Sunday, March 6, 2011

How do different design characteristics of a boat effect its performance?

Canoes and kayaks are designed in many different ways.  Boats are usually designed in those ways with certain performance characteristics in mind.  Not all boats are built to do the same thing and accordingly, when a boat is designed, the shape of the boat is made so that the hull can perform well for the conditions it was made for.  The Old Town Canoe Company (http://www.oldtowncanoes/) has a good outline of hull characteristics and the purpose of those characteristics.  Below is an outline.

Canoe Anatomy: Size & Cross Section*

Length
Longer canoes will have greater hull speed, better tracking and greater potential for carrying capacity. Shorter canoes will be more maneuverable and lighter in weight.

Width
Width, or beam, as it is called, is given in two measurements: the beam at the gunwale and the beam at the 4" waterline. The 4" waterline beam has the greatest influence on performance. Wide-beamed canoes offer great stability but may be somewhat slow. Narrow canoes may be less stable but afford better efficiency and hull speed.

Depth
Greater depth allows for increased carrying capacity and better water-shedding ability. However, deep canoes can be harder to handle in windy conditions and will be heavier. The shape of the bottom of the canoe and how it blends with the sides will influence its performance. Stability of a canoe is affected greatly by its cross section.

Entry Lines
The shape of the bow where it cuts the water will have an effect on the canoe's performance. A very sharp, knife-like entry will cut through the water easily and provide efficiency. A blunt bow will add fullness and give buoyancy in waves, thus a drier ride.

Symmetry
Symmetrical canoes have identical ends, bow and stern. They offer more-versatile designs and convert more readily from tandem to solo. Asymmetrical canoes are usually designed for a particular specialty.

Flat Bottom
Flat bottom canoes offer great initial stability; that is, they feel very secure on calm water. Flat bottom canoes are great for sportsmen and general recreationalists looking for steadiness.

Shallow Arch Bottom
Shallow arch bottom canoes have less initial stability than flat bottom canoes, but good secondary stability. As the canoe is leaned, it will balance on its side and resist further tipping. Shallow arch canoes work well in waves and whitewater. Shallow arch bottom canoes offer the best all-around performance.

Round Bottom
Round bottom canoes have very little initial stability, but may have good or even great secondary stability. They are designed for speed and efficiency. Round bottom canoes are usually fast, specialized canoes.

Keels
A keel will help tracking in short canoes and will help the canoe's resistance to crosswinds. Keels also work well on canoes used with outboard or electric motors, as they decrease sideslipping. They would not be appropriate on a canoe used in whitewater or situations where quick maneuvers are essential.

Flair, Tumblehome, Straight-sided
Design options for the sides of the canoe include flare, tumblehome or straight-sided. Flare will shed water and increase secondary stability. Tumblehome gives a narrower beam at the gunwale, which allows for easier paddling. Depending on where, with reference to the waterline, the tumblehome begins, this may decrease stability, (historically this feature began at the waterline, decreasing stability, hence itÕs name "tumblehome", in general, tumblehome on our boats begins at least 4" above the waterline at maximum capacity so as not to detract from stability). Straight-sided canoes are a compromise of the two. Many canoes will incorporate one, two or all three of these in different areas of the hull.

Canoe Anatomy: Rocker**

The curve of the keel from bow to stern is called rocker

Straight Line





A straight keel line has no rocker, which allows for exceptional tracking ability but lacks maneuverability.


Moderate Rocker





Moderately rockered canoes are usually straight with a rise toward the ends. Most general recreation canoes have a moderate rocker.


Heavy Rocker





An extremely rockered keel line offers exceptional maneuverability but will not track well.



*(the above Canoe Anatomy: Size and Cross Section information is found on The Old Town Canoe Company's website here: http://www.oldtowncanoe.com/canoes/anatomy/size_crossSection.html)

**(the above Canoe Anatomy: Rocker information on is found on The Old Town Canoe Company's website here: http://www.oldtowncanoe.com/canoes/anatomy/rocker.html)