: Hi there, Bill and Mike.

: I've been working on an adjustable skeg as well, and thought I'd toss in my
: two cents'... .

: Other builders who have added skegs to their 'squirrelly' boats have been
: using a longer, shallower skeg shape than Greg's with good success. I
: (non-expertly, mind you) theorize that rudders and skegs act differently:
: Rudders work by creating drag as well as by moving the center of lateral
: resistance aft, while skegs function by 'only' moving the center of
: lateral resistance aft. That is, a skeg should work as well even if its
: drag profile is zero. So, with a longer, shallower skeg shape (with the
: same area), one can minimize the drag component while keeping the
: relocation function.

: I don't have pictures yet, but imagine perhaps the old F-111 swing-wing
: fighter bombers. The wings' surface area stays the same, but with them
: extended, more drag profile is created, while the wings in the swept back
: position act more like fins.

: This should make the system more efficient by creating less drag, yes?

some varied thoughts:

i think a high aspect glider wing has less drag than a wide chord wing short wing of same area for a given effectiveness. the same thing can be seen in that the foils of hydrofoils are very high aspect. why continue to have more surface drag after already changing the water flow characteristic? But that would mean a long skinny skeg sticking out the bottom of the yak – more prone to breakage and harder to make. So to me, one reason that skegs are low aspect is that it has been easier to build them that way .

i would include most(all?) cable and rod deployed skegs here. But here there is the added issue of deployment design. How can a rod/cable twist around say 90 deg and still work as a compression member? I haven’t seen one yet that addresses this issue and that’s why these typically move only in the region of 30deg deflection as the more deflection, the more likely kinked cable in pushout.

{ as an aside, in gregs design you see that at full deployment he has sacrificed a sig amount of potential area(the back cuts out) that could either reduce the total size or make it more effective. Hes also noted that by raising the skeg rear, that the actuation line angle is reduced.}

the other reason is that often skeg pivot support is very small for lateral forces. you often hear of skeg 'humming or rattling' at speed. (some cases it can be just sideplay but has support). there is much less leverage on this joint if the leverarm (skeg) is not way out there. therefore the typical low deployment angle

also often at this pivot point skegs are slotted or cut away in order to fit (not just gregs) over the pivot pin. This reduces the sideways strenght of the skeg itself to less than half what it could be right at the location it must be greatest. So don’t deploy too much or wiggle and snap.(or at sooner size for size)

a different confounding issue at this point is that the designer has to preselect the amount of clearance betw skeg and box. And more importantly between skeg pivot area and box. What is the lateral area of support going to be in the region of the pivot?? You have to predecide. Big support – greater likelihood of sand/gravel jamming. Less – crappy wobbly skeg or high drag box . or vary?: does the skeg top stay wide for a wide pivot bushing and narrow blade. Etc, etc, etc. - I want full support, so the skeg will be a tight fit, but I know the compromise.

looking at foil rudder effectivenss max at abt 7deg deployment(vs abt 12-15 for non shaped(-saw a sealine display)) points out to me that lift plays a role in rudders. but skegs are always inline w/ the yak and if sideslipping even then the angle is real real low. so slightly(slightly) different issues. (there a lots of events when similar - like the conditions are variable inthe sea)like an unfoiled skeg has got to be a joke and how many of those do you see? want max effectiveness at low angles.

to me the beauty of the skeg and retractable(fully) rudder is that you can vary the effect over the whole range of deployment from absolutely nothing to something. I would 'never'(bad word, i don't really mean never ever) want the skeg or rudder to be only partially retracted or folded. why, when the whole idea is variation? same with the amount of deployment. why have just enought to turn or go straight - i want as much as i can get - so i can play with it and use it in a whole variety of circumstances. if it's too much, big deal, i'll just retract it a bit and save it for later when i do.

So using your example for the best of all worlds, supported pivot, long skinny skeg, deploy from a low aspect low area to min size you can or your yak bottom can live with ( I want nothing – fully retracted) to high as possible given the deployment system you choose.

And you would have to give up most effective drag profile b/c it would be for only one speed/condition.

Anyway some thoughts good or bad.