An old favourite from my hovercraft phase. Runs really well on land and especially water. Although no reverse, it will auto-rotate on the hover, so when pointing in the desired direction on with the propulsion with the brushless motor and away she flies. Realistic in operation. Looking a bit work worn now. Could do with up-dating with Lipo batteries which would make it even lighter. Seen here with lift motor running with skirt inflated. Steering interesting, with twin air rudders. Must get some videos of the action.
I dont uses mixes, but do use exponential and rates (spektrum dx6i) with my twin screw brushless 4 foot fireboat. When at speed rates on, then it turns nicer, no roll, when going slow rates off so turns are sharper, if that makes sense. Mixing the throttles.. interesting not thought of that, but it will lose power/speed. We use mixing on planes for taxiing, particularly on water, but once airborne its off. My avatar has this as the cheapo motors just wont balance so it compensates for this on the water. With the boat its easier to control with rudder input. I like the thinking though!😁
From what I have seen of Airboats (including several in Florida many moons ago 🤔) two rudders are predominant. Offset Twin rudders seem to be smaller, not so long front to back and single rudders huge and seem to have been used only on very early versions of airboats. Must be a reason why they evolved to slimmer twin rudders. My guess is better response with less braking effect and consequent loss of speed in turns and / or less effect from cross-winds. Whatever, have fun with it, but watch out for the alligators 😲😉 Cheers Doug 😎 PS can highly recommend a visit to an alligator farm 😲😲
I would have thought that, every thing else being the same, 2 rudders will probably, maybe, give twice the turning effort, possibly. Does the position of the rudder(s) in relation to the thrust of the prop affect the effectiveness of the rudder though? A single rudder immediately behind the centre line of the prop will have the max air flow at the top and bottom of the rudder blade, so presumably behaves differently to twin rudders on either side of the centre line where the max thrust would be in the central part of the blade. (I think!) The other option is of course suck it and see, and change it if needed. Hard to believe I know, but I am not an aerodynamicist! Chris
[Score: 9/10] 30"/4000g Aeronaut Pilot LKBM 04 Capable of 12mph and a runtime of 50mins Twin Propellors (4 Blade 30mm) Direct Drive to a Graupner 600 speed (4 Blade) Powered by NiMH (8.4v) 5Amp/h Batteries Controlled Through MTroniks (40Amps) ESC - Comments: Took me 7 months to build. Has twin esc so I can control each prop individually, twin rudders, a sound system, horn, working anchor windlass, 4 individually controlled lighting setups (cab / dashboard lighting, navigation, pilot and search lights), spinning radar etc. She gets up well on a plane, probably a bit over powered!
Hi Mate and welcome to the forum, (mad as hatters!!!) I have built the 46" and before you get to far in you need to decide if your having single or twin motors, and rudders, that way you dont fall foul of bulkheads, and shaft mountings, mine has Graupner 700bb motors on 3s lipos, but i am up-grading them to brushless soon, have the new ESC,s and the motors are on order. Great model to build and sail, attracts a lot of attention. Mark
Props by ChrisG Chief Petty Officer Posted: 2 months ago
