8 or 9.9? With the weight being the same, the 9.9 seems the better option. Pounding into chop can be a real Hp. sponge. Just because you have more power available doesn't mean you always have to use it. As far as fuel consumption goes, yes, if you are using all the power you have available you will use more fuel for more Hp. There would be very little difference between the two at a specific speed at or below hull speed, and quite possibly the larger rated motor would give you better economy by being throttled down compared to the smaller rated motor. If you look at a fuel consumption/output graph of most engines you will see a rather sharp rise in consumption as the output gets closer to maximum. I see the T9.9 is 212 cc and the T8 is 197cc. The High Thrust version of the T 9.9 is 232 cc, and one pound heavier than the T9.9. Not a lot of difference, same gear ratios, and only one pound different in weight. Personally I would opt for the 9.9 and discipline myself not to use more power than I need at a given time. Less fuel, longer life, and a reserve of power if you find wind, chop and current against you.
As far as shaft length goes, unless you cannot lift the leg out of the water for some reason, the long shaft is the best option. When motoring ahead of short steep seas, it is not uncommon to have the prop come out of the water, or at least close enough to the surface to cavitate. Conversely, it is not unheard of to drown the power head just after the stern squats into the trough. These are probably the two most common arguments against outboards in the old outboard vs. inboard debate on sub 30 foot boats. The long shaft, run a little deeper than normal helps on both accounts.
As far as price goes, it doesn't really look like an issue.
Around my neck of the woods, most of the fishing guides are going with the Yamaha, and every yacht owner I have talked to about the Yamaha has nothing but good to say. One owner of a 25' has the 9.9 new last year and thinks he might have a bit of overkill, but admits he has never been out in nasty weather where he might need all he can get.
My boat has the outboard waaayyy out there, with a reverse transom, and the electric start/remote is almost essential.
Last edited by feetup; 05-26-2008 at 12:34 PM.