@shemandr has a good idea. If you are uncertain about wresting the O.B. into the cockpit, that would be an alternative. Regarding JB weld. In years past, I owned an old Ford Ranger. A major oil change company (lets call them spiffy lube) cracked my oil pan when tightening the plug then claimed they didn't do it.... to replace the $20 oil pan you had to take out the transmission first ($300 labor)... so the mechanic took pity on me and cleand out the oil pan with acetone, filled in the old threaded hole with JB weld, then tapped a new plug into the pan. I sold that truck five years later and it was still holding.
Since your job is above the water line, I don't see a reason to buy the more expensive JB weld Marine.
If it were mine, I'd pull the split completely apart and then weld the entire crack with JB weld. Put a pipe clamp on low pressure over the board.... (or replace the boad). I think the JB approach would be a quicker repair since you won't have to drill new holes etc. Plus if you don't already have pipe clamps, you can use this project as an excuse to buy more tools....
I have two of these and I find uses for them all the time (see pic). The pipes are sold separately at lowes. You adjust the "clamp" on the left to fit the job and then squeez it down using the screw on the right. It is a great way to glue a lot of boards together into a larger board or a stout block.
If you set it all up and have time to let it sit overnight, I would go with Gorilla glue. Gorilla glue expands as it cures so it will fill any voids in the wood (which is why you need clamping power to make it work well). I have destroyed a wooden joint made of Gorilla glue by smashing it against a tree until if failed and the joint did not fail at the glue seam. The wood failed. But I'm confident that JB weld will outlast that piece of wood also and it will be ready to use in a few hours.
Edit: If you go with JB weld, use a relatively low clamping pressure. You don't want to squeeze all of the JB weld out of the joint. If you go with Gorilla glue, use a medium-high clamping pressure but start of with a well saturated joint. Wipe off the glue that squeezes out of the joint.