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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 LEGO® powerboat ever by at least 10%.
About this creation
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 LEGO® powerboat that goes like stink!



Controlling 3 motors at once with a LEGO® 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:


Overview

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 LEGO® speedboat to date, beating out former speed champ Nadine by at least 10%.

That's darned fast for a LEGO® 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: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 LEGO® 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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Declassified

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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Specifications


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 kg
Displacement volume:1.05 x 10 -3 m3
Depth:68, 58 mm (bow, midships)
Waterline length:545 mm
Waterline breadth:142 mm
Draft at keel:20 mm (midships)
Freeboard:38 mm (midships)
Midship section area:~2.5 x 10 -3 m2
Waterplane area:~7.0 x 10 -2 m2
Block coefficient:0.68
Prismatic coefficient:0.76
Wetted surface area:~n/a x 10 -2 m2
Midship coefficient:~0.99
Waterplane area coefficient:0.90
Length-breadth ratio:3.8
Breadth-draft ratio:7.1
Slenderness (length/displacement) ratio:5.4
Form factor:0.59


Performance measures

Hydrodynamic regime:High-speed displacement
Installed power:7.4 W at 7.4V
Installed power to displacement ratio:7.0 W/kg
Critical speed:0.92 m/s
Trial length:13.3 m
Average trial speed:1.09 m/s
Average trial Froude numbers:0.47 based on length, 1.09 based on displacement
Average trial Reynolds number:6.7 x 105
High-speed index:0.97


Design features

Construction:Aside from outdrives, mostly studded
Hull:74x18x7 LU City Lines hull (Set 7994)
Propulsion:Triple outdrives
Motors:3, 1 XL on each prop
Propellers:Third-party 55 mm 3-blade (Counter-rotating side props, left-handed center prop)
Gearing:3-stage 1:8.33 overdrive
Prop separation:194 mm right to left
Steering:Differential power to props (no rudder)
Electrical power supply:Twin 7.4V PF rechargeable Li polymer batteries
IR receivers:Two V2s
IR receiver connections:3, 1 for each motor
Modified LEGO® parts:Prop hubs
Non-LEGO® parts:Props and electrician's tape (bottom fairing)
Credits:Original MOC

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Footnotes

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 LEGO® 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.




References

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 Kelvin’s angle? European Journal of Mechanics B/Fluids, v.46, p.164–171

Please click here to see the complete list.

