Tom,
There are no meaningful relationships to height,width etc that I know of.
I really do not know what you mean by the diffuser effect.
Most everything that Tommy Lee and I learned about specific design parameters we learned emperically.I'll bet between the two of use we have built over 150 test boats.
About "aero dynamics" here is what we did learn.There ain't nothing aerodynamic about a tunnel boat.Tunnel boats are aerodynamic train wrecks.
Back over 15 years ago David Lee [Tommys brother]was commisioned by a big $$$$$ full scale tunnel boat owner to build an aerodynamically slippery full size tunnel for Formula One racing.
Well David hired this very high dollar aeronautical engineer that specialized in aero-dynamics and the engineer designed a boat that was supposed to be slippery in the air.David then had Tommy Lee build a 1/4 scale model of the boat and they took it to a wind tunnel at the Huntsville space center for extensive wind tunnel testing at about $400.00 an hour as I recall.
Well after many many hours and a ton of $$$$$$ ,the short story is a tunnel boat is about areodynamic as a brick.
There aren't enough days left in my life to start a physics class here but there is turbulent flow and dirty eddys all over any tunnel boat.Every place you have a sharp corner or sharp vertical to horizontal intersection you have a aerodynamic nightmare.
Here are some rules of thumb that we do know that does work.
1.Flat sponsons[no dihedral] go fast but don't turn worth a sxxt.Flat sponsons [no dihedral]really lack directional control and react significantly to propeller torque.
2.Narrow tunnels and boats with reduced frontal area are great on SAW boats.
3.If you don't want to run a turn fin,15 degrees on a 2" wide sponson bottom is the minimun dihedral you need to turn the boat.As you increase the diheidral up to say 19 degrees,the boat will turn great but as the dihedral increases straight line speed [mph/kph] decreases.
4.I absolutely disagree with the previous post that rocker in sponsons is put there to make up for a design deficiency.That is total BS.
Full scale tunnel boats use long flat sponson bottoms to turn very sharp.Full scale tunnels make the boat hook to turn.
If you want a model boat that is very user friendly to drive and set-up you put in a bit of rocker.
Long flat wide sponsons are very user unfriendly in model tunnels.To go fast you have to run the boat very nose high and the minute you wet them up the boats speed reduces significantly and the boat hooks.
5.Non trip chines on a properly designed sponson are absolutely useless.In fact they they help the boat "trip" rather than discouraging tripping.
Actually so-called "non-trips" should be called "corner trips" to be exact.
6.Rounded edges on a sponson bottom are usually the kiss of death.
7.Control of the release of water off the bottom of a sponson is the biggest factor to keeping a tunnel boat on the water.
8.Super light weight is not-necessary on a SAW boat.In fact tunnel boats can be too light.
9."Everything" you do on a tunnel boat is a compromise.
I'm tired!!!!
