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Dave and Anke
triloboats swirl gmail daughter com

Monday, May 13, 2013

The PROMISE of Speed


Showin' 'em what FAST is!!
The PROMISE of Speed

Scows and barges have a reputation for being slow, which I and TriloBoats have done little to assuage. But Great Lakes racing scows have always been among the fastest monohulls, adjusted for length. Lately, high-sided, bluff-bowed racing scows such as MAGNUM, here, have been running with the big boys... and whuppin' 'em!

Note the 'saucer' bottom, which could be described as three dimensional rocker. 
Francois Chevalier’s 100ft Maxi Scow yacht and WallyCento superyacht concepts

The heeled, immersed area of the scow hull form remains nearly in-line (less power loss to cross-hull flow) and much larger (more righting arm to stand up to sail). The broad-yet-low-resistance forward area of the scow rises over waves, where the fine entry of the sharpie-style digs in and absorbs more of a wave's stopping power.

TriloBoats are optimized for DIY construction, not speed. Their large deadflat, amid-ships, plays an important role in minimizing lofting, layout, cutting, spiling and bevelling. Sheet materials (e.g., plywood, foamboard and copper plate/bronze angle) are easily incorporated. Curves are few and simple (no recurve and lying in a single plane).

But the hard angles at the bow slow the boat in steep chop. The ends are thus carried high to keep them clear of the water, but the resulting curves are more abrupt (lacking a 'good run').  The long deadflat is not as fast as a rockered bottom. A merely rockered bottom is not as fast as a 'saucer' bottom.

NOTE: I've only
heard it asserted that rockered bottoms are inherently faster than deadflat ones, but never come across actual evidence. Fact is, many commercial tow barges have large deadflats, despite their apparently efficient use over long hauls. If anyone can point to substantial evidence, one way or the other, I'd love to hear of it!

SKROWL, by Quenet Yann, is a brilliant, DIY interpretation of a MAGNUM scow hullform.  Using multiple chines, he approximates a saucer bottom. Using foam-carved corners, glassed over (forward and outboard), he softens inefficient entry angles and planes at the bow. In combination, this should be a very fast hull form at any size. In addition, he outfits the boat with gofast bells and whistles... high aspect foil daggerboards, twin rudders, powerful rig (he has others than shown in this lines plan).

My guess is that this style scow will tend wider for their length than pointy boats, though windsurfers (same hull form) successfully tend long and narrow.  For a cruiser/live-aboard, however, the ability to achieve speed in a boat that's wide for its length is a welcome feature.

So naturally, I find myself musing on the spectrum, represented by TriloBoats on one end, and SKROWL on the other. As usual, it is a 'morphing' process of small steps. I've left many possibilities out, here, hitting only the highlights. Keep in mind that these sketches are but crude characatures, exagerated for clarity, and don't represent likely proportions or curves.

Each step along the way eases some of the inherent drawbacks of a TriloBoat, at a cost in money, building time and effort. Involvement of resins and synthetics tend to increase. The easy incorporation of other secondary sheet materials (principally copper, angle and foamboard) becomes more and more complicated.
Payoff needs to be considered, as always.

Anke and I build on a shoestring, usually in marginal and/or time limited conditions. Since we like to copper plate, it takes some tricky work to handle the new curves. It's difficult to fasten copper to glassed foam. A fast hull with a our slow rig (etc.) won't make the most of the investment. And, truth be told, we're already fast, off the wind, and prefer not to sail in sloppy headwinds, where the SKROWL approach really helps.

There are drawbacks, as well, even once built. Rectangular storage is very hard to give up, even though the slopes involved are small. Bronze angle is tough, tough, and can make the difference between shrugging off a rock and major repairs (SKROWL bows can't use angle at the vulnerable, forward quarters).

One more concept to throw into the blender. Phil Bolger's ADVANCED SHARPIES (AS) are 'box' sharpies whose bottom curve in profile matches their side curves in plan. The idea is to create a symmetrical chine... this tends to equalize pressure on either side, reducing or eliminating drag from turbulent, cross-chine flow. LUNA (our AS) did, in fact, slip right along and tracked beautifully.

