Thank you frenchphil. I thought everyone was going mad.
The purpose of a jackplate with setback is primarily to
a) Raise the motor to reduce appendage drag off the gearbox& prop.
b) Shift the CG rearwards
c) Look cool - apparently
'Cleaner' water - yeah right.
Downsides of a jackplate can be:
a) You might not want to shift the CG back.
b) Jackplates tend to be a weak link.
c) Your transom takes much more load
d) The boats handling can go out the window - so you actually end up running slower to stay in control!
And I'm sure others!
Anyone know why you'd want a load of setback, and have to run with a bowtank filled up?