On a cruiser, do you really want direct drive (yep, opinion question). Pros: Low end torque, use gears to get on speed, easy to install Cons : Weight of gear box, size might limit location I am looking at changing from direct drive to gearbox, any real advantages?
Not that I have an opinion as to which is best, but off the top of my head here are a couple other considerations to adding a gearbox: Cons: Additional noise level, added complexity and failure points, depending on configuration it could add some maintenance, the gears can give a place for bits of broken hull to find their way into. Pros: can drive 2 shafts from one motor (usually requires custom design) , and as you have mentioned, the additional torque is a really significant plus.
Mechanical side: More torque, but as mentioned above, takes up more space & adds possible failure points. Electrical side: Allows motors to run at more efficient rpm's for given speed, which translates to less ah burned for the same speed. So you could run longer on a set of batteries, or install smaller batteries, saving space / weight. Overall, I like the flexibility of having an ESC + gears in my drive layouts. Nowadays you don't have to change gears to get on speed (just adjust throttle endpoint), but I like the torque for acceleration.
I am an unapologetic gearbox user. They get the motors out of the soup, they let the motors run higher RPM where they are happier and the gear-down provides more torque. If you don't want the noise you can look into belt drives.
Nick brings up a good point, gears allow a shallower propshaft angle while keeping your motors relatively high and dry. That means less maintenance if you survive, and keeps your speed up even with water sloshing around in the hull. Extra torque is questionable - I once ran an experiment with several identical hulls, the only difference being their propulsion. One had a high-torque geared drive 280, the other used a low-powered 365. With identical propellers and matched top speeds, there was no difference in acceleration or deceleration. I did a dozen side-by-side drag races, and there was no measurable difference in acceleration or deceleration. Same with my turning experiments: no measurable difference just because of the gears. At least, that was my determination with the lightweight, low-drag hulls I tested with. Larger and heavier hulls will probably see more benefit, these were very light ships at only 2lbs each. Eventually the geared 280 melted when it got tangled in weeds. The 365, with much lower power requirements, survived that same fault without issue. No need to guess what I replaced the geared 280 with.
