Those running 115's on a 20
 

I know this has been covered alot. Not a speed demon, etc.

Just looking for some insight from guys running 115's on a 20.

I found a smoking deal on a brand new Yamaha 115 2 stroke carb engine. Late model 2007 never been installed leftover. I had my heart set on a Zuke 140 but this deal is half the price.

Just looking for some reassurance that the performance is adequate. I already have a fully restored 23. My 20 is going to be for running around, back bay fishing, etc.

Anyone care to share performance numbers on a 20 SF with a 115 2 stroke?

Different animal, but back in the late 70s, my dad bought a 20' Grady CC with a 115 Rude on it. From what I remember, that boat would top out around 33, but I don't know what kind of load it had when it did it. I imaging your SeaCraft would be a few mph/kts faster. Not sure of the cruise numbers.

I saw the ad for that motor as well. Good luck. That's a good buy.

Personally, I think 115 hp is plenty on a 20.
I run a 1983 115 Merc Inline 6 on a Seafari. I'm pleased with it performance wise. I use a Quicksilver Black Diamond 13-3/4 x 15 alum prop.

Out of the hole and on plane instantly and tops out at 36 mph @5500 rpm.
Idles around at just under 2mpg.
3500 rpm gets 2.3 mpg and 21mph
4250 rpm gets 2.5 mpg and 27 mph
5000 rpm gets 2.4 mpg and 31 mph
5500 rpm gets 2.1 mpg and 36 mph

My motor is only about 300 lbs but I have 2 group 27 batteries in the stern hatches. The Yamaha 115 is about 60 pounds lighter than the 140 Zuke. That can be significant on a 20 inch transom. A little less concern on the 25" transom. Also worth considering are the E-tec 90 (325 lbs) and Etec 115 and the 115 Optimax (both about 375 lbs).

Keep us posted. Must be a bummer having to make such a decision:D

Brian - i pulled the trigger on it. It's a good deal on a proven engine and will save me alot of pennies.

McGillicuddy - if i can get those numbers i will be perfectly happy for sure. Do you stay on plane at 21mph without tabs????

mrobertson,
Nice score. Yeah, I stay on plane easily to about 15mph. I will be putting trim tabs on as I seem to lean to port a wee bit when running NW.

The gear ratio on the Yammie is also 2:1. For me a 17P was ok but when I went to a 15P every aspect of performance improved. Including top speed and economy. I believe you'll get better economy with that Yamaha - probably over 3 mpg at 4000rpm.

I would love to see what that engine does with the same prop I use.

You might consider a 4 blade semi-cleaver prop as you'll have more weight aft in the cc. Check out PowerTechs SCD4. That Yammie IS a proven motor. If you can, get the Yammie controls, everyone claims they're great.

I'm very interested to see what i get out of mine.

I cut the tank down to 50 gallons and im moving it forward as far as i can. likewise, my batteries will be under the console. I mostly do fly/light tackle fishing so i'm usually pretty light when fishing.

im thinking more and more this 115 was a good idea, im stoked!!!

Congrats, nice score. Good Karma!

You made a great choice with that 115! I ran my Seafari for 31 years with a 300 lb 1975 115 Evinrude cross-flow motor on it and it was a perfect match for the boat. Back then motors were rated at the powerhead, and it was actually only about 90 hp at the prop! That newer motor should be at least 25 hp stronger than what I used to run! I have trim tabs and a Doelfin on the motor and could plane at 12-13 mph with a very heavy Bahamas type load, ~ 80 gallons of gas, up to 4 scuba tanks, and a couple of big coolers full of ice and groceries. It also had a 2.0:1 gear ratio, and I ran a 13 3/4 x 15"pitch OMC SST prop that was a perfect match for it. You might be able to run a 17" pitch with a lighter boat and a little stronger motor. We used to cruise all day long at 4500 rpm and about about 20 kts (~ 23 mph) at about 8 gph, with zero durability problems. It was still running good with about 1000 hrs on it when I sold it prior to repower with the E-Tec. I seriously considered going with a 115 E-Tec, but the V-4's weren't yet in production in 2006 when I was ready for a motor. I made 6 trips from Palm Beach to the Abaco's (Green Turtle, Great Guana & Man O'War Cays), about 160+nm each way, and I averaged 2.8 mpg over those 6 trips, running heavily loaded each time. The most speed I ever saw with that motor was about 35 with a light load; I could run at least 32 anytime even with a heavy load. Don't know much about those Yamaha's, but from what I've seen they appear to be pretty much copies of the newer OMC's. I'm sure it's loop charged, which should help fuel burn. On that lighter boat, I'd think you would easily get 3 mpg and maybe 37-38 mph WOT with a good stainless prop. (I think Gillie would get a little better mpg if he ran a stainless prop!) Motor should be set up with AV plate at least 1" above the keel.

I run a 4 stroke Yamaha 100 in a 20' master angler. Not a speed demon, but tops out at 33 dragging a hydroshield skeg mounted hydrofoil thru the water. Plus I have a kicker on the stern, too. Cruise is 20-24MPH.
I think a 115hp two stroke would be great. You wouldn't need the hydroshield so it should be faster, so Bushwacker's 37MPH estimate makes sense to me.