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Comments

 I made it 
  March 24, 2016
Quoting Clayton Marchetti Wicked! Soon you'll be making a hydrofoil:-)
Thanks, Clayton! I wish! Getting a LEGO boat up on plane is the Holy Grail. Getting there will take non-LEGO props and a hull that doesn't yet exist.
 I like it 
  March 24, 2016
Wicked! Soon you'll be making a hydrofoil:-)
 I made it 
  November 29, 2015
Quoting Nick Barrett I must admit, I had the same thought as NFP looking at all those blue axle joiners, although they do look nice. It's a real speed king, this!
Many thanks, Nick! I'm really torn about those axle joiners. They're on the list for our next round of pool trials.
 I made it 
  November 29, 2015
Quoting David Roberts Excellent! At this rate, it can't be long before you reveal the first all Lego hydrofoil (perhaps an impossible dream, like the all Lego aeroplane!). I keep looking at the big, Lego fans that I bought cheap on Bricklink and I'm sad that they can't be driven and have blades in contra-rotating directions. I wonder if Lego will ever produce a decent water propeller?
Thanks, David! Alas, water's very picky about its propellers. A friend who works for TLG recently suggested on the employees' version of LEGO Ideas that they abandon their long-standing anti-thrust policy and introduce a line of working boats with decent props and some go. It got the employee votes needed to go to review in 2 days, so there's hope.
 I like it 
  November 29, 2015
Excellent! At this rate, it can't be long before you reveal the first all Lego hydrofoil (perhaps an impossible dream, like the all Lego aeroplane!). I keep looking at the big, Lego fans that I bought cheap on Bricklink and I'm sad that they can't be driven and have blades in contra-rotating directions. I wonder if Lego will ever produce a decent water propeller?
 I like it 
  November 29, 2015
I must admit, I had the same thought as NFP looking at all those blue axle joiners, although they do look nice. It's a real speed king, this!
 I made it 
  November 25, 2015
Quoting Nerds forprez I like speed, and I like boats! Bam! I'm in love! One quick question.... if speed is what we are going for, wouldn't it be better to replace all those blue connectors (although very fashionable) with just axles? If you need them to be stronger your can always reinforce them with 1/2 bushes, although I think they would be plenty strong without the reinforcement. The connectors rubbing against the vertical liftarms might be creating some undesired and unneeded friction.
Thanks, NFP! Darn, those strings of blue axle joiners were my one concession to cosmetics! I always make sure that all shafts have a bit of play before putting boats in the water, but your point's well taken. The back-torques from the props at the 36t gears are pretty high, especially at speed, but the 2 short outer drive shafts could certainly be bare axles with little if any loss to torsion. The long center shaft is probably a different story, but I should try it both ways in a timed pool trial to find out. Not sure which would weigh more -- an axle coated with half-bushes or a string of 2L axle joiners, but it's easy enough to measure. With the drive shafts turning at only 240-300 RPM, the relative axial moments of inertia probably don't matter.
 I like it 
  November 25, 2015
I like speed, and I like boats! Bam! I'm in love! One quick question.... if speed is what we are going for, wouldn't it be better to replace all those blue connectors (although very fashionable) with just axles? If you need them to be stronger your can always reinforce them with 1/2 bushes, although I think they would be plenty strong without the reinforcement. The connectors rubbing against the vertical liftarms might be creating some undesired and unneeded friction.
 I made it 
  November 25, 2015
Quoting Oliver Becker Screw, screw, screw your boat...! Again wonderful stuff from you, Jeremy! :)
Thanks again, Oliver! Interesting that the automatic screening process held this but was smart enough to pass my use of the plural many times above. Now if they could just come up with a filter for bad puns! ;^}
 I made it 
  November 25, 2015
Quoting Didier B Nice swimming pool ! 5/5 for the mecanism but 1/5 for the overall design... Bouhhhhh !
Thanks, Didier. Yeah, it's not going to win any beauty contests, but since I built it strictly for speed, it had to be bare-bones. Per Nils' suggestion, I plan to make a "show" version with more visual appeal.
  November 25, 2015
Nice swimming pool ! 5/5 for the mecanism but 1/5 for the overall design... Bouhhhhh !
 I made it 
  November 25, 2015
Quoting Nils O. Very clever and extreme cool looking! A speedboat body structure on top would look even cooler (even with the disadvantage of adding weight). Anyway, great job! :-))
Thanks, and great idea, Nils! I foresee a show version with sleek bodywork that comes off easily to yield the no-frills go version here. Coming up with the bikini-clad girls will be the hard part.
 I made it 
  November 25, 2015
Quoting Locutus 666 Excellent build! And great performance! A cool toy if you have a pool! :)
Thanks, Locutus! Yes, definitely a pool toy now. When my first sbrick arrives any day now, and the boat's no longer subject to the exasperating limitations of the PF remote control system (which hardly deserves the name), the play value should go way up. Then it'll be safe for lakes and ponds where going in after it isn't feasible. Can't wait!
 I like it 
  November 25, 2015
Very clever and extreme cool looking! A speedboat body structure on top would look even cooler (even with the disadvantage of adding weight). Anyway, great job! :-))
 I like it 
  November 25, 2015
Excellent build! And great performance! A cool toy if you have a pool! :)
Jeremy McCreary
 I like it 
Matt Bace
  November 24, 2015
Impressively fast! I'm having a hard time coming up with any ideas that could make this boat even faster -- ducted screws, perhaps?
 I like it 
  November 24, 2015
Screw, screw, screw your boat...! Again wonderful stuff from you, Jeremy! :)
 I made it 
  November 24, 2015
Quoting Oliver Becker Well, my english maybe a little bit strange for the MOCpages guards, Jeremy! Should be just a quotation of a song I know... Nevertheless, you will see it 24 hours later, sorry! Great MOC, that's what I wanted to say... ;)
Thanks, Oliver! I'll keep an eye out for it.
 I like it 
  November 24, 2015
Well, my english maybe a little bit strange for the MOCpages guards, Jeremy! Should be just a quotation of a song I know... Nevertheless, you will see it 24 hours later, sorry! Great MOC, that's what I wanted to say... ;)
 I made it 
  November 24, 2015
Quoting Gabor Pauler Jeremy, I'm just thinking about that more streamlined pylons of screws could improve speed further. If I were you, I would try series of 3×1-stud technic levers pulled on 2 paralel technic rods, plus a 3rd tecnic rod shaft rotating in the central hole of technic levers.
Thanks, Gabor! Hmmm, let me work on that -- perhaps something akin to the Z-drive struts I used on RT Vanna.
 I like it 
  November 24, 2015
Jeremy, I'm just thinking about that more streamlined pylons of screws could improve speed further. If I were you, I would try series of 3×1-stud technic levers pulled on 2 paralel technic rods, plus a 3rd tecnic rod shaft rotating in the central hole of technic levers.
 I made it 
  November 24, 2015
Quoting Matt Bace Impressively fast! I'm having a hard time coming up with any ideas that could make this boat even faster -- ducted screws, perhaps?
Thanks, Matt! Me, too. Ducts are usually for lower-speed, bigh-thrust workboats. At high speeds, the added appendage drag becomes prohibitive -- especially in a LEGO implementation. The best chance for higher speed that I see at this point, and I'm not hopeful, is a set of =slightly= smaller props. That pool trial's on the to-do list.
 I made it 
  November 24, 2015
Quoting Gabor Pauler Wow! Serious triple screws!
Thanks, Gabor. It's conceivable that a 4th screw on its own XL would further increase speed, and the hull could probably handle the added displacement from a seaworthiness perspective. But as I'm sure you can appreciate, top speed is a highly nonlinear function of the number of screws due to a tangled web involving total displacement, draft, wetted surface area, and wave-making, viscous, and appendage drag. Given the tanker-like displacement hull and the boat's current position on the steepest part of its speed-resistance curve (per its top speed Froude number of 0.49), my sense is that 3 screws is the end of the line. That said, there may be a little more speed left in this boat with slightly smaller screws.
 I like it 
  November 24, 2015
Wow! Serious triple screws!
Jeremy McCreary
 I like it 
Kain .
  November 23, 2015
Nicely done
 I made it 
  November 23, 2015
Quoting jds 7777 Awesome! So your entering it into a competition? It really does go fast!
Thanks, JDS! Not this one -- we have a better bet now for BrickWorld.
 I like it 
  November 23, 2015
Awesome! So your entering it into a competition? It really does go fast!
 I made it 
  November 23, 2015
Quoting Kain . Nicely done
Thanks, Kain!
 
By Jeremy McCreary
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