After deciding to go with a single fin and fin box design for my Kaholo 14 build, (giving me and the board greater versatility) I created a reenforcement sandwich that would also serve as a leash plug foundation. Using balsa sheets from a craft store and some of the extra ply that came with the kit I designed the sandwich. Solid and incredibly light. While other designs for a fin box reenforcement only attach to the hull bottom I opted to make it as rigid as possible by running it to the deck.
Created balsa/ply sandwich that will butt against #11 bulkhead and tailblock, hull botttom and underside of deck...
Balsa/ply sheets glued together...
..while positioned in hull, but NOT to the hull at this point. Note wax paper separating sandwich and hull as sandwich is glied together.
Sandwich glued into place and then sealed with coat of epoxy. I also glued another small piece of ply at the stern end of the balsa sheets to complete the framing.
Measurements taken off a centerline string running from bow to stern. fin box traced and ply and balsa cut cout using blade
Fin and centerline string used to assure proper alignment.
Created a "weighted box frame" to secure fin box into epoxy and glass as it set up. Flash Gordon would have been pleased...
Once set, ground fin box down flush with hull bottom.