Unless you have room to mount the kicker directly on the transom, I would not buy one. If you have to purchase a mount that is spring loaded to raise and lower the motor, don't waste your time or money. I had a 9.9 on a 20 footer and it performed well.
I know what you mean Ken. I took my Scout out about 15 miles on Wednesday and found some nice Kings (to 48") and a lot of Spanish. I only go when we've got the weather like now. I'm always concerned, but the fish call.
I would think a 9.9 or 15 would be more than enough. You're only going to get to displacement speed, so more hp is not really better. You could probably even get by with something like a 5 hp. Try to find one or buy a very low pitch prop. This will let the motor rev up and not lug it with your big boat. If you have a jon boat, or think you might get one later, then get the 9.9 or 15. Otherwise a 5-6 hp would be a little cheaper. I think someone was selling a 5 hp on the classifieds a week or two ago.
Wouldn't get less than a 8hp, if you get into any wind or current you'll need that as a min. If you buy new try and get a high thrust model. If you get a standard model put a dual thrust prop on it, it'll make a big difference.
8, 9, or 10 horse would be my choice. I'd stay away from a heavy 4 stroke and go for an old two stroke. You won't go any faster than the boats displacement hull speed, which will be about 4.5-5 knots, so 15 or 20 hp buys nothing except more fuel burn. The high thrust motors used for sailboat auxilliaries make excellent kickers because they have a gear ratio and prop sized to get the best out of the motor at displacement speeds.
I've used a 2 horse on a 16 footer and a 2.5 on an 18 footer. Dad pushes his 24 footer nicely with a 3.5 Nissan. These are small, but they get the job done. I have an 8 on my 18 footer now and it seems like a bit much. I keep it around 3/4 throttle. Like Pocketfisherman said, you do get to a point where you are wasting power. When I was a kid, we used a 4.5 Evinrude on a 27 foot Halter CC. It got us home twice from offshore. I've heard great things about the Yamaha high thrust models. If you've got the cashola, go with these. Only drawback is they aren't going to be good for a little jon boat if you have one. Many will say this is not enough horsepower, but I've used all these combos with great results.
I must respectfully disagree with Roby though. The Garelick stainless steel mounts are really excellent and when you need that baby, it's great to have. The old OMC mounts were even better, but they are tough to find these days. Just make sure you run it and keep it tuned up. I don't think anyone should run a boat without a kicker. I never will. They've saved my dad and I too many times. - Coach
I have an old OMC kicker mount only used twice I will sell for $50.00 if anyone is interested.... It has been sitting in the attic for about 15 yrs. Brand new when I bought it back then for about $175.00....
The only high thrust models avail. now are 4strokes. yamaha has a 8 & 9.9 in the h.p. range you want. Both avail. with 20 & 25" shafts the 8 has a neat feature, power tilt. not avail on the 9.9. You can use either on a jon boat, you just won't get as high a top end speed like the standard models. I would get a 2nd prop to help offset the high gear ratio if using on a jon boat.