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Posted: Tue Jun 27, 2006 10:20 am
by tech_support
Lets look at the weight of the equipment first:

Electric motor: 25 pounds
solar panels: 144
batteries: 540
gas engine: ?
fuel tank: ?
other people?

your looking at a load of about 1,200 pounds minimum.

To wake board you need some serious power. 25 hp would only work if the boat was super light (which it will not be with all those batteries).

We need to get a lot more HP, if you want it to plane.

We need a clear requirement for the boat. I have seen some of the student design hybrid projects and they have rules for the competition. Usually there is a over all speed part and a distance/efficiency part to the competition. A solar/gas hybrid boat powered by 25 hp that will pull a wake boarder just is not possible – we need to set priorities as to what’s important


P.S. Robert, are you from Texas?? 8) 8) :D :D :D

Posted: Tue Jun 27, 2006 3:05 pm
by Rick
Robert W. wrote:The electric motor produces 20 hp and weighs 25 lbs.
I work with a high school robotics team which uses a LOT of different DC electric motors. A 20hp motor weighing only 25 pounds is really unlikely, and if you do have one, you will probably need to cool it with something like liquid nitrogen. The heat buildup in such a small motor would be a killer. If my brane remembers correctly, that is about 15,000 watts, or, a LOT of heat to dissipate. Are you sure that is 20 hp continuous, or only some short-term rating?

Batteries -- 540 pounds of batteries. That's, what, six or seven deep-cycle marine batteries? Maybe a total of 500 amp hours, assume a half-discharge cycle since total discharge is generally a really bad idea, that 20hp motor using 120 amps, you'd really only run a couple of hours before it would run out of juice. Don't worry about that, though, since it would have fallen off plane long before. Maybe an hour of real use, tops. And that 20hp electric motor would only get about 600-700 pounds on plane anyway, which is less than your gear weighs, let alone passengers and the hull. Oh, yeah, pulling a wakeboarder will use even more power.

I won't even go into how long it would take those solar cells to charge the batteries... I don't think 48 square feet of solar cell would generate more than a few amps, would they?

It's a fun thought exercise, but I, for one, would really like to see your math before suggesting that it's even possible.

Of course, if you just use Joel's estimate of 1,200 pounds, you could just drop a 50 hp outboard on it and you should be good to go -- even if you don't hook the electric motor to anything...

Posted: Tue Jun 27, 2006 3:30 pm
by tech_support
I just found the CD rom that was given to me by team "Hyprop" of Melbourne community college (I think that is where they were from). They were using a small gas motor that was converted to run on hydrogen. They ran a water pump to push the boat. The "boat" was a tiny 8' model of a sportfish hull that was donated to them.

Why not a small generator that runs off LP or Hydrogen? Or even Bio diesel/electric.... now we are talking :D

Posted: Thu Jun 29, 2006 3:42 am
by anonymous
I think Robert is pulling the wool over some eyes. When I was a kid it would have been great if someone donated to me a boat or the makings of a boat with the ability to tow my friends at little or no cost.
Wish I had thought of it though :lol:

Posted: Fri Jun 30, 2006 9:58 am
by tech_support
We do get this quite often, but I give them all the benefit of the doubt and try to help as much as possible. Those who are really doing such a project are normally willing to listen.

Funny story; I had a guy in Palm Beach ask if we would donate C21 plans for his middle school shop class – “yeah rightâ€

Posted: Fri Jun 30, 2006 10:25 pm
by smilinmatt
As an engineer, I can personally attest that the primary purpose of engineering school is to drive all the creativity out of you. It's not that they hate originality, it's that you quickly learn that the phrase "it works in theory", is just another way of saying you ignored the important variables.

I think a more realistic challenge may be to pull a skier (preferably one with lots of upper body strength) using a solar powered boat. In that case, a boat reaching hull speed fast enough to plane a pair of skies would be ideal. Back to the canoes lashed together...