Friday, October 19, 2018: After many years, the Nautilus Minisub restoration is high on the priorities list again. I've posted a page (Refurbishing4) documenting my progress, but nothing detailing the process; so today I've started this blog.
BACKGROUND: We emptied the shop and laid down an epoxy floor; no cement dust in there anymore. Got all the tools and equipment set up for the car, motorcycle, diving helmet, and submarine projects.
LEMONS TO LEMONADE: Having to order parts and special tools by mail is slow but that also gives me time to refine the design. This week I came up with a way to locate the motor in a better part of the hull and do away with the 36" interconnecting shaft, pillow block bearings, and couplers.
THE PLAN: (1) bench-test the motor; (2) watertank test some propellers; (3) remove most of the sheet metal and framing from the sub's superstructure; (4) remove the top of the cabin; (5) make an access hatch in the roof of the pressure hull aft of the passenger compartment; (6) install the drivetrain, dive plane / rudder actuators, and aft ballast valve actuators, et al; (7) install all other pilot controls and systems; (8) make and install an improved pilot access hatch with a 1/10th scale wheelhouse structure attached; (9) reinstall all original exterior framing, sheet metal, and viewports to the hull and superstructure; (10) check weight and balance; (11) proceed to Float Test #10.
Once she's operational again, we'll experiment to find the right propeller; then do the scale exterior detailing to replicate what's seen in the movie.
At 48 volts, the ME1117 motor cruises at 6hp and sprints at 19hp. I've chosen two nine-inch propellers; a 7" and a 10" pitch. The 7" will be quicker off the line but the 10" will be faster at WOT. If we only spin the 7" at 2500 rpm, with a 30% slip that's a boat speed of 11.6 mph; 16.6 mph with the 10" pitch. She'd cruise between 4.6 and 6.6 mph turning 1,000 rpm.
Those are calculated estimates of potential, but (1) the unloaded motor is capable of 4000 rpm; and (2) a submarine is not limited by the bow wave which restricts top speed in displacement hulls; so we're optimistic. Optimal performance with minimal cavitation is the goal.
A more radical prop and/or more powerful motor would be an easy swap; but anything close to those speeds would be fast enough for our purposes.
Tuesday, November 06, 2018: As of today we have the four propellers we want to test. A 9 X 7, 9 X 10, 10-1/4 X 10, and a four-bladed 12 X 12. This will show us how the motor performs with props designed for its horsepower rating, and also how it handles larger, more radical propellers.
For submarines, the name of the game is maximum thrust for minimal cavitation. That means large, big-bite props turning slowly. The four blade bronze 12 X 12 will show us how she handles a big load with direct-drive; should punch out of the hole nicely but that won't have the highest top speed.
Eventually I'll want a five-bladed hammerhead prop as seen on the Disney Nautilus. I actually went against my nature and looked into a 3D printed prop but the price was a ripoff and after I thought about it a "Polaroid part" on my handmade submarine would really suck. So I'll cut it out of steel, bend the blades to the desired pitch and stress relieve them, do some contouring, and adapt it with a hub. Simple. I will have a substantial pitch angle per blade so I'll need to gear that one down 2 to 1. Fortunately, ready-made gearboxes for this motor are available.
Sunday, December 02, 2018: Ordered a 2:1 GEAR REDUCTION for the drivetrain. Also, hand-fabricated an adapter bushing to mate the metric prop shaft to our SAE 12X12 propeller. Ready to assemble for bench testing.
Monday, December 03, 2018: I've been planning to run the driveshaft through-hull bearing box from a Kawasaki JS-550 jetski in the submarine because (1) it's watertight, (2) can turn at 6,000 rpm, and (3) I have one. But it's uncertain what the box's depth capability might be and it's probably not more than one additional atmosphere.
So last night I designed an improvement to the mount so that now when the shaft leaves the pressure hull it enters a watertight pressure-compensated chamber before reaching the propeller. With two watertight bearings fore and aft in that secondary chamber; no water should reach the JS-550 box and no additional (depth compensating) air pressure should enter the pressure hull.
I'm happy with how the design turned out but the best part of this is, those watertight bearings usually sell for about $120 each plus shipping, and last night I bought two of them for $40 each INCLUDING free Priority Mail to Hawaii. So basically I got those $120 bearings for $25 apiece. Love that eBay! J
With jobs like this; first I have to recognize the problem, then invent a way to solve it. THEN I have to design the adaptation in such a way that it can be manufactured, installed, serviced, and removed easily if needs be. Did all that last night and the bearings should be here in a week. Very happy with the progress we're making so far.
Tuesday, December 04, 2018: BENCH TESTS, BOAT SPEED, ETC.
Apparently, those who say my Nautilus Minisub is limited by factors that govern displacement hull speed are unaware of the venerable Mark 14 torpedo.
Depending on which online hull speed calculator is used; at 20.5 feet in length, it should only be able to reach a top speed of 5.9 to 6.1 knots and no more.
Surprise! The Mark 14 torpedo can travel at 31 knots for about 8,000 meters; or 46 knots for half that distance.
According to those same online hull speed calculators, the Nautilus Minisub's top speed is between 5.9 and 6.1 mph. But as I've just shown: those calculators don't work with submersibles.
So what will she really do? We're about to find out.
This week I will assemble and test the Nautilus' new electric drivetrain; on the bench and in a water tank.
According to the technician's printout that came with this motor, it has already attained 4500 rpm on the bench unloaded, and is capable of about 5,000 rpm WOT at 48 volts.
Power output is rated at about 6 hp sustained and 18 hp during one minute sprints.
This same motor can drive a full-sized motorcycle at more than 50 mph so it has plenty of torque.
