Some good additional ideas have been posted on the topic. Here are a couple of pictures that I have that show my experimental set-up (sort of). They were taken of other projects, so they don't completely focus on the engine exhaust. I used a 4" to 3" aluminum elbow reducer from the hardware store at the Beckson port on the engine box. Just spread the tangs on the 4" side and it wedges right in. Then with 3" dryer ducting I came straight up to the opening port by the icebox. I cut a piece of 1/8" plexiglass to fit exactly in the port and drilled a three inch hole in it. That let me leave the port open all the time and remove the screen so I could poke a louvered flush hose vent inside and connect the dryer duct to it. Down in the engine compartment I was able to just wedge a square computer fan into the foam sound insulation right in front of the Beckson opening. Wiring was really crude...two clip leads; one to the back side of the battery selector switch and the other right to the heat exchanger drain petcock. So when hooked up the fan runs all the time. I do un-hook it when we are anchored or sailing, but when motoring and back at the dock under battery charger, it runs pretty much all the time. The real obvious improvement is that the inside of the boat smells a lot better. There is no hint of diesel odor or just that hot engine smell that we could detect before. During the winter, when I have to pull the vent back inside to close the port so the rain doesn't come inside, we have noticed that the boat starts to take on a stuffy smell. This even though we leave the hatch over the shower cracked all the time and I have two fans inside the dorade vent box with a small solar panel on the deck in that wierd compartment forward of the vents.
All in all it think the engine blower is a good addition and have been agonizing over the placement of a more permanent location for the exhaust as well. I have considered the coaming on the outside of the stern as near to the center as possible. The problem is not being able to loop the ducting upwards right at the vent. I really like that clamshell that Dave showed and thought about putting it inside the forward end of the aft starboard coaming cubby hole (A in the photo). Again it wouldn't loop up much, but would be protected. When I wash the boat I might need to be careful and not blast the water in there. Dan suggests putting it on the locker on that side. Since all my extra lines hang on the inside then the the next closest for me is the side of the cockpit (spot B). Then I could loop it on the other side. My only concern in the cockpit like that is that is where the dog stays and I don't know if there are any exhaust byproducts that wouldn't be good for her.
In terms of routing the ducting, I have removed my batteries from the hole down in the starboard locker, so I think I can bore through the wall and have access into the area under the aft berth from inside that locker which is then behind the engine/transmission. That should still be fine in exhausting the engine compartment. I still need to scout that out.
I have a three bank battery combiner (that I bought before I realized two banks of batteries were right for me) that is inside the starboard locker next to my battery charger. I think I can wire my exhaust fan to the unused third bank post of the combiner as it will be off when the engine is off and on (combined) after the house bank reaches the proper charge via either the engine running the alternator or while at the dock and using the battery charger.
I've only been working out the details for this project for about three years. Don't want to rush into it.
Allan
