Mechanical Advantage: It's a Matter of Leverage

It's a matter of leverage.

-- Cap'n Jack Sparrow from Pirates of the Caribbean

Mechanical Advantage: It's a Matter of Leverage

Katy Burke, in The Handbook for Non-Macho Sailors, points out that the veriest foredeck ape can be plucked from deck and flung across smoking water by the merest shrug of the sea.

For millennia, sailors have fought physics with physics. The mass and momentum of natural forces vs. the leverage of mechanical advantage. They might not think of it as such, but the humblest sailor and the great Archimedes are of a kind, brain amplifying brawn to shoulder the burden at hand.

Simple machines – the inclined plane, the lever, the wheel and axle, the cam – are reliable, easy to build, maintain and repair, and cheap! These spread effort over distance (or, one can also say, over time).

Mechanical advantage or purchase is the proportion by which one's effort is multiplied.

For example, a halyard with 2:1 advantage (two to one) takes twice as much line, and twice as long, as the same halyard with no advantage. That sucks, you say? The 'advantage' is that, at any point, we only need apply half the effort albeit for twice as long.

This is like making two easy trips to carry in the groceries, rather than getting it all in one, heavy go. Same groceries, same overall effort expended over twice the distance and time. But at any given point, we're not staggering under the load.

The astute reader will note that there is some overhead to this... you're carrying your body as well as the groceries, so doing it twice takes a toll. Friction can, too. There are diminishing returns to advantage.

The inclined plane (also wedge and screw) spreads lift over its length (advantage = height to length). A block and tackle spread lift out over length of line rove between blocks (advantage = the number of moving lines through the block attached to the load). A lever spreads out the length of throw(distance between up and down) at the lift end over that at the handle end (advantage = throw at load to throw at handle).

Clear as mud? There are many excellent sources which cover the physics and uses of simple machines far better than I can do here. I'll list two of my favorites, below.

Simple machines, or combinations of them, underlie all the manual tools on board. From halyard to handy-billy. From winch to windlass. From sweep to jack. Simple machines working for you to provide mechanical advantage over the forces we face.

As you explore their possibilities, here are a few tips and things to keep in mind:

Consider safety. Though mechanical advantage help us tame large forces, they are still large forces! They can get out of hand. Even watered down, they can pinch, crush, break or strain. Consider setting up as fail-safe as possible, and, where possible, stay out of harms way.

Consider your body. We are the draft animals hitched to these simple machines. Our bodies work well if used in accordance with anatomy and within our limitations. Line up with effort, use the right muscles for the job, avoid effort while twisted, don't jerk and respect your limits!

Consider ergonomics. Is line thick enough to get a grip on? Are handles well shaped for hands, with enough clearance for fingers? Do you find yourself stooping or on your knees to use gear?

Consider your leads. Leads (literally, angles along which lines are led) allow one to line up for an effort with ergonomic efficiency. Is footing good and plenty? Is the body well positioned for an untwisted effort? Is there enough elbow-room for the effort? Simply improving the leads can make a difficult or impossible effort easy.

Consider stowage. Is stowage close at hand? Easy to access in a timely fashion? Secure? When stowed, are decks, gangways and leads clear?

Consider arranging enough advantage for the least physically powerful member of the crew. It is downright dangerous to face a task for which one has not the strength (or weight). Something's gotta give... something that must goes up too slow, down too fast or neither at all. A shoulder sprains or finger breaks. Sufficient advantage may slow the job, but it gets done without trauma.

Consider that you can (generally) lift more than your own weight. Once you've lifted your feet off the ground, that's it for effort applied. But if you arrange your tools so that you are lifting from your feet (with your legs), you can generally exert a fair amount more than you weigh.

Consider work stoppers. Cleats, pawls, dogs and stoppers can take the load off to catch your breath or tend to an emergency. Something at hand, quick to make fast and fast to free can be a big help!

I'll end this section with a cautionary quotation:

When you combine ignorance and leverage, you get some pretty interesting results.
― Warren Buffett

* * * * *

By combining simple machines, we can accomplish any job on a typical cruising sailboat. We can raise sails and sheet them. Raise and lower anchors and masts. Load and unload cargo or deadweights. Move the boat over water or land(!).

As basic and essential as knots, simple machines are vital tools in the sailor's kit.

Two helpful books books introducing simple machines. Both very accessible (not a lot of math or physics). Both written by sailors, with sailors in mind.

A Handbook for Non-Macho Sailors by Katy Burke -- Apparently out of print, but worth it's weight!

Moving Heavy Things by Jan Adkins -- Focused on Mechanical Advantage

On a Cold and Dark December

Snow Storm: Steam-Boat off a Harbor's Mouth
By Joseph Mallord William Turner

...

