PV Gap

Clayton Said:

Would a muscle powered hybrid make sense for a boat's drivetrain?

We Answered:

Tahini:

You should concentrate on the "muscle to electric generator" interface, with which you generate electric power or propel your craft.

Reasons for my "warning":

1. Muscle Effciency.
One of your issues is the vast difference in efficiency of the human muscle as a function of its contraction speed (from near 100% down to maybe 10%). The automotive equivalent is the well known "torque vs RPM" plot. Your muscles in effect perform like a race car, their plot being a steep "needle", in comparison to a more desirable FLAT torque curve. Incidentally, that is why a bicycle needs so many "speeds": You are never pedaling at the optimum RPMs.

2. Physiology:
Your heart "operates" at an average of < 50W. But its peak loads can be as high as 1000W (1.5HP). Incidentally, that is why a human pedaling a bike is so "superior" to any gasoline or electric "assist engine", which provides such peak performance only when the engine weighs several times as much as the bicycle.

==>
3. What I am driving at, is that "constant RPM pedaling" is NOT the best or even a desirable mode of power generation/ motion. You should study the physiological load cycles and especially the seating position of your driver, before you finalize the drive train in your water commuter craft. E.g. a constant repositioning of the driver may give a much better efficiency, by as much as a factor of two.

Note, there is a wealth of information in your university's library on the physiology of Aleutian Inuit kayak paddlers (no kidding). They are the highest efficiency "propellers" known among us humans. Also, you might want to consult the physiological data base on the pedal propelled "Gossamer Albatross Human Flight" project. I do not know if he is still around, but Dr. Paul MacCready from AeroVironment in L.A. has spent years studying your issue. MacCready was also a professor at Caltech in Pasadena.
----------

Finally, please take a look at the first SERIOUS attempt of an electric bike. To be introduced shortly here in the US by Schwinn. The components used in that bike, Lithium Polymer battery, shaft drive (i.e. no chain), and the planetary 6-speed transmission might be ideal also for your project.

Vicki Said:

Powered by the Universe?

We Answered:

Sure are solar powered boats.

Solar boats are electric boats, with independent, quiet and clean engines, whose batteries store free energy from the sun.

http://www.solarnavigator.net/solar_boat…

Roger Said:

What's a good title for my science fair project? Hints? ?

We Answered:

Since size is also part of an object's shape, none of my titles include the word size.

Propeller Shape Effects

Propeller Shape Effects in a Solar Powered Boat

Boat Speed vs. Propeller Shape

Twisted: Effects of Propeller Shape On Boat Speed

You need to catch the judges' eyes, so (word-wise) something like my last suggestion is more likely to make them stop and think "So what's this one about?" My other suggestions are kind of boring, but are at least descriptive in fewer words than your long title.

Have a photo of the boat in the water, maybe including you timing it or showing an instrument recording data or something like that.

Have a prominent graph that shows one of your more interesting results. For example, boat speed may increase with prop size to a certain point and then drop off again as the prop gets too big for the power available from your battery/motor.
Judges love graphs.

Neatness counts!!!

Have some examples of the different types of props that you used.

When you need a break from your work, go take a walk around your local mall. Notice how retailers and other advertisers try to attract your attention with words, pictures, objects and other devices (sound and lights for example). What do you find effective? In other words, which displays in the mall did you pay attention to and which ones did you find uninteresting.

Don't pay much attention to the product being sold. Pay more attention to what caught your attention and why.

Think about how you could incorporate some of those same ideas into your project.

Todd Said:

How do I raise money for a group engineering project in college?

We Answered:

sponsorship. See if any local materials companies or engineering companies are willing to put some money forward in exchange for advertising space on your boat etc.

Most universities manage to get either free or heavily discounted components too.

As far as i know there aren't usually grants in place, because the competition holders want the engineers to take the initiative and get experience in business as well as engineering.

Craig Said:

how do you make a boat go fast with an air propeller?

We Answered:

You want to increase the thrust and lower the drag.

Increase the thrust by making the area of each blade as large as you can without noticeably slowing down the angular speed of the rotation. So you want to minimize the mass as you add area to the blades, as mass enters into the kinetic energy equation which means more work needs to be done for a given angular speed.

By increasing the area of each blade you are increasing the amount of air whose velocity vector is altered by the blades. That means you'd have M dV > m dV where M > m is the mass of air whose velocity is changed by dV. M dV = dP a change in momentum.

And that change in momentum is what gives you the thrust. In case you're wondering dP/dT = F where F is the thrust from the fan, dP is the momentum change, and dT is the interval of time over which that momentum is change. Note that a faster angular rotation will yield a smaller dt < dT and a consequent bigger F. But I suspect you can't futz with the speed of the fan.

As to the hull. Build a catamaran, with a twin hull; so that each hull is very streamlined. That will cut the coefficient of drag, which is a major contributer to drag friction that your thrust must overcome. Also ensure each hull has a low cross sectional profile. This is what the hull looks like when looking at it end on, straight at the bow. The smaller you can make that cross section, the less drag will be created for given speeds through the water. Also make the boat as light as possible; so that it rides more on the surface than otherwise. Water creates more drag than air for the same velocities.