Girder Construction in Square Boats

Rotary Girder

A term used when a person is referring to something technical about which he has no real knowledge.

Originally used in the movie "Tommy Boy" with Chris Farley.


[CAUTION: This post is a 'rotary girder' on my part, based on my take-away from technical information that was more or less over my head in its fine detail. While our experience has apparently confirmed my understanding, common sense ajd a grain of salt are advised.] 


Girder Construction in Square Boats

Girder construction is fundamental to TriloBoat and most other box barge/scow/square boats, especially when built with sheet materials.

A girder separates parallel faces by edge-bonding one or more faces at a substantial angle to them (in square boats, this angle is typically 90deg). Relevant examples are box, I, H and T girders. Separated faces are prevented by this attachment from moving, relative to one another.

This enhances rigidity in two ways:

• Stress loads try to bend the girder. The face away from the load lies along a longer radius than that toward the load, so acts in tension to resist flexion (bending). That face can't appreciably stretch, so until it fails (it or the edge-bond tears asunder) the girder resists the load.
  
• As the stress tries to bend the girder, the connective faces at right angles to the stress resist torsion (twisting). Its region toward the stress acts in compression while that away from the stress acts in tension (try bending a playing card on edge). That face can't appreciably stretch, so until it fails (buckles or tears) the girder resists the load.

The wider the separation of a girder's faces, perpendicular to the load, the greater its rigidity. The greater the cross section of its faces in line with the load, the greater its rigidity.

Clearly, the edge connection along all adjoined faces must be very strong.

Metal girders, built from sheets may be welded. Typically, they will not require further reinforcement along their edges.

In wood construction, we seek excellent glue adhesion (a function of surface area and the glue's working PSI), and/or substantial fasteners. Notably, the strength of a timber, running along that edge is secondary. It provides surface area for adhesion, but does not, itself, come under significant stress unless the bonding mechanism (glue or fasteners) fail. It is the bonded faces which provide strength, not the timbers framing the girder.

An interesting phenomenon in materials is that stresses tend to run along outer skins. Two relevant consequences:

• Web Frames - Generally, you can cut large, rounded edge holes in girder faces without losing significant rigidity. If the face material is substantial and stresses are low (or distributed) then simple cutouts suffice. If not, the edges of the the cutouts can be framed to resist buckling. This feature is especially useful for internal bulkheads, windows, and hatches.
  
• Solid Structure vs Girder Failure - We've noticed in solid ply leeboards that, in hard going, we may crack a veneer (the outermost 'skin') to leeward (the side of stress loading). From that point, in fairly short order, it will walk through the board, veneer by veneer (actually, transverse veneers put up no resistance... in effect, we lose two at a go).
  
  By separating sheets of ply in a girder arrangement, however, the full thickness of ply is now the 'skin', and all its veneers work in concert at full strength. Unless the leeward sheet of ply tears asunder or its edge bonds fail, the board holds. This holds generally true as well for solid vs hollow spars.

*****

Square Boat = Box Girder

The hull and decks of a TriloBoat comprise a modified box girder. Sides are edge-joined to bottom and decks at near right angles to one another. In addition, transverse bulkheads (among which I'll include transoms) internal to this girder form sub-girders.

Picture attempting to bend the hull up or down at the ends, like a banana. You will be strongly resisted by the vertical sides.

Try bending laterally, like a banana on its side. You will be strongly resisted by the horizontal bottom and decks.

Try twisting it, or collapsing it sideways (like a cardboard box with its endflaps open). You will be strongly resisted by the bulkheads.

These are analogous to the major forces acting on any hull as a whole.

Hull areas which are curved - the bottom end curves and crowned decks - have a great deal of inherent resistance to stresses from outboard. Their inboard skins work in compression to resist; the principle of an arch. Accordingly, they require less internal support.

