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R/V Stormin' Norma
Stormin' Norma is a 1.1 kg RC motorized 1:120 model of a marine geology research vessel. She's fully outfitted with functionally realistic deck equipment and does a realistic 12 knots at scale.
About this creation
Please feel free to look over the images and skip the verbiage.

On this page
Intro
Photos and text
Props
Prop walk
Table of features and stats




Introduction

Inspiration for the R/V Stormin' Norma (hereafter Norma for short) came from my own professional interest in marine geology -- specifically, the interactions among ocean floor topography, seafloor volcanism, plate tectonics, and related mantle flows.

The "R/V" designates a research vessel, and yes, solid rock flows when it's warm enough and pushed hard enough. (Think of frozen butter placed in an oven: It's brittle enough to shatter with a hammer at first but becomes easy to spread long before it melts.) My research is based largely on the data ships like this collect.

"Stormin' Norma" is our affectionate nickname for my mother-in-law, as sweet and kind a woman as you'll find -- until you get her to a 49ers football game. We just stand back and cover our ears.

Typical activities for a marine geology research vessel include
  • Detailed seafloor topographic mapping (the basis for the seafloor detail you see on Google Earth) using high-resolution sonar
  • Magnetic seafloor mapping to reveal the magnetic patterns locked into seafloor lavas as they cool
  • Seismic imaging to see what's under the seafloor surface using either (i) temporarily deployed ocean bottom seismometer (OBS) arrays to record seismic waves from naturally occurring earthquakes, or (ii) hydrophone stringers towed behind the ship to record echoes from underwater air-gun blasts
  • Collection of various kinds of seafloor rock and sediment samples for identification, mineral make-up, chemical composition, and dating
  • Direct imaging and investigation of seafloor geological features -- especially volcanic activity, hydrothermal vents, and faults -- via deep-diving ROVs (remotely operated vehicles)
  • Deployment and recovery of AUVs (autonomous underwater vehicles that roam the seas on their own for months at a time, gathering and transmitting various kinds of data).



Accordingly, the R/V Stormin' Norma is specially equipped with
  • A deployable ROV stowed on deck when not in use
  • A deployable AUV stowed in a deck-level hold when not in use
  • A knuckle-boom deck crane used to deploy and recover ROVs, AUVs, and OBS arrays and to load and unload equipment and supplies while in port
  • A long hydrophone stringer on a large stern winch reel
  • A large fantail A-frame for deployment, towing, and recovery of hydrophone stringers
Propulsion is provided by twin stern drives, each powered by its own M motor under independent PF remote control. None of the equipment listed above is powered, but the crane, A-frame, and hydrophone winch offer fairly realistic manual actions.




Photos and commentary

Norma from above with her ROV and AUV away.



Norma is currently based on the Coast Guard hull (CGH). I like the orange color, but this hull lacks the volume and breadth needed to support a top-heavy model ship displacing 1.1 kg on its own -- hence the sponsons (buoyant outriggers).

Of course, no real work vessel of this size (~50 meters in length at full scale) sports such appendages. Their sole purpose here is to add much-need buoyancy and roll stability. Norma's seaworthiness depends on them.



Each sponson consists of two Technic air tanks sealed with short sections of pneumatic tubing plugged with pieces of 3 mm bar cut from a lance. The tanks are positioned vertically so as to be no more than half submerged. Any deeper, and the much-needed righting moments they provide would be greatly reduced.

The sponsons are positioned longitudinally to shift Norma's center of buoyancy forward to balance the weight of the superstructure, receiver, and battery box. They also improve top speed by reducing the wetted area of the hull.



I prefer Norma's current color scheme, but truth be told, the rare and very expensive blue 74x18x7 LU City Lines hull (CLH, 57789c01) used by Nadine above would have been a much better choice for a research vessel of this class. Specifically, the CLH would model a 73 meter vessel at Norma's scale of ~1:120. Most of her scaling inconsistencies would then vanish.

The CLH would also eliminate Norma's totally unrealistic sponsons. Its much greater volume would better support Norma's superstructure and equipment loads with freeboard to spare. Her roll stability would be vastly improved by the CLH's greater breadth and much higher breadth/depth ratio. The CLH's greater slenderness and much greater waterline length would also make her faster.



The white superstructure houses the PF receiver, which draws power from a PF AAA battery box in the hold below. (The much lighter and longer-lasting 7.4V lithium rechargeable battery would have been a much better choice, but all of mine had better things to do.)



