: As Paul implies the folks who developed these craft had no deck openings
: except the cockpit coaming(s). Their intended use was hunting and not
: transport.

After a kill was made you had to get the meat home... that is usually the hard part of hunting . The entire animal of parts thereof were carried either on the deck or inside the kayak and sometimes this load would be several hundred pounds.

One only has to look at the Eastern arctic Inuit kayaks to see that they were designed for long distance transport in big seas. Some of their single man craft were up to 27 feet long and 27" wide with a carrying capacity of well over a thousand pounds. These hunting/cargo haulers usually carried a large part of their load on the rear deck but a fair portion could be carried belows decks as well.

In Alaskan waters there were deep kayaks which carried the load inside the kayak and there you will see large cockpit openings to make this easier.

With modern kayaks there is no doubt that having a kayak with hatches is potentially safer than one without - but one must practice self-rescues in rough conditions to bring out the potential benefit.