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.