performance with 150 etec on 20' SF
 

What performance should I expect from a 1974 20' SF with a 2011 Evinrude Etec 150 on a bracket. looking to replace my flats boat with a Seacraft for inshore and some offshore fishing, but would like to keep a 40 mph cruise speed and low 50s max.

I had a 20SF with a new carbed Johnson 175 on the transom - had a T-top - but I think 40's cruise speed is pretty optimistic - my WOT was about 45 and my cruise was 30 to 35.

In my experience of offshore fishing, very seldom will a 40 mph cruise speed work out in the blue water, even with my 23'er. I would be happy, my back would be happy, my wallet would be happy and my passengers would be happy if I would average 30 to 35 mph versus trying to run more than that in slop. Use the "search" function and see Bushwacker's posts on his 20' Seafari performance numbers with a 150 etec/bracket.

You must be used to boating in flat water if you expect to run those sort of speeds. Don's right, typical offshore conditions will not allow those kinds of speeds in a 20' hull unless you want to be airborne most of the time! The 20' SeaCraft hull is built like an aircraft with hollow fiberglass stringers tied together with balsa cored decks, so it's very strong but relatively light. You'll find that it will start to go airborne at about 20 kts when seas get over about 3'. A Bracket may add about 3 mph in top speed, but because it shifts weight aft, the ride in rough water will be worse and I'd expect it to get airborne easier. If you run a bow-lifting Viper prop, and don't have a T-top, you might see upper 40's in flat water, but your low speed planing performance will suffer and you won't be able to hang on plane below about 20 mph. A 4B Cyclone prop is much better for offshore use and should let you hang on plane down around 12 mph, but you'll sacrifice some top speed. The 20' SeaCraft hull was designed to run 20-30 mph in rough water, not 50 mph in flat water, so maybe you should be looking at a bass boat.

I had mine up to 50 mph one time with the top down and a very light load in a light chop and it chine walked enough that it would have thrown me out of the boat if I hadn't been really hanging on! At that speed, the outer panels of the hull are completely out of the water, so it's not very stable.

I've made the 160 mile run over to the Abaco's a half dozen times, and even with very heavy loads in the cabin, which significantly improves the ride, we did well to hold a 20kt cruise in the 2 ft square waves commonly encountered on the Little Bahama bank.

yeah, I wasnt looking to get those speeds offshore. I'll be using mine as a near shore, inshore boat mostly as I have a 25' for offshore. But I wanted something versatile enough to use whereever. I guess I dont really need 40mph cruise up the intracoastal, since in my area the regulate the channel speed to 25 in many areas. But there are times when its calm and a longer run from the ramp to the fishing spot.

I do want to maintain the low speed planing abilities. I can hold plane at about 18 mph in my 25 but to hold plane at 12-15 would be great.

That live well in the transom will exacerbate the aft balance issue. I have mine under the LP/
chairs and she loves the weight there. Really noticeable. She sits right down and feels far more planted.

Mr. Whacker has tried as many props as anyone here. He is always trying to get the last
Nth bit of performance outta his rig. My brother has the Cyclone 4 bl on his ole Mako
221 with a 225 HO etec. He loves it. These 20`s love nothing more than stern lift .

There's another live well under the console seat. That should help with balance. The batteries and oil tank are also on the console. Not sure what size feel tank.

Optimum cruise with a 14.5 x 15P 4B Cyclone prop on my rig, with a full cruising load, is anywhere between 22 & 28 mph at up to about 3800 rpm, at over 4.0 mpg. WOT is about 5400-5450 which matches the optimum WOT range of 5300-5500 for my 2007 motor. The optimum RPM is up around 5500-5750 for the later E-TECs, but your CC model is lighter than my Seafari, so you may still be able to spin that prop up to optimum speed for your motor, provided your AV plate is above solid water.

I want your ruby slippers.
4 mpg?

Why? I easily get that with my 1968 19' and 2004 Evinrude 150 DI. Of course, my boat is basically Coosa except for the actual hull, so a bit lighter than most.