The trim on outboard motors allows one to raise or lower the motor(s) and because of the prop angle and the cavitation plate affects the bow down/up. It can smooth out a ride to some extent. With twins it has a little capacity to affect the "list" from side to side that can be caused by weight distribution. Trim tabs are much more effective at both of those functions. They have much more surface area and are on the outer corners of the stern. They allow substantial correction for list and are much more effective at adjusting fore and aft trim. You find them on many different boats and they are a well-proven add-on. They come in both hydraulic and electrical versions. There are good discussions about them on the site. Another some what less common addition is a permatrim, a large "plate" attached to the cavitation plate on an outboard. It (they) function like the outboard trim but affect things much more. We have both trim tabs and permatrims on C-Cakes and use them all the time. The permatrims are so effective at trimming the bow we end up using the trim tabs just to control the lateral trim to keep the boat level from side to side.
