i have a 115 2 stroke mariner on my 20 fter and i usally cruise at 25 mph. it will go faster but with the fuel prices and all. i'm also in mass and do alot of fishing around the vinyard. i'll keep my eye out for something for you. moved my battery to the bow to lesson some of the weight in the back this spring. like the guys say on thr site. the less weight aft , the better the boat cruises. i don't like the water coming threw the rear scuppers and leaking threw the wire hole and into the bildge either. this may help.

mercury is the way to go if you can find one, i have a 94 200XRI with 2003 power head, lots of power at 395 lbs. gas thirsty but shes got power bottom, middle and top!

Although self-bailing at the dock is an obvious issue with a 500 lb motor, it's not the most important IMHO. The OPTIMUM motor weight for the 19-20' hulls is around 300 lbs because that's what they were DESIGNED FOR! As you increase motor weight above 300 lbs, your min planing will increase from around 12-13 mph up to the low 20's and the ride will get worse! You can offset some of that adverse CG shift by moving batteries, consoles and gas tanks, but the boat performs much better overall with a lighter motor. I'm speaking as a guy who's "been there, done that"! I ran my boat for over 30 years with a 300 lb V-4 and it handled great in all sorts of conditions. When I repowered, I increased motor weight by about 130 lbs AND added a bracket with 30" setback, both of which significantly shifted CG, with significant negative impacts on min planing speed and ride! Self bailing at dock is still acceptable because of the big flotation tank on the Hermco bracket (I would NEVER install a NON-FLOTATION bracket like a Stainless Marine or a Porta on a 20!) With the help of a 4B stern lifting prop and a fin, I finally got ride and handling back to about what it was, but it took a lot of tweaking!

Bottom line, the boat will perform best with a lightweight 2-stroke. As others have suggested, a Yamaha 2S V-4, an old Black Max Merc V-6, or a mid-90's OMC 60 degree V-6 all have good power/weight ratios and would work well. Send a PM to Big Shrimpin . . . I'm sure he can fix you up or help you find a good deal on a motor.

you might find a nice fresh drop on powerhead at scream & fly - I can get you references from there on the seller - Frank Mole Transport over there runs the whole east coast and could throw a motor or powerhead in his truck easy, he's based up there

Power for a classic 20'
 

I really appreciate this thread. Like my man Teasem I like to to be able to go home when it's time to go home. I use to run south out of Angel Fish Creek (Northern Key Largo)We sometimes would end up 20-50 miles to the east or maybe south so coming home was usually trying to beat the sunset. Here in Central Florida I have fished from Steinehatchee to Tampa Bay and I'm still the same way; "Let's go find some fish" and I continually end up 2 hour's from the boat ramp. This new 20 footer project will be fun and getting to the end result is the fun part. So I'm all ears when I read about powering these classic 20cc's.
I can really appreciate the effect of how the center of gravity will effect a boat's performance and attitude. So what really can you expect with running a later model 6 cylinder verses a 4 cylinder? What I had thought up to today was that the hull would be okay as long as the motor weighed as close to "400lbs" as possible; and one of the the ultimate motors of choice is the DF140 weighing a tad bit more. I figured the 150 would get the boat to the mid to upper 40's and a 175 maybe 50/51 a 200 low to mid 50's. The 4 cylinder's maybe upper 30's. but great fuel economy. Of course I agree completely your only going to go as fast and safe as the sea allows you; thoroughly understood! So the question is; with a full transom and some sort of floatation bracket, the batteries up front, a standard 49 gallon fuel tank slid forward, a livewell under a leaning post, a raised deck and scuppers out the back, What is the ideal motor?
Like Dave I enjoy re-inventing the wheel and trying to acheive the perfect or best balance for the hull and my specific needs. For me it's a livewell full of frisky bait in the am. and a cooler full of dead fish in the pm. I need rod holders a good bottom machine/gps and good tunes.
When I was a "wee lad" in the early 70's and these 20's started showing up they were the ultimate fishing machine. The best of the best fished out of them. Heck in 1972 I think all they had was a 3 or 4 cylinder outboard; my dad replaced a '68 100 horse Evinrude with a new 125 Johnson on a 18' Thunderbird and it was huge! All the larger boat's ran I/O's or inboard's. From that point forward the outboards grew bigger every year and in 1981 I had my own 235 Evinrude on my boat.
So please chime in. What motor do you have on your 20 ft Sea Craft? does it porpoise, do you have trim tab's? does it self bail? how fast does it run? how many gallons do you burn doing what you do? Are you happy with it's performance or how would you improve it?
The ultimate goal is to share the vast array of knowledge here and improve and modernize these classics so they'll be around another 40 years from now.

Thanks' Wild Bill

I have a 375lb Mercury Optimax 90hp. I have the Seafari 20, so I have more weight forward than the CC. WOT with normal load is 33-34. Cruise is 22-24 mph at 5.3 to 5.7 mpg.
I had tremendous problems with ethanol with this motor (12K in warranty repairs), but no problems since I stopped using blended gas.

Thank you for everyone's input. I decided against the ox66. Turns out the marina also had a 2007 f115 with 34 hours so chances are in going that route. The 115 weights about 15 lbs more then my current motor but the fact it's a newer 4s and I know it's history will put my mind at ease when out fishing. I've never fully trusted the mariner and I've got a yammie 4s on my other boat and love it.