Pairing engine size with boat size

[JimS123]

The 4 Strokes are certainly Porkers, and are a lot slower with the Holeshot. I can see why there are a lot of People asking if they can Ski with 115s and even larger engines, when with 2 strokes, a 40, even less would have pulled them up

I have 2 of those porkers. A 1-liter 60 and a 3-liter 150. Both are raised on the transom and the SS props were selected to achieve optimum rpm performance.

Both jump on plane in an instant, with ZERO bow rise. On different boats with similar HP / weight ratios, vying the same course, my 1952 2-stroke uses about 7 gal of gas, my 1974 2-stroke uses about 5 gal of gas, the 60 4-stroke uses 3 gal and the big porker 150 uses 4 gal.

That awful 150 porker will get to about 35 mph in seconds at half throttle. At that point if the throttle is pounded it will push you back in your seat and hit 53 mph.

Other than the porkers I have 65 other 2-strokes. They get run on sunny Saturdays on 2 old classics, just for fun. I can fix them all and all are tinkerers.

I can't fix the 4-strokes, and of course they cost a lot more.

As my old fishing buddy used to say: "I didn't buy a boat to save money".

 

[BWR1953]

Hello all, I have a 17 foot Glasspar Seafair sedan with a 90 horse two stroke Johnson on the back. I would really like to upgrade the engine for the best combination of efficiency and power, the boat came with a 75 horse Johnson that ended up being dead, and I was able to find the 90 to put on the back. Right now the boat tops out at around 33 to 35 mph. I don’t know how much the boat weighs full of fuel and gear, I need to look up the dry weight which I remember being somewhere around 1500 or 1700 pounds, the engine is around 300, and the fuel and gear probably add an additional 500 or so pounds. So all said and done it probably weighs somewhere around 2400 pounds? How do I figure out What engine size will produce the best efficiency? Would going back down to a 75 hp tend to increase or decrease efficiency? Would going up to 115 hp tend to increase or decrease fuel efficiency? I'm not as concerned with top speed, anywhere in the high 20s is probably enough for me. I also understand that propeller choice will have something to do with it. I’m in my research phase as I want to upgrade to a four stroke, but I want to make sure I make the right choice. Thanks in advance.

I had one of those boats 25+ years ago. Pretty neat.

Mine had an old 75HP Chrysler 2-stroke on it and it cruised along at about 25MPH. Zero issues getting on plane. I used it in the Chesapeake Bay, the Upper Potomac and the Lower Potomac. Great old boat. When I left MD and moved down here to FL, the guy that I paid to help me unload the moving truck just had to have it, so I sold it to him immediately.

I like your idea of going with a 4-stroke which is close to the max weight of the then-era 150s. I'd expect you to get better mileage and be happy with overall performance.

 

[jimmbo]

I find that if you put a 2 stroke and 4 stroke side by side, and both hit the gas, the 2 stroke will be across the lake and back before the 4 stroke is on plane

 

[KJM]

It don't sound like you are really concerned with high speed and hole shot and such more so just decent speed with good gas mileage. If thats the case then definetly i'd go for 4 stroke. I have a f90 Yamaha on my 19 ft fiberglass and couldn't be happier. The gas mileage is unbelievable compared to the old inboard I previously had. I've been out twice in the last week fishing and left the engine running the whole time out. I haven't burned a 1/4 tank yet. My old engine would have burned about 3/4 tank for the same.

 

[Thirsty Endgrain]

It don't sound like you are really concerned with high speed and hole shot and such more so just decent speed with good gas mileage. If thats the case then definetly i'd go for 4 stroke. I have a f90 Yamaha on my 19 ft fiberglass and couldn't be happier. The gas mileage is unbelievable compared to the old inboard I previously had. I've been out twice in the last week fishing and left the engine running the whole time out. I haven't burned a 1/4 tank yet. My old engine would have burned about 3/4 tank for the same.

Yep, I currently have a line on a 2001 Merc 90hp four stroke, carb'd. I need to go see it and check condition, compression, etc. I would prefer EFI I think, but it's just so hard to find anything right now. It's $2500 OBO. Maybe if I can get it for $2k I'll consider it. My current Johnny gets like 3 MPG maybe, and it pretty much sucks down my two 6 gal. tanks seemingly no matter where I go or for how long. So yes, I'm set on a four stroke. I'd like to find a 115, there are a couple but they are far far away, like $600 just in fuel for the round trip...

 

[BWR1953]

Yep, I currently have a line on a 2001 Merc 90hp four stroke, carb'd. I need to go see it and check condition, compression, etc. I would prefer EFI I think, but it's just so hard to find anything right now. It's $2500 OBO. Maybe if I can get it for $2k I'll consider it. My current Johnny gets like 3 MPG maybe, and it pretty much sucks down my two 6 gal. tanks seemingly no matter where I go or for how long. So yes, I'm set on a four stroke. I'd like to find a 115, there are a couple but they are far far away, like $600 just in fuel for the round trip...

And how long would it take for the 4-strokes to repay that $600 cost?

 

[Thirsty Endgrain]

And how long would it take for the 4-strokes to repay that $600 cost?

Appx 12 fishing outings

 

[Thirsty Endgrain]

Is it worth it in this day and age to upgrade my 90hp Johnny 2 stroke to a carbed Merc 90hp 4 stroke? Or do you just go EFI without much deliberation?

Taking into account that money is not no object.

 

[BWR1953]

Appx 12 fishing outings

Sounds like a plan!