion before launch.
In both LUNA and ST, we coated the plywood hull with a 'gasket' of thickish PU (for different reasons, but the result was the same).
On LUNA, we sailed for a while with ablative, copper bottom paint (cuprous oxide is the toxic ingredient). When we could afford copper plate, we smeared fiber re-enforced roof patch (asphalt base) everywhere, and fastened with bronze screws (heads counter-sunk flush in over-kill, 1/4" plate). This held well, but we suspected that the gasket effect of the PU wasn't complete protection against water intrusion. The screws tore it up a bit at the edges. Noted to selves to use a thicker layer in future.
On ST, after the glue attempt, we fastened with bronze ring-shank nails (no tar, but the PU layer was thicker), heads slightly countersunk in 1/8" plate. Seems to be holding well.
In both cases, the fasteners mar the perfection of plate smoothness (like installing barnacles). Thus the glue experiment. The 'best' method would attach without any fastener bumps or dips... a DIY challenge. We use a pattern of one fastener per sq foot, and every six inches along seams where plates meet. At this schedule, even LUNAs 250lb plates only loaded at about 10lbs/fastener. They only work in tension... the hull takes over all compression forces. I HOPE there're no significant sheer forces... that would mean plates in motion! 8) Bronze angle along the chines, screwed with longer, heftier screws further lock things down.
Traditional approach (generally using lighter copper which shouldn't be subject to grounding) is to layer paint, tar, irish felt (tarred wool) in various orders, and copper. Fasten with bronze ring-shank nails.
It's the Irish felt that gaskets the fasteners, in this case. My feeling is that's great if not grounding. But if taking hard or iffy ground, I like the idea of thicker plate, butted hard as possible against the hull. No slack to get a tear going. My theory is that force dissipates more effectively, reducing any force focused on one, local point.
RE Longitudinally adjustable off-centerboards:
You're right. Occam's razor would go for fixed position boards.
BUT, when stowed (raised clear of the water), their horizontal length would BLOCK THE WINDOWS at anchor. Noooooooo!! This solution lets us pull them clear of their 'slot' and stow dead aft, clear of the windows.
So we violate the mantra, as we often do, when benefit exceeds cost. In this case, the gorgeous, unobstructed view from the cabin pays for complexity.
That being said, they're not TOO complex. I'll post on 'em, sometime soon, to share their workings (with pics or drawings). The extra hardware was surprisingly cheap, too. All DIY or off-the-shelf.
A day's handling, is position for underway, lower and raise depending on whether sailing shoal or not, stow at day's end. Less work than leeboards, considering we don't have to tend them between tacks.
They have the additional benefit of being able to adjust the CLR (Center of Lateral Resistance). When running, they can be brought way aft to improve the sailplan's lead, reducing tendency to round up. Turns out ST tracks very well on her 'railroad' chines and doesn't need the feature, but might come in handy in some designs.
Love the design discussion -- it helps so much with clarifying the various considerations!
ReplyDeleteCould be worth considering changing the word for the Triloboat transformation -- as those horrible surgeries are unfortunately not gone, and have had a terrible impact on some readers families. It'll be a nice day when the word, never mind the practice, have fallen out of use! Not to mention, one likes to think that Triloboat adaptations to LUNA lead to nice, positive outcomes... such a wise, sensitive, together boat, after all!
-- Shemaya
Hi Shemaya,
DeleteGlad you like the discussion... helps clarify my thinking, too, to sweep it together in an intelligible pile.
And you're right... lobotomy's not a matter about which to be flip. Thanks for pointing that out. In the future, I'll try to be a little less 'clever' and more thoughtful.
...upon reflection, I realize that I'm in a self-depricative mode.
DeleteI consider Phil Bolger's AS concept to be one of the true revolutions in design. It accomplishes what the Hereschoff MEADOWLARK and later the Bolger MANATEE intended... capable cruisers in reach of DIY amateurs.
I'm a little sheepish to have taken his BRILLIANT design and 'dumbed it down' to TRILOBOATS... what I think of as 'the lowest common denominator' among boats. They have their distinct virtues - not least among them that they fall in reach of a wider DIY crowd than even the AS - but they fall short of brilliant, to my way of thinking. I stood upon the shoulders of giants and leapt, not upward but down. 8)
I would offer that it's a little soon to determine direction of motion from said shoulders :-)
DeleteIn addition to what you've mentioned above, there are other contributions in the Triloboat design. For example, a few years before I came across your work I had been looking into sailing barges. I had visited the gundalow (http://www.gundalow.org/) in Portsmouth New Hampshire, and been impressed with its sailing rig and working history in that river. I became interested in a manageable, more personal sized sailing barge as a result of thinking about wheelchair access -- think "pontoon boat access with better seaworthiness, and sailing capability."
Alas, all I found were references to much larger boats, all working boats from before modern engines, and too large for what I had in mind. Admittedly, my research skills have limitations -- but they're not completely pathetic! Some pictures of Asian working boats also showed a bit of promise. But the bottom line was that there was no easy answer, and, since I would be starting from complete scratch with no boat-design background if it came to developing the concept myself, I set the idea aside.
So on a personal level, I've been delighted to see your designs, and based on that previous search I think that they fill a substantial void in the wider world. It's not just the DIY aspect, or the careful use of limited resources aspect -- it is also, as you've discussed, shallow draft, drying flat, outstanding buoyancy, and interior space. With fantastic windows! And now tested, under conditions that are demanding enough to really mean something. It's a substantial piece of work. Thanks so much for doing it, and for sharing the results!
Cheers,
Shemaya
Curious what the sail area of the Trilo-Luna would be? Can you hazard a guess on sail area for a 24X6 trilo?
ReplyDeleteHi Gomez,
ReplyDeleteLUNA has 530sqft. TriLUNA would have more displacement and be able to stand up to more... say 750ish?
LUNA's plan already ate up the longitudinal room, which means we'd have to increase by adding upward. That means heavier masts, more line, more mechanical advantage for raising/lowering.
Raising the sailplan raises the CE... we try to keep it low as sudden williwaws can pounce out of a calm day. With all sail set, it can get ugly, even with a snug rig.
Sigh.
RE T24x6 Sail Area:
That'll depend on a number of factors.
A light camper/cruiser adaptation, possibly unballasted (could be TRILOBYTE, B'TUGLY or similarly styled), would be much less area. A small, ballasted live-aboard, could be more.
Where you cruise will have a lot to do with the choice, as well as the manner of cruising (e.g., racer vs. cruiser vs. downwinder, etc.). Experience weighs in (though I'd rig for experience that WILL come). Even choice of rig makes a difference...
All these are reasons I don't specify rigs in most plans... too many ways to go. I could try to cover them all (inadequately) or nail them down to a few possibilities... a few sizes that fit all and none.
My advice is to research rigs you're comfortable with, and size 15% to 30% larger than equivalent round hull of that length and beam. Adjust up or down as other factors dictate.
One cool thing about Junk RIG is that you can build tall and sail with a panel or two reefed in reserve.