I don't think the difference will be significant. Just combine both keels into one and see what u get. Any 4 or 5kw motor will push your 20' boat just fine. The real engineering will be matching a prop and possibly reduction gear to your motor for most efficient operation with your hull. And placement of several hundred pounds of batteries. Do you already have a prop a shaft and shaft tube stuffing box? If not, you might consider an electric outboard, since you already have an outboard mount. You can buy them ready built, or convert an old gas outboard to electric, simply replacing the engine part with an electric motor. What range do you have in mind? If you just want it for docking, 3 or 4 flooded lead acid group 31 batts will do just fine, for a fairly low price. If you hope to be able to motor for half a day, you will need a more high tech battery bank, to keep the weight down and still give a reasonable ah capacity. LIFePO4 is getting a lot of good press. Lead acid flooded cells give the most ah per buck but they are very heavy, and I am guessing you would want to keep battery weight as low as practical in a boat that size. Another thing to consider is motor type. A brushed dc motor is the cheapest way to go, especially if you consider how cheap the controller is, but you don't want a brushed motor if you have any propane or gasoline accessories onboard. Most electric sailboats have BLDC motors, Brushless DC. These are pretty much the same thing as a 3 phase permanent magnet AC motor, the difference being the power supplied. Commutation is through hall effect sensors or optical encoding, though some small motors are controlled using back EMF. The controller will generally cost as much or more than the motor. Good luck with your project. I researched for 2 years before finally buying components a couple months ago for the repower project I am just now completing. Don't get in a hurry and start buying stuff that a few months from now you might decide isn't what you really want. Try to base your design on one already proven in boats similar to yours, if possible. Most 20' sailboats use outboards and that is where I would first concentrate. If you know someone who has a big 36v trolling motor, you might ask to borrow it for a day and see if a trolling motor would work. You might pick up a used one for a couple hundred bucks, and get off light, since the controller is built in. All you would need is the batts.
| Reply via web post | • | Reply to sender | • | Reply to group | • | Start a New Topic | • | Messages in this topic (3) |
No comments:
Post a Comment