I have another suggestion,

Use the 3 motors of your choice, Astroflight 25’s Graupner 600’s whatever- I do like the Astroflight option though..., use one ESC to control the throttle of port & starboard motors, and use a simple “on- off” switch to power the center motor for forward only, like mfr 02 said, it is a waste to have the center motor for reverse only. The on-off switch can be powered by a servo which will be used for extra forward thrust only. The PT will really sing with all three motors opened up and will be manageable with the two motors on an ESC for cruising and scale maneuvers. You have plenty of cruising options there.

Batteries:

I think that NIMH or LIPO is the best way to go. You are going to need lots of “MAH” to give you runtime so (3) 5000 MAH packs would be the way to go for about 10-15 minutes depending on throttle habits. You can probably milk it with the one motor running on the on-off switch some of the time.

I have seen NIMH batteries reach as much as 10,000 MAH, perhaps 3 of them on 12Vcould help you get closer to the ½ hour mark, but running fast motors & an ESC that long will require water cooling to keep them from over heating.

Something to keep in mind is weight. PT’s have sort of like a pin tail type stern so it does not take much for the transom to sink below the waterline. For that boat, strategize battery placement and try to stay light, especially when powering with 3 thirsty motors.

ESC:

Use a marine ESC. Astroflight also makes an ESC if you go that route, or find any of the other marine type ESC’s. If you can get one water cooling ready, even better.

Here is the site for Hobby City, they have plenty of marine ESC’s there on the cheap. Pick one with reversing capabilities.

[link]http://www.hobbycity.com/hobbycity/store/uh_index.asp[/link]

If you want higher quality, go for the Astroflight. It has reversing capabilities.

[link]http://www.astroflight.com/index.php?main_page=index&cPath=17&zenid=docc10v0j ua7n668pom7i6bc9ggemdka[/link]

-Rich.