Fastest boat yet: Triton . Triton is a very fast no-frills 1.05 kg, 7.4 W triple-screw monohull speedboat based on my favorite hull. An average speed of 1.09 m/s from a standing start makes her our fastest LEGOŽ powerboat ever by at least 10%. . Please feel free to look over the images and skip the verbiage.
Personally, I'm fine with the fact that 6 of my last 7 uploads have been all about spinning tops, but the trend didn't go unnoticed by certain products of my other on-going obsession -- powerboats. So, in the hope of putting an end to the nasty glares coming from the boat shelf, I hereby present a recently declassified boat.
Q: What do you get when you add a center screw on its own XL motor, V2 receiver, and PF Li polymer battery to our reiging top-speed champ, twin-screw Nadine?
A: A long, blue 7.0 W/kg LEGOŽ powerboat that goes like stink!
∧ Controlling 3 motors at once with a LEGOŽ handset takes practice. Watch for the final burst of speed at 1:54 as the driver finally gets the hang of the piano-style remote control handset shown at the beginning.
This handset simplifies driving a bit by making it easy for a single finger to make both outer screws go either full forward or full astern. The middle IR transmitter isn't used here. (Controlling Triton will get a lot easier when she gets an SBrick and the customizable smartphone-based control interface that comes with it.)
∧ The driving in this night pool trial is better, but the boat loses her center prop at 0:16.
On this page:OverviewDesigned for speedComparison with NadineDeclassifiedSpecificationsFootnotesSelected references
Triton is a no-frills 1.05 kg, 7.4 W triple-screw monohull speedboat based on the venerable 74x18x7 LU City Lines hull. An best speed of 1.09 m/s (Froude number ≥ 0.47) makes her our fastest LEGOŽ speedboat to date, beating out former speed champ Nadine by at least 10%.
That's darned fast for a LEGOŽ powerboat by any standard, and her true top speed is probably a good 5-10% higher.1 Better yet, Triton retains nearly all of Nadine's seaworthiness.
∧ Triton's CLH accommodated the 3rd screw and powertrain with only a slight increase in draft and wetted surface area and no significant loss of initial or dynamic stability.2
At midships, breadth, draft, and freeboard measure 142 mm, 20 mm, and 38 mm, respectively. Credit for much of Triton's stability goes to her breadth and especially to her high breadth/draft ratio (7.1). The latter far exceeds that possible with any other unitary hull.
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Designed for speed
The most important factors behind Triton's unmatched speed are fairly straightforward:The highest installed power (PI = 7.4 W) we've put in any boat by at least 50%No-frills outfit and my best lightweight construction to maximize the all-important installed power / displacement ratio (PI / Δ)Large, highly efficient third-party props -- her only non-LEGOŽ parts -- to make full use of the mechanical power delivered to the prop shaftsMaximum possible load waterline length (LWL) for a LEGOŽ unitary hull (LUH) to minimize wave-making resistance at speedVery little plastic in the water aside from the hull to minimize appendage drag∨ Close-ups of the electrical and mechanical powertrains appear below.
∧ The triple "XL/8.33/55" drivetrain (XL motor, 1:8.33 overdrive, 55 mm prop) represents an educated first guess based on experience with Nadine. An upcoming trial with 52 mm props will complete her Motor/gearing/prop (MGP) optimization.
The rationale behind our outdrives and third-party props is discussed here.
∨ Triton's performance also benefits significantly from her twin V2 receivers and PF Li polymer batteries. Doubling these components keeps her current-hungry XLs well-fed while allowing her to complete several back-to-back 25 m runs at full power without tripping thermal protection.
Compared to standard-issue V1 receivers, the rarer and more expensive V2s relay electrical power from the batteries to the motors much more efficiently, are willing to deliver much higher currents to the motors, and tolerate higher internal heat loads before thermal shut-down. And they're no lousier than the originals as receivers of remote control commands.
The Li polymer batteries weigh much less than other LEGOŽ options, deliver much more current than AA and AAA battery boxes loaded with alkaline or even NiMH cells, and do so without the voltage sag that plagues alkalines in particular.
∧ Encouragement to transform twin-screw Nadine into triple-screw Triton came from a section on multi-screw propulsion in the book above by renowned hydrodynamicist and naval architect Donald A. Blount. Blount is one the world's foremost designers of high-performance motor yachts. Indeed, one of his boats -- the sleek 67.7 m, 1,000 mt GT/MY Destriero -- has held the trans-Atlantic speed record (53 knots average!!) for 13 years now.
So, when Don Blount says that 3 screws can outperform 2 in (scaled) settings not unlike Nadine's and Triton's despite the added displacement and appendage drag, you'd better listen up.3
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Comparison with Nadine
∨ Below are Triton and Nadine (lower photo) for direct comparison. They're my 2 fastest boats.
∨ More of Nadine...
Best pool trial speeds are 1.09 m/s for Triton and 0.99 m/s for Nadine. However, Triton's even faster than the 10% spread in quoted speeds would indicate for 2 reasons: (i) Both speeds represent averages from standing starts. (ii) Triton was clocked over a much shorter course (13.3 vs. 24.8 m). True top speeds were probably 5-10% higher than these averages in both cases but moreso in Triton's.