Hello Doug Thanks for all of the useful information and yes it is a 'Black Art' and I have been party to some heated debates regarding props on large passenger carrying boats. I was highly amused by the link to 'Raboesh' which if it wasn't a Chinese company should have been. The model I am building is a Rother class lifeboat which will have twin props and a single rudder and I have read that due to the limited swing of the rudder the turning circle of the boat is much improved by having independently powered motors. Not at that stage yet still early days of the build. Thanks again and best regards Chris G
Hi Roy, Happy New Year 😉 Twin screw rotation is case of 'Horses for courses'! It's a Black Art and much depends on the hull shape, especially at the stern and the orientation of the rudders to the shaft lines. What you write is correct for slow, short fat displacement hulls, like tugs and rig supply ships etc needing good slow speed manoeuvrability. Especially those with one rudder per shaft. For long thin hulls (naval ships) and deep V and planing hulls (Fast launches and power boats etc) inboard turning screws are preferred to concentrate the thrust behind the centreline of the hull instead of dissipating it out into the open water. It also concentrates the thrust onto the rudder when only one rudder is fitted on the centreline. Outboard turning screws tend to push the stern up and bow down. Inboard turning tends to suck the stern down and raise the bow. So making planing easier. You only made one mistake in your description: "when using the props to assist a turn, i.e one prop turning clockwise and the other anti-clockwise". The props turn in opposite directions when both are running ahead, or both astern. When turning, one ahead and one astern they then both turn the same way thus producing the combined side thrust. I was advised to use inboard turning props on my H class destroyer (twin screws single rudder) by an ex RN Captain I met at the local lake here in Munich about 30 years ago! @ Chris: What type of boat / ship are you building? Cheers Doug 😎
[Score: 8/10] 35"/2700g ILLINI LOYAL Capable of 12mph and a runtime of 60mins Twin Propellors (5 Blade 50mm) Direct Drive to a 775 JOHNSON TYPE (5 Blade) Powered by NiMH (8.4v) 3Amp/h Batteries Controlled Through DIMART 320A FAN-COOLED (15Amps) ESC - Comments: ANOTHER ON THE WAYS: SALVAGED DUMAS ABS HYDRODYNE HULL, 35 X 10 X 2" ORIGINALLY IN THE AMERICAN BEAUTY KIT. MY INTENT IS TO SCRATCH BUILD FROM THIS HULL, A SINGLE-DECK TWIN SCREW LINEHAUL TOWBOAT WITH A FUNCTIONING TELESCOPING PILOTHOUSE. THEY ARE COMMON ON THE UPPER ILLINOIS RIVER WHERE THERE ARE FIXED OVERPASSES OR LOW OBSTRUCTIONS SPANNING THE WATERWAY. THE DES PLAINES AND CALUMET RIVERS IN THE CHICAGO AREA ALSO HARBOR THESE PUSHBOATS. THE PLAN IS TO KEEP HER LIGHT WITH A LOW CG, BUT POWERFUL ENOUGH TO PUSH SOME SCALE WEIGHT; I RECKON 775 MOTORS WITH 50MM 5-BLADE WHEELS WILL SUFFICE. THIS BOAT WILL BE STEERED WITH STANDARD RUDDERS, NO FLANKING RUDDERS, BECAUSE I WANT TO KEEP IT SIMPLE. (K.I.S.S.) I AM STILL BRAINSTORMING THE SYSTEM FOR RAISING/LOWERING THE PILOTHOUSE; POSSIBLY A SERVO WINCH & CABLE OR LINEAR SERVO. A PNEUMATIC RIG IS ALSO A POSSIBILITY I RECKON. SHE WILL BE WEARING THE ORANGE TRIM AND MIDNIGHT BLUE PAINT SCHEME OF MY SHOP-ILLINIWEK MARINE SCALE SHIPYARD. I USE LIGHTHOUSE LED's & MINI SWITCHES FROM THE SEATTLE AREA EXCLUSIVELY, 9V, 3MM. HARBOR MODELS 1.5V WORKING RADAR & MAYBE A 6V WORKING DECK CAPSTAN WILL BE ADDED. SHE IS MY 5TH ADDITION TO THE ILLINIWEK MARINE FLEET, AND WILL OF COURSE PUSH AHEAD THE MATCHING BARGES. GO FIGHTING ILLINI!
Does any one have experience of models with twin motors in the Fairey Huntsman and Swordsman? (Or any boat) Would like what size the model was - what motor(s) were used and prop sizes, and was there any 'mixing' of motor control with rudder control.
