Hi Hank

I rechecked some earlier calculations on surface area, I posted a drawing of my blade sitting in 5 positions, each rotated 12 degrees from the previous. Normally I would use around 20 square inches, the mid position. each positon shown would result from approx 3/4" movement of the control knob. A long pie shape with the trailing edge angle at say 45 degrees would offer much the same . I looked at that blade shape but could figure an easy to maintain cable housing system until I saw Ross's skeg box. I can envision a pie shaped blade with a control lever mounted at a right angle to the leading edge inside the skeg box would allow responsive and linear control of the blade. Furthermore, if the control lever was not fixed permanent, the blade could retract into the box if it were to encounter an obstacle from either direction.

Greg

: Hi All,

: After viewing Ross's post showing his work on his retractable skeg [nice job
: Ross] I thought I would raise a question on skeg design...

: The retractable skegs that I have seen are relatively narrow and project
: quite a ways below the hull. This "penknife" style would result
: in substantial leverage being applied to a small support area at the pivot
: point by normal forces on the skeg. Contacting the bottom while moving
: forward would apply a large force to retract the skeg [probably not a
: problem] but a sideways or reverse direction force has the potential to do
: structural damage.

: My initial [half-baked] thoughts on a retractable skeg would make it a low
: profile that it did not protrude far below the hull line - 3 or 4 inches
: max; it would have a full radius on the leading and the trailing edge so
: that would not "catch" on anything when backing up. The blade
: would be long enough to have the required surface area and it would be
: fully supported over the whole length by the slot in the hull. The skeg
: box can be a lower profile and fit more out of the way further back in the
: hull.

: The other thing I am going to look at is using rare-earth magnets to
: "connect" the skeg to the actuator lever. The idea being that I
: do not have to deal with a hole thought the bulkhead [that may leak] to
: run a cable and I could "attach" a magnet anywhere on the blade
: which is not possible with a cable. The other benefit is that If I did hit
: a solid object with the skeg that the magnetic field would just
: "shear". Operating the control would re-engage the magnets. I
: have been playing with a few different sizes of those magnets from Lee
: Valley - you can't imagine how strong they are until you try to separate a
: pair of the 1 inch ones. I have been using them to clamp scarf joints -
: they will easily "couple" through 1/2 inch of wood.

: After paddling Greg's Guillemot with it's retractable skeg I am definitely
: going to be building one into my Guillemot. I see it like a trim tab on an
: airplane - you can live without one but then why would you want to?

: Any comments/suggestions on this kind of design??

: Thanks,

: Hank