250-HR Yamaha 70 report

[Matt Gurnsey]

Based on your loading, and based on the comment "It's only in strong tidal flows and bar crossings where she struggles a bit" I would suggest something bigger than a four stroke 70.

The Yamaha 70 is a great motor and I was really impressed with it on Greg and Cynthia's new Lund. But if you feel the Johnson 70 struggles "a bit" then a four stroke outboard of the same horsepower will struggle quite a bit. Four strokes don't have the low and mid range torque of a two stroke, so while in theory you may have the same top end with a 70 four stroke as a 70 two stroke (horsepower is horsepower), the four stroke may not be able to get the boat up on plane when loaded, and may struggle significantly in bar crossings.

Evinrude rigged a 29' boat with twin 250's- one Yamaha four stroke and one Evinrude E-Tec two stroke. When running on one engine, with the other engine out of the water, the Evinrude two stroke would get the boat up to 36 mph. The Yamaha four stroke 13 mph.

Why? It's not that the Yamaha is a bad motor (it's a great motor), it just doesn't have enough low end torque to get the boat up on plane and the two stroke does. Now I know that the hull shape (Deep V) amd horspower are vastly different from what you have now, but I think the results are indicative of what you could expect.

One wrinkle to add into this discussion- what year is your 70? Before 1988 or so engines were rated at the flywheel, they are now rated at the prop. So an old 70 might have only been about 65 at the prop. Maybe even less now if it's tired. So the new "70" might have more horsepower than the old "70". That may help some.

As always, just my observations, thoughts and opinions, and worth every penny that you paid for them....

[Aurelia]

With 2 large coolers, oversized kicker, dinghy, and other fishing gear plus how many people on board, I would not consider your load to be on the light side at all so a small engine would be a bigger challenge for you.

See if your local dealer will allow you to trade it back in with minimal losses on a larger motor if the 70 doesn't work out. Maybe the rigging could be reused from a 70 to a 90?

[Adeline]

Thanks for the great replies...

I guess 70 horses ISN'T the same 2-stroke vs 4-stroke.

One thing's certain though...Adeline is morbidly obese (like her skipper ???) .

It's just that everything looks so good, I just have to bring it all with me.

Well, maybe I COULD leave just one case of beef-stew at home.

I think I'll run Johnny 'til he blows up.

Maybe by then Yamaha will have a new svelte F90.

[A Fishin C]

If I were looking at a repower my 22 cruiser I would look seriously at the Yamaha 115. My 90 runs 20 mph at 4600 rpm.

I think a 115 would do 20 mph at about 4000-4200 rpm which is quieter and more relaxing cruise. I need to do 20 mph min and 4600 rpm is loud.