For electric motors: 1-3 HP. The 1HP
Torqeedo 403 would be excellent for the AI. The
3HP 1103AC would be even faster but a bit heavier and more expensive.
For gas outboards: 2.5 HP Short Shaft. The
2.5HP Suzuki is the best choice.
There are many good posts on this forum about motor choices and motor mounting for the AI and TI.
I've covered all of this in detail in these two posts:
Torqeedo 403 Ultralight Motor / Hobie TI Application GuideOutboard Motor / Hobie TI Application Guide & 403 ComparisonI highly recommend reading both before making any decision.