I had this, or something like this typed up earlier, but deleted it because...
I don't have a boat, I've never had a boat, though from time to time I've been in one.
I have, however, fished Ambleside from shore a lot, while wishing I had a boat.
I think the answer is that it would depend a lot on the wind/weather, and the timing of the tide, and the tidal coefficient.
On high coefficient days, there are parts of the estuary that generate some pretty powerful water currents I would be very wary of, long lines of standing whitecap waves that more ore less just stay there, with very fast rips going this way and that.
Otoh, there are many days when it is a balmy, placid surface that a belly boat would likely be fine. I've seen dinghy's, kayaks, and canoes used safely.
I should think that with a 14' boat and a 9.9 motor that you'd be able to very effectively fish that stretch, as long as you used common sense and resisted the urge to be a hotshot, if you get those urges.
Even on the days where the water is super turbulent, it's only for a short period of time while the tide turns over from slack to incoming.
That being said, I will repeat that I don't have a boat and never have, there could be an awful lot going on out there that I'm not aware of, standing on the sandbar wishing I had a boat...