The wing loading is counted in PSI, pounds per square inch, if you divide the weight of an aircraft by its wing area, you will find it is much less than the hydrofoil.
I got the following from the internet, it might not be accurate
The UH60 has a disk loading of 9.7 lbs/ft²
The UH1D has a disk loading of 5.25 lbs/ft²
The R-22 has a disk loading of 2.75 lbs/ft²
The B-29 has a WING loading of 69 lbs/ft²
The P-51D has a WING loading of 50 lbs/ft²
The Cessna 150 has a WING loading of 10 lbs/ft²
A typical kite hydrofoil board has the foil area of approximately 1 square foot and needs to carry the load of a person plus the force generated by the kite, which can easily double the weight of the rider.
Gotcha!!! You are 100% correct that it has a higher wing loading....not force...not stress...but wing loading..... the "wing loading" you are quoting is only 1 SMALL part of the stress that a wing experiences and all things considered it is somewhat irrelevant on the scale of material stress.
As an example your hydrofoil would experience a combined stress of 200lbs over 144 square inches or roughly 2psi....paper machet could handle this loading without falure (our bladders take about 8 psi.)
The stress you need to concern yourself with is bending stress. that is the lever arm that is trying to rip the blade off the rotor of the helicopter or your foil off it's attachement point to the fusi.
When comparing a helicopter blade to a hyrdrofoil you are forgetting that the helicopter blade is lifting about 1000lbs on a 2 m lever. Your hydrofoil is taking around 200 lbs at about 25cm?
the helicopter blade needs to be MUCH stronger. http://en.wikipedia.org/wiki/Bending
However in the case of your light loading STRESS is not the target parameter cuz your fins aren't breaking they are wobbling, it is STIFFNESS.
look to the section 7.2 on cantilivered beam with uniform distributed load. http://en.wikipedia.org/wiki/Euler-Bernoulli_beam_equation
w= wobble (at the tip)
w = qL^4/8EI
q is the wingloading
L is the wing length
E is a material property (elastic modulous)
I is a geometric property usually proportional to the thickness^3
practically speaking this means the following
your wobble is FAR more sensitive to changes in length and thickness than ANY material properties you can throw at it.....this is a problem you can more easily and cheaply fix with SHAPE than material..... make it shorter, make it thicker,
If you're trying to choose materials the one with the highest elastic modulous will be the best
Advanced materials just allow you to get a longer and narrow shape (higher aspect) which is mostly of concern when trying to go faster.
Now as to your density of water vs air. Yes water is more dense but aircraft are much faster and bigger. The property which takes both of these into account is reynolds number We did the calcs on an earlier post and the reynolds numbers for racing fins were somewhere around that of a cessna or other low perfomance air craft....you're not dealing with fighter jet loading my friend.