For a similar experience: I row, and occasionally use a cycling mirror to keep track of what's behind me -- that is, what's in front of the boat. When rowing (sculling) you face backwards. This occasionally presents navigational issues.
The mirror is almost completely useless. It's rather less useful on water than it would be on a bike.
The problem is orientation.
With a fixed mirror, you know where things are in relation to your vehicle (car, boat, bike, etc.).
With a head-mounted mirror, on a bike, you still have a generally fixed landmark to orient off of: the road, which over short distances exhibits to a good first-order approximation a high degree of linearity. That is: it goes before you, it goes behind you, you can draw a line between two points, and you have a pretty good idea of where things are relative to your position.
In a boat (dingy or rowing shell), there is no road (a straight marked rowing course might be different). Without a mirror, you generally navigate by occasionally checking over your shoulder to see if your dead reckoning is about right, then line up your stern (the back of the boat, but directly in front of your line of site). And you hope that nothing pops up suddenly in front of your bow (a buoy, a fixed marker, a swimmer, driftwood or debris, another boat, a breakwater, a dock, a pier, a sea lion, a cruise ship, a seagull, a submarine, a pelican, a whale .... and yes, I've encountered pretty much all of these at one point or another). You check over your shoulder at reasonably frequent intervals (every 10-20 strokes -- about 100-200 yards).
The mirror gives you some sense that there's something somewhere behind you.
It does a really crap job of telling you just where that something is.
If the field of view is large enough, you might be able to orient off the bow of the boat, but generally it's not and you're not fully stable enough to take advantage of that.
I generally row without the mirror.
And I keep my car's side-view mirrors adjusted so I can just see the sides of my car on the far inside of the mirror, to better judge positions of other vehicles relative to mine, blind spot (US flat mirror standards) be damned.
The mirror is almost completely useless. It's rather less useful on water than it would be on a bike.
The problem is orientation.
With a fixed mirror, you know where things are in relation to your vehicle (car, boat, bike, etc.).
With a head-mounted mirror, on a bike, you still have a generally fixed landmark to orient off of: the road, which over short distances exhibits to a good first-order approximation a high degree of linearity. That is: it goes before you, it goes behind you, you can draw a line between two points, and you have a pretty good idea of where things are relative to your position.
In a boat (dingy or rowing shell), there is no road (a straight marked rowing course might be different). Without a mirror, you generally navigate by occasionally checking over your shoulder to see if your dead reckoning is about right, then line up your stern (the back of the boat, but directly in front of your line of site). And you hope that nothing pops up suddenly in front of your bow (a buoy, a fixed marker, a swimmer, driftwood or debris, another boat, a breakwater, a dock, a pier, a sea lion, a cruise ship, a seagull, a submarine, a pelican, a whale .... and yes, I've encountered pretty much all of these at one point or another). You check over your shoulder at reasonably frequent intervals (every 10-20 strokes -- about 100-200 yards).
The mirror gives you some sense that there's something somewhere behind you.
It does a really crap job of telling you just where that something is.
If the field of view is large enough, you might be able to orient off the bow of the boat, but generally it's not and you're not fully stable enough to take advantage of that.
I generally row without the mirror.
And I keep my car's side-view mirrors adjusted so I can just see the sides of my car on the far inside of the mirror, to better judge positions of other vehicles relative to mine, blind spot (US flat mirror standards) be damned.