When choosing a small boat, we are often attracted to the aesthetics of its form and how easily it will glide or plane when powered by paddle, oars, or small motor.  Sometimes neglected in our considerations is how stable the hull will be, particularly when not moving.  Shifting about in a small boat while underway is generally a recipe for disaster, but we often need to move about or even stand up in a boat at rest in quiet water.

I became acutely aware of this a several years ago when I took up fly-fishing.  Previously, I had been content to spin- or bait-cast from a sitting position in my 15 ft., narrow-beam Old Town Sportboat.  But once I took up fly-casting, I wanted a solid platform from which to stand and make long-distance casts to spooky fish.

That set me on a quest for a more stable boat.  I still wanted one that could be paddled – - so I could creep up on a fishing spot – - but one that would also handle a small motor.  And, if the motor should conk out, I wanted to be able to row the boat back to my truck and trailer.

For boats that weigh over 1,000 lbs, distribution of passengers may have only minor influence on resting stability.  But for boats less than 500 lbs (what I was looking for), the center of gravity can be drastically shifted with the addition of one or two occupants.  Beam is often cited as a measure of a boat’s stability, but, as I learned as I dug into the subject, gunwale to gunwale width is only part of the story.

Let’s first look at two geometric forms that represent the general extremes of a midsection, cross-sectional hull shape – - namely a semi-circle and a rectangle.  Very few boats match either of these but some kayaks and peapods often approach the semi-circle shape while flat-bottomed skiffs more closely resemble the rectangular form.  Canoes tend to be more intermediate, although most traditional ones are closer to the rectangle (with rounded corners).  Using basic mathematical concepts, boat designers can calculate the center of gravity for these two shapes.  For the rectangle, this point lies midway between the vertical and horizontal sides, at the intersection of the diagonals (see figure).  For the semi-circle, the center of gravity lies above the mid-point on the vertical radius of the circle (figure).  The exact formula for determining this point is 4r/3π.  Thus, the geometric center of gravity for the 20″ x 40″ rectangle is 10″ down from the “gunwales” while for the half-circle (that is inscribed within the same rectangular area) it is approximately 8.5″ down from the “gunwales”.

What does this mean in physical terms?  The center of gravity, or center of mass, is the point in an object about which its weight is evenly balanced.  How does this relate to our two objects?  If these represent midsection hull shapes, we can determine the theoretical angle at which they would capsize.  For an object to be in stable equilibrium in a gravitational field, a perpendicular line drawn through its center of mass must run within the boundaries of its base.  If tilted until this line is outside the base, the object becomes unstable and topples over.  If we had a complete circle (or really a closed end cylinder) we could rotate it 360 degrees and never be outside the base.  Perhaps that is why so many thrill seekers have gone over Niagara Falls in a barrel.

On the figure I have drawn the “tipping” angle (beyond which the object topples).  It is approximately 110^o for the circle and about 62^o for the rectangle.  This tells us that the round bottom boat can tilt much farther before capsizing than the rectangular boat (both boats, of course would need to have waterproof decks to actually reach these angles).

But this is just part of the story.  Capsizing a boat not only depends on the tipping angle, but also the wetted surface – - the contact area between hull and water.  Water molecules chemically bond through weak hydrogen bonds to submerged hull surfaces.  These bonds will be stronger for hulls that are hydrophilic.  Waxes and hydrophobic plastics or paints can weaken this bonding – - which improves hull speed but reduces stability.  The greater the wetted surface, the more hull stability is improved.  The rectangular form has a larger wetted surface and this enhances its resting stability over the curved hull form.  Another plus for the rectangle is a wider distribution of waterline mass, and this acts like a counterweight when an occupant shifts away from the center.  Together these two factors provide enhanced dampening of hull rotation.  This is important because a person can be flung out of a boat by rapid rotation that falls well short of the tipping angle.  When you are flailing your limbs and gasping for air, your most urgent concern is not whether the boat fully capsized.

How do all of these factors help to determine the type of boat to purchase or build?  Favoring the rectangle hull is: lower center of gravity, greater wetted surface and wider waterline mass distribution.  In support of the circular hull is: a larger tipping angle and incrementally greater increase in wetted surface area with increasing load.  This can be seen in the figure by imagining a load added to each hull and observing that the wetted surface would increase approximately as the hypotenuse of an imaginary triangle for the circular form versus a shorter vertical leg of the triangle for the rectilinear form.  In general, if you want a boat that will be used in rough water and you will be sitting low in the hull, then a more circular or ellipsoid shape, with decking, will be the most seaworthy choice.  If, on the other hand, you want a boat with greater stability at rest in quiet water, then a hull closer to the rectangle form is a better choice.  Clearly, for both types, stability can be enhanced by increasing hull length, as this increases wetted surface.  Even planking choice can be important.  Lap-strake planking increases wetted surface area compared to carvel or strip planking.

The multitude of hull forms available attests to the notion that the perfect all-purpose boat does not exist.  Some kind of a modified ellipse may be the best overall compromise.  In this discussion, I have not mentioned reverse curves (or flare) between water-line and gunwales.  Clearly this would help to beat back chop and reduce wind-driven spray while underway, but has little effect on resting stability.

After examining a lot of drawings, photographs and articles on small-craft designs, my final purchase was an 18 foot, Old Town, square-stern cedar canoe built in 1946.  It weighs less than me, yet with a flat bottom (carried well forward), a moderately wide stern and long length it provides me with plenty of stability for fly-casting while standing.  The plumb sides allow for comfortable paddling, but a lack of reverse curve or flare above the waterline increases the chances of getting wet from wind driven spray when motoring in a chop.  I addressed this by applying stem to stern spray rails built according to dimensions given to me by Jerry Stelmok.  Both Jerry and Rollin Thurlow put these spray rails on the 20 foot square stern canoes they build in Atkinson, Maine.

With a set of oars and rowlocks and a 5hp motor, I am beginning to cover a lot of Maine’s lakes and rivers.  Your choice of boat might be quite different depending on how and where you like to fish; but thinking about hull form before buying or building may avoid later regrets.

Fly fishing boat

Bruce Weymouth wins raffle quilt with fly fishing motif made and donated by Ramune Dailide!

At the December meeting, Bruce Weymouth was the lucky winner of this fall’s raffle of a custom-made quilt featuring fly fishing motifs.  The quilt was made and donated by Ramune Dailide, proprietor of Surface Matters Longarm Quilting.  There were many disappointed members in the audience as they hoped that they had the winning ticket, however everyone was a winner through the $395 of donations that were raised by the raffle.

The course is designed to expose students to a varietty of tying tools. techniques and materials in order to give them a solid foundation in this sport. The evenings will start with a dicussion of the pattern that we will be tying and the materials used, followed by a demonstration of the pattern by one of our instructors. The students will then head to their vises to practice the pattern under the tutelage of our staff. There should be ample time for each student to complete a number of flies each night. As time allows we will also show variations of the patterns tied in class, different types of fly tying vises and sneak in a little informaiton on the life cycle of the life forms that we are trying to imitate.

The course fee is $35 and includes all the necessary materials and the use of fly tying tools during class time. Those students that already have tying equipment are more than welcome to bring it. Class is limited to 24 students on a first come first serve basis. All students under 17 years of age must be accompanied by an adult. Everyone participating will be required to sign a waiver form
Please make checks payable to

Penobscot Fly Fishers

Brewer, Maine 04412

Tying Registration
If you have any questions please feel free to contact Joe Beaulieu at 207-299-0634 or jpbeaulieume@gmail.com

We look forward to seeing you all in class.

Joe Beaulieu, Course Coordinator

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