Large, flat panels left unsupported - say, deadflat areas between bulkheads - are not inherently rigid. Their inboard faces work in tension, and allow considerable flex. So I often recommend girder furnishings; furnishings built as boxes bonded to bottom and sides. Like the hull entire, these resist flexion and serve to much reduce the open flats within the hull, stiffening the flats and contributing to overall rigidity.

A final technique is to double hull surfaces (decks, sides and/or bottom), making girders of them. Simple longitudinal, bulkhead spanning stiffeners (rub-rails, leeboard guards, etc.) suffice, in conjunction with girder furnishings, but doubled is hell-fer-stout.

Girders within girders within girders! The result, robustly joined, is an exceptionally rigid hull.

Perhaps you've noticed the care with which a competent crew will crane and block a Curvy Dog?

In the water, CDs use monocoque principles to distribute stresses widely, diminishing their point loads. Try to crush a raw egg on end between the palms of your hands... you can do it, but it's surprisingly hard. But use your finger tips and you can easily rupture the shell. Out of the water, wracking forces and point loads from poor support can wreak havoc on the hull and its interior joins.

Not to disparage Curvy Dogs, but out of the water, they are like fish out of water.

A girder boat, on the other hand, remains rigid on land or sea. It can be jacked from any girder interstice, side-to-side or end-for-end, or cantilevered from three, poorly placed high points. Not that these are best practices, but they happen, and afford little concern. You can practically juggle them!

*****
It seems to me that the fiber strength of the materials in use (ply and connective timber) in PSI (Pounds per Square Inch, or equivalent) is the limiting factor for adhesive bonding. Many modern glues well exceed the failure thresholds of the woods they bond.

Two strategies: a) increase the glue surface area to sufficient (increase timber faces or tape n' glue), and/or b) through-bolt on a schedule that raises the strength of the bond.

I personally favor glue-centric approaches. We've used 1 1/2in gluing surfaces, minimum, for structural joins along the outer hull in ZOON, LUNA (32ft) and SLACKTIDE, with no signs of failure. Fasteners were light and I consider them only useful for temporary clamping pressure (structurally negligible).

I'm unqualified to recommend this much reliance on adhesives. Consider running your construction solutions by an qualified Naval Architect for approval. Consider backing up the adhesives by through-bolting along the major hull edges, from both outboard faces. Err on the side of caution.

Girder construction is found from houses to bridges to jetliners to super-tankers to skyscrapers. Without girders, much of the modern world's architecture would be impossible.

So let's gird ourselves for DIY!

Girders within girders... walls and deck are ply/foam/ply
If additional lateral rigidity were deemed necessary,
lockers could have fixed lids with hatches cut into them.

Musings on the Economics of DIY

The Floating Neutrinos' SON OF TOWN HALL

Crossed the Atlantic...

Viewer discretion advised.

If you don't build your dreams, someone will hire you to build theirs.

-- Tony Gaskin

In fact, most home projects are impossible, which is why you should do them yourself. There is no point in paying other people to screw things up when you can easily screw them up yourself for far less money.
-- From The Taming of the Screw by Dave Barry



Musings on the Economics of DIY

I've been trying to wrap my head around some of the big picture economics of DIY. It's fuzzy. My head hurts. Here's what I got:

Okay. We face the question of where we lie along a spectrum between Do It Yourself (DIY) at one extreme, and Throw Money Around (TMA) at the other.

Pure DIY would be a neo-plastic (vs neo-lithic) venture... bootstrap ourselves up and into a vessel using only found materials. Living, as we do, in the Age of Waste, found materials cover a lot of ground not available to our ancestors. With large enough doses of time, ingenuity and skill, one can clearly bring a vessel into being from our wilderness of natural and unnatural abundance without dropping a single penny.

Pure TMA is entirely a market transaction. We sell our time, ingenuity and skill out to the highest bidder, or for the highest return in Money. We then hand said Money over for a turnkey vessel. 'Course, there's the little matter of overheads along the way.