Antennas and running lights dot the top of the superstructure. The antenna under my finger doubles as a remote battery box power toggle.

Centered behind the bridge is a radar enclosure with stacks on either side. The scaffolding bridging the stacks provides mounting points for floodlights used during night operations. (At times, vessels like Norma must work around the clock.) On the deck behind the superstructure are rails for the AUV carriage (see below).



Next astern is a stowed yellow and black knuckle-boom deck crane used to deploy and retreive AUVs, ROVs, and OBS arrays while at sea and to load and unload equipment and supplies while in port. Its manual action is quite realistic. The crane's too large for the hull, but that's the smallest I could make it without sacrificing functionality. The twin M motors providing propulsion are visible behind the crane.

Further astern is the winch reel that stores, deploys, and retrieves Norma's single hydrophone stringer. The latter consists of a chain of 6 or more 21L strings with end studs and climbing grips. The near side of the winch has a ratchet and pawl to hold its position, while the far side has a handle for manual operation.

Mounted on the fantail is a manually operated trawler-like A-frame used mainly to let out and haul in the hydrophone stringer and to keep it away from the props while it's being towed. The orangle friction cylinders hold its position fairly well.

Finally, we come to the twin stern drives discussed below.



Closer look at the forward and port sides of the superstructure. Empty airplane windows were used wherever possible to reduce superstructure weight. The door on the bridge doesn't open. Forward floodlights illuminate the foredeck at night as needed. If only LEGOŽ made a white whip antenna! The running lights are almost US Coast Guard-compliant (see below), but only the bow lights have LEDs. There are 3 large marlinspikes on each side of the deck.



Foredeck details. The bulky bow light housing represents a partially successful attempt to meet Coast Guard requirements for visibility from various angles. For example, the red port-side bow light should only be visible from directly off the bow to [105]° astern on the port side but shouldn't be visible from any angle on the starboard side. Ships of this size must also have two white lights atop their superstructures, with the higher one toward the stern, and one or more white lights on their stern as well. Visibility permitting, had Norma been in strict compliance, other boats would have been able to get an idea of her size and her heading relative to their own at a distance at night from the running lights alone.



Closer look at afterdeck features. Near the center is a somewhat oversized yellow and black ROV stowed on its deck platform with its dual robotic arms tucked in to prevent damage in rough seas. Behind the ROV is the knuckle-boom crane, here ready to deploy the torpedo-like AUV in the background to the ROV's left.

The hydrophone stringer would look a lot more realistic when deployed in water if the joined end studs, meant to represent floats, actually floated.



Oblique close-up of the forward and port sides of the ROV. The floodlights above and stereo video cameras below are all mounted on 2-degree of freedom (DOF) gimbals to provide maximum coverage of the scene before the ROV.

Downward-pointing floods are mounted on the bottom of the ROV as well. The ROV's 3-DOF port robotic arm is nicely seen. This ROV model is ~50% too large for the hull, but inclusion of characteristic functional features trumped fidelity to scale once again.



A typical ROV pose while working at depth -- or maybe it's just upset about something.



The thin 1x3 liftarm running down the center lifts up to provide a grab for the deck crane. The ROV's twin props are too large.



Knuckle-boom crane deploying the ROV over the starboard side. Thanks to its 2 friction cylinders, several pieces of 3 mm bar, and a few strategically placed shortened 2L and 3L black friction pins, the crane can hold its position against the weight of the AUV despite the thin liftarm construction. The heavier ROV's a different story.



Now it's the AUV's turn to take a swim. The trans-yellow nose piece covers its forward sensors.

ROVs are typically deployed a few hours at a time, whereas AUVs roam the ocean for months and thousands of kilometers at a time, collecting and transmitting data all along the way.

Among other things, AUVs are used to monitor the health of our oceans -- something we can no longer take for granted. If current trends continue, our beautiful blue planet, often aptly referred to as the the "blue marble" or the "water planet", may soon become known as the "yucky-colored flotsam planet".



Now out of its sling, this AUV's next move will be a very long and slow dive to a depth of several kilometers followed by an equally long and slow rise to the surface many kilometers from this starting point. It will then repeat this cycle many times during this deployment.

By exploiting solar power while near the surface, gravity during their descents, and the lower density of shallow relative to deep seawater during their ascents, AUVs have very low power requirements. Much of their power is consumed in telecommunications, primarily for GPS georeferencing and transmission of data collected along their journey. Seawater temperature, density, and chemistry are the data most commonly collected.