An ADVANCED BARGE (AB) could utilize the same principles, and be SKROWLed, as well.

So here's a gander at such a beast, adapted from a T32x8:

One solution to the copper plate dilemma would be to carry the forward bottom higher, SKROWLING forward and above the end of the copper plate (Bottom and Sides) with its bronze angle. This would make the curve more abrupt, and therefore less slippery, but that's what compromise is all about.

Another would be to leave it low, and copper in the more traditional manner -- narrow strips of thinner copper which can follow the curves. Fastening is still a problem... still, epoxy sockets for barbed or threaded fasteners are one among many possible solutions. Where there's the will, there's a way.

A few thoughts about the after arrangement shown... it is a modification to the simple, box barge shape, intended to compliment the faster, TABed and SKROWLED bow. Essentially, the flat bottom is divided into three 'panels', and the outboard ones are twisted from flat at their forward ends, increasingly angled, aft.

This 'faux' multi-chine could be achieved by darting the flat expanse of bottom material (similar to a tailor's dart in fabric). The mid panel is raised to the desired curve. The outer panels' outboard, aft corners are jacked up and a bit in, twisting them from flat, forward to canted at the transom. Tape N Glue along the matching seams.This draws the sides slightly inboard for a bit of aft, side curvature. More can be added, if desired, by trimming the outboard edges.

By lowering (easing) the aft curve, better release is achieved for a slipperier hull. The canted, outboard panels clear the water, when heeled, avoiding (box barge) transom dip and drag.


In conclusion, TAB and/or SKROWL adaptations of TriloBoat hulls should result in  slipperier, more easily driven hulls. Coupled with a powerful rig and efficient lateral resistance, I believe these hulls could be quite fast while retaining most barge/scow advantages, including relatively easy construction.


  1. In an interview with Phil Bolger, he said that the issue with dead flat run, is eddying along a hard chine, but he had discovered that if the chine had a small radius along its length, the eddying problem went away. His hypothesis was confirmed with his Dovkie design, which has a dead flat run and radius chine.

    1. Hmm... very interesting. I wouldn't call the DOVEKIE radius 'small', exactly, though compared to slippery devils of ROMP lineage, it is.

      Stephen Redmond's ELVER has a DOVEKIEish shape, but the angle between sides and bottom is not radiused. It would be interesting to hear his comments.

      B'lieve I'll invite them!

      Thanks for your input!

      Dave Z

  2. I built a 6.5 foot dingy that was an advanced barge shape with the same curve to the sides and bottom. I cut out all three panels at the same time, drilled and stitched them while they were flat and then opened it like a small portabote and inserted the bulkheads. Performance wise the boat rowed well, and seemed to tow without to much drag, but then so would a bolger tortose! The advanced shape you are drawing up looks very interesting. it would be nice to see a 3D image to help visualise it.

    Bolgers stepped cutwater seems like a perfect match with the barge shape to improve performance and reduce pounding? If it was also extended to the stern it would give you a strong skeg to make for a good rudder attachment position.

    1. Hi Ben,

      Interesting... on that short a hull, it may have another advantage in adding displacement at the ends.

      Our Bolger NYMPH was great, rowing, but tender both side-to-side AND fore-and-aft. Not a problem until we tried to get in or out. One or the other was manageable, but both together about dumped us, once or twice. Got me thinking about barge shapes to dampen pitch and roll... the cutwater would extend that tendency.

      I would like to do a 3D drawing, too, but my CAD system (free version of Google SketchUp) isn't up to it. I could upgrade, but don't have time to tackle the learning curve.

      Anyone? Anyone?

      I agree RE the cutwater, both fore and aft. I drew one into B'TUGLY (available at and the T40x20 Catamaran (merely a doodle... no plans available... sorry).

      In B'TUGLY, designed for the AroundInTen (Ten foot vessels, around the world race), the steps provide a narrow, secure sleeping platform low in the boat. Many designs use the step for battery/ballast in electrically propelled vessels.

      That all being said, we've been pleasantly surprised how little pounding we experience in SLACKTIDE. Little to none, in fact.

