A Geared Twin Oval Boat

[Jim Allen]

Since moving to North Carolina & finding several running sites such as the Charleston Model Boat Club Site, Falls Lake & City Lake Park Lake, I have decided to complete this project. When my first geared twin was built, the only usable propeller was an Octura 2170 (6.500" leading edge pitch X 9.000" trailing edge pitch X 2.750" dia). Presently there are many propellers available such as Octura's 2175-2 blade & Abc 3020-3 blades that can use the HP & torque available at the prop shaft.

CMD's twin hull has a total length of 46" X a 19" spread inside the sponsons. The 1 to 1 gear ratio used doubles the HP & the torque while the engine RPM's remain the same. With an all up weight of 16 lbs; approximately 14 HP; 460 in ozs of torque; & 28,000+ rpm at the prop, the original boat was very fast & very stable.

The gears, which are AGMA class #12 quality have been throughly tested at 32,000+ RPM with no problems.They are made of the same type of pre-hardened material as the gears used in John Bridge's "Lead Sled" & Ron Walker's "Black Rushin" hydros. The gears require no lubrication & run exposed. The engines used are the same reliable .90 cu in engines I used in the straight away boat. All other parts, including the ball & pin universals, solid titanium drive shafts, hardened steel rudder & skid fin, engine mounting system, the engines, pipes, carburetors, etc., have been throughly tested. G-10 fiber glass sheets, carbon fibre mat & cloth will be used through out the hull's construction.

http://gallery.intlw...x.php?cat=10141; page two; non-reversed geared twins; upper lefthand corner of the screen

Jim Allen

 

[Buckshot]

I'm looking forward to watching your progress Mr. Allen.

 

[SayMikey]

A guy used to come to a few races here with a twin geared. He said once in a while a tooth would spit out, Id shroud them from causing injury and any thing getting into them... Wish I could remember his name

 

[RodneyPierce]

Same here! Cant wait to see more!

 

[Al Hobbs]

Years ago, I watched Jim Whitlatch run twin OPS 60 engines geared to one prop. The hardened gears were exposed and had to be greased every run. When the engines were running, a film of grease was thrown into the air.

Jim set NAMBA speed records with this set up in a Wing Ding rigger.

Three years ago Jim stopped by the NAMBA Nats to say hello and he had the gear and engine assembly for sale. I bought them because they are a piece of model boating histroy.

Jim, I think it is special that you are putting this project together. I look forward to hearing how it goes for you and I would really like to see it run.

Al Hobbs

 

[Jim Allen]

A guy used to come to a few races here with a twin geared. He said once in a while a tooth would spit out, Id shroud them from causing injury and any thing getting into them... Wish I could remember his name

Many people have attempted to build a geared twin hydro. Some people used Boston gears that were arrow case hardened. Some used various types of bronze alloys combined with linen based phenolics. None of these types were successful. The gears must be top hobbed with carbide cutters & are made of AISI-4340 (certified un-leaded steel). The hardening & tempering to 45 Rc must also be certified. The gears are 20 pitch; 20 degree pressure angle; 30 teeth; 1.5" pitch diameter. They are .0003" tooth to tooth with .0005" total composite. The front ends of the engines used are full hard AISI 0-1 tool steel with the IDs & ODs of the front ends ground at the same time to insure concentricity. This ensures the correct alignment in both axes when they are inserted in their jig bored holes in the engine mount. No gear chipping or wear has been found if this procedure is followed.

Jim Allen

 

[Jerry Dunlap]

I saw John Bridge's "Lead Sled" back in 1974 in his basement in Detroit. He was quite a guy and his wife, Pat, was great. John and a couple of the guy's in the Detroit model boat club picked me up at the airport and forced me to drink beer and eat pizza.

Twins are definitely cool.

JD

 

[Tim_Duggan]

I have always loved looking at the photo's of your craft Mr. Allen. Would like to hear them running some day if video is possible!

Given the massive HP figure and also the prop selection constraints, would it be viable to sacrifice a little prop torque & alter the gear ratio ever so slightly to overdrive the prop and spin a wider range of propellers at an even higher prop rpm than 28K?

If starting via the centre gear, this propshaft overdrive would act as an underdrive to the engines when starting also.

Tim

 

[Terry Keeley]

Very, very impressive Jim as always, man I'd love to see this run...

Ron Walker came over to Flint quite a few years ago and ran the "Black Rushin", man what a sound!

 

[Bob Morton]

Hi Jim,

Great Project as always,maybe you can race it at the 2012 Nats. ( -_- ).

Bob

 

[Jim Allen]

"Given the massive HP figure and also the prop selection constraints, would it be viable to sacrifice a little prop torque & alter the gear ratio ever so slightly to overdrive the prop and spin a wider range of propellers at an even higher prop rpm than 28K?"