If the AUV is onboard while Norma's at sea, it's stowed in a deck-level hold within the superstructure. Between the open hold doors is the AUV's carriage on its tracks. Below the base of the deck crane is the stowage platform for the ROV, which is too large to fit in the hold. One day, I'll add a hatch that will allow the ROV to be stowed below deck.



A larger dockside knuckle-boom crane next to the AUV's dockside carriage. Thick liftarm construction and 3 friction cylinders allow it to hold its position against heavier loads than the deck crane on Norma can handle.



A better look at the hydrophone stringer, winch reel, and A-frame.



Close-up of the winch reel and its starboard handle for manual operation.



Close-up of the A-frame pulley. The climbing holds representing the hydrophones run through the pulley without much trouble, but the coupled end studs representing the stringer floats jump off the pulley now and then.



Finally, a good look at one of the stern drives. The low-drag struts are quite sturdy, and the gears are held solidly in mesh. The inverted-V arrangement of the struts gets the props out of the ship's wake field for reasons I won't go into here.

As configured in these photos, each drive is powered by an M motor controlled by a regular (not V2) IR receiver. The AAA battery box beneath the superstructure contains 6 NiMH rechargeables putting out a combined 7.2V. Modified 2-blade 5.5L "twisted" props (see below) are fitted to the stern drives, which gear up the M motor's shaft speed by 1:5.

This setup results in a top speed of 0.56 m/s, which at 1:120 scale corresponds to a very realistic 12 knots or so. Under these conditions, the M motor's shaft speed, as measured by hand-held laser tachometer, is ~200 RPM, which is ~67% of the motor's no-load speed of ~300 RPM at 7.2V.

A good rule of thumb states that DC motors deliver maximum mechanical power when loaded such that shaft speed falls to 50% of the no-load speed. Since top speed is limited by the motor's maximum mechanical power output, the M motors are running too fast in this configuration and need to be loaded down a bit more.

One way to increase the motor loads is to gear up the stern drives even more, but here we run up against the limited selection of applicable LEGOŽ gears. When I tried this, Norma slowed down, because the next higher overdrive ratio available with a reasonable number of gears (1:8.33) was too high.

Why so big a ratio jump? Because these stern drives have been carefully optimized for adequate length, reasonable weight, and low drag, and I wasn't about to mess that up for an intermediate ratio requiring many more gears.




Props

Props offer another path to increased motor loading, but the limitations here are even more severe. The LEGOŽ Group seems to have some kind of anti-thrust policy when it comes to propellers. Bottom line: LEGOŽ props are useless or close to it in marine applications.



Many LEGOŽ props can't be mounted in a torque-friendly way without resorting to (gasp) glue or tape. Even then, most deliver little or no thrust for lack of diameter, blade angle, blade area, hydrodynamic blade profile, or various combinations thereof.

All of the propellers shown above suffer from inadequate blade angles, and all but the orange one (which has no blade angle at all) lack axle holes.

The large and very expensive wind turbine blades from with LEGOŽ Renewable Energy Add-on Set are the most notable exceptions to these comments. They can't be beat WRT thrust generation in air, but they're useless as boat props by virtue of excessive length and blade area.



For example, the LEGOŽ 3-blade 3L-diameter prop has a decent blade angle, but its slab-like blades are too short and not the least bit hydrodynamic, and its total blade area is far too small to produce meaningful thrust. Running several of them in series doesn't help much. The stab at a ducted prop configuration shown here looked great when fully assembled and added a little thrust, but mostly just added drag.



Lots of boats on YouTube use 2-blade 9L props, either singly or in pairs to form 4-blade 9L props like the one seen here at top left. IMO, the only thing this prop has going for it is its axle hole. Unlike the 3-blade 3L props, the blades are nice and long and have airfoil-like cross-sections, which are essential to efficient thrust generation in both airplane and boat props.

Two- and four-blade 9L props produce a good bit more thrust than 3-blade 3L props, mainly via much greater diameter. However, they're still poor performers by virtue of very shallow blade angles and little total blade area, even in 4-blade configuration.

Prop supports reaching deep enough into the water to fully submerge their large 9L diameters invariably generate a significant amount of appendage drag. The minimum water depth for safe operation is also greatly increased.



The blades on the 3-blade 9L prop and the 4-blade 9L next to it are identical in every way, including the meager blade angles. Interestingly, however, the 3-blade prop manages to deliver a little more thrust with even less blade area (go figure).