Hi Neil, You read too much!! 😉 Before you give yourself the work of altering the rudders see how she performs with the twin ESC & rudder mixer. For slow manoeuvring, especially in reverse, I'm pretty sure the rudders will be almost irrelevant, apart of course for controlling the mixer and hence motors. If you use the P94 in Mode 3 you can spin the boat on it's axis😉 The guys with small rudders in front of the props most likely don't have twin ESCs and a mixer. Two maxims: Why complicated when simple works! If it ain't broke don't fix it! I intend to 'suck it and see' first. Whatever you do have fun with it, but don't 'over engineer', cheers Doug 😎
[Score: 9/10] 35"/4500g CG-40564 Capable of 15mph and a runtime of 45mins Twin Propellors (4 Blade 50mm) Direct Drive to a 775 JOHNSON-TYPE 6-12V (4 Blade) Powered by NiMH (8.4v) 3Amp/h Batteries Controlled Through HOBBYWING (15Amps) ESC - Comments: DUMAS 1:14 USCG 40' UTB. REPRESENTING US COAST GUARD UTILITY BOAT CG-40564, WHICH CAPSIZED DURING A RESCUE ATTEMPT ON THE COLUMBIA RIVER BAR ON 17 JAN 1961. HER CREW WAS FORTUNATELY RESCUED. SHE WAS ASSISTING CG-52301, A 52' TYPE F WOODEN MLB, WHICH FOUNDERED WITH THE LOSS OF ALL HANDS. IT REMAINS THE WORST SMALL BOAT RESCUE DISASTER IN COAST GUARD HISTORY. THIS IS AN UNUSUAL SCALE BALSA PLANK-ON, COVERED BY 2 OZ FIBERGLASS. I USED MINWAX POLYURETHANE FOR AN ALTERNATE TO RESIN, WHICH TURNED OUT WELL, AND CAN BE DONE WITH MINIMAL VENTILATION. WITH BIRCH PLY DECK & CABINS, 1/8" SCRIBED SHEATHING COVERS THE DECK BOW TO STERN AND MAHOGANY TRIM LEFTOVER FROM ANOTHER DUMAS KIT IN MY SCALE SHIPYARD. STOCK D/C FITTINGS WITH SOME SUPPLEMENTAL PREMADE AND HANDMADE ITEMS. SHE FEATURES TWIN RABOESCH 4-BLADE WIDE FLUKE WHEELS AND MATCHING RUDDERS; WORKING HATCHES WITH STOWAGE AREA FOR ANCHOR & TOWLINE, LIGHTHOUSE 9V LED NAV LIGHTS AND FLASHING LED LAW ENFORCEMENT BLUE LIGHT (RC CONTROLLED). I'M ADDING A MOUNT FOR A SCALE BROWNING M2 50 CAL THAT I WAS ABLE TO PRODUCE ON MY 3D PRINTER. THAT'S AN ADVENTURE IN ITSELF. THIS WAS MY FIRST REAL PLANK ON BULKHEAD, AND BALSAWOOD CAN BE A LIL TRICKY, BUT WILL ALWAYS BE THE STANDARD OF WHICH I COMPARE ALL MY SUBSEQUENT BUILDS. MY FATHER BUILT RC AIRCRAFT, AND ALWAYS PREACHED THAT YOU SHOULD OVERBUILD IN ORDER TO SURVIVE A CRACK-UP AND FLY ANOTHER DAY! THAT'S MY CREED WITH BOATS. OVERBUILD!!! THANK YOU DAD! BTW-FYI-MR. ARNOLD PALMER WAS A US COAST GUARDSMAN (YM3) 1950-53
Dave, mtroinks have switches, so maybe when it had the pair of vipers, they where for the esc's? I would disconnect the red signal wire from the receiver end on the "y" harness, and use a separate 6v receiver supply, I have a number of twin screw setups, with a cheap battery monitor, if the esc fails, you still at least have rudder control, if the feed esc goes down, power is lost to the receiver, ensure you have a failsafe set at zero throttle. With spectrum, its usually automatic, unless...... you have reversed the throttle! that means you throttle will go wide open in event of esc failure. Easy test, on the bench, all set up to go, make sure all the props etc are clear, just turn your transmitter off, see what happens, nothing should! Have you done the range test? you might have been lucky having it go in reverse, Also, the gunner that is holding the esc wire, is he wearing a Teflon glove? His hand might get hot
I wanted total motor control on my large, heavy twin screw harbour tug. The rudder is pretty useless serving only as a sort of trim tab so I went the simple route: Each (brushed) motor has its own ESC and independent power supply so left and right Tx sticks control their appropriate motor. By doing this I am able to have one full ahead, the other full astern, to turn on the proverbial sixpence or for slick docking alongside