Most of us lie somewhere in between. We scavenge and improvise, stay flexible and open to windfall, lavish our very own labor on DIY. Yet we TMA for tools, for uniform or exotic materials (e.g., plywood and epoxy), for hardware (forged and galvanized anchors), for rent and utilities.

Insofar as we TMA, theory goes that our time is worth more traded for Money than in direct application to the job at hand. We go on to trade Money for materials worked by specialists (or specialist processes). Theory goes, we get a better return on our time if we TMA than if we DIY.

But that's a shaky assertion. Those overheads - and the little perks we use to carrot our way through the misery of the marketplace - have a way of eating up a paycheck. If you add in all the prep time, energy and $$$ (gone to apprenticeships or education) required to command a decent wage... well... Money doesn't seem so efficient. Matter of fact, relatively few find their way past making it to living their dream.

One of the things I love about looking at boats built with early technologies is that all those boats were viable, DIY vessels! Not a stick on them was manufactured, bought and paid for, at least in the modern sense. Hulls were usually built by their owners in wood stopped with home-brewed pitch. Anchors were hand-made and they worked. Ditto capstans and winches. Ditto line and blocks. Sails were woven by hand and loom before machines could do it for us.

Not an inch of those vessels was out of reach of any one of us, today. What's more, we can now cross-pollinate ideas from cultures that never met. What's more, we have modern understandings of physics which inform our solutions. What's more, we have the material advantages of abundant, cast off plastics, composites, metals, line and fabrics. All overflowing dumpsters, junkyards and landfills. Smothering the once pristine beaches of the world. There are folks who will pay you to haul their unwanted materials away.

DIY is an education; a crash course in all the skills and knowledge that comprise your vessel. Design and lash up, weld or forge your own anchor, and I guarantee you'll know more than the sailor who paid for theirs. Knowledge which may well come in mighty handy in some far and lonely place. TMA can't by ya love, Baby.

So the impovisational path is a Low Road I much admire.

For various reasons, Anke and I have talked ourselves out of this approach. We've always wanted to go sailing (not spend forever building). And we've done okay. But looking back, I'm not so sure we made the best bargains.

We build quickly with the help of Money. But, if you count what goes into earning that.Money - hours on the clock, overheads, perks- it could well be well into net loss. Worse, the Money Economy is slowly shutting down the world through which we would sail. Our participation grinds a little bit more away.

I look back and count up the years gone for Money gone to 'speed' the process of getting on the water. Five year plans for six month boats. Hmmph.

Mighta shoulda just gone dunnit.




PS. On one of our first boat jobs, I was sanding away with a random orbital. Being a skinflint by nature, I was running each round of sandpaper into the ground. To save Money, of course.

Our employer observed this for a bit, then said, "You need to change that paper every three to five minutes."

"But won't that burn through sandpaper like toilet paper?", I sputtered, incredulous.

"Dave, materials are cheap. Labor is expensive."

And it's true.

That's the economic good of DIY... we don't have to pay for our own labor, beyond righteously sore muscles, here and there (work safe, though, or all bets are off!).

The THINGS We Do for Art

Three semi-circles join straight edged framing
Larger to smaller arcs from inboard out

In a minimal interior, what you don't do is as important as what you do.
Nate Berkus

The THINGS We Do for Art

Moderation in all things, I suppose. In this case, I'm thinking of the balance between Quick 'n Dirty Git 'Er Done, and trim-works.

Trick is, not to get carried away.

Trim - in the broad sense of framing, cutouts and rounds - definitely purtifies a space. It delineates areas of paint and may eliminate taping. It helps with cleanup, and keeps spores from their corner crack strongholds.

We know of several builders of simple boats who whizzed through construction of hulls, decks, rig and gear, only to bog down in a jewel box interior. Drown in umpteen layers of varnish. Be brought low by dark, exotic woods, intricately molded and joined. These were their boats, and I applaud their results.

But me? Seems to me that complex interiors befit complex hulls; simple interiors for simple hulls. It seems a mere matter of proportional investment.

