Tunnel hulls

[Brenton Harrington]

need help with adjusting the outboard motor .How to mount the motor to the right height any suggestions.

 

[MarkTanski]

I start out prop center a little below the sponsons, depends on so many things in a tunnel though, power, prop, hull, balance.

It's a balancing act between CG, prop depth, prop angle, just a matter of keeping notes and doing lots of testing until it runs nicely aired out with minimal bobbing.

Never seen two run the exact same setup even if they are the same hull. CLose but not the same.

Make one change at a time, run it and see how it goes. If you make multiple changes at once you never know what works or doesn't.

 

[lohring]

It very much depends on the prop and hull. We have been testing 7.5 nitro tunnels (the Leecraft XT-460) with electric power plants and found that they need a very different setup than with the nitro engines. If you run the prop deep on a nitro boat, the boat runs less loose. The same setting on an electric tunnel torques the right sponson unto the water, flipping the boat. Electric motors increase their torque with load while nitro motors have a constant torque. You can't run too big a prop for the same reason. The nitro motor will stall, but the electric motor won't.

Generic advice for 3.5 tunnels is to start with the nitro settings and see what happens. It helps to have an experienced tunnel racer around for advice.

Lohring Miller

 

[julianconde]

I start out prop center a little below the sponsons, depends on so many things in a tunnel though, power, prop, hull, balance.

It's a balancing act between CG, prop depth, prop angle, just a matter of keeping notes and doing lots of testing until it runs nicely aired out with minimal bobbing.

Never seen two run the exact same setup even if they are the same hull. CLose but not the same.

Make one change at a time, run it and see how it goes. If you make multiple changes at once you never know what works or doesn't.

I would have to agree with mark.

Julian

 

[RCRACER158]

Brenton,

Mark and Lohring are correct on all of the details. Something else to consider is, the type of lower-end you are running. The distance of set-back(distance from the back of the sponsons to the propeller) determines your prop-shaft height. The Lawless and OS are close in measurement, but have a much further set-back than the K&B and Hyperformance Bullet Drive.

Also the different hulls have different transom locations.In addition the type of prop you choose changes the set-up, 1440 style props tends to lift the tail more than an X-series prop. Just something to think about.

Jimmy Johnson

 

[Brenton Harrington]

Brenton,

Mark and Lohring are correct on all of the details. Something else to consider is, the type of lower-end you are running. The distance of set-back(distance from the back of the sponsons to the propeller) determines your prop-shaft height. The Lawless and OS are close in measurement, but have a much further set-back than the K&B and Hyperformance Bullet Drive.

Also the different hulls have different transom locations.In addition the type of prop you choose changes the set-up, 1440 style props tends to lift the tail more than an X-series prop. Just something to think about.

Jimmy Johnson

 

[Brenton Harrington]

Brenton,

Mark and Lohring are correct on all of the details. Something else to consider is, the type of lower-end you are running. The distance of set-back(distance from the back of the sponsons to the propeller) determines your prop-shaft height. The Lawless and OS are close in measurement, but have a much further set-back than the K&B and Hyperformance Bullet Drive.

Also the different hulls have different transom locations.In addition the type of prop you choose changes the set-up, 1440 style props tends to lift the tail more than an X-series prop. Just something to think about.

Jimmy Johnson

 

[Brenton Harrington]

Thanyou for your comments. I will start changing things one at a time .

i have been adjusting things for awhile now and nothing had really been

changing much.I for got to say the bottom end is Lawless.

Brenton