In theory you will not be able to troll as slow w/ the 50 as w/ the 40.
Both engines should idle in gear at about 600 to 700 rpms. The 50 will have
a slightly larger prop in terms of pitch so you will be moving faster.
Probably only by 1 mph or so. However, your minimum speed is based on this
rpm.

On a boat rated for the 75 - I would personally not go lower than the 60 but
you have to decide. W/ the 50 chances are you will be wide open the whole
time you are pulling the tube. Do you really want to run the engine wide
open all the time.

--
Tony
my boats at http://t.thomas.home.mchsi.com

"Marko" wrote in message
om...
I'm prepared to go with the 50hp if my dealer is willing to work with
me. My boat is rated for a max of 75hp so no problem there. My only
question is can I troll as slow with the 50hp as I can with the 40hp?
I have little experience with 4-strokes but I hear you can idle right
down to 1 mph.

Thanks for the responses.