A discussion centering on differences in motor weight might be a right answer, but it's the wrong question. As you point out, the difference in weight is not that significant. What is significant but not mentioned is that the loads on the entire boat generated by a 90HP motor at WOT compared to a 50HP motor at WOT are 90/50, or 1.8X. 140/50=2.8X. And so on.His concern is for safety of the people if the equipment is handled wrong or excessive weight. I pointed out that variations of a few hundred pounds are well within the normal range of variation. Just inviting someone to go boating can bring in 250 pounds.
In fact, a frequent contributor to this board hit an underwater obstacle at high speed with the lower unit on his upsized motor. I believe it was the first time he had it out. Instead of the motor kicking up without damage like a 50HP probably would have, the 120 (might have been 140, I don't remember which) nearly ripped his reinforced transom right out of the boat. The boat suffered extensive damage; insurance and or the installing dealer paid for it, but as I recall his brand new boat was out of commission for an entire season for repairs, which as I also recall ran to the high thousands $$. No mention of what happened to his insurance rates. I dont recall the name offhand; if you search the archive you'll find the whole story.
I'm not trying to discourage you from installing a larger motor. Many have done so with success, and if I'd had the $$ I would have done so myself a few years ago. Just be aware of all the implications.
