The question of how big an air motor you need isn't as clear cut as the size of the boat. If you run an alternator, you can hear the RPM's on the air motor go down when you cut the lights on. There is a conversion of Watts to HP, and there is no way around it. Volts x Amps = Watts. And 746 Watts = 1 HP. So the more lights you drive, the more Watts, and the more HP you'll be taking from your air motor. In general, you'll be fine with the 13 hp. engine on an 18 foot flounder boat. There will be times you'll wish you had some more oomph. But if you go with the big one, there will be times you'll wish you didn't have the extra weight hanging right off the back of the boat. Everything about a boat is a trade-off. Everything.
I believe that there is a point where more above-water lights just won't help you that much. Several reasons for that - the easiest to talk about is glare. But you can keep adding lights, and not have it translate into more fish in the boat. On that boat, you could install 8 of Jerry's LED's and have about all the above-water light you can make use of. If you aren't satisfied with that, find a way to rig some under-waters. You'll be able to spot more fish, and to flounder in more conditions, with under-waters. The trade-off is simplicity.
Install some red LED cabin lights. They won't mess with your night vision, they help people find the fish box, and mostly they help people not stumble and fall on those dark moonless nights.
Get yourself a GPS/chartplotter that updates on shorter intervals. (More times per second.) You're going to be running at night, and in fog. Some of the older GPS designs only update once per second (1 Hz), and that simply isn't enough when the fog is thick above you as well as in front, and you can't see any stars. Make sure it updates at least 5 times a second. Some update 10 (I think they are all GLONASS units), and you can just trust me that it's a big plus on foggy nights. Then make sure you have a mounted, backlit compass on the console to go with it.
There is no substitute on a flounder boat for floating shallow. There are only two things that determine that. The amount of boat in the water (displacement), and weight. You already have the boat, so you can't change the displacement, so worry about weight. Don't shrug off an extra 40-50 lbs. here or there. I know guys who put in a small gas tank, to save weight, then carry another 7.5 gallons of gas in cans, in the back of the boat.
Okay, I lied. It's not really two things that determine how shallow you float when floundering. Or at least there is a third thing that sort of modifies one of the other two. Weight distribution will determine how your boat is floating. Ideally, you want the weight distributed so that you're floating perfectly level. That's the position that will get you floating the shallowest. Put all the weight in the back of the boat, and you'll drag bottom all the time, even though the length and width of the boat is the same. My boat gets "squirrelly" with three big men up along the front rail. Figure out how many people you'll be with, most often, and plan your weight distribution accordingly. Put your gas tank and battery in the middle of the boat, under the console, unless you plan to flounder with three people a lot, and need offsetting weight at the transom.
Your gigs are going to be your push-poles, when you get hung up, and they're the thing that actually puts fish in the boat. Don't cheap out on them. And get gigs with barbs. If you have a fish box with a scraper, you won't have any problem getting them off the barbs, but you'll leave a lot fewer fish in the water with holes through them. I used to have some weird sense of pride that I didn't need barbs - but I outgrew that.
I'm going to say one more thing about the size of the air motor for the three people who will read this far, just because most people don't understand this part. These engines don't have an infinite RPM range. Spin the same prop, same pitch, at the same RPM's, and it doesn't matter what size engine is spinning it. A bigger engine will spin a bigger prop and/or a higher pitch. Both of those things will have you going faster at idle (unless you do something like dragging weights to slow you down, or if you're pushing a bigger boat). The Honda 390 cc and 688 cc engines both have a max RPM of around 3,600 RPM. So if you can get 3,600 RPM with your prop, you wouldn't get any more with that same prop if you went to a bigger engine. Bigger engines let you spin bigger props with greater pitch, and without a greater load (weight/drag), that has a trade-off on how slow you'll go at idle. The drag of underwater lights will slow you down at idle. Pull them up, and the bigger prop will let you go much faster. But without something to slow you down, the bigger engine and prop would likely have you going too fast for many people to flounder. It's all a trade-off, and it's about balance.
Redfish Rick has, in my opinion, the best flounder rig in existence. It's 25' long, if I remember right, and has underwater lights. He needs the bigger air motor. He's also going to be out floundering on nights that you won't be, in an 18' boat. You should do fine with the 13 hp engine. Just know that there are times when the wind is howling that you'll think you should have gone bigger. Just remember that the trade-off is low-end speed all the rest of the time, and extra weight hanging off the transom.
Sorry about the length, but you asked. :biggrin:
