Thanks for the advice. I've been looking around and talking to other boat owners in the area, and have just about decided that I'll go with Yamaha. For the same reasons mentioned - a reliable product with good dealer support.
So now the decisions (besides when).
8HP vs 9.9? The 9.9 is only a few pounds heavier and $300 more expensive. So if either one would easily keep the boat at hull speed (if necessary), I'm wondering what the extra power would do for me. Less strain on the engine (longer life)? 20% more engine displacement, would that mean 20% higher fuel consumption?
20" vs. 25" shaft? I'll need to replace my motor mount either way, so which one would you choose? My logic leads me towards the 25", in that the power head and tilt handle would be more accessible. What would be the downside?
Thanks again for the great advice!
Your prop configuration is going to mean more than your HP here, in my opinion, as you can't go faster than 5 knots with a displacement hull. You should discuss power curves and prop pitches with other sailors who understand the concepts. Basically, as a sailboat auxiliary O/B, you want to move large chunks of water, which infers a lot of torque. This argues for the 9.9 HP, but they aren't all created equal. I noticed, for instance, that my 9.9 HP Honda BF100 long-shaft moved my Zodiac onto the plane more slowly than my 25 lbs. lighter Mercury 9.9 HP two-stroke short shaft, but that the top speed was better with the Honda once up on the plane (20 knots vs. 18 knots). Conversely, the Honda worked better as a "tow motor" when I needed to lash the Zodiac to the sailboat when the inboard had issues. The Honda was markedly quieter and cleaner burning than the Mercury, but this is generally the case.
You want a nice clean acceleration without cavitating the prop on a sailboat...whereas an outboard for a planing boat should provide "burst" acceleration...sort of the opposite. So discuss with other outboard users and figure out the weight penalties, etc. A lot of people use 5 HPs around here for 4,000-5,000 lb. 24- and 25-footers, like Sharks, but I notice they tend to run them at top speed to get to the start line.
A note on Hondas: "Hard to start" is relative. My 1985 BF100 and my 2008 BF2 (the air-cooled 27 pound four-stroke) have the exact same "habit". When cold, pull the choke out full and give two rapid pulls. Nothing may happen. Then, push the choke in to the half-way point...give a rapid pull and it should start. Let run for 30 seconds before easing the choke in.
The fact that a semi-antique Honda four and a brand-new model respond identically makes me think that this is a "Honda thing" and not some kind of brand-wide flaw. Nonetheless, Yamahas are also hardly ever a bad choice.
Re: shaft length. This again is a function of your tolerance for weight off the stern, your motor lift arrangements, the height of your transom and the likelihood of the prop clearing the water while in a seaway. Generally, long shaft is preferred, but again, find out what works for boats with similar set-ups. I like motor wells in smaller boats, but they aren't common these days.