There is enough unit-to-unit variation in the Fenix lights that I wouldn't count on this.

The bigger problem is run-time. How many night-time hours were they in the water before being picked up? The light has to last that long with no battery changes.

While I agree the HDS is by far the cream of the crop it is not buoyant. This is a case where a cheap plastic float strobe that can be seen from any direction is better than the gold-plated best-money-can-buy gadget.