A Geared Twin Oval Boat

Intlwaters

Help Support Intlwaters:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
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 !
The construction of the jig bore machine is what seperates it from a milling machine. The Moore jig bore, invented in 1924, was named after its inventor Richard F. Moore. It allowed the worlds metal cutting industry to have an additional decimal place of accuracy. This machine when combined with a Heidenhain .000050" digital readout (.000020" resolution) can easily locate holes accurately. Milling machines with .0001" digital readouts (.0002" resolution) would not have this accuracy. Google Moore #3 jig bore.

Jim Allen
 
Hummmmm. The BS is flowing. Let's not destroy this thread

No reply needed

Nails
amen, nails. i know & race with jim. if you've never talked with him, or seen his shop, you are missing a great opportunity/learning experience. super guy, & can walk the walk & talk the talk when it comes to machining process's B) .
 
How's the twin project moving along Jim?
I have many of the key pieces made, engine mount, strut made of 7075-T6, ball & pin universals, carbon fiber cowl, rudder assembly with hardened steel rudder,etc., but there is still a long way to go. I'm about 95% finished with the single engine AB 80 rigger that uses the de-tuned .90 straight away engine.

What takes up a great deal of my time is the research, dyno & lake testing work that's done on new stuff such as tuned pipes, toroidal heads, carburetors, custom spark plugs, stronger crankshafts for gas engines, better connecting rods for gas engines ( 24,000 to 28,000 RPM), etc.

Thanks for asking.

Jim Allen
 
One thing we have found in several model and full scale projects is that speed is often more about propellers than power. We deliberately try to use sucessful existing propellers. In our electric hydro this meant a quick change gear up drive to match the 5000 rpm brushed DC motor to outboard hydro props that turned around 10,000 rpm.

In internal combustion models we found that propeller rpm was limited by the engine so speeds were limited. Zenoah powered boats were held to speeds around 100 mph for years by their peak rpm. Only by seriously increasing the pitch of stock and custom propellers were today's 107 - 108 mpg speeds reached. The GX1 record of 109 mph is purely a result of the higher rpm of the Quickdraw, even though it's well past its power peak. I think even nitro records are starting to be limited by maximum engine rpm.

Electrics are free from this limitation. The question is now what rpm gives the best efficiency. My feeling is that a pitch to diameter ratio of 2 or less should be best even though we ran much more than this in our latest SAW record boats. There is no question that the propeller and its shaft are a major part of a boat's drag, so gearing two engines together should be better than conventional twins. Gearing up means drive line drag gets magnified by the gear ratio. Our first attempts at model gear up drives was not successful. At this point I think a straight or slightly bent solid shaft suported in ball bearings is needed. If engines can turn 28,000 rpm with good power I think the nitro SAW record can be beaten with a modified 2170 and no gear up. The ultimate model record of over 140 mph will take a gear up drive.

Lohring Miller
 

Latest posts

Back
Top