Why do Naval Architects Never Enter Cardboard Boat Competitions?

Marickovich, Adam M.	3:15 PM (23 hours ago)
to me, dmarickovich

Nick,

I have been drafted into a duct tape boat team in our engineering department.  How would you recommend building such boat? 

I feel like you’re our secret weapon to glory.

Nicholas Marickovich	11:11 PM (15 hours ago)
to Don, Adam

Adam:

Naval architects rarely enter such contests, as we have a horrible fear of failure.  Everyone would be like "wow, Nick's boat will be awesome, he's a naval architect" and when it turns out to suck, well....

But here are some thoughts at first blush.  You could probably arrive at many of them yourself...but then naval architecture isn't rocket science.  

So let's see....what would I do.....

I think the one dude in the picture probably has the right idea.  A canoe type shape would be best because you end up with a pointy end forward and a streamline shape aft.  I'd try to make one big enough for two people to power.  On the other hand, I THINK that at the relatively low speeds you are going to be running at frictional resistance will be your main resistance factor as opposed to wave making and hydrodynamic drag....a square stern would reduce your overall surface area and your skin friction.  The hull form I'd probably adopt is like a narrowish row-boat. I'd make it about as wide as a canoe....It should be wide enough to accomodate the people.  

You have to try to balance these two things:

1.  The more boat you can get out of the water the better.  A long, narrow boat will yield a shallower draft, lower skin friction, and cut through the water better.

2.  Unfortunately you are building with cardboard, so you can't build but so long a boat....the material couldn't handle the hull stresses.  What that sweet spot is I don't know.  I'd take my cardboard and make sandwhich panels out of it (i.e. take three pieces of card board and duct tape them together to make a thicker piece of cardboard) depending on how much time I had and how much I cared.

Build a boat that two people can power.  One person forward and one aft.  Put the heavier person aft....boats trimmed by the stern seem to be generally faster.  Add a skeg (an appendage aft that is a rudder but stays fixed) to help you go straight.  

I can't think of how you'd actually make a keel.  I think if you have a skeg your steering will be good.  You'll end up with a flat bottom boat with wall sides.  Consider making some cardboard knees http://themodelshipwright.blogspot.com/p/shipbuilding-terms-and-phrases-i-j-k.html to join your side walls to the floor of the boat for structural integrity.  

Of course, the boat must float....Make sure the weight of the volume of the water displaced is greater than the weight of the people who will be in the boat!  Becuase it is wall sided, if you just take the area of the boat bottom and multiply it by the side wall height you can get the volume in cubic feet....freshwater has a density of 62.4 lb/cu ft.  As long as the volume times the density is greater than the weight of the people inside, your boat will float.  

You want a fair bit of freeboard (the amount of the boat that sticks above the water) to keep water out.  Just keep in mind that the more free board you have the more suspetible you are to wind loads if it is a windy day.

Phew.  I think I see why naval architects don't enter boat building competitions.... 

Marickovich, Adam M.	8:30 AM (6 hours ago)
to me, Don

Wow…there’s more to building a cardboard boat than I thought huh!

Thanks for the help, a lot of this stuff I didn’t know.  A little rudder is a pretty good idea.

Nicholas Marickovich	2:35 PM (4 minutes ago)
to Adam, Don

Well, it is possible I am overthinking this.