Water Tunnel

[medevac121]

Anyone know of any plans that might be available on building a water tunnel for testing scale model boat hulls.

Pat

[mo´s]

pat,

below you can find a rendering of a water tunnel. it shows only the system.
i´m thinkink about one too and hope some specialists can help to optimize it.

tom

[tom28571]

I'm no specialist but have done some model testing. I initially tried to devise a towing tank or moving water system like the one shown. Problems immediately arose with the size and cost of such a system. First, models need to be fairly large to show much correlation to the real thing. 4' in length is generally given as the minimum size that will give decent results.

Second, the cross section of the tank channel must be large relative to the immersed hull cross section to avoid near edge effects. These two issues alone make an amateur test tank unworkable for most of us. The tank gets so large and takes so much water that we just don't have the room or bucks to make it work properly. There is a reason that professional test tanks are so rare and cost so much to use.

I used towing tests in a natural waterway alongside a skiff to observe the action of a 4' model and measure its drag versus speed. I did not attempt to project the drag to the full scale hull but did measure and observe the effect of different configurations, including hull shape and displacement.

Not ideal, but I found it very helpful.

If you find any reasonable plan available for a home built test tank that is verified to give good results, I, along with several others would like to hear about it. Not holding my breath though.

[fcfc]

Are you an amateur tester, or do you intend to build a business to make money from boat testing ?

If you are an amateur, I guess that building all your models at scale 1:1 (the real thing) would cost less and give more accurate results than any useful water tunnel you could build.

[eschwarm]

mythbusers made one for testing aerodynamics of a pickup truck, tailgate up or down for best mileage. it was plywood, oval shaped and much like mo's picture. for getting the water to circulate, they used one of those fishing trolling engines, i think they are electric. they are very compact and available at west marine. i believe they fiberglassed the plywood to waterproof it. you will need a grid in the water to get rid of the turbulence caused by the propulsion source(propeller).