Repowering a 50-60hp SSV151

[pyro225]

Hi guys - if you've followed any of my posts you'll see i have two glastron ssv151s. They are used 60% river 40% lake. some of my original posts were trying to get the best outboard to be a jack of all trades - going real slow when necessary and having a good top speed when also necessary. I've decided on a different path as i think i will compromise with this.
I think i am going to keep other my i4 80 or i6 90 merc for the lakes and repower the other boat with either:
80s Johnson 50/60HP
Early 90s Evinrude 60HP
Early 90s Yamaha 55HP
All the above being twin cylinder.


I was wondering generally which is the best of these? Also i notice the yammy is 100:1 oil so will save a bit there. My other questions are about top speeds when correctly propped and the kind of economy gains i will get from them all compared to my 80merc and which of the 3 will be best on fuel.

Nearly there now!

Thanks

 

[steelespike]

Speaking very basically These are all going to use about the same fuel at wot.(wide open throttle)
About 6 gph at wot.I think the Yamaha uses 3 carbs. I think J/E 50 uses 2 carbs.
The 60 probably 3 carbs. The 60 probably use about 7 gph at wot.
It seems to me that 2 carbs would do a better on fuel and are less complicated.
The 80 merc will use about 9 gph and the 90 about 10 gph at wot.

 

[pyro225]

Hi sorry they are all 2 cylinder so surely max 2 carbs? also thrown in the mix is a Suzuki 60 2 cylinder would that be similar?

 

[steelespike]

Larger carbed 2 strokes will use fuel at a rate about 12% of the rated hp at wot,possibly more.
Fuel use is the same whether a houseboat or a runabout the speed achieved determines mpg.

 

[pyro225]

Ok so if Im just doing 15 mph which would be better on fuel a yammy 55 or my 80 or 90 merc? Also isn't it worse for fuel on a planing hull

 

[steelespike]

Thats nearly impossible to figure. Assuming the same boat The 80 and 90 surely have a different power curve than the 55 and very likely a different great ratio.
Also we have how many carbs to deal with?Then we may have different technologies as well.
Disregarding the differences; logic says that it should take the same amount of hp to plane the boat.
Very basically; usually "displacement speeds" produce the best mpg But at something like 6 mph and boats designed to produce really efficient displacement speeds can produce automotive type mpg.
The best cruising speeds are usually at just on plane to about 1000 rpm higher.

 

[pyro225]

hmmm ok see what you mean so if I'm below planing speed it won't make much difference? thanks btw