test tank, test wheel, or dyno and flushette

[outboardnut]

Hi Everyone.
Well I'm having a little trouble and venturing into the unknown. Looking for a little insight, input from experienced minds is appreciated.

I'm trying to be able to tests larger HP (up to 135 HP or so) outboards here at my shop.

I just built a LARGE test tank and bought a bunch of test wheels, only to find out that I am creating to much cavitation to be able to go on a very long virtual test run without overheating.

I can run a 40 HP motor in my tank with no test wheel just fine.

I stepped up to a 65 HP Merc motor today for the first time....and the prop was to much for my tank.

I modified a 15 spline OMC test wheel so it would fit on my merc....just ground some off the back so it would slip on OK. The wheel is supposed to be for a large v-4 engine, but it is barely enough brake for my 65 HP.

Is my tank wrong or do I just need to scratch the whole test wheel and plan on lake trips forever or dynometer?

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here is a link to a video of the boil I am getting....if the one above doesn't load : http://www.youtube.com/watch?v=2mRZXqRE2jY I just uploaded it if it isn't showing up come back in five minutes and try again

Picture of my test tank and wheel:

 

[tashasdaddy]

Re: test tank, test wheel, or dyno and flushette

what size is your tank, most i see are 5' x 10' fully covered have a 6 inch flue at back end for exhaust, and a cover that sides around the motor.

that 65 looks like it has a weak impeller. too long to get tale tell, and weak stream when reved up.

 

[Randybeall]

Re: test tank, test wheel, or dyno and flushette

Clean the water in your test tank, that oily crud is likely going to ruin the impeller on anything you run. What it looks like is that you need some space infront of the lower unit so the water can circulate to the water pump intake. As it stands now the foamed up water from the impeller is all it can suck up and that means air in the cooling jacket. As TD suggested a vent at the far end to allow exhaust gasses to escape and find some way to let the water pump take in clean water. I would think the impeller is toast or the seal on the pump is sucking air.

 

[JB]

Re: test tank, test wheel, or dyno and flushette

Get a dynamometer and quit messing with half way solutions. Then there will be no guessing about what is going on.

To properly test anything over 50HP you need a swimming pool with recirculation.

 

[gss036]

Re: test tank, test wheel, or dyno and flushette

I wish I had a picture to post but don't. A local shop here built what looks like a cement loading dock, but angled deep enough to get the outboards, etc, into the water deep and enough volume to keep the water circulating. They alway keep fresh water running into the hole while running motors, it really works great, but a lot of expense for the orginal set up. They have been in business several years and do a lot of repairs and new installations.

 

[Dhadley]

Re: test tank, test wheel, or dyno and flushette

Randy hit the nail on the head - you need space in front of the lower unit to let water circle back around. Without that space the test wheel will push all the water away. No good for prop bite or the cooling system.

When we used to use the test tank for big motors (anything 50 hp & up) we put the flushette on and kept water to the motor all the time. That way you're always getting fresh, cool water no matter what happens with the water in the tank.

 

[tashasdaddy]

Re: test tank, test wheel, or dyno and flushette

great idea.