Originally Posted by freyaflys
re ssobol remarks and trim down, have spent last few days in light chop off Mull. A lot of porpoising greatly reduced by trimming right down as opposed to level trim, with no loss of speed and much happier passengers. My question is when is trim up ( above horizontal) useful ? Trim gauge may now be useful. Yes I know its useful to avoid shallow obstacles but when else?
You have discovered the "feel" comments made above.
Trimming up (and for the anoraks out here, I'm going to say this in a "touchy feely" sort of way) On my setup, trimming up "unloads" the engine, and so allows for greater RPM at the same throttle (you can hear the engine "running free"). This means more speed for less throttle, so conversley you can for a given speed throttle back a touch, in theory drinking a touch less fuel. (althoug hIhave yet to find enough open falt water to put numbers to this theory)
The down side is if you keep nudging it out it will eventually start ventilating at the slightest provocation. For my boat on flat water, somewhere slightly below there appears to be optimal. Show it some waves and it will be down "a reasonable way".
Like I said, a bit "touchy feely", but hopefully help to to compare to what you found?