Question on power
 

Hi. I have 1970 20 ft cc Seacraft.Always ran 115 Johnson cross flow which is fairly light.320 lbs or so. Now I'm looking to repower without adding 80 plus lbs. Any opinions on a 90 hp Yamaha 4 stroke being able to push her?Thanks

Lackler, I just purchased a 1989 20' with a f115 on it. It will run abut 40 at full throttle. That's still a little slow for me. I'm considering up grading to a f150 once I determine if it's safe to put a 500lb motor on the boat. I see other people running them but want to preserve the transom as much as possible. It's never been rebuilt and I don't wish to have any problems with it. I'm in Baton Rouge if your looking to pick up a f115 with 460 hours on it.

I know guys run the new 90 etech and love them on the 20s. Search for posts started by fly4navy. He has one and I think he has posted some numbers. Etech is a two stroke so it will def be lighter than the yami 4 stroke. Prob better economy and everything else than the yami and I have a 115 yamaha.

An F150 is not an "upgrade" on your Seacraft 20 hull.

I have a 2000 carburated Yamaha F100. Basically the same outboard- a little higher redline. I am happy with it. I run a Solas Amita 4 15" pitch prop. It is 4 blades and aluminum. And it stern lifts nicely.

Dragging a below surface foil and a kicker, I can hit 34 MPH. If I dropped the foil and kicker, I bet I could pick up a few MPH. But the "hydro shield" foil/wing that runs below the prop makes for very nice planing speed and helps lift the 58 lb kicker and main engine out of the water nicely. Hole shot is very good with this prop on this boat.

Without a kicker, I bet that prop or maybe the 17" pitch version would let you run something like 37 MPH and maybe plane down to 13 MPH without tabs. I think there is more in it with a better prop (stainless, more tuning) but a $120 prop should get you this far. I think the hole shot on the 15" is much better, though. I have both and keep the 17" pitch as my spare.

I put batteries under the console, and dropped the fuel tank size to 20 gallons and put it under the console. That helps balance. The great MPG of the Yamaha means that 20 gallons is a lot of range: ~100 miles. And a 5-6 gallon Jerry can on the deck can be a reserve tank.

Then I filled the old fuel tank compartment with foam and under the cap to help make it nearly unsinkable.

The engine itself is quiet and very corrosion resistant. The older carburated ones have small jets and don't like dirty fuel with ethanol in it. You just have to be good with filter changes and draining fuel bowls when you store it. EFI would be nice.

Why would you say its not an upgrade, thats a nice motor?

Indeed the Yamaha F150 is a fine motor. I simply believe overall performance of the 20 hull will suffer with a 480+lb motor back there.

I'm sure others would suggest otherwise. Just my opinion.

Original poster asked if a 90 hp Yammie 4-S would push his 20. I think it would be fine.

Second poster brought up the 150 idea which I tried to inhibit based on the very weight he expressed concern about. Granted in my response I failed to express why I felt that way.:o

my 200 merc is 415 - can't imagine much more working very well

I went through the same process about a year ago as I had an almost new 90 E-TEC and considered installing it on my 74 20 ft. CC (20 inch transom). I never did that however and went with a new 115 E-TEC and sold the 90 with my old boat So....I am just not sure what the performance woulf have been with the 90...but can tell you that the weight of the 115 E-TEC (at about 380 lbs.) is just fine and leaves my scuppers dry in just about all stages.

Thanks for the info.It still concerns me toting around extra weight.I have seen another 20 in my area with a 135 etec and it really looks like it squats.