help building boat for school

[freakdude208]

I'm building a boat for physics and need some ideas on how to make a boat hold the most mass. The boat has to be no bigger than 25cm tall, wide, and diagonal. I need some ideas. Please help me.

[greg simpson]

i take it you mean 25cm cubed?

flat bottom,flat sides of no more than 1/3 of your allowed height,made of balsa wood availiable from a model shop very cheaply and glued using a waterproof glue,probably also available from your local model shop.

basically as your boat is briefed only to take weight,not to be efficient in moving thrugh the water,a box is what you are after,like a barge,but with square ends.

search barges on google for more inspiration.

hope it goes ok.

[freakdude208]

Yes, its not used for movement as much as holding weight. I'll look up barges but I was also thinking of putting upside down cups as sort of a pontoon. would that work better?

[rxcomposite]

Originally Posted by freakdude208

I'm building a boat for physics and need some ideas on how to make a boat hold the most mass. The boat has to be no bigger than 25cm tall, wide, and diagonal. I need some ideas. Please help me.

Take a cross section and do some trial calculations.
A half circle gives the most area for the least surface area.
A rectangular section with the sides half as long as the width comes in second.
A triangular section is the worst.

Then find which waterline will give you much volume. a rectangular shape combine with a 2:1 beam to draft ratio (barge like) will give the most volume but give you the most drag.

NA's measure the "fattiness" of the boat by the Cb or Block Coefficient of the boat. A high Cb means the boat is FAT.

[Skippy]

fd, what level/grade are you at, and what are the rules on getting outside help?

I don't understand upside down cups. A pontoon is fully enclosed. If you're looking for max carrying capacity, then you definately want a monohull. Pontoons are for extra width and stability with decent speed.

What are the other factors involved? Is speed important at all? Are the diagonals horizontal only? Then a cylinder might be best. Or do they include all possible directions? Then something similar to a half sphere might be better.

[rxcomposite]

I mean the hull underwater. anything above the water can be straight or slanting outward.

[rxcomposite]

Freakdude,

I spoke too soon. When we say boat, we think of a boat shape. The shape that will hold the most volume for a given surface area is a sphere and the formula is
Volume= 4/3Pi*radius^3
Area= 4Pi*radius^2
A hemisphere (half a sphere) would resemble something of a boat. Just divide the results by two.
Engineering formulas exists that will give you the most volume for the least surface area.
1. Upright cylinder, the depth height must be 1/2 of dia.
2. Horizontal half cylinder- length must equal diameter
3. Square base/Rectangular sides- Length and width the same but depth= 1/2 width.
4. Square- all sides equal

Here is the tabulation.
Form Width/Dia Depth Length SA Vol
Hemisphere W 0.798, SA 1.00 Vol 0.133
Upright Cylinder W 0.652, Depth 0.326, SA 1.00, Vol 0.109
Horizontal Cyl W 0.652, Length 0.652, SA 1.00, Vol 0.109
Square/Rect W 0.578, Depth 0.289, Length 0.578, SA 1.00, Vol 0.096
Square W 0.448, Depth 0.448, SA 1.00, Vol 0.090

You can play around with the figures if you want to have a nice boat shape. I will assume you know the basic formulas.

[Robjl]

Hi,
I can't resist these challenges, unfortunately the people who come up with the competition don't always think out the rules well. ... then when some-one comes up with an aberrant solution that the judges don't like they disqualify it!
Have you posted ALL the rules?

"I'm building a boat for physics and need some ideas on how to make a boat hold the most mass. The boat has to be no bigger than 25cm tall, wide, and diagonal. I need some ideas. Please help me."

If these are all the rules....
1. It doesn't have to be a solid shape...make it hollow that way it will be stable when the load is placed IN it.
2. The half a sphere is good...work out the volume displaced with a half or full sphere? Consider...a full sphere still has the same maximum dimension (length or beam or diagonal)!
3. Or make up a hollow box shape with the maximum diagonal length of 25cm

Build the best.. that's what we all do.
Good luck.
Hope you will let us all know your final design

[Sander Rave]

Just a thought ;-) putting enough power in an object and everything wil float...

[safewalrus]

Simple

Take a plastic bucket, put the weight in the bottom (ballast), put into water - one 'boat'

[rxcomposite]

Originally Posted by Robjl

Hi,
2. The half a sphere is good...work out the volume displaced with a half or full sphere? Consider...a full sphere still has the same maximum dimension (length or beam or diagonal)!

Robjl,
I think we have outsmarted the teacher. I suspected this was a trick question also.

A sphere? Yeah, why not? It will have the same widhth length, and diagonal no matter how the teach measure it. The teach didnt say what is going to be loaded into the "boat" anyway.

Rx