Is that still VMC ?
The JAA syllabus for the PPL includes some very basic instrument flying training. It is limited to the ability to fly a 180° turn in IMC, just in case a pilot enters a cloud by mistake. And you can beleive me, this happens, hopefully not frequently, but periodically.

Most of time, pilots flying just below a layer of clouds enter it because the layer is getting down, or because they get distracted and climb that extra few feet. Suddenly anything gets white outside, the pilot realizes what’s going on, push the column, and everyhting is normal again.

But there is another case where the notion of VMC vs. IMC becomes much more subtle than the simple “in cloud” vs. “out of clouds” definition. When flying over the sea, with a high pressure haze layer in example. Under such circumstances, you can clearly see the sea when looking down, but there is no clear natural horizon, as sky and sea seem to merge in the haze.

Boat or plane ?
While flying in such conditions recently, under an IFR flight plan, I experienced a brief spatial disorientation because of an extra factor. I just finished a left turn after receiving a clearance direct to some point in my flight plan, and I had a short glance to the right.

At this moment, I saw a white spot with a white trailer, on a blue background. My brain interpeted it as planes with condensation trails in the sky, and he concluded that we were still in the left turn. I had to look at the artificial horizon for a few seconds to convince me that I was flying straight and level !

So what about these planes is spotted ? They were in fact boats on the sea, looking similar to planes because of the trail and background color. Even as a trained IFR pilot, I needed all my confidence in the instruments not to start a corrective manoeuver.

Trust the instruments
Once again, the basic rule of IFR must be reharsed here, and it also applies to VFR pilots flying in such conditions: trust the instruments ! The likelihood of an instrument failure is much less than of disorientation.

And even if you’re a VFR pilot, it is certainly legal to fly in such hazy condition over sea, but it is certainly questionnable. If you have some open sea crossing to fly and suddenly feel uncomfortable, keep the following things in mind:

1) If your plane is equipped with an autopilot, it is the good time to use it
2) Even if your fly manually using the instruments to help maintaining attitude, you’re still VFR, and have to look outsite for traffic
3) In case of haze, it is much better to have the sun in your back than in front, so turn around if it gets really bad
4) Again, trust the instruments

With all of that, your flights in situations with an un-clear natural horizon should be uneventful, but never tell I engourage such flights, nor I encouraged you flying VFR in IMC.