Some months ago, focusing more on how it would look than how it would work, I built an internal rudder that when deployed, projected perpendicular to the hull, thus working as a brake instead of a rudder. (And not very well at that)

Still focused on aesthetics, but more knowledgeable about what constitutes turning momentum, I’ve since built another integral rudder that actually works. Essentially, 3.5” down from the sheer line, I cut out a 4” X 11” section from the stern of my 20’ Pygmy Osprey double. I installed a bulkhead 3” forward of the cut out, and for strength, filled the keel and sheer sections aft of the bulkhead with epoxy/silica. I enclosed the top and bottom of the cut out “rudder” section. To avoid turbulence when deployed, I fitted a matching conical piece to the open end, then drilled the centers of the circles and the reinforced sheer and keel sections for the full length rod that would rotate the rudder. Once everything was fitted, the rudder matches the hull lines with about 1/16 inch clearance at the top and bottom The vertical cut in the hull very closely matches the rudder while the conical section rotates inside the hull. The opposite side stays flush to the hull due to the matching conical shape. You can see it's a rudder, but it conforms perfectly to the lines of the boat. (Similar to Dagger’s Sitka rudder, but stronger due to the keel, and, I believe, more effective. : Sea Kayaker review-Oct ‘97)

At prox. four knots, with the rudder fully deployed to 35 degrees, the Osprey turns 90 degrees in less than twice her length and feels a bit like a car’s rear wheels breaking loose in a power skid. This is great, but there is an unanticipated effect. The glide of the Osprey is now so much better, I wish I had some way to quantify the difference. Even my ethereal wife, who has been known to obliviously paddle with her blades reversed, said, “Tom, what happened... why is it paddling so easy?” Too subjective, I know. I understand a normal flip up rudder causes some turbulent drag, but the change doesn’t simply feel like less drag, it feels qualitatively less. A skeg’s drag is used to correct for weathercocking. Is it that significant? Short of expensive tank testing, does anyone know of a way to measure/calculate the difference. It’s obviously not a real problem, just pleasantly perplexing... like my wife.

Thanks,

Tom