Is a tunnel for the prop better than regular bottom? or will it restrict flow?

[clctrader]

I converted a 26' CC from twin outboards to single diesel. I am currently making the stringers on a mold and will be laminating them soon. This will be a trailered boat and I want to make it as easy to launch as possible. I was wondering if I make a tunnel for the straight shaft prop, It will defenetly have more clearance on a trailer.

But will it hurt my top speed or will it improve it ???


ANy help on the subject would be great,

Thanks...

[Village_Idiot]

Tunnels will almost always hurt your top speed. They will also hurt your reverse thrust, thus making it harder to back the boat off of the trailer. About the only benefit for tunnels is for operation in shallow water, and even then they can be tricky to set up for decent overall performance of the boat. If you don't have to run in shallow water, you should consider avoiding the tunnel.

You might be better off modifying the trailer. I've seen custom-built trailers that had an additional tongue just for launching/loading. This tongue can be slid out to extend the hitch an additional four to six feet from the trailer, thus allowing you to back the boat/trailer further down the ramp without getting your tow vehicle wet. You might check out some sailboat trailers as they are more prevalent there.

[jehardiman]

What VI said. In truth, the reason to use tunnels for the prop is to be able to swing a larger wheel within the same or restricted draft. This is why you see them on towboats so often, the efficency gained by the much larger wheel offsets the drag penalty. Unless you are thinking about turning a significantly larger prop, the tunnels will only hurt preformance.

See this thread.
Propeller tunnels information