I discussed this subject with a friend that works at a boat building museum and also checked several other references. Here's the scoop on red oak:

While the porosity of red oak can be a problem for boats and ships that live in the water full-time, it is not an issue for kayaks, which are typically removed from the water and allowed to dry between uses. If you're still concerned, a coat or two of linseed oil - particularly on the end grain - will effectively seal the wood from significant water intrusion.

BTW, salt water is an excellent wood preservative. Giving your boat a bath in the ocean is good for it. Rinsing it off with fresh water is a mistake, at least as far as the wood is concerned.

Splitting is caused by differential drying (the outside dries faster than the inside and shrinks, causing cracks. This is primarily a problem with oak over 2" thick, which requires special handling to avoid checking and splitting. Red oak will not split in the thicknesses used in kayak ribs and coamings, since such thin parts dry evenly enough to prevent any serious stresses from occuring the wood. Again, an oil finish on the wood is beneficial, since it retards both moisture intrusion and drying, which helps keep the moisture content of the wood consistent thoughout.

Red oak will turn black if it comes into contact with iron and moisture. It's a reaction caused by the tannic acid in the wood. I observed this when machining green, red oak. Black streaks appeared on the wood after a few hours, where it had made contact with a cast iron band saw table. The streaks were easily removed, since they were only on the surface.. This will not occur when machining dried red oak. FWIW, you can use this to your advantage to create black wooden parts. The technique involved is called "ebonizing".