Best way to achieve correct troll speed in tidal current?

Its my first time trolling an inlet and I was pedalling pretty hard only to be moving at .5mph on my gps. My downrigger line with 4lb ball on it was nearly flat. When I turned around I was trying to keep from hitting 5mph by only pedalling minimally. Then I realized to hit my target speed, I can't just guesstimate. What's the most accurate way to do this? Do I have to measure my drifting speed? Perhaps DR line angle is more accurate?

Even in the open ocean the current can foul your troll.  An inlet may be impossible to effectively troll due to currents.

Yeah, I'm definitely staying out of it the fastest time of the day, but even at times before and after slacktide that movement is still steady. Thankfully I still have access to the shallower less affected areas just outside of the current channel. But there were boats hooking up while clearly in the faster water, and it appears they were sitting still but trolling forward or even backtrolling through it.

It likely comes down to lead or downrigger use then.

As a new guy, I've been wondering about this. When you're on moving water, wouldn't your GPS speed be basically irrelevant? GPS speed is measuring your speed across the Earth's surface, but when trolling, shouldn't we be concerned with the speed of our bait through the water? Which means we'd need a FF with a speed wheel?

I'm less than a novice, just been thinking about this issue.

It's all abount line angle  https://www.fishusa.com/Luhr-Jensen-Troll-Speed-Indicator

It's all abount line angle  https://www.fishusa.com/Luhr-Jensen-Troll-Speed-Indicator

Thanks, so it is line angle. I had no idea there was such a device, but its brilliant because its basically an independent downrigger ball with nothing attached, so there's no drag variable. Ill have to craft some sort of downwards pointer off my laketroller's boom to replicate this. Maybe GPS speed on a calm day at slacktide will give me the the target angles I need at typical depths I troll at with the specific rig I run.

As a new guy, I've been wondering about this. When you're on moving water, wouldn't your GPS speed be basically irrelevant? GPS speed is measuring your speed across the Earth's surface, but when trolling, shouldn't we be concerned with the speed of our bait through the water? Which means we'd need a FF with a speed wheel?

I'm less than a novice, just been thinking about this issue.

Exactly. Maybe your GPS wouldn't be completely irrelevant though. It could give you some point of reference.