racked boat spacing?

Ok all you arodynamicists; I can rack 2 canoes as much as 1 1/2 feet apart or real close on my truck.Other than wide apart alowing easier acess to tie down is one way more effecint than the other? Wide seems more affected by trucks on the road.


We need access to teh NASA Ames
Research Center wind tunnel. The only way to do this is to run full-size real world tests. I am going to nominate Mike McCrea to do the coordinating. I want to see the drag numbers for a Ford van with 4 open boats on top!


Not so!
I could run this on our Computational Fluid Dynamics package.

All I need is a 3D solid model of the geometry for whatever cases you want.

I was hoping to ride inside teh van while in the wind tunnel!


I can’t help there
But if you make CAD model of yourself I could put that inside the model of the van.

What scale do you need?
We can have Mike make a balsa model of his van and boats.


Your welcome, Mike!

We need to know
If the seats are in or out ?



Efficient how?

– Last Updated: Oct-20-08 4:53 PM EST –

Efficiency is notoriously difficult to define well. You could run some trials to see if hull separation affects mileage if that's what you mean. I assume you mean how to mount the hulls to prevent them from interacting in a bad way, say by vibrating themselves into pieces or lifting off the truck or something.

The air boundary layers on the hulls at highway speed are going to be less than an inch thick, so if you mount the hulls at least a few inches apart, they shouldn't interact too much, unless there's a big crosswind or truck wake. Wake interactions are fairly impossible to predict, so if would be off to the wind tunnel.

I'm a big believer in noise as an indication of problems - if you tie them up there and they don't sound horrible or rattle around, you're probably OK. I think most problems come from ropes or straps that vibrate in the wind and tear up either themselves or the boats. I used to use a boat cover until I realized it was flapping around a bit, de-polishing my boat while I drove.

Boundry layer
Thanks for the boundry layer spec.That was the reason I spread them apart,but it seems that is not necessary.It definatly feels less affected by trucks and sounds better when they are racked close together.Yes my reasons for asking were drag and resistance to turbulance.