      At anchor, there's a ripply rush of sound from the bow, even in exposed conditions.

      On the wind, we're heeling, so shouldering over waves with a V down. Occasionally, in very bad, steep chop, we'll lift and drop with a thud, but only if the wave arrived at just the wrong angle/moment. And by the time it's this bad, we're usually thinking of running off for shelter, anyway (25-30kts, depending on current).

      Off the wind, no pounding, ever, even when running upright (we usually broad reach).

      One extra reason we've not used cutwaters on our vessels is that it complicates the copper job. Doesn't rule it out, at all, but adds material for the vertical walls and a cover strip for the angle between cutwater sides and hull proper.

      A mild downside of a cutwater is that it lowers the forefoot, which will dig into a steep beach sooner. With the flat bottom, running up and stepping off can be done in slippers!

      One question is what to do with the interior of the cutwater. Fill it with foam? Use for deep storage (ventilation issues)? Or open completely into the interior?

      All of which makes design so fun!

      Dave Z

  3. I could suggest Hull designer by carlson. Simple and free, then input it into freeship, or I use crossroads to convert it into a DXF file that can be inpput to ACAD or my old demo version of rhino 3d. it maybe also possible to input the files into google sketchup, as it already seems like you have good skills with that program. For hull designer

    For a great 3d file conversion program. I convert hulls VRML files to DXF

    It would be interesting to do some tests on hull shapes with different models. It may be your simple barge is much better (or rather much less worse) than at first glance. It gives maximum stability, the sharp chines at the bow are less likely to be hit square by a wave than a more advanced barge shape(with curve of chines and sides the same) and to windward (with leeway) the eddying over the bow chine on the leeward side may be reduced? Anyway I guess what I was thinking was that with the simplicity and low cost, the inefficiencies in the barge may be more than compensated for by adding some extra length to the hull. How does the barge compare to Luna speed wise?



    1. Hi Ben,

      I'll have to pass for now on your CAD advice, though it sounds good. I barely keep up with what I've got!

      My feeling is that you're right in your box barge hull analysis. I went over a lot of the things we've traded at the expense of speed (in The comPromise of Speed). But take away all but the hull shape, and I think our assumptions will be surprised.

      In answer to your question (how does SLACKTIDE compare to LUNA, speed-wise... ST's is the only form for which I have data... comparisons are relative to Hull Speed):

      On the wind, speed is similar, on the slow side. I attribute this to our compromising set of conditions, which are similar. It's hard to say how much is the hull form, since we do so much that would horrify a racer.

      Off the wind, SLACKTIDE is slower. I attribute this to the abrupt aft curve, resulting from her short length (relative to draft), and the decision not to stretch it (maintaining high, aft displacement). We got what we wanted from it, at the cost of inducing drag from a relatively poor run.

      My expectation is that, the longer a barge becomes, the easier her end curves for a better run and higher speeds. I'm guessing that, by 32ft and 1ft draft, the differences will diminish or disappear. Alternatively, one could design with shorter deadflat than I favor for a better run at any length.

      A friend suggested a poor fella's hydrodynamic testing device: a balanced beam (like a kid's mobile) suspended over smooth-flowing water trailing competing models, each floating in the stream. The more efficient model should pull ahead of the other.

      Haven't tried this, yet, but someday!

      Dave Z

    2. You will find the hull designer program really very easy to use, gives displacement, heeling and all parameters. I find it far easier than anything else I have seen.

      I would be more than happy to help you out with any problems. unfortunatly I have not mastered google sketchup so can't help you with that, from what I have seen it doen't handle complex shapes well, but maybe thats just me?

      I might try to model a few hull shapes for you and run them through the resistance calcs on freeship if you like. just let me know the length, beam, and displacement, and maybe flat bottom length and I should be able to roughly get some idea of resistance.

      The biggest benefit of the advanced barge shape would be a reduction in the bow digging in problem and a reduction in the eddying forward and aft. will be interesting to see if it's worth the tradeoffs.

