Ok, here goes. I have a drag boat. In that drag boat, there is a strut. This is the piece that holds the propshaft in place just in front of the prop. Meaning about .250" in front of the prop. It is LOADED!
On a hydro, the lower half of the prop carries the weight of the back half of the boat. The boat runs 8.0 et @ 55 to 160 mph. About 900 hp into the propshaft.
Best case scenario if the strut fails, it rips the bottom out of the boat, and the boat sinks. Worst..well, RIP.
So, the strut is a tube welded to a vertical .500 plate to a horizontal .500 plate. Or a "t" with a tube on the bottom.
1) Do I need to preheat? If so, how hot, and how critical is the preheat temp.
2) Filler metal.
3) Some flexing would be much better than cracking.
4) What am I forgetting?
As you can see, this is a critical piece. I know for a fact my buddies was welded without preheating. I read many threads and wonder if that was the right way to do it. (I did not do it)


PS, I only have a 180 amp mig welder. I have a Dynasty 300 tig.