Throw a Curve, or Knuckle Under?

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...

• Barge or Scow - Square 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.
• Dead-flat - A planar stretch 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'.
• Raked End - Bottom which connects dead-flat and transom with a plane.
• Knuckle - The angle between dead-flat and a curved OR raked 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'. Raked ends, 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).

Knuckles clearly disturb the clean flow of water. But in the heavy timber construction common to the day, the chines are quick and inexpensive to shape. MILTON's ends do have some curve, but slight enough to be easily fashioned from a grown tree. This will help reduce the angle, and therefore the resistance of the knuckle.

A bigger mystery is 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. I haven't found a good explanation. It's possible that it's a holdover from the out-of-favor cod's head and mackerel tail that was a leading paradigm for many centuries.

Speed-wise, that's got to hurt... the steep bow throws water forward, wasting energy and slowing the boat. There may be other properties that paid for the loss of speed. The extra 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 little turbulence and drag. A good thing.

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St. Michael's Sailing Scow

This one has raked ends, 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.

Power variations can be found around the country, with aft rake eliminated and the dead-flat extended to the transom. This allows it to get up on step.

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. Compared to MILTON, she should move quite well. But her steep bow angle limit her gains.

ALMA may have had to occasionally face steep head seas at the mouth of SF Bay, 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 little if any penalty, especially when heeled. The easy, aft run does seem to be more generally important for speed as shorter, more abrupt 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 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. Note the raked aft end. This is optional. Either end may be curved or raked.

My preference is curved at both ends. In plank-framed plywood construction, I consider them easier to build curved than raked.

Using tape'n'glue construction, raked ends may be a bit easier to build than curves, but not by much.

Either way, performance gained from curved ends will quickly pay off the low extra, initial cost of curves, and keep paying for the life of the boat.

If you do choose a raked end, better aft than forward. 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. 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. It boils down to trading off sleekness and speed vs. displacement / interior volume. The more you carve away, the faster you are, but the less you can carry, and with less elbow room.

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Two last thoughts:

• The more heel - or the higher the expected seas - the higher the ends have to rise, 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. On flat water, garveys - light scows with low ends and freeboard - are among the fastest monohulls under sail. But in a chop, forget it.
  
  
• 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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