Location of Water Pickup
by Joe Bloggs
(Ft. Lauderdale, FL)
I am building a step hydro hull, and would like some help in locating the position for the water pickup, to cool the electronics.
It makes good sense to cool the electronics inside an RC boat with water. The thing to remember is that it comes at a price.
The water pickup is creating a drag that inadvertently is reducing the boats maximum speed. You don't get something for nothing.
So the idea is to pick a spot on the hull where the water pressure is the highest while minimizing any obstruction of the laminar water flow along the hull.
One answer I've read says it should be placed slightly behind and on the upward-moving side of the propeller. This came from an old book by Vic Smeed from the 50's, so it may be a bit out-of-date.
I've only built one model where I installed water cooling for the electric motor I had installed. It was a shallow-v of my own design.
At the time I didn't know any better, and mounted the water pickup in the hull just above the prop, and perfectly centered. I believe the tubing I used was regular silicone RC fuel line, about 1/8" ID. The pickup was flush with the hull (again, I didn't know any better).
This setup worked fine. The motor water jacket was a simple copper refrigeration tubing wrapped around the motor can and held in place with a hose-clamp. Since this was a relatively smooth path for the water, I did not need much pressure.
On any RC model boats these days, you almost always see a 45-degree cut facing forward. The idea is that you get increased pressure into the pickup. However, you also get more drag.
So, ultimately you probably need to experiment or chance it. If you choose to experiment, don't do it with your boat. Use a "representative" setup and implement your findings to the boat (took me a while to grasp this concept).
A block of Styrofoam, an extra prop shaft and a bathtub may get you far. Best of luck!