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You can calculate the physical limitations of speed on a motor if you have the gear ratio and prop pitch. I've run two stroke 30s before on Classics and couldn't hit 40mph. Mid 30s maybe.
yes. RPM *gear ratio*60* Pitch /12/5280 = theoretical max.
multiply by that by .9 for slip to get something realistic.

2:1.05 gear ratio would = 1.05/2
 
What are your thoughts on this engine, has anyone tried one out yet?
I am considering one to replace my 2004 Mercury 25HP 2-Stroke on my Custom Gheenoe with center console.
At 126 pounds the new engine would only be 12 pounds heavier than my current 2-stroke and can include power trim among a list of seemingly great features.
http://2017newproducts.yamahaoutboards.com/f25
From the Yamaha site below:
THE REDESIGNED F25
Completely reinvented, the all-new Yamaha F25 is the lightest 25-horsepower outboard on the water—two stroke or four stroke. In fact, it’s SOHC 2-cylinder design creates a power-to-weight that’s not only class-leading; it’s category-jumping, taking on Portable performance advantages. Once that sinks in, you’ll realize it means 25 horses can boldly go where they’ve never gone before. Jons. 14-foot aluminum fishing boats. The bed of your truck. While its streamlined design is up to 25 percent lighter, it still manages to pack in exciting new features—like battery-less EFI and an optional electric start kit. The completely reimagined Yamaha F25 Portable four stroke. It’s one of the most exciting outboards to hit the water in years.
BATTERY-LESS EFI
The F25's electronic fuel injection system provides smooth running and greater fuel efficiency than the previous F25. And the system operates without a battery, thus reducing weight so if you want to go light, you can. The New F25’s battery-less system was designed to require minimal effort for manual starting through an auto decompression device and a short pull. (A battery is required for electric-start capability.
QUICKER THAN TWO-STROKE
The new F25C outperforms the traditional Yamaha 25-horsepower two stroke. So it’s the perfect power for 14- to 16-foot aluminum boats and similar craft.*
*Testing conducted by Yamaha at Yamaha’s US Test Facility on a G3 Model 1448 under heavy load conditions.
OVERALL PERFORMANCE
The F25’s SOHC, 2-cylinder design, optimally balanced crankshaft and labyrinth exhaust deliver smooth power, and its Microcomputer Ignition adjusts timing to maintain optimal engine performance, economy and power under all conditions.
What was the lowest price on the short shaft electric start version? Also never found a chart with the weights of the different models?
 
What was the lowest price on the short shaft electric start version? Also never found a chart with the weights of the different models?
Someone with an owner's manual should be able to post the weight chart for us of the different models.
 
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