Sounds like a good candidate for electrification. But do consider going to 48v or at least 36v. Line losses are considerable at 12v and this will reduce your range from a given battery bank. Over 50v and you have different standards to conform to. 48v is a happy medium, and is commonly used for boats under 35 feet. An electric outboard might be the way to go for you. Especially if you already have an outboard mount. You might even try a 36v trolling motor. When I say try, of course I mean borrow someone's motor to try before buying one. Be realistic about your power and speed needs. There is a huge difference between motoring at 3kt and motoring at 4kt or 6kt. Big difference between motoring in a protected marina and motoring into wind and chop. We usually don't need nearly as much power as we think, or as much as vendors or builders want to sell us. But there are situations where an underpowered boat is a real PITA. Spend a few months researching before you start buying stuff. Even if you decide to go with a professional installation. For smaller shoal Draft boats, weight of batteries is an important factor. Flooded lead/acid batts are economical and store a lot of juice for the buck, but are heavy. AGM, LiIon, LiFePO4, and other types of batteries cost more but store more energy per pound and offer more mounting flexibility. I am guessing that a BLDC motor of 4.5 to 5kw will be quite enough for your boat, and these motors are fairly cheap. You will need a compatible controller too. A brushed DC motor can't be used if there are propane or gasoline appliances or accessories aboard, but a DC controller is cheaper than a BLDC controller. A salvaged motor and controller from a golf cart could be used, but you would not have regeneration and you would need a reversing contactor. Another consideration is matching motor torque and speed to prop. With a small enough prop and a motor designed for slow operation you could do without a reduction gear, but more likely you will need a reduction of some type. Belt drive is common, and enclosed gearboxes, too. Typical ratios are around 2:1 but some AC motors will want up to 4:1 ratio. A lot depends on your prop, and if you are willing and able to change it or maybe cut it down. If you don't use a reduction gear, you still need a thrust bearing so the shaft isn't simply pushing and pulling on the motor, though a few such as the Lynch motors have them built in. Last but not least is the mounting, and this is where a professional installer can save you a lot of headaches. Obviously there is no universal mount that drops in and bolts up to every boat and every motor, so some amount of custom fabrication is required. Or go outboard and save the hassle.
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