laceys lane said...

well done, love the underwater shots- from 3 positions. a little bit air bubbling collecting around the back ss pin from the paddle strokes.

any speed difference, did you get your stability.

mate looks like a top class job you did in the making process

cheers

It did work.. Noticeable.. but not by much.. I'm thinking maybe a little too much flex.. and I want the s/s rods evn longer.. I'm getting some 6mm allthread in s/s and I'm going to add another one in between the two.. (making that three) and have them about an inch longer.

Water has very little density close to the surface.. You just have to lift a boat prop up and when it gets 4-6" from the surface it spins up like it's in air.. To get stability grip you need to get past that 4-6" and the fin in that area is not doing much.. The deeper the better but too long will add weight.. increase drag.. and make the board un-paddlable in shallow water.

I'll let you know how my idea works.

DJ

You're right.. There is some play in the box.. and I wil pack it next time to try and less'n the slop.. and that bit of flex might even be doing some good.. and it didn't feel any slower.

I think tapeing the fin box will do more good than shaping those threads.. maybe i'll do both.

DJ

Thanks for your ideas and the link.. Your idea might work better if it was tracking that I'm after but I'm only after 'stability' to help with board tippyness.

IMO two, three or four shorter fins with a total fin area of let's say.. 40 sq inches.. would have no where near the same effect on stability as one fin that's 10" long and 4" wide even tough they have exactly the same total fin area.. The fin that gets down past that 4-6" of surface water will have much better stability because it's reaching the denser water.

DJ

Thanks.. So it's pressure and not density.. I remember reading about it once.. There is a depth that is close to the surface where the pressure sudddenly changes and it's not just a gradual change from the surface of the water to the deepest depth in the water.. There's a word for that point where the 'pressure' changes.. Any idea what that is.. or what depth that is?

DJ

Every 10m of water is approx 1 ATM in pressure. That is why divers regard the first ten meters as the most dangerous, biggest change in pressure. Ie it doubles from surface

laceys lane said...

dj, you need to set up some mini hydraulics. drop the fin down deeper and then pull it up in the shallows

Tank testing.. ..

I'm also wondering if our foils are right for our very slow paddling speeds (not surfing or catching runners) .. I'm pretty sure our fins should be thicker.. High speed fins are thiner with the thickest point being further back.

DJ

blueseven said...

Has anyone investigated a "ballasted fin". Radio control sailboat type keel with weight in a torpedo at the lowest point, might work. I would think it would help with stability and wouldn't slow the board down too much.

No.. But that's an interesting idea..

Boats have a separate fin (rudder) for direction.. and that ballasted fin is there not so much for stability but for keeping the boat from laying over due to wind in the sail.

DJ

My fin mod #2.

DJ

I'd imagine sticking the fin all the way forward in the box - or even adding a box further forward would reduce the roll as well....but then you'd lose some of the straight tracking.

My fin is pretty solid now and should be fine.. A can imagine a fin like that being used as a rudder might be a bit risky.

I tested my fin out today.. and also plucked out a few of those nasty bad starfish.

The new fin worked great.. It made a big difference.. It was 11 1/2" long.. Now it's 14 1/2" long..

DJ