Unfortunately, the 3-blade 9L prop has a pin hole rather than an axle hole at its center. You can mount it on a 3L friction pin with bush (as I've done here) and then mount the bush on an axle, but the prop will slip on the pin if you subject it to enough torque to propel a boat like Norma -- or even a small speedboat -- at a reasonable speed.

The only way I know of to keep the 3-blade 9L prop from slipping on its shaft at speed is to (gasp) glue the prop to the 3L bush-pin first, as I've also done here.

If you're beginning to think that props are more complicated than they look, you're on the right track. And if you're beginning to think that I'll stop at nothing to get more thrust, well, you're right there, too.

If you can find an acceptable torque-friendly way to mount it, the best LEGOŽ prop by far is the 2-blade 5.5L (44 mm) "twisted" prop. Two examples are seen here in yellow. It's got more pitch than any other LEGOŽ prop and respectable total and relative blade areas. It also benefits from the fact that 2-blade props are the most efficient, all other things being equal.

Unfortunately, 2-blade 5.5L prop has a very odd center hole that's larger than a Technic pin hole. The hole's also splined inside (to mate with what??) but too small to lock onto a Technic bush. Near as I can tell, the only torque-friendly way to mount this prop on a Technic axle is to (gasp) glue it to 3L friction pin with bush shortened enough to let the bush and prop hub bond directly to each other, as seen here in both cases.

A securely mounted 2-blade 5.5L twisted prop with unmodified blades produces much more thrust than any other LEGOŽ prop -- including the 9L props.

The difference between the two 2-blade 5.5L examples shown is that the one on the left has unmodified slab-like blades, whereas I've hand-sanded the blades of the one on the right into airfoil-like cross-sections. This simple but time-consuming modification greatly improves thrust.

All this means that the modified 2-blade 5.5L twisted prop used in the reference configuration described above is the best I'm going to do WRT optimizing Norma's motor loads and top speed short of a motor change.



One way to gauge the thrust produced by a boat prop is to aim the prop against a wall, hold the boat in place, turn on the power, and see how high the prop wash climbs up the wall. The method's crude, to be sure, but it's useful for rough comparisons. Here, Norma's poised for the test with modified 2-blade 5.5L props mounted.



With the power on now, you can see how high the prop wash rises against the wall of the tub. None of the other props shown in the photo before last can push its prop wash this high up the wall at this distance with an M motor geared up 1:5. Nor do any of them agitate the water to this extent.



Same test with the same props viewed from a different angle. Power off.



Power on.



Another look at the 2-blade 5.5L twisted prop: Totally unmodified at bottom left; mounted but not sanded at top left; both mounted and sanded into a proper blade shape for a propeller at bottom right. For comparison at top right is a black 2-blade 40 mm (5L) non-LEGOŽ RC boat prop glued to a 3L friction pin with bush for mounting on a Technic axle.

When mounted on Norma as configured above, the modified 2-blade 5.5L LEGOŽ and 40 mm RC props deliver comparable top speeds.


Prop walk
The RC props do have one advantage, though. The twisted props are left-handed, whereas the RC props here form a counter-rotating pair, meaning that one is left-handed and the other, right-handed. To produce straight-line motion, counter-rotating props have to be driven in opposite directions.



Mirror-image counter-rotating 55 mm props on Tramontana.

To determine the handedness of a prop, view it from astern while the boat's moving forward away from you. The top of a right-handed prop will spin to the right. Equivalently, determine which end of the hub faces forward, lay the prop on a table with that end down, and place one of the blades at 12 o'clock. If the right edge of that blade is closer to the table than the left edge, it's a right-handed prop.

Since the deeper blades of a prop have more "bite" than the shallower ones at any given moment, a left-handed prop will push the stern of a forward-moving boat to the right, causing the boat to veer to the left.

This effect, known as prop walk, will likewise push the stern of a boat with a right-handed prop to the left. With twin props of the same handedness, prop walk is roughly doubled, whereas with counter-rotating twin props, it's largely cancelled.





The prop walk induced by twin LEGOŽ props of the same handedness is tolerable on Norma, but only because she's rather slow to turn. It can be a big problem on smaller, lighter, more agile speedboats like Trident (upper photo) an even Laverne (lower photo).

Unfortunately, The LEGOŽ Group has never offered counter-rotating prop pairs. Most LEGOŽ props are right-handed, including both 9L props.




Table of features and stats
All measurements taken at rest in fresh water (density 1,000 kg m-3).


