Will a 10ft SOT be too small for salt water usage?

I have a 10ft kayak, emotion stelth angler, and take it in the ocean all the time, mainly to dive off of. It's plenty stable for me and quick, but it does not track straight at all. It zigzags with every paddle stroke. I wish it was larger for more storage of gear, but I like how light it is when I have to move it around by myself.
Why do you not use her kayak as a tandem and both paddle it?

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Tandem kayaks and tandem bikes can put a marriage in serious difficulties.

I've heard them described as Divorce Machines.