Relative to Nadine, Triton has 23% more displacement (1,050 vs. 855 g) and draws 25% more water (20 vs. 16 mm) but is only 1% longer at waterline (~545 vs. 540 mm). Waterline breadths at midships are the same.
Identical hulls and negligible differences in waterline length, breadth, and slenderness mean that both boats would encounter very similar wave-making resistances at Nadine's top speed. However, Triton would face (i) added viscous resistance due to her greater draft and wetted hull surface area and (ii) ~50% more appendage drag due to her 3rd screw.
So how did Triton end up 10% faster than Nadine? The answer is simple: A 30% advantage in installed power to displacement ratio (7.0 vs. 5.7).
That extra power allowed Triton to climb most of the way up her wave wall (Froude number Fr = 0.47), whereas Nadine gave up close to the bottom of hers (Fr = 0.43).
The significance of the Froude numbers is explained here.
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∨ When I first showed Triton to long-time boat racing partner Shawn Kelly, he made me promise to keep it under wraps. Since he saw her as a potential entry in the boat races at BrickWorld 2016, these night trial shots were all I could post at the time.
Now that we have a better entry, Triton's been declassified.
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Dimensions and hull form coefficients
All measurements taken at rest in fresh water (density 1,000 kg m-3).
Overall dimensions:592 x 144 x  mm (LxWxH, excluding outdrives)Displacement:1.050 kgDisplacement volume:1.05 x 10 -3 m3Depth:68, 58 mm (bow, midships)Waterline length:545 mmWaterline breadth:142 mmDraft at keel:20 mm (midships)Freeboard:38 mm (midships)Midship section area:~2.5 x 10 -3 m2Waterplane area:~7.0 x 10 -2 m2Block coefficient:0.68Prismatic coefficient:0.76Wetted surface area:~n/a x 10 -2 m2Midship coefficient:~0.99Waterplane area coefficient:0.90Length-breadth ratio:3.8Breadth-draft ratio:7.1Slenderness (length/displacement) ratio:5.4Form factor:0.59
Hydrodynamic regime:High-speed displacementInstalled power:7.4 W at 7.4VInstalled power to displacement ratio:7.0 W/kgCritical speed:0.92 m/sTrial length:13.3 mAverage trial speed:1.09 m/sAverage trial Froude numbers:0.47 based on length, 1.09 based on displacementAverage trial Reynolds number:6.7 x 105High-speed index:0.97
Construction:Aside from outdrives, mostly studdedHull:74x18x7 LU City Lines hull (Set 7994)Propulsion:Triple outdrivesMotors:3, 1 XL on each propPropellers:Third-party 55 mm 3-blade (Counter-rotating side props, left-handed center prop)Gearing:3-stage 1:8.33 overdriveProp separation:194 mm right to leftSteering:Differential power to props (no rudder)Electrical power supply:Twin 7.4V PF rechargeable Li polymer batteriesIR receivers:Two V2sIR receiver connections:3, 1 for each motorModified LEGOŽ parts:Prop hubsNon-LEGOŽ parts:Props and electrician's tape (bottom fairing)Credits:Original MOC
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1 This 1.09 m/s speed was clocked over a relatively short 13.3 m course from a standing start. Top speed is probably 5-10% higher.
2 In fact, the CLH is probably the only LEGOŽ unitary hull capable of supporting 3 XLs in a monohull boat with a reasonable margin of safety WRT both stability and freeboard. Lena II proves that the much shorter and slower Family Yacht hull can easily handle 2 XLs, but I have my doubts about a third.
3 A 4th screw on its own XL might conceivably increase top speed, but I doubt that I'll pursue that. The hull could probably handle the added displacement from a seaworthiness perspective, but the drivetrains would have to be redesigned from the ground up, and the gamble doesn't seem worth it. Here's why.
For starters, top speed is a highly nonlinear function of the number of screws due to a tangled web of trade-offs involving total displacement, draft, wetted surface area, and wave-making, viscous, and appendage resistance. All of the resistances increase with speed, but each in its own way. At speed, the resistances added by the 4th screw could easily eat up the added power.
Triton's top-speed Froude number (Fr) also casts doubt on further speed gains, as the current value of 0.47 already puts her well up on her wave wall (the steepest part of her specific resistance-Fr curve, with specific resistance defined as total resistance per unit displacement.) Getting a tanker-like displacement hull like Triton's City Lines hull to Fr = 0.47 is a substantial achievement. Going beyond that would be very difficult with any number of screws.
However, it might be possible to wring a bit more speed out of Triton with with slightly smaller (52 mm) screws or lower-drag outdrives.
Blount, D.L., 2014, Performance by Design (self-published book)
Molland, A.F., Turnock, S.R., and Hudson, D.A., 2011, Ship Resistance and Propulsion: Practical Estimation of Ship Propulsive Power, Cambridge University Press
Noblesse, F., He, J., Zhu, Y., et al., 2014, Why can ship wakes appear narrower than Kelvins angle? European Journal of Mechanics B/Fluids, v.46, p.164171
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