Since you are fishing for salmon, you won't be happy using one of your F150s for trolling. You will need to get your speed down to less than 2.0 mph for effective trolling unless you are using lures. Since you'll be trolling with the current, the best way to do that is with a kicker. The only other way to get down to that slow of a speed is to use a Beefy Bag or a else drag a 5 gallon bucket.
The second reason to get a kicker is that you'll find that most big 4-strokes "make oil" when used for trolling for long periods of time. The engine will not put out enough heat to fully warm up during prolonged trolling, particularly in the cold water conditions under which you will be fishing. Raw fuel will wash down past the rings and dilute the crankcase oil. This is even a problem in Florida where folks start out with the oil a half quart down and change the oil when it reaches the full mark. Fuel dilution can result in premature engine wear. Given the number of hours that you will put on them when trolling, it doesn't make much sense to wear out your big engines.
While I live in Florida these days, I still keep a boat on the West Coast and fish out of BC quite a bit. Over 12 years I have logged only about 600 hr on my main engine and over 5000 hr on my 8 hp kicker. Changing 0.7 quarts of oil on the kicker a couple of times a season (it makes oil also) is no big deal compared to servicing the main engine.
