Throw a Curve, or Knuckle Under?

<- Knuckle Aft ; Curve Forward ->

You can compromise without violating your principles, but it is nearly impossible to compromise when you turn your principles into ideologies.

-- James Dimon

Throw a Curve, or Knuckle Under?

It's an odd thing about barge / scow jargon... if it's out there, it keeps itself well hidden. So I'm going to arbitrarily grab some terms to use. If you use them in public, some scholar is likely to take a swing at you, so be warned. For the purposes of this post...

• Box Barge or Scow - Square-ish sectioned vessels with a bow and stern transom. Since these examples are all called scows, I'll follow suit, today. But it's six-of-one, half dozen of t'other... a matter of local custom.
  
  
• Dead-flat - A rectangle of mid-bottom (no rocker, V or arc... flat like a table top).
  
  
• Curved End - Bottom which connects dead-flat and transom with a curved 'plane'.
  
  
• Raised End - Bottom which connects dead-flat and transom with a plane.
  
  
• Knuckle - A hard angle between dead-flat and a curved OR raised end that does NOT fair smoothly into the dead-flat.

Let's take a little stroll down Memory Lane. The following models represent four treatments of the flat bottomed scow:

Great Lakes Scow MILTON  

MILTON is a real 'knucklehead'. Both ends raised, steep forward and easy aft. This was very common around the great lakes, and showed up elsewhere around this country and others (e.g., the German Rhine and coastal traders).

Knuckles clearly disturb the clean flow of water. MILTON's raised ends do have some curve, slight enough to be easily fashioned from a grown tree. This will slightly reduce the angle, and therefore the resistance of the knuckle. But still...

In the heavy timber construction common to the day, knuckles were relatively quick and inexpensive to shape by less skilled workers, especially at the steeply raised forward end. They were beasts of burden that took a beating, so had generally short lifespans... economical construction would be important.

 why the blunt bow angle and easy aft end, once common (we'll see it in ALMA, below), but which is contrary to most modern practice?

Speed-wise, that's got to hurt... turbulent, drag-inducing flow the whole length of the hull, and the steep bow throws water forward, wasting energy. Any hull that wastes energy is harder to drive toward hull-speed, and this seems profligate.

There may be other properties that paid for the loss of speed. The extra initial and reserve buoyancy to lift over short, steep or confused seas (endemic to the Great Lakes, and the North Sea)? Many Dutch coasters have extremely blunt bows, it's claimed, for this reason.

Easy aft ends, though, release water smoothly, with less turbulence and drag. This might ease the waste where reserve buoyancy is less important?

One point of note: MILTON's length to beam ratio is high as scows go, reducing drag relative to its hullspeed, winning back some of the losses to knuckles.

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St. Michael's Sailing Scow

This one too has both ends raised with knuckles, but now both are at a low angle. It should move much more easily through the water. But you can see that, it's traded off some volume by doing so. This hull should be more easily driven over flatter water.

BTW, the line between scows of this type and garveys starts to get fuzzy. More thesis material, if you care about such things.

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San Francisco Scow Schooner ALMA

Another cargo schooner, ALMA, has lines similar to those of MILTON, but her ends are both curved AND faired into the dead-flat, eliminating the knuckles. Compared to MILTON and setting aside her lower length to beam ratio), she should move quite well. But her steep bow angle limits her gains.

ALMA may have had to occasionally face steep head seas in SF Bay, especially at the mouth, where current meets the westerly, Pacific swell. As with MILTON, buoyant lift may have made up for speed lost to her abrupt bow. In both cases, distances to cover under sail were circumscribed... speed may not have been their top priority.

Another possibility is that this is a vestige of the cod's head (blunt) / mackerel's tail (fine) design rule of thumb that lasted well into the 1800s. It's been 'debunked' by modern theory and tank tests, but only in terms of speed. In the broader range of compromises, the approach could pay for itself in other ways.

My guess is that the relatively blunt bow carries relatively less penalty, especially when heeled. The easy, aft run does seem to be generally important for speed as shorter, more abrupt aft curves create more turbulence and drag.

ALMA's end curves are chine-logged with scarfed sections of heavy timber. Compared to Milton, this would have been slower and more labor intensive to build. SF had a lot of skilled Chinese, working in virtual slavery.

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Confederate Attack Scow

Despite the killer name, these were pretty common along the Gulf of Mexico coast, and were used more for smuggling than battle, though that did occur.

These are TriloBoats' closest scow ancestor. Both ends curved AND faired AND relatively easy.

The leeboards were quite common in these boats, too, especially in smaller boats where uninterrupted hold (or cabin) space is at a premium.

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TriloBoats T32x8

So here's one of mine (ketch rig not shown). Note the aft knuckle. This is optional. Either end may be curved and/or knuckled.

My preference is curved at both ends. In framed plywood construction, I consider the fair curves easier to build than knuckles. The relatively thin sheet materials, require strong reinforcement along the knuckle. Tape 'n Glue methods help, but not much.

Either way, for most of us improved performance gained from faired ends will quickly pay off any low, extra, initial cost of construction, and keep paying for the life of the boat. Especially if we're burning fuel to drive the boat!

If one does choose a steeply raised end, I'd say better forward than aft (as shown above). Turbulence created at the bow has the whole hull to work on, dragging and slowing the boat.

My end angles are somewhere between those of cargo schooners and the smaller scows, favoring the latter (both somewhat easy, and a bit easier forward than aft). I'd like to relax them even more, but other trade-offs muscle in (e.g. supporting lieveaboard weight distributions, or arranging longitudinal, full-length bunks in the bow... too easy a bow clips a bunk's foot in smaller hulls).

If you design your own, you'll find your own set of compromises. Generally, the more you carve away, the easier the hull is to drive, but the less you can carry, and with less elbow room.

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Considerations:

• When heeled higher ends help, especially at the bow. Low ends plow their transoms sooner. Pinching in the sides toward bow and stern transoms helps by shortening their radius from the center-line, helping clear the leeward waterline.
  
  
• Most scows are designed to ride up and over waves, rather than bash through them. Where steep seas are expected, lower bottoms provide more initial lift and reserve buoyancy. In extreme cases, this helps prevent pitch-poling (the bow is far less likely to spear into the back of the next wave). In general, bluff ends dampen pitching.
  
  
• The easier the bow angle, the sooner it will pound, a consideration when motoring, or anchoring exposed. The boat is upright, then, and when bow and wave angle match up, it's like hands clapping.

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Barge and scow hulls are often viewed as unseaworthy. Yet box barges reliably carry a good deal of the world's freight on the high seas. 

A case in point:

In New Archangel (now Sitka, Alaska), the Russians built an artificial lake from which they harvested ice in winter. It was warehoused till spring. When scows similar to ALMA arrived with timber and other supplies from the SF Bay area, they sold and loaded the ice - buried in sawdust - for the backhaul.

Point is, those boxy hulls carried out coastal trade along a good stretch of the grueling west coast of North America, absent engines and, for the most part, charts!

Meanwhile, on flat water, garveys - light scows with low ends and freeboard - are among the fastest monohulls under sail. But in steep chop, forget it.

Across the centuries, sailors and merchants have returned to the scow for its economy, load-bearing capacity, stability and seaworthiness. The sleek hulls of the Age of Sail - commercially speaking - are all but gone. But scow and barge are alive and well.

Something to think about!

Scows come in all sizes!