Don't know about a Merc, but last year up in Canada I was fishing in the middle of a bunch of guides with 115 horse Yamaha 4 strokes on 18 foot Silverstreaks and they trolled right down - they don't even bother to carry a kicker. This is trolling for sockeye at barely 1 mph even. I can troll under 1 mph with my Yami 25 on my light Smokercraft if I throw a bucket out, and I have never experienced fouling even after hours of grinding. These new 4's idle just like a car engine, so you can probably get away with it.