Tunnel Handling Question (video included!)

[Ben_Sorkin]

Hi all!

My Uncle and I built a small tunnel last year and I just recently got it all rigged up. It's running the aquacraft 1800kv motor with a swordfish 120A esc on 3-4s Lipo.

Right now it is running a 2 blade 47mm glass filled prop (same prop with 3 blades runs a little better). It runs up to about half throttle nicely, however anything after that and it wants to barrel roll clockwise (looking at the stern). I am fairly confident this is a result of prop torque, so I figured I would try a smaller prop. With a 40mm 2 blade glass prop, I can pull the trigger all the way with a 4s pack and all I get is cavitation.

Any suggestions?!

https://www.youtube.com/watch?v=bjJY4VrqS_0

Many thanks,
Ben

[Rumdog]

run 4s, with the 40mm prop. And ditch the glass filled prop for at least a CNC aluminum prop, or better yet a beryllium/copper.

[HTVboats]

On 4S the starter props for a "spec tunnel" I would recommend an M440 Octura or Grimracer 42X55. Next question is what lower unit are you running? And what size tunnel boat dimentions, brand? Plus you are turning left hand corners with a left hand prop which turns better right as prop torque lifts the left side.
Mic

[Ben_Sorkin]

On 4S the starter props for a "spec tunnel" I would recommend an M440 Octura or Grimracer 42X55. Next question is what lower unit are you running? And what size tunnel boat dimentions, brand? Plus you are turning left hand corners with a left hand prop which turns better right as prop torque lifts the left side.
Mic

Thank you for the reply! I'm actually not running a lower unit, it's set up with a stuffing tube/rudder assembly.
Specs: 19 inches physical length, 7.5 inch beam, 3.25 inch tunnel width. See pictures:
photo1.jpg photo2.jpg photo3.jpg photo4.jpg


-sorry, some are rotated

[forescott]

hmm, 19 inches in length with a 47 mm prop. That may be your problem

[grsboats]

Hey Ben nice Project .As you do not have prop adjustments I would suggest to try a smaller prop than the 447.Also your water pick up is causing lot of drag submerged.Anyway still doing tests and have fun...this is the main purpose of this hobby.Gill

[BHChieftain]

I have a 29" woodstuff tunnel hull with an OS Max lower, it runs great for sports running on an m440 (Ul1 2030kv, 60A AQ ESC, 4S ). Some folks put an m445 on it, but you would need a bigger ESC for that.

Chief

[Ben_Sorkin]

Thanks for the replies guys!

Maybe I'll switch up the water pickup system to something with less drag.

As for props, the 40 mm is definitely too small to get it up on plane, and the 47 mm is too large and creates too much of a prop torque effect.

I'm thinking about getting a Graupner K Series 42mm to see if that will get it on plane and not cause too much prop torque. Do most tunnels run submerged props or surface piercing props? Do you guys think I should be looking at three blade props considering it's a surface setup?

-Ben

[steveo]

Try with the smaller 40mm carbon prop with the strut bottom dead level with the sponsons which is typical for a cat/tunnel. For me it seem this size hull is over powered it may still twist at higher rpm with the narrow width

[steveo]

Ok i see u cant adjust the strut