We select a few circular containers to trace, with radii that work well together (judgement call). There are only a few ways things come together in a square boat, and we'll use a given size for each, typical situation. If several arcs are present across a bulkhead, we'll use larger ones inboard, diminishing radius as we work outboard. A 3in radius or thereabouts - whether traced or cut with a hole saw - is convenient for the smallest.

There's nothing particularly practical about these standards. Larger radii provide bigger 'knees' between framing and therefore more structural support; something to keep in mind. But we have a pretty free hand.

Trick is, not to get carried away.

Rounding tool with 1/4in and 3/8in cutting ends

Finish rounding can be simple as well. We round corners with a 45deg sawcut, tangent to the desired arc,  and rasp smooth. Edges get rounded to a 1/4in radius with our handy dandy rounding tool (or rasp over endgrain). Sand smooth, and done.

Note: A router with a round-over bit is very fast, once set up, but we find that, given router set up time, we are often faster by hand. And lacking a router table, our handwork is often superior.

In a few cases, we may use a bit of molding to cover a raw join. Shim any carpentry voids and caulk (trim in a tube), with a small, finger fillet for ease of cleaning.

All this froo-froo lies along a very slippery slope. One can always go a bit further. Trade time for a higher level of perfection. Complexify. We raise the bar, here, and go back to rework there. Before you know it, things have gotten out of hand.

Trick is, not to get carried away.

Simple Effects
Ends are merely bedded and butted...
Ply backing provides knee strength

Straight cuts followed by rounding.
Note the caulk running along the sole lines.

In this case, trim serves as landings for platform panels (eg, fold down dinette)...
Longer, tapered ends and rounded corners save hang-ups and shin bark.
Simple, lapped joints.

The good news is that these simple techniques can be relatively quickly combined to dress up the spare, box lines. Some of it is faux (unnecessary); added merely for looks. One could very easily do with even less and use paint to 'frame' the interior. But we like it.

Bad news is that even at this low level, vanity exacts a price. I figure we've spent nearly a quarter of our build time on aesthetics, compared to even simpler, trimless approaches. Yeesh! But we hope to cash in on years of pleasure in the contrast of oiled cedar and paint.

Whatever path you take, you'll likely find that a style of your own quickly evolves. Your boat will have a look that reflects your sensibilities in ways that 'classic' styles seldom do. If you build more than one, you may find that each have the feel of home.

Trick is, not to get carried away.

Introduction to THE FREEDOM STORY by Garry 'Gary' Hoyt

Tortola Sloop

On the sea, Mon, you got to be free!

Introduction to The Freedom Story by Garry 'Gary' Hoyt


Among the inspirational, formative writings that shaped much of my sailing philosophy, an essay penned by Garry Hoyt - sailor, cruiser, racer and inventor - stands out.

In it, he presents the thinking behind his ground-breaking series of Freedom Yachts (read his full essay, here).

But what really caught me was the story he tells to introduce the concept.

His words were enshrined in a promotional pamphlet spied among my local library's reject treasures. I snagged it, and carried it with us for many years, before losing it (and nearly our boat) to mischance. I searched the internet high and low without success until today, when I found a scan at FreedomYachts.org (thank you, Folotp!).

So, here I cast Garry's pearl of wisdom; a parable for our Dark Age of Consumerism:
[Note: I have broken up long paragraphs for easier, on-line reading. Otherwise, all is as I found it.]


Introduction to The Freedom Story
by Garry Hoyt - Originator, Freedom Concept

Somewhere between the stately clippers of the late 18th century and the spin-out specials of the SORC, sensible sailing design seems to have lost its way.

Perhaps the problems started when sailing ceased to be the main method of locomotion for international trade and became more of a rich man's sport instead. But whatever the reason, there has been a dreary lack of progress and even some discernible regressions in the field of cruising design. The slightly better speeds shown by modern sailing boats when compared with their forebears of a century ago are more to be accounted for by the improvements in building materials - aluminum, dacron and fibreglass - than by any actual advances in design.

