I was recently looking at geared motors that are 12 volt and come in a variety of rpm out puts 75, 100, 200, 300, 500, and so on. What are the actual gear ratios needed for desired speeds?
1:1 to about 3:1 is probably the range most boats are in, I'm sure there are outliers. There isn't one ratio for any given speed.
What is the best way to get desired speed? In most cases that do not require too many trys to get right.