It all has to do with prop pitch and gearing. If your prop is pitched in such a way that you're maxing out at 6 kts, adding motors wont necessarily give you more top speed. The pitch numbers that are usually stamped on your prop indicate how many inches of travel the propeller will theoretically travel per each rotation. For example, if your rpm is 3000 and you have a gear reduction of 3:1, your propeller is spinning at 1000 rpm. Now take into account, let's say for simplicity's sake that you have a 12" pitch, your boat should move 12" per propeller revolution, or 1000 feet per minute. That equates to about 11mph (in a perfect world). Since water is a fluid (duh lol), the prop of course will slip a bit and not travel the full 12" per rotation. if you ran multiple motors, you would likely have less prop slip, which can also be achieved by placing a larger diameter prop on the boat. The expectation of doubling your speed by running 2 motors at a speed that produces 6 kts was highly unlikely because the propellers can only propel you so far at a given rpm. the speed increase you experienced was likely caused by less prop slippage (more props "biting" into the water and achieveing "traction"). Furthermore, I would caution you about running your kicker motor at full tilt in the water, while exceeding its capabilities with your main motor, as you are no longer encountering a load on your kicker which can cause an over-rev condition and possible engine damage. A lot of kickers do not have electronic rev limiters built in and are limited solely by the prop size and pitch and simply cannot run any faster due to the engine simply not being able to produce enough power to go faster. By removing the load on the kicker while using the larger engine, its encountering almost no load, and you can hear the rpm on the kicker rise substantially. Sorry for the lengthy comment, it certainly was an interesting and entertaining video to watch. It was nice to see theoretical propeller functionality in practice in the real world, and for that you've got a like on this video from me!
It all has to do with prop pitch and gearing. If your prop is pitched in such a way that you're maxing out at 6 kts, adding motors wont necessarily give you more top speed. The pitch numbers that are usually stamped on your prop indicate how many inches of travel the propeller will theoretically travel per each rotation. For example, if your rpm is 3000 and you have a gear reduction of 3:1, your propeller is spinning at 1000 rpm. Now take into account, let's say for simplicity's sake that you have a 12" pitch, your boat should move 12" per propeller revolution, or 1000 feet per minute. That equates to about 11mph (in a perfect world). Since water is a fluid (duh lol), the prop of course will slip a bit and not travel the full 12" per rotation. if you ran multiple motors, you would likely have less prop slip, which can also be achieved by placing a larger diameter prop on the boat. The expectation of doubling your speed by running 2 motors at a speed that produces 6 kts was highly unlikely because the propellers can only propel you so far at a given rpm. the speed increase you experienced was likely caused by less prop slippage (more props "biting" into the water and achieveing "traction"). Furthermore, I would caution you about running your kicker motor at full tilt in the water, while exceeding its capabilities with your main motor, as you are no longer encountering a load on your kicker which can cause an over-rev condition and possible engine damage. A lot of kickers do not have electronic rev limiters built in and are limited solely by the prop size and pitch and simply cannot run any faster due to the engine simply not being able to produce enough power to go faster. By removing the load on the kicker while using the larger engine, its encountering almost no load, and you can hear the rpm on the kicker rise substantially. Sorry for the lengthy comment, it certainly was an interesting and entertaining video to watch. It was nice to see theoretical propeller functionality in practice in the real world, and for that you've got a like on this video from me!
Interesting! Would have thought it would added more.
physics.... drag
Ddd