rodndtube.com's (OLD) MyPaipoBoards Forums. Reading but no posting on the OLD forums.

[surffoils]

Those pics show what a nice shape you got going there ! Lovin it.

[global ernie]

that just looks fast, do you think you could reduce the fin size further? i think simmons was quoted that the faster your going the less fin size you need. what is the toe in and cant angles? have you surfed a finless version of this board? and how deep is the concave and how far does it run up into the board? 500 words or less or we could discuss it over 3 million beers!

[kid]

DISCUSS OVER BEERS!!!!! Ok, I have a beer, so....Yes I reckon the fins could be smaller. I recall from "Jonathan Livingstone Seagull", that wings, and thusly fins, have a greater effect at a higher speed, thereforely, I might find that as the board moves faster (due to the lower drag from smaller fins) the fins might be just as, if not more effective, if smaller, but with a deeper foil. The concave is only 15mm deep, and runs up about a third of the board length from the tail. The fins have no cant, but they are toed in to a point around 6 inches past the nose of the board, on the virtual centre line. I am torn now between making another, slightly longer and wider version, or just cutting the fins off this one entirely to see how it works. My guess is that it will still be fast, but that the vertical hold will be compromised somewhat! Thoughts?
_________________
"It's not a beer-belly, it's a displacement hull"

www.deluxepaipo.com

[global ernie]

I would rather a bottle in front of me than a frontal lobotomy.
have you considered installing FCS style plugs, there is a generic brand on the market now, much cheaper and as good a quality. nor a great puzzle to fit them into a solid timber/ply board but you would have to glue some blocks on the deck (rounded/smoothed down unless your a masochist) to give enough depth for the engineering specs. FCS is a pretty straight forward installation, you can use polyester or epoxy. the tooling cost is not to expensive if you already own a good electric drill.
there are some finmakers that will do fibreglass fins to fit FCS. dont quote me but i think fluid foils at ballina might, you can send him some templates and money and he will knock em up for you. this system would enable you to do some mix and match R&D. i could film a vid of a thruster or quad installation if you like and post it to you or you might know a local board builder who could take you through the process.
send me a pm if you like and i will get you the toolings specs and fill you in on the nuances if required.

[Uncle Grumpy]

[ccsurf]

Did you take this thing out yet? how did it go?
_________________
ya

[puurri]

FWIW my take is that cant and toe in only work at specific hull speeds and wave shapes. Root chord of fins and parabolic rails are probably the more important parameters; plus fin rake (no more than 57 degrees) over the range of potential speeds.

[rodndtube]

[puurri]

Root chord is an aeronautical term referring to the transition area from wing to body (fin to hull). It appears that unless there is a "fillet" or transition piece then turbulence (drag) is the result. Some glassed in fins used to have some form in order to brace the fin against side and torsional forces. Root chord contributes to lift and diminishes drag.

Perhaps a filet of Sikaflex might help boxed fin systems.

I posit that there is a relationship between fin length vs drag and consequential vortex shedding due to several factors. Aeronautical manuals and a quick google on Swaylocks gives a variety of elipses to choose from. I favour equally shaped fins sides over a wing profile and don't favour cant or toe in as it only works to optimum in a certain speed range. Cant is probably what adjustable canards do in for aircraft control systems.

I believe that the 57 degree is the optimum longest single length over the leading edge of the fin but a wiki on aeronautics would be a good idea. FWIW I don't favour excessive rake and extended trailing surfaces past the fin base's mid point (just my thoughts).

[bgreen]

Those with an interest in fins might find something of interest here:

http://www.4wfs.com/knowledge/general-knowledge/

Bob

[rodndtube]

Try the root URL and then browse around in the Knowledge section:
http://www.4wfs.com/
_________________
rodNDtube
"Prone to ride"
I love my papa li`ili`i