Ask Triloboats.com: 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:

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, also common (we’ll see it in ALMA, below), 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.

St. Michael’s Sailing Scow

This model 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.

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.

ALMA may have had to face the steep head seas at the mouth of SF Bay, where current meets the westerly, Pacific swell. As with MILTON, it may make 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.

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. SF had a lot of Chinese, might-as-well-be-slave labor…

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 it did occur.

These are TriloBoats’ closest scow ancestor. Ends curved AND faired AND relatively easy.

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

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 it easier to build curved than raked.

Raked ends have the edge in tape’n’glue construction, but not by much. The performance gains from curves will, I believe, quickly pay for themselves, and keep paying. But that’s me.

If you do choose a raked end, it’s best astern. Turbulence created at the bow has the whole hull to play, dragging and slowing the boat.

My end angles are somewhere between the cargo schooners and the smaller scows. I’d like them to be a bit easier than they are, but other trade-offs muscle in (e.g. arranging longitudinal, full-length bunks in the bow).

If you’re design your own, you’ll find your own set of trade-offs. It boils down to trading off sleekness for speed vs. displacement / interior volume. The more you carve away, the faster you are, but the less you can carry, with less elbow room.

*****

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.

For the next few weeks to months Dave Zeiger of Triloboats.com will answer one of your shantyboat living questions each week or so. Dave will draw upon his years of experience in boating… in living aboard.. How do you handle discharge of sewage? What are your food storage secrets? Send your questions to shanty@shantyboatliving.com.

Originally posted 2011-12-25 08:40:42.

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