Add on board stabilizers...

[magentawave]

You have probably already seen this one.

[blackeye]

Have you considered the DSS style foils? They are the ones extending outboard near the waterline on some performance sailboats.
https://www.google.ca/search?q=dss+sailing&source=lnms&tbm=isch&sa=X&ved=0CAcQ_AUoAWoVChMI4aa6ztWMyQIViKWICh2Qcw9F&biw=2560&bih=1260

For a paddleboard they could be canted or curved upward so that if the board is trimmed neutrally, they are not immersed, or minimally immersed. If the board rolls, they would immediately create lift and prevent further roll. They could be fastened on the deck, curve down at the rail and sweep upwards as they extend out.

[SUPflorida]

These are interesting approaches to stabilize a narrower board, that all other things being equal,  would be unrideable...or at the least too fatiguing. 

It would be great if someone had three boards of the same manufacturer/model/length with different widths ( say 28", 26", 24") to give a real world test 1) How much stability does the appendage approach adds. 2) How large do the appendages have to be to produce stability of 28" or 26" board in the 24" width. 3) How much stability do the appendages impart when the board is static, or moving at minimal speed. 4) Does the drag of the appendages on the narrower boards exceed the resistance of the wider boards without the appendages?

[PonoBill]

Same basic idea as the foils blackeye, but more likely to be at least partly submerged when you don't need them. Interesting though, I'll have to give that some thought.

[blackeye]

Ah, Pono I understand better. Your Hydroptre foil suggestion would have them out of the water, or mostly out, when the board is level and would only come into play with heel/roll.

If the DSS style were also high then dropped down closer to water level it might be more or less the same effect. The difference would be whether the horizontalness of the foil proceeds outward or doubles back inward.

One way or the other, if the one end of the foil, ie either the root (DSS) or tip (Hydroptre) of the foil was always in the water or nearly so, the righting effect might be more gradual and worth the drag penalty.

We may have to think of some sort of shape that changes lift characteristics  as the board moves from displacement to planing. Too much sudden lift on one side would be just as bad as no lift at all.

[heyheysup]

This was a very interesting topic. What did you make in the end talldude? A lot  of good ideas...

[TallDude]

Lately my shop time is down to zero. The stabilizers are still sitting there on my work bench, as well as to have cut blocks of foam up on my racks for new boards to shape. I have all the parts, just need to glass and assemble the foils. The thing is, I also have an old longboard that I want to cut the rails off of, so I can attach them to the rear half of the board. I would just Velcro them on (or something to that effect) so they would be removable. This was my original idea, but the foils became a diversion.

Lately I've been thinking I could get flexible foam rubber extrusions in the shape of a cove moulding. Similar to what ULI uses on their Wiki rails and just stick it on. It could be an 1-1/2" to 2" cove with the cove facing down. Basically a stick on chine. I could play around with the height to water line and length, then maybe glass something mechanically removable later.