Welcome to the forum.
You are doing very well to pedal a rig that size at the speed you do!
Perhaps the most knowledgeable and committed pedal boat designer is Rick Willoughby, no longer on this forum. He does have a website, and facebook presence as Rick Will.
In terms of the weed problem, Rick has designed, and will supply a folding prop, or instructions for making one. These are folded at rest, and the act of spinning them draws the blades out, so to de-weed you just stop pedalling, the blades fold back, and the weed should fall off in the stream as the boat glides forward. He has also done a lot of work with props you can lift out of the water easily for stubborn weeds. http://www.rickwill.bigpondhosting.com/Propeller.htm
I don’t know what kind of prop you are currently using, but generally, high aspect ratio props, usually two blades, are suitable for pedal power. Many people use a correctly sized model aircraft prop.
In terms of a redesign, I would say definitely go smaller if you possibly can.
The hull, ideally wants to be narrow, and up to about 25 feet long for best efficiency. I appreciate that if you are living aboard, your needs for load carrying are likely to be much higher than most pedal boats. A catamaran design might be a way forward, giving you a large, stable platform with skinny hulls.
If you want to make way in any sort of a breeze, then reducing the height and complexity of your superstructure is a must. Wind blowing on a large superstructure will very easily overpower human power.
The Escargot design by Phillip Theil may be of interest, and a straight forward build. It does have a rather large wetted area, and still a fair amount of windage, so for pretty sheltered conditions only, but should still be much easier to pedal than your current boat. http://thistinyhouse.com/2012/pedal-...d-shanty-boat/ http://shantyboatliving.com/2012/esc...ats-germany-2/ http://www.gruene-flotte.de/index.php?hauptrubrik=100
If you go this route, I would definitely look to Rick Will in terms of the drive and prop design.
Hope there’s a starter here. I am no sort of naval architect or boat designer, but I have cobbled together my own pedal powered catamaran which I am pretty happy with.