"A Comparison of Hull Designs"
- Wisconsin Versus Florida -

by
Dr. John A. Gilbert
Co-Faculty Advisor, Team UAH

Another ConcreteCanoe.org exclusive!

As mentioned in "The Front Line" ... I think that the Florida Gators will give the Wisconsin Badgers a run for their money on the pond.  So...

The question is: "How well will "Gladigator" stack up to "Descendant"?

Disclaimer

Please remember that the opinions expressed here are my own and do not reflect those of Team UAH, ASCE, ACI, ConcreteCanoe.org, and/or the sponsors of the 2007 NCCC.  I'm grabbing at straws in rendering the two teams' designs... but I think that most of what I say will be right on the mark.  If you come to Seattle...  you can make your own assessment and I'll see for myself.

Analysis

The figure below shows what I think that the two boats will look like.  I've included cross sections at the widest points.  The dimensions may be slightly off and the wall construction may not be accurate... but I think that the shapes will be dead on.

"Descendant"

Last year Wisconsin's  hull design team improved maneuverability, increased stability, and reduced frictional resistance.  They maintained the design theory from the past several years while pursuing these goals.  Chances are that "Descendant" will exhibit good acceleration, top speed, turning abilities, and straight line control.  The team will enhance these attributes by taking stem, deadwood, and rocker into account.

I think that Wisconsin's hull designers will keep the widest point aft of the midpoint, incorporate an asymmetrical rocker, rely on a flat bottom, and go with hard chines.  In order to increase maneuverability, the boat will be designed to turn around two axes of rotation, thus allowing both bow- and stern-initiated turns.

A rocker will be incorporated to enhance overall maneuverability.  The team will most likely rely on a variable rocker profile to improve straight line control and stern-initiated turns... by decreasing the lateral plane area in the bow and raising it in the stern.  The designers will skew the lateral plane by cutting away the deadwood portions of the stems... to a greater extent in the bow than in the stern. 

Last year, the team performed an elaborate analysis to establish the chine geometry that yielded the best stability characteristics.  When "Descendant" is leaned on edge, its chine will act like a curved keel, enabling the hull to turn itself.

The hard chines enhance maneuverability but tend to increase wetted surface area... which increases friction.  But the design team will counter the friction associated with the chines by decreasing the length, the largest contributor to overall area.   They will also vary the prismatic coefficient with crew weight... to achieve better acceleration for two-paddler sprints and improved glide for three-paddler endurance races and four-paddler sprints.

For additional information from the Wisconsin designers, see: "Concrete Canoe Design: A Practical Perspective" by David I. Blodgett, Concrete Canoe Magazine, (2)1: 30-32, 2007.

"Gladigator"

Over the last 5 years, Florida’s design teams have developed increasingly swift and maneuverable hulls.  This year, the Gators refined their reverse rake stern to further optimize hydrodynamic performance, and integrated components of previous designs to fit new parameters.  One of the outstanding features of "Gladigator" is its radical asymmetry.

This year the designers synthesized the bow and stern rockers with a soft chine design to allow their teams to obtain  the optimum balance of speed, stability, and agility.  The soft chines in the bow reduce the section area and help to minimize the wetted surface area in this region... where flow is more laminar and, as a result, frictional resistance is high.

Last year's team observed unexpected sluggishness off the starting line due to the truncated reversed rake stern. To combat this, Florida's new boat will be designed with a reversed rake stern that comes to an edge rather than an oblique plane.  This more closely resembles modern crew shells rather than America’s Cup yachts. This refinement will allow "Gladigator's" hull to maintain superior hydraulic performance while still allowing it to function efficiently at a variety of water levels as would a traditional canoe hull.

The team conducted small-scale tests of various bow and stern modifications to validate their new design.  A basswood model was constructed at 1/6th scale with interchangeable resin bows and sterns. Each desired bow and stern combination was placed in a hydraulic flume and pulled through the water by a falling weight.  Six to ten trials were conducted for each combination with three different weights.  At constant velocity, hydraulic drag force on the model is equal to the weight of the falling mass. Therefore, all tests run with a given falling mass are subject to identical hydraulic forces, so that the fastest model exhibits the highest efficiency.