My first tests will be direct drive, 1:1 ratio, coupled to a bearing-supported driveshaft and 12X12" four-bladed bronze propeller.
Calculated with a 30% prop slip, all I need to hit 6 mph is 754 rpm.
If I cruise at 1000 rpm that's a prop speed of 8.0 mph.
And if all I get at top end is 2000 rpm out of the prop, that's still 15.9 mph and in this boat that will be scary.
If 2000 rpm is a strain in direct drive, I'll use a 2:1 gear reduction to get that same prop rpm while the motor spins at a cooler and more efficient 4,000 rpm.
(In effect, it's kind of like shifting gears in a car; where the transmission gearing reduces the load on the engine and enables it to operate more freely.)
What will the actual RPM be with the propeller submerged? I'm within days of finding out and the anticipation is driving me nuts.
Film at eleven. J
Monday, January 14, 2019: BATTERIES! FINALLY!! YIP-EEEEEE!!!
No, I haven't bench-tested the motor yet. Schnit happens. Priorities, interruptions, holidays, etc. I did get the right bearings for the propeller support and made other advances; but BATTERIES are what's been delaying the motor tests.
Remember: Vulcania is a volcanic island in the Pacific ocean; sometimes, supply is difficult. The companies with good prices wouldn't ship to Hawaii and their CSR's were literally too stupid to comprehend why they could and should.
Long story short; at the last moment before I was gonna have Doc receive the batteries and ship 'em to me here (bless your heart, brother) I found a company that had them at a low price with free fast shipping to Hawaii. As I write, I have the four-battery pack enroute via Priority Mail; first one arrives today and the last two by the end of the week or thereabouts.
So now we have a 48-volt 35 amp/hour battery pack that weighs in at about 90 pounds. That's what we'll run for drivetrain bench tests and open water proving tests. If I want to double the amp hours, I can mount a second pack; they're not very big and I can fit it into CG.
Free shipping deducted, I'm getting these for about $55 per battery and that's rock bottom in today's market. Battery Bill wants exactly twice that for items stocked here in Hawaii. But they don't have enough of them and what they do have has been sitting on a shelf for a long time. So it's like I bought all four batteries for $220 plus shipping. I scored.
Of course, I could pay about five times more and go to a lithium pack but in this application the weight savings aren't needed so the extra expense and complexity of the lithium battery is redundant.
These are deep cycle SLA batteries intended for the demands imparted by motorized wheel chairs, trolling motors, and the like. Not a starting battery, per se. This is the right kind of battery for the submarine.
I've been wondering what kind of Cold Cranking Amps these 12V-35AH batteries put out. I saw a report where actual tests put that value at 650CCA. That gives us an idea how hard these puppies will crank at WOT, and 650 is pretty respectable; what you'd expect out of a physically larger battery intended for heavy duty use; starting a large V8 engine as in a truck or the like.
According to the online info specs: the ME1117 draws 120 amps continuous and 220 amps peak for 1 minute. With the 35AH pack, that's 48 volts for a maximum of 17.5 minutes; or 9.54 minutes of 1 minute sprints.
Actual endurance will vary because (1) I'm not going to suck the batteries flat; and (2) when I'm just maneuvering I'll be using way less than continuous (cruise) power.
We'll know for sure what the numbers turn out to be when we bench test it; soon, now that the batteries are in the mail. But looking at these numbers and considering the actual energy demands test operations will put on the pack; it looks like we'll get much better performance and endurance than we had in 1991.
P.S. I just rechecked the ME1117 info page online and it says 80 amps continuous; not 120. Both values are listed without any explanation, so that's how I got it mixed up. But if that's accurate then she'll cruise at about 6 hp for 26.25 minutes; not the 17.5 minutes I mentioned above. Even better.
So if we're cruising at about 8 mph, with the 12V-35AH SLA battery pack, I should be able to travel about 3.5 miles and still ram a ship. Double that distance if I drive slower. LOL!
And again, I can double that with a second SLA pack. But considering the mission this boat is built for; that oughta do it.
P.S.S. WAIT! It's even better than that! I just checked the dynoplot printout and at 1000 rpm the unloaded motor is only drawing 29 amps. Factoring drag, etc; let's say it takes 35 amps to turn our direct-drive propeller 1,000 rpm for a cruise speed of 8 mph. That's an hour endurance at cruise speed and a range of eight statute miles. And that should be more than sufficient for our purposes.
Looking better all the time.
BUT WAIT! THERE'S STILL MORE!
Let's say our one minute "ramming speed" at WOT is 16 mph. That's 1408 feet per minute; about 470 yards; almost five times the length of a football field.
(In scale, that would be like the real Nautilus travelling almost 2.7 miles at top speed on an attack run.)
If we take it easy on the motor and limit the NautMini's ramming runs to 100 yards, she'll cover the length of a football field in about 12 seconds.
And with about 9-1/2 minutes of ramming sprints available, she is easily capable of more than 40 such 100-yard ramming runs per battery charging cycle.
And we can calculate an estimated maneuvering speed and endurance, too. The unloaded motor draws 10 amps at 500 rpm; so let's guess we can get 500 rpm prop speed out of twelve amps. That's almost three hours maneuvering at 4 mph; covering a distance of nearly 12 miles.
At about 1/10th scale, if we propel the Nautilus Minisub at a speed of 16 miles per hour; that's like a full-sized Nautilus traveling at about 160 mph and of course that's ridiculous.
An actual speed of five to six mph should be all the NautMini needs to mimic the velocity of the full-sized Nautilus at ramming speed; not to create a realistic bow wave; but to move realistically in terms of scale distance travelled.
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