My idea of a perfect pass is to first signal my intention to the slower vessel with a horn signal (one short blast if passing to starboard; two short blasts if to port).
From colregs inland
c) When in sight of one another in a narrow channel or fairway:
(i) a vessel intending to overtake another shall in compliance with Rule 9(e)(i) indicate her intention by the following signals on her whistle:
− two prolonged blasts followed by one short blast to mean “I intend to overtake you on your starboard side”;
− two prolonged blasts followed by two short blasts to mean “I intend to overtake you on your port side”.
(ii) the vessel about to be overtaken when acting in accordance with Rule 9(e)(i) shall indicate her agreement by the following signal on her whistle:
− one prolonged, one short, one prolonged and one short blast, in that order.
What do most folks in the ditch do?
For the record, the description of the horn signals into my text about overtaking is not mine, but was inserted by Jeremy McGeary at CRUISING WORLD, who edited the piece... I generally use simply one or two "longish" blasts, it often depends upon the horn being used... The horns on many boats don't seem to be up to repeated, prolonged usage, and the mechanical air horns on many larger boats can take an unbelievably long time to recycle, the compressor often running for a minute or more after usage...
It is extremely rare for the slower vessel to acknowledge a horn signal in kind, most folks will simply wave, or begin to slow down/move over in response...
Many people communicate with VHF, but in my view that is generally unnecessary, and often results in a proliferation of needless chatter on 16... And, with all the talking on VHF, I feel horn signals are often far more effective in "waking up" many skippers on slower boats, many of whom never see me coming... Never ceases to amaze, how rarely so many folks on slower boats seem to steal a glance behind them - especially considering doing so habitually is often the best guard against straying from the channel and going aground thru so many stretches of the ICW...
Using a VHF when running a fast boat can be problematic in these overtaking situations for a couple of reasons... First, the names on the transoms of most sailboats are generally very difficult to read from a distance, and are becoming more so each year with the proliferation of dinghies on davits. Chances are, by the time radio contact is established, I'm already on top of the guy... More importantly, running a fast boat in a narrow channel, my hands are already full, I don't have a 3rd hand to be activating a radio mike... Bringing a large yacht from a plane down to idle speed in a narrow channel bordered by shallow water in close proximity to another boat is often no simple trick. One hand for the throttles, the other for the wheel which will usually require a major correction as the boat suddenly settles into full displacement mode, and veers dramatically away from the edge of the channel in an effort to seek deeper water... Tough to manage all that, and be talking on the radio as well - especially when a horn signal can so easily convey one's intentions. Obviously, exceptions can often apply, and sometimes a radio call is definitely warranted...
None of this is rocket science, most ICW rookies come to quickly understand the drill pretty quickly... But it all hinges on the slower boat's willingness to cut their speed, and if they refuse to do so, well, then they're just gonna create problems for themselves...