Hello fellow fisherman,
I am in the process of adding many useful fishing additions to my 2012 25SC. I'm not sure if we share the same transmission model number or not, but as far as adding a trolling valve to my transmissioin, it's a very good way to go, very easy installation. My boat in idle now goes between zero - 3.5 knots and anywhere in between with a twist of the vernier type cable (like a prop or mixture control on a small airplane).
We can talk about why I chose a trolling valve over an outboard if you'd like, feel free to ask me any questions through PM or more preferably another post here so others may gather the info as well.
Pictures of my trolling valve installation (along with rod storage rack, and autopilot installation) are in my photo album, just click on my name. Some useful install tips are in there as well with each picture.
I can't quote you a price because prices change ( but expect to pay around $1,000 all said and done), but I highly recommend you go through Richard at Ranger Tugs, he'll get you all set up with everything you need for a competitive price and factory knowledge (and maybe even a matching can of Yanmar paint!).
If your transmission is different that the models installed on the later model boats and you have the option of going electronic trolling valve vs mechanical, you want the mechanical for a few reasons. Less expensive, more reliable, and better fine tuning.
Rob
