Ian,
For some reason, I missed your reply when I compiled my conclusions. Indeed, the Wilson shell looked about 3.5 inches and the Reeves shell was at least an inch and a half bigger. I just saw that as three inches extra for the four of us. That's a lot square footage. I banned the kids from walking on the gunwales at all times, even when parked up and followed the rules myself.
I'll discuss today with builder and see what potential there is for gunwale reduction. I'm pretty keen on idea - and as you said, if you can reduce the risk and not use the gunwale, then perhaps it's not a bad thing. I'll still have it in servicable usage in non-slip paint but not as a day-to-day feature.
Lastly, you mention the business of using the stern as a hopping off point, not the bow. There's clearly loads of different ways that people get into risky situations. I wonder what the most risky departure point is on a narrowboat? Actually, what's the safest then, the stern I suppose, but only when it's not moving towards large concrete structure in shallow water..?
Food for thought.
Callum.