Before I start, I'm not into boat modeling until I started with this. But I have been with RC Aircraft for some time. So I have a little knowledge on things like radio gear and amps etc. I must also warn you that this maybe a bit long winded, so I must apologise now.

I'm a serious angler and lately have been fishing a big lake and alot of the regulars use baitboats, so rather than sit back I bought one myself. This was a cheap one but has a good hull and it is just right for what I want it for. It is 70cm long powered by two motors which are sort of jet like (see pictures). These are powered by a 12v lead acid battery. The only problem it is a bit slow, especially into a headwind. I would like to upgrade it. Rather than use the jets on it, I was thinking of using a single speed 600 and keep it still on 12v, so I'll use the 600 12v motor. The motors on it look small and are probably 400-480 size brushed. Also the transmitter is like a TV remote control, which means no trim and this is a problem at the moment because it is stronger on one motor than the other. So I will also change this to a 2.4ghz transmitter.

Would love any advice on how to acheive this, especially prop size, direct drive? and bits that I will need.

Many thanks Nige.

If you are going to upgrade the driveline, go for something brushless, as it's not going to be any more expensive than a new brushed setup, but it will outperform any brushed setup by far.
The easy obvious choice would be to use the existing waterjets and just hook up new beefier motors to it.
The question is if the waterjets can take the strain of these new motors. I let you be the judge of that, I havent seen them..
The next question is your hull. What is it made of?
If its vacuum moulded ABS plastic, then don't waste any money on upgrading it. Sooner or later it will crack, you should just get a better hull.
If its a fiberglass hull, then it might be good.

You should also replace that lead acid battery while you are going at it.
A LiPo battery doesn't cost much, but it has way better energy density than a PB battery.

And for the transmitter question, how does this boat steer?
Does it have a rudder, or does it steer by putting differential thrust on the waterjets?
If its the latter, you will need a computer radio with a good array of mixing capability in order to run it as intended.

I agree.

Iwould go for it- when the motors blow up, they prob will if you go for a 4cell lipo Iwould take the flaming opportunity to upgrade to two brushless prop motors, they will be way more efficient than the fans were.

Actually if you are investing in batteries, and your charger can handle it, Iwould look in to A123s. Heavier than a lipo but you can use their entire capacity (not 80% as with lipos) and you can charge them 5times or so quicker than even a lipo!