bertram31.com

Guys,

When I move the exhaust outboard of the stringer, I will need to replace the exhaust thru hulls. Where can I get one that will fit the transom angle and is there one available with a flapper?

Thanks in advance.

http://catalog.buckalgonquin.com/item/t ... r/00te600f

Thanks Mike!

John,

I had mine made by my inox guy.
It doesn't show well in the pic, but the flaps are at an angle so that they remain closed at rest.
If I were to do them again, I would further accentuate that angle so that the flap weight keeps them shut even when the boat rolls.
There is a rubber liner on the inner side.

john why do you need a flapper ? i have same bronze 6" exhaust with built in down angle to meet 6" exhaust hose on inside .

Bob,

The 31 may be different, but the 28 hull has no depth, at least outboard of the engines where the exhaust tubes are.
As a result, the engines are mounted so that the exhaust tube is parallel to the sea level (very little inclination), and , as if this was not enough, the turbos are also very close to sea level.
When I bought the boat it had no risers and the water in the exhaust tube was moving back and forth to the point that I had issues with the turbos.
I added custom risers and improved the exhaust through hulls; no more turbo issues.
Needless to say that my 240 Yanmars are the biggest engines one can fit in there without having to increase the height of the engine covers. They clear the cover by less than 2cm, I think one engine even leaves a push mark on the top insulation.

the 31 with 70 degree x 6" SS fitting at bottom of exhaust below vertical run on sprinkler head will give a perfect angle to muffler and then to exhaust at transom .you can go in reverse as fast as boat will go with water coming over transom gunnels filling up cockpit floor till it get dangerous while backing down on giant tuna or swordfish without even a through of slugging the engines (ask me how i know).

Bob,

I don't think I do need flappers after reading Bruce's post about where the corrosion in the exhaust ports in the heads were coming from. The mechanic who is handling the head replacement for me suggested I had an issue with water coming up over the risers that had caused corrosion in that location. Bruce dispelled that as the issue and explained the more likely source of the water.

John-

I'm guessing you're moving the exhaust to 6" because you eventually are going to go with diesel. I have Detroit 8.2 mechanical diesels in Crows Nest. I put flappers on, as they seem to help with the diesel exhaust smell. My wife is doesn't like the diesel smell, and a set of Racor filters on the breathers and flappers on the exhaust helped a lot. Just a thought.

John

You don't need flappers.
They are not used in most production boats.
Height above water line from exhaust elbow to waterline is the most crucial measurement.
Flappers only partially fix failed installations.
We put the old boat through her paces many times, anchored with engines off in large seas and coming back on different gamefish, number six was always alive and well.
Simple surge tubes help
Piss poor planning will always lead to piss poor performance.