small fin for flat water paddling

[oakfish]

I have an old 11' Bic Jungle board that I use for cruising the shallow marshes.  It has a single 10" fin that makes the board track really well.  Unfortunately, it's  a little long for some parts of the shallow marsh.  How short of a fin can I install that would still allow the board to track well?  I'm not racing or going long distances, but I do need it to go straight.

[HanaSurf]

On my 12' Hobie ATR11 I use Larry Allison Batfin. Not the expensive fiberglass one,He has a rotomolded(plastic)....sorry Larry one that has foil and works GREAT. I love here in marshes off the ICW. Works almost as well as the Fibre one and holds up great to shell and oyster bed abuse. It's a keel fin and improved the tracking and stability on my board. Still manurveres well in tight places. I think they are $60 in the click it style. It's 8.5 inches. He also has a round keel style fin in this series that's 7.5 inches that I think would work great with these planing style hulls in shallow conditions.