While listening to the moaning of the wind, 

And thinking what a solemn thing it was 

To move on 

Through the lonely darkness, 

Over an unknown abyss, 

Whose depths were secrets as profound as Death

...

-- From A Christmas Carol by Charles Dickens

On a Cold and Dark December

This time of year, in the waning of the last moon, in advent of the longest night, my thoughts turn to those who have made their living on the sea.

It is said of the artist, Joseph Turner, that he asked to be tied to the mast of a steam-boat leaving Harwich in a storm.

Leaving. Harwich. In a storm.

We're talking the German Sea of the North Atlantic. The graveyard of the Spanish Armada and countless others, beside. Legendary for its ferocity. Merciless.

They left by soundings, tapping their way with line and lead over and between invisible shoals that could wreck them. Heading into the storm.

For the artist, tied to the mast, his terror and awe were poured onto canvas, capturing a furious moment for all of us not so exposed.

For the crew... well... it was just another day, another night at sea. A schedule to keep. Likely setting forth at the end of a long day of lading. Weary, but ready. The tools of their trade well in hand.

Not one of them were tied to a mast or to anything else, for that matter. One hand for their selves, one for the ship. Blow high, blow low, blow sideways.

We sailors of the present day have seen a thing or two. Nights when it's darker than dark. When snow blinds us and the wind shoves us at the unseen shore.

But those sailors! Those sailors were made of sterner stuff than can be found in our easy times.

On a cold and dark December...

...They took to the sea.

Q&D Shelves

Wish I had a pretty little girl, 
I'd put her on a shelf, 
Every time she'd wink her eye 
I'd climb up there myself.
 -- Old Joe Clark


Quick and Dirty Shelves

Boats can have a lot of shelves in them, often in odd spaces. Over time, we worked out a formula that  lets us zip 'em out without a lot of head-scratching.

Basic idea is that a (plywood) shelf between walls (dividers, bulkheads, what-have-you) has a support rail attached along its lower, far edge, and a fiddle/support rail attached along its upper, near edge and overlapping the Cleats. 

Cleats are attached to the vertical walls at either end, with room for the support piece to slip behind with a little wiggle room. This locks the shelf against horizontal movement (may need screws if you anticipate tossing them vertically!).

Advantages include:

• Quick, standardized construction
• Easy installation and removal (for cleaning, painting, etc.)
• Flexibility (can be adapted for size, loads, clearances)
• Uses up a lot of smaller plywood offcuts
• Relatively easy to go back and rework spacing, if desired (just move cleats)

If you wish to get a bit fancier, the fiddle can be rabbeted along its underside to cover the raw edge of the shelving material.

You can angle the far end of the cleats to a point... this allows the shelf to be lifted upward as if it were a lid, rotating around its far edge in contact with the points, until the support face fetches up against the angled cleat end (the sharper the angle, the higher you can lift the shelf). This can be useful in tight spaces where you need a little extra room to un/load the space below it. For example, a tote that fits snugly may need a little extra to clear fiddles and such along its near, lower edge.

We found that our locker openings don't let us insert full length shelves. We ended up cutting this type in two, mid-length, and putting a lip under one of them along the cut. A short, rabbeted piece is attached to the back wall, rabbet up, straddling the cut (also with a little wiggle room). The lipped side needs some support at the near, cut corner... we use twine attached to the next fixed point above it, rather than build struts. This approach has been much easier than installing a divider, and doesn't break the run of shelf length.

An idea to shelve away!


*****

Bonus Tip:

Can't recall where I read of this, but could well be The Sailor's Sketchbook by Bruce Bingham, under 'removable fiddles'.

Another simple locking device is to make pegs that fit into matching holes. These can be made of wood or metal.

One cool way to do it is to drive a (bronze) screw in the peg location, burying the threads but leaving the shoulder exposed. Hacksaw the head off and smooth with a metal file to leave a protruding peg. Put the piece (shelf, removable fiddle, table, etc.) in place, over its supporting surface and tap over the screw with a hammer, denting the receiving surface with the exposed peg. Drill a (slightly loose) hole at that spot. If everything is done reasonably square, the peg slips into its hole, forming a sheer lock, preventing horizontal movement.


 Bonus, Bonus Tip:

A recent brainstorm is to use heat to flatten and shape PVC to form springs. A hole drilled through the PVC to match a peg forms a lock that can be released (sprung off the peg) with gentle pressure.

Works for door latches, removable step locks, drop down bin locks, hatch locks... spring shapes  and applications are limited only by the imagination!.

You can find lots of info on shaping PVC through sources like this one, drawn from the way-too-cool world of PVC bow-making.