Water Tank

Hi everybody,
some of my friends starded to build up a water tank. The idea behind is the one consisting of measuring “qualitatevely” the resistance offered by differents model hull like the IOM and M class.
The water flux should be varied from 0.5m/s up to 2.5m/s.
The enrgy is coming from an outboard engine of 4hp.
Do not tell us that we are crazy, we know that, but if some one has got similar idea, we will be glad to have some exchanges .
In attachment some preliminary pictures and a drawing showing the basic principle.

the design :

the instrument to measure the water speed :

the preliminary construction :

Following pics

the balance !

First modification


Hi Claudio,

Sounds very interesting.

The one thing that comes to my mind is something that Jay Evans the former coach of the US kayak team called “Bottom Effect.”

When you paddle a kayak in shallow water it takes noticably more effort to keep it moving. I would expect that if all else remained the same (water speed, boat etc) the bigger the cross section of the tank the more valid your readings would become.

Almost certainly you will be able to measure the difference between hulls, but not the drag of a hull under open water conditions.

If I make one it will have to be for the 10 cm to 15 cm range of hull sizes! :wink:


Yes Pete,
Thank for your interest.
We are aware of the problem, but it will come into conflict with the power of the engine.
Actually we have only that OutBoard motor.
We do not pretend, at the moment, to achieve some drag measurements, but only “relative” visual comparaison between hulls of the same lenght.
The actual volume is about 1.2 m3 , enlarging the section by 10cm, the water volume will increase to 1.8m3 (+ ~50% more)


A most imaginative project. You have done some real thinking here and made an interesting project. I hope that you will share some of your observations with us about various hull forms under test.

Keep up the good work.

Thats awesome. I want to build one, and have the space but no real reason for one. I even have an 8hp honda and 3hp yamaha outboards in my basement. I really like the device for measuring the water speed.

i have also thought about using a dinghy to tow two models on a large “scale” and whichever hull has more drag it pulled back.

a text illustration:



[some documents about tank testing](http://eric.schwarm.googlepages.com/tanktestingpdfs)


this is exactly what Frank Bethwaite did when selecting the best dingy sailing boat for his experimental work. This sketch extracted from his book ‘High performance Sailing’

This method of testing may be appropriate for dinghy sized boat around 4 meters, I will doubt to obtain useful data by towing relatively small RC models. Any one got this type of experience ?


That lookds very interesting, I wonder if anyone has ever used there or a friends pools that you can swim in but not move anywhere. I was thinking of trying that same idea in a river near my house. I will wait till the ice is gone.

I think L. Francis Herreschoff described testing models by towing pairs of similar sized boats on a bar to see which had the most drag. Possibly in “Common Sense of Yacht Design” or maybe in one of his more casual pieces of writing. At least I know I read something like that quite a while back.

Your pictures are amazing!


A.B. & Pete,
I went around in my region searching for a river having a calm flow of about 1.5 - 2 m/s
Unfortunately there is nothing like that.
This solution could be ideal , just a rope and a simple preloaded spring. more drag, more pull on the spring.
It will nice if the Herreschoff paper could be published.

Some years ago , after having read the Bethwaite book, I was thinking that similar thing could be done at reduced scale. Just an RC motorboat with electric propulsion, a crossing bar and two models + a micro video camera to remotely observe the bar rotational angle or a dynamometric balance . The speed could be video controlled with a Speedwatch mounted on the motor boat or with a GPS. The motor boat does not need to be complicated , just a wooden plate with a motor/propeller and a rudder control. So far, nothig, has been done to my knoledge.

Hi cladio, neat idea.
Your merc is a 2 stroke? Are you exiting the exhast into the water?
If it is ,and you are, you will have oil and gas in your water soon.
Could could skew your results/ stain or even attack your hulls.

I do not knows. Interesting observation that I will trasmit to the friend