I have dry exhaust on my boat with mufflers at the very end, but the exhaust has a drain on the bottom that prevents me from putting a nice trim ring over the pipes. Wanted to know if I can cut the pipes shorter, cut off the drain and maybe put some sort of gussets to hold the inner and outer pipe together. The exhaust is an inner and outer pipe, not a small pipe running at theta to carry the water.

I'm not 100% sure if I understand what you're asking. My pipes were dry and completely sealed at the ends. They had a small drain hole at the bottom and the large water outlet fitting at the top. I had the very end of the pipes cut off so it was 2 separate tubes then it was rewelded with openings left in so all the water exits from around the circumference of the pipes. Is this sort of what you're asking?

That is basically what I'm asking. I want to cut them a bit shorter and remove the drain at the bottom so that the water mixes in just before the exit. I figure I need to do something to make sure the inner and outer pipe stay in their positions so weld in a spacer of some kind.

My inner and outer pipes had dams in them to force the water to the top of the pipes so they would always fill completely before the water exited. I guess these would hold the two pipes in place in my situation. I have to retract my statement about my pipes being simply cut off and rewelded around the edge. It's a shame I have to refer to pics of my own stuff to remember what it looks like. They were much more extensively modified than I thought, probably to the point of being cut apart and reassembled to some extent. This is how they currently look. They used to be seperate pipes all the way to the end and completely sealed with a small drain at the bottom and a large discharge at the top. I have no idea how my current setup would work with exhaust.