115 etec on 20’ Seafari

[doug7488]

Hey guys
I know this has been covered to death but I can’t find a definitive answer
Finally put my 1977 20’ Seafari with 2019 115 etec in yesterday

-13.75 x15” 3b aluminum prop from my old V4 110
22mph @ 6000rpm
I think the hub was slipping

-13.785 x17 3b stainless “viper”
28 mph @ 6000rpm

I’m pretty sure it ran 32 mph with the old 110
That’s all the props I had to try

I would think the etec has 25 hp more than the 110

Any thoughts on props?
Thanks in advance!

[JBASS02]

I haven't messed much with props and have a slightly different setup so this is just for reference. I have a 90 etec on a SF 20 with aluminum 15x15 and it tops out low 30's with gear and fuel. Make sure you have your engine at the correct height.

[Vezo, Part II]

My 1977 Seafari, just sold, with a 2006 Etec 150 had a three blade Viper that sucked. Was told to try a 15 x 15 PowerTech four blade. Actually ended up buying, I think a 14 3/4 x 15. Awesome! Did not have it long enough to determine planing but the hull loved it. No bracket.

Vezo

[doug7488]

Nice!
I’ll look around for one
Thanks Vezo!

[Bushwacker]

Your “115” E-TEC is probably about 125 hp at the prop.

You’ll first need to make sure your AV plate is above solid water before you do too much experimenting with props. Also make sure your tach is accurate - analog tachs are notoriously inaccurate and can be off by several hundred rpm, so can cause you to pick the wrong prop! IF you don’t already have one, I’d recommend one of the Evinrude digital tachs that plugs into the engine computer.

My Seafari used to top out at about 32-34 mph at max load with my old 1975 V-4 115 (rated at power head back then; it was probably about 100 hp at prop.) My best prop was an OMC SST 13 3/4 X 15 3B stainless prop. The blades had enough cup that I was able to raise motor 1 or 2 holes that let me pick up about 3 mph compared to the same size aluminum prop, so that’s a good improvement once you find the right size aluminum prop.

If you haven’t already done so, check out the E-TEC Owners group website - they have tables for all the various motors showing the OPTIMUM WOT rpm, which is what you want to shoot for. The V-4’s have a 2-position valve in the exhaust that’s prone to sticking if you over-prop the motor and run cheap oil, both of which will cause carbon build up. Best to run XD-100 oil and have dealer set it up to run only that oil, as it will run ~ 100:1 mix and not carbon up.

Check out my Sticky post on prop testing In the performance section - lots of tips there on how to find the right prop.

[Fr. Frank]

I'm going to echo Denny here. Go to mounting height before spending too much time with props.

I used to run an '06 90hp Optimax on a 20' Seafari and I eventually got a WOT speed of 36 mph at 6050 rpm running a 4 blade PowerTech OFS 15" pitch. The 90 Opti was actually about 110 hp at the prop. As a SeaCraft dealer back in the early 1980's, I sold a number of new 20' SeaCrafts with only a single 85 hp Johnson on the back, and even one with a single Johnson 70 hp which ran fine with a top end of about 25 mph.

I had to raise my Optimax 90 to where the AV plate was 1 3/4" above the keel before I could get above 32 mph with ANY prop, and most of them wouldn't get me above 30 mph.

[doug7488]

Not sure of the exact measurement but the cavitation plate is up around 2”
I’m waiting on some props to try
Hopefully this weekend
I’ll let you know what I end up with
Thanks!

[Capt Terry]

My AV plate 1.75" above keel was pretty good on my ETEC 150 HO powered 20' Seafari with a 5 blade High Five prop, but when I redid the transom last year raised it to about 2.375" from keel to bottom of AV plate. A better position; a little more WOT RPM, better steering feel on my non-feedback, mechanical steering, perhaps a little more bow rise and porpoise tendency sometimes (which will be fixed by trim tabs). One of my barefoot friends likes to run at about 44 mph. Before the transom redo could get him to about 41 MPH GPS speed on a boom and full length bimini up.

[FishStretcher]

MPH or knots?


I get 32 MPH with a giant T-top on a 20 master angler.



I have a Yamaha F100 with a cheap aluminum 4 blade stern lifting prop from Solas. It's far superior to the 17" pitch. I pull about 5900 RPM.


I also have the skeg mounted wing (hydro shield?) that makes massive stern lift and great pitch authority. But it has to cost me a knot or two in drag.