  4. played with a few designs. Interesting though I don't really trust the results as it is very hard to calculate the formation of eddies and drag. I suspect the formulas in freeship use the prisimatic coefficent rather than anything more complex. but anyway all speeds at 150 lbs resistance, 5.7 tonnes. 32x8 ft. speeds in knots with Delft and Kaper resistance predictions.

    heavily rockered bolger type barge with flat sides. draft 1.5 ft 5.1knots delft/6.3 kn Kaper

    Cutwater trylobarge draft 1.2 ft 5.4kn and 6.5kn

    standard trylobarge draft 1.23 ft 4.7kn and 5.4 kn

    V bottom fwd and aft barge draft 1.22 ft 5.1kn and 5.8kn

    v bottom fwd and aft+ cutwater 1.175 5.3kn and 6.4 kn

    This gave a poor result for a standard trilo barge as you suspected due to the steep ends. more rocker, V or a cutwater all increased the speed. If the results are accurate I don't know? but it does show that in theory bolger was on the right track speed wise with his heavily rockered designs and cutwater concepts.

    1. Hey Ben,

      Very interesting stuff! What say we continue this via email (contact me at "triloboatsATTgmailDOTTcom".

      Perhaps you'd be interested in doing a 'virtual interview' on your results? We could set up uniform assumptions and post the results in graphic form?

      It would be great to have some hard comparison data!

      Dave Z

  5. Posted on behalf of John...

    Dave and Anke,

    Nice to see your blog re-activated.

    You mentioned that your next (and last??) boat likely being a 32' to 36' x 8' TriloBoat. Those dimensions are strongly reminiscent of Luna, your AS-32? Do the hulls shapes of this proposed TriloBoat differ from Bolger's AS-series only in that the T-Boats are straight-sided for their full length, and that the central portion of the bottom is flat rather than rockered? Are the shape advantages of the T-Boats compared to the AS-series primarily construction-related, or are there major sailing/sea-worthiness differences too?

    Do you think either the AS-series or the T-Boat series could be designed to be viable go-anywhere, handle-any-seastate, ocean-cruising sailboats --- in addition to their wonderful shoal-draft, easy-to-live-in and easy-to-build shape?


    1. Hi John,

      The dimensions are reminiscent of LUNA (AS31x8x1.1).

      The differences between an AS and standard TriloBoat are as you mention, with the critical difference that the plan view (side) curvature does NOT match the profile (bottom) curvature. An TAB (Triloboat Advanced Barge) would match these curves.

      I would say that the AS-series are definitely better sailors; they have a slippery shape, spin on their short waterline belly when upright for very nimble tacks, then heel over to increase water-line for high hulls peed on the wind.

      TriloBoats are much easier to design and build, with less material waste, and carry more on a given footprint (especially draft). As sailors, they're (likely) slower for their length, and have a bigger turning radius (less nimble, especially tacking).

      RE seaworthiness -- I would say there's little difference, so long as they are built, rigged and handled for reliable windward progress in heavy conditions.

      We were able to claw our way into 45kts with both boats (about a half knot made good in neutral current). Both cases were sea-trials as we normally run off to shelter well before then. On the open sea (with which we have no experience, I favor the idea of heaving to and/or sea-anchor sooner rather than later, and feel that either hull would do fine.

      Motion-wise, we've found both to feel 'shippy', even in short, steep chop that has had some of our Curvy Dog friends rolling and yawing queasily. The square sections, I believe, dampen roll and yaw. Barges seem to dampen pitch better than AS hulls (as one would expect), with more displacement toward the ends. Neither hull seemed to pitch excessively, however.

      So yes, I think both could easily handle all-condition cruising. Bob and Shiela Wise have pretty well proven the AS hull at sea. Triloboats should be similar, I'd think, and very-bluff-bowed (though curvy) Dutch Botters and New Zealand Scows range far and wide.

      Interestingly, I've heard it said that Botters were developed for short chop in North Sea waters. Like TriloBoats, their bluff bows have enormous reserve buoyancy that refuses to 'bury' in the waves, and instead rides up and over them. The usual argument is that a fine bow cleaves through... they may have other values, but I'm not sure that's a plus!

      Dave Z