Most of the original geared twins were over driven 25 to 50 percent. With a 2 to 3 ratio, engines running at 20,000 RPM could give a prop shaft speed of 30,000 RPM. Doing this increased prop shaft RPM but decreased the prop shaft torque & HP. There is no reason for me to do this since I have developed completely reliable engines capable of 32,000 RPM. These boats must use solid drive shafts with ball & pin type universals. The units made by Octura Models could not survive & if one engine broke its aluminum rod, it took out the other engine as well.

The geared setups built by Jim Whitlatch, Earl Mundt, Ron Brounshidle, Ron Walker & others were built this way. Some had enclosed gear boxes & engines reversed to give left hand prop rotation. Jim Whitlatch's geared set up when mounted in Del Parks hydro named "The Rattler" became the first R/C boat to exceed 65 MPH, setting a 1/16 mile record in 1970 of 66.765 MPH, with a one way pass of 68.98 MPH. Ron walker's boat made an official pass of 100 MPH, but never duplicated the run again.

I started on this project in 1988 & have solved all of the problems these early boats had. I take my hat off to all of the original developers of geared twin boats & I thank all who have shared the valuable knowledge they gained. Many thanks to Ron Walker, John Bridge, Gerry Betke, Tom Hyner, Ed kalfus & others.

Jim Allen

 

[Charles Perdue]

Mr. Jim. looking forward to hearing them AND seeing them run. Be sure to get some videos. I have been wanting to try twin 45's with a geared or gear belt setup.

Charles

 

[Tom Foley]

Awesome Jim as usual ! can't wait for the Hi Def videos ! Now will it be electric or rope start !!

 

[Jim Allen]

"Now will it be electric or rope start !! "

On the first boat I did use the rope starter. After converting everything to the Mariner S-650 starter, running on 19.2 volts (thanks Mic), I don't think I will be using the rope to start anything. 600 in ozs of torque at 4,000+ RPM will start anything I'm going to use. All belt breaking & belt wear problems have been eliminated with the use of Gates Truflex 20" V belts (2L200).

Jim Allen

 

[Jim Allen]

Mr. Jim. looking forward to hearing them AND seeing them run. Be sure to get some videos. I have been wanting to try twin 45's with a geared or gear belt setup.

Charles

Mr. charles,

Do not be timid about trying a geared twin. The critical things to watch out for are the alignment in two axes of the three gears to keep from having to crown shave them & the gear mesh. Gears that are running at these speeds will destroy themselves if the mesh is to tight. If the mesh is to loose they will just make a lot of noise. I have two master gears, one that is .0002" over & one that is .0002" under the nominal size to determine if the gear mesh is correct.

Spur gears have no axial thrust component & they can operate at 98%+ efficiency. (Dudley's gear handbook)

Jim Allen

 

[Jeff Schindler]

Mr. Jim. looking forward to hearing them AND seeing them run. Be sure to get some videos. I have been wanting to try twin 45's with a geared or gear belt setup.

Charles

Mr. charles,

Do not be timid about trying a geared twin. The critical things to watch out for are the alignment in two axes of the three gears to keep from having to crown shave them & the gear mesh. Gears that are running at these speeds will destroy themselves if the mesh is to tight. If the mesh is to loose they will just make a lot of noise. I have two master gears, one that is .0002" over & one that is .0002" under the nominal size to determine if the gear mesh is correct.

Spur gears have no axial thrust component & they can operate at 98%+ efficiency. (Dudley's gear handbook)

Jim Allen

Jim,

Like all, I admire your work! I am scratching my head though as to the 0.0002" under and over size. Is the based on the ground outside diameter, or the teeth profiles? I would think the proper gear mesh on the pitch diameters would leave substantial clearance between the outer tooth diameter and the minor diameter of the mating gear.

I too would like to try this someday with rear exhaust .21's because you would not need to change the rotation, and have the pipes come cleanly out the back

 

[Dasboatman]

"...John and a couple of the guy's in the Detroit model boat club picked me up at the airport and forced me to drink beer and eat pizza. "

Hey JD,

Yeah, Uh Huh!!! Drug him, clawing and screaming out of the airpot...........................???

Here are a couple old pics that might look familiar to you JD. CHEERS !!! Bob

 

[Jim Allen]

"I am scratching my head though as to the 0.0002" under and over size. Is the based on the ground outside diameter, or the teeth profiles?"

The measurement is taken at the pitch diameter using the wire method. The value of the measurement over the pins will tell when the pitch diameter is correct. The measurment has no allowance for backlash. The center distance between any two gears is set at a plus .0002" distance. This is why the engine mounting block was jig bored to an accuracy of .00005".

Jim Allen

 

[Tom Foley]

Jim , could you please give a quick explanation of the process of jig boring VS just boring it on a mill ? I have always wondered about the specifics of this process . Thanks !

 

[Derret]

The BS is flowing now.....