Just how seriously we have gone astray was vividly illustrated to me some years ago in the Caribbean.

We were taking a new cruising/racing machine out on her trial run. No expense had been spared in giving this superboat every possible technological refinement. When we had finished admiring the Barients, the Loran, the Sonar, and single side band and the gleaming array of dials, we scanned the horizons for a victim on which to test our speed.

The only target in sight was a large and cumbersome Tortola sloop, crammed with cement bags. vegetables, children and several goats, and powered by a tatty old battenless sail. Well, even though this didn't present much of a challenge, we set out to make short work of her. Winches whirred, lines hummed, and lips were whetted for the kill!

Except, somehow, maddeningly, that wretched old sloop just wouldn't come back to us. True, we were gaining on her - but agonisingly slowly. We were finding out just how good - despite appearances - that design of a Tortola sloop was, especially in 25 knots of breeze, on a reach.

After all, it was the product of 300 years of constant testing. And when a boat went well, they went back and built another just like her, only changing when they were sure they had one that went even better. That's how progress used to be separated from change.

Anyway, after sustained hiking by all members of the crew, and determined efforts to keep our new wonderboat drawing, we finally came abreast and passed the old sloop. The new owner, who had paid richly for the ability to leave the competition in his wake, looked particularly relieved.

The conversation onboard changed at this point from how well our boat sailed to "how well she rated". We happened to have a lady novice aboard who had the temerity to ask, "But doesn't rating well mean sailing well?" Embarassed by such ignorance, we explained (with the patience that experts reserve for the very young and the very inexperienced) that ratings were something quite apart from performance. "I see," she said, but I don't think she did. Poor girl - what naivety to confuse a good rating with good performance.

So on we went to our harbour destination, beating that old-fashioned sloop by a full 3 1/2 minutes. Naturally we used the engine a little at the end, to manoevre in to the beach, so that did give us a small advantage.

Fortunately we also had our modern depth finder switched on, giving us an admirably clear picture of what was below us. And if only that coral head which we glancingly struck had been below us, we would certainly have spotted it. As it was, we just bounced off, which we all agreed was a great tribute to the strength of our modern fibreglass construction and indeed our 6 1/2 feet of draft was a small price to pay for our high performance fin keel.

We were just getting our 160% genoa down (after sending someone aloft to clear the halyard which had jammed in our high performance airfoil forestay), when that old sloop came swooping by, turned cleanly into the wind and neatly dropped her anchor in about four feet of water, right off the best bit of beach. Quite frankly, we all thought it was a bit cheeky of him to show off and anchor there when we were left about 90 yards offshore.

However, the prospect of a piping hot meal out of our super electric stove soon gave us something else to think about. We sat around, watching the refrigerator, the oven, the lights and the hi-fi all humming away together. It was wonderful to see how modern science had triumphed over all the inconveniences of nature.

That was just about the moment we discovered that some sort of electrical malaise had drained our batteries to desperately low levels, causing the slow demise not only of our oven but also our entire electrical life support system. I mean, what do you do with half-cooked beef stroganoff? And no water because the pumps won't work?

After some argument, we decided to requisition help from the only source in sight - the native sloop.

After ten minutes of wrestling with the inflatable dinghy (specially packed for quick assembly in an emergency), and ten more minutes of trying to row this impossibly ungainly design into 15 knots of trade wind, I came alongside the sloop.

Light was streaming from their battered old oil lamp, and on the ancient paraffin stove, they were cooking a delicious-looking kingfish which they had caught on the way. I ignored the admittedly enticing aroma of this primitive fare and explained our plight.

At least the native skipper was polite enough to appear puzzled rather than amused. There wasn't much he could do to help us, other than give us some water, which he quickly tapped off a simple barrel on deck.

But he did pass along some advice as I was leaving.

"Mon," he said gently, "those conveniences got you all tied up. On the sea you got to be free."

He was so right he even rhymed.