Overall dimensions:
424 x 210 x 88 mm (LxWxH) excluding stern drives and antennas

Overall weight:
1.1 kg (2.42 lb)

Construction:

Studded and studless features on a 51x12x6 unitary hull with side bulges (62791c01)

Scale:
Variable, but ~1:120 for hull

Hull type:
Displacement

Hull length at waterline:
380 mm

Draft:
~100 mm

Top speed:
0.56 m/s actual, ~12 knots scale

Froude number:
0.29

Roll stabilization:
Port and starboard sponsons, 2 sealed pneumatic tanks each

Special equipment:

ROV, AUV, knuckle-boom deck crane, hydrophone stringer and reel, fantail A-frame

Propulsion:

Twin stern drives

Propellers:

Twin modified 2-blade 5.5L "twisted" props (4745)

Motors:

2 -- 1 M for each stern drive

Lights:

1 LED pair in bow running lights

IR receiver connections:
2 -- 1 for each motor

Electrical power:

7.2V PF AAA battery box with rechargeable NiMH cells

Modified parts:

Props and shortened friction pins in deck crane and A-frame

Non-LEGOŽ parts:

Gorilla super glue (gasp) to secure the props to 3L Technic pins with bushes for torque-friendly mounting

Credits:

Entirely original MOC




Comments

 I made it 
  October 21, 2014
Quoting jim mcdonough interesting,did you try heating the prop up and manually twisting each blade to increase pitch,also whats the reason for the props to be swung out like that,to get thrust through water you rely on either a kort nozzle to push the thrust in the direction you want to go or the underside of the hullto stop the power going the the suface,bear in mind that is mostly for towing or moving a deep drafted heavy ship,amazing you managed to cram all that into your ship,
Sorry for the long reply. You've raised valid real-world issues that also apply to working LEGO powerboats -- but with some big twists. WRT heat and twist: I'll definitely give that a try if I ever go back to LEGO props. After building this model, I abandoned LEGO props for vastly more efficient 3rd-party counter-rotating props made for RC boats. WRT under-hull and ducted props: The miserable performance of LEGO props has little to do with operating environment -- they're just lousy props. Well-designed props like the RC props I use now direct thrust aft well with no need for external flow guides(think stern drives and outboards on real speedboats). Besides, mounting and powering a working prop =under= a LEGO unitary hull would add a great deal of weight, mechanical complexity, and appendage drag. In the real world, ducted props like Kort nozzles deliver gobs of thrust at low boat speeds but generally lose their advantage at the higher (scaled) speeds intended for this boat. The failed LEGO ducted props shown above might have worked with suitable props and compatible ducts, but the required parts simply don't exist. WRT inverted-V stern drives: Splaying the drive struts outboard has a number of advantages, at least in the LEGO realm. (i) Most importantly, it improves inflow to the props by removing them at least partially from the hull's wake field. When tested against vertical stern drives on this boat and several no-frills speedboats (coming soon), the inverted-V speed advantage was quite noticeable. (ii) Splayed stern drives also improve maneuverability in the absence of working RC rudders. Steering with differential-drive twin screws alone eliminates the big hit in weight, mechanical complexity, and appendage drag that working rudders would entail and makes the boat easier to operate. (iii) I find it easier to minimize stern drive wetted surface area and roughness with this design. In my experience, once you have decent props, drag reduction becomes Job No. 1 in the LEGO powerboat biz -- especially wave drag. (My speedboats all top out at Froude numbers in the 0.40-0.50 range, where most of the total resistance comes from wave-making.) WRT cramming: Way too crammed for my taste. The research vessel part of this boat will soon be moving to a much larger (and faster) 74x18x7 City Lines hull to reduce the crowding and scaling discrepancies seen here.
  October 21, 2014
interesting,did you try heating the prop up and manually twisting each blade to increase pitch,also whats the reason for the props to be swung out like that,to get thrust through water you rely on either a kort nozzle to push the thrust in the direction you want to go or the underside of the hullto stop the power going the the suface,bear in mind that is mostly for towing or moving a deep drafted heavy ship,amazing you managed to cram all that into your ship,
 I made it 
  February 28, 2014
Quoting Matt Bace A good-looking ship with power functions is something you almost never see. Great job on this one!
Matt, coming from a consummate ship builder like you, I consider that the highest of compliments.
 I like it 
  February 27, 2014
A good-looking ship with power functions is something you almost never see. Great job on this one!
 I like it 
  February 24, 2014
beautiful details ! crazy functions on the propellers ;-)!
 
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