Firstly, lets get the smoke issue out of the way. I don't think you have a smoke issue. What you are getting is cooling water washing
soot from the inside of the system and it's running down the hull
. It's going to happen no matter what, it's just that with a system so long as your's, it's going to happen a little faster.
Now on to the system it's self. From what I can see (great photos by the way) I "think" you are safe from water
running in, BUT, it could be better and safer yet. So lets start at the beginning.
outlet should be cut down lower. Much lower as in say 25-50mm above your loaded water line level. This is so you don't have the uggly black stuff so noticable down the hull
. Directly on the inside of the hull, you should have a 90' bend and a riser going straight up to just under the deck
level, a 180' bend and the pipe going straight back down again, another 90' bend and the pipe off on the direction it will run through the hull. This run needs to be kept level'ish so as water does not pool and block of the hose. Back to the riser, this acts as a gate to sea water when a wave slams against the hull. Because of mostly back pressure int he system, water can not be forced up the riser and flood the system. It also allows exhaust cooling
water to be "blown" out and keep the exhaustas clear as possible. Yousee this as the slow "pulsing or purging" effect of water rushing out and then nothing for a few seconds.
From then on, the system I think will pass. Maybe not pretty, but I think it will be OK. I reckon if you get your guy to do the above at no extra cost, then he can put it down to a learning
Personally, I don't like commenting on peoples work. I have learn't over the years, there are often reasons why things are done the way they are, that are sometimes not conveyed to the ones like us that then have the freedom of passing judgement.