Cutting it in the middle might not be a good idea, as the joint will be subject to stress from flexing both from waves and from being pulled up on the bank while unloading and loading.
I'd probably cut it into three pieces, a bow section, a midsection, and a stern piece. That would keep the lengthwise pipe solid at the point of the most flex/stress. You'd also want to maybe add some drops (vertical pieces) so each part of the frame is boxed (that is, braced in three dimensions).
(I've built quite a few cat frames and run them in a wide range of conditions.)