|Phil Bolger's ROMP... one Ideal Hullform.|
Considering Curvier Dogs
Despite going to great lengths to avoid curves in TriloBoats (slogan: Avast, ye Curvy Dogs!), I love 'em!
Why curves? They tend to improve hydrodynamics, reducing drag and turbulence so that the hull is easier to drive (this is the one that counts, especially to windward). Curvy surfaces are stiffer than flat ones, so require less structural support. And they're oh-so pretty!
Why not curves? On a given footprint, they carve volume and displacement from the hull, and deck area. The only way to regain that displacement is to go longer, wider or deeper, upping initial costs and long-term maintenance. And the curvier a hull, the harder it is to copper and/or insulate with sheet materials. The further storage areas vary from rectilinear, the more problematic they become. The harder it is to jack, block and roll.
To pay their way, relative to boxier hulls, curves have to overcome those why nots for a clear, net gain.
In our case, since we're practically married to dumbed-down versions of the junk rig, the prime advantage of curves (speed to windward) is moot. A slow rig won't be helped much by a fast hull. As curves are inherently more costly ($, time and energy), they push much harder against our low budget ceiling. And in a bad chance, should we lose the boat, smaller investments are easier to walk away from.
But it's worth a look!
There are a few ways to approach hullforms (I'll defer types such as sharpie, dory, barge, etc. for later):
- By section -- V-, U-, Y-, wineglass, multichine, flared, square, etc..
- By construction method-- carvel, lapstrake, strip-plank, sheet plank, molded, quick-molded, etc..
High EROEI (Energy Returned On Energy Invested) + ultra-shoal draft+ copper plate possible.
Survivors are sections U-, flared and square. Construction methods strip plank, sheet plank, quick-molded. These are relatively quick and generally less expensive to construct.
I started this post with the lines drawing of Phil Bolger's ROMP. Her hull form is one I consider to be near ideal for an ideal world. One with soft bottoms and/or expansive, deep harbors and low dock fees.
Descended from Thames River Barges, it retains their square mid-section, so load carrying and form stability are near maximum. But the hard chines have been rounded to a severe U, eliminating cross- and near-chine turbulence, and the ends are drawn out fine for improved hydrodynamics (read speed).
This hullform is one slippery devil!
The strike against her is that she is not easily copper-plated. Thinner sheets can be stripped and applied in the traditional manner, But heavier ones will not follow her curves without planishing, and overlapping strips are time-consuming and create drag. If one did manage to plate the deadflat area, the transition to thinner, upper sheets would make the latter vulnerable to rocks on grounding.
There's also the problem of lofting. Lofting takes considerable time, and - more critical in our case - a lofting surface. A large, smooth, covered floor, available for an extended period, is hard to come by in our life.
Bolger went on to develop the ST. VALERIE, and later the VOLUNTEER hullforms. These each have a rockered, transversely flat plate. SV's sections are similar to ROMP's - essentially U-section, rounded at the chines).
VOLUNTEER, on the other hand, is dory section, with sides slightly rounded in section plan. Getting warmer! The bottom plate is easily armored, and the sides quickly pull up and away from dangerous rocks. Still has to be lofted...
Meanwhile another thread has been working up through my id. The Master Curve Method produces a hull from a single master curve. Lofting is limited to this curve, laid out full-sized, which is then used to lay out frames to be located on stations.
And, if there is a deadflat in this hull, it can be arranged such that the sections over the deadflat are identical... all their frames can be laid out once and copied. And over the deadflat, all waterlines and buttocks run parallel, so no spiling!
So I worked up a cartoon.
Don't worry about understanding all the scribble... it never reached the 'fair copy' stage, nor is the design anywhere beyond 'first stab'. Suffice it to say that this hullform could be quickly laid out and strip planked cove-and-bead (easy curves allow thick, red cedar planking for passable insulation). It can be quick molded over,hybrid copper plated (and relatively cheaply compared to a box barge!) and topsides h painted or simply oiled to finish.
Problems are that, to make up displacement on a given footprint, it must have much greater draft, relative to square sections. Deadrise, low in the hull mean that a raised sole must be added to clear furnishings, increasing work and weight, reducing headroom and/or increasing freeboard/windage.
And it's going to heel a lot more than we're used to, and/or take more ballast to make up for lost form stability.
Emm. Er... (stretch this out over months, with relapses)....
And ditto for the trimaran(!) designed along similar lines (I'll spare you the reasons). So much for our best shot at a truly Curvy Dog.
Sharpie / Dories / Scows (less -boxy types)? Great ones out there. Culler, Bolger, Colvin, Parker, Benford, Roberts, Kirby, MacNaughton. I can even lay out these types so that lofting is held to a manageable minimum.
But they carve away a lot of displacement and interior volume with flare, plan and profile curvature. To get the displacement we would like, we have to deepen the draft or go with a wider and/or longer hull.
We could square up the mid-sections. That would increase displacement, form stability and efficient storage. But on any reasonable LengthsOverAll - flaring out toward the ends - we blunt the waterlines, trading the type virtues with less in return. Again, the only alternative is to lengthen the hull... this works beautifully, but we end up with more boat than we want to handle.
Another Bolgeresque Advanced Sharpie (as was LUNA)? Square sections, copper plate enabled, great handling. Do have to increase the draft, but...
Bottom line, LUNA wasn't much better to windward than SLACKTIDE, if at all (under dumbed-down Junk Rig. Having sailed both, extensively, confirms my feeling that a fast hull is no more efficient than the rig driving it.
But she was a lot harder to build, and the curves (on 31ft) squeezed us.
Over the course of time, miscellaneous counterpoints accumulated, over time, and chipped away at curves' already imperiled EROEI.
- Pointy bows reduce the working foredeck area. Ditto aft, and, since the sides are not parallel, we lose some perks (for another time).
- The extremely large windows we've come to favor don't fit as well to some curves, and glass is not an option. It's harder install the interior and components against curved surfaces.
- Curves create triangular or trapezoidal storage spaces, which are awkward and often hard to clean.
- It's easy to cover exposed edges between copper sheets if they meet in plane or at 90deg... not otherwise (short of brazing or welding).
So our curvier candidates slowly fell by the wayside. Every boat mentioned is a wonderful type that works well in many situations (most, even), returning lasting value for the energies invested.
But for us - where we sail and how - they just don't justify their costs.