The Time Out guide to Bangkok calls them "quick, exhilarating, but very cramped and logistically awkward". Yeah.
The canal boats are a commuter service and a fast way across town during rush hour. They really beat standing in a packed non-air-conditioned bus which is jerking along at walking speed in rush hour traffic. On the other hand, Bangkok isn't Venice, and these canal boats aren't vaporetti.
You climb down into the boat, grabbing hold of the cable running along the edge of the roof tarp. Be careful of that tarp; if it's wet it may dump a neckful of water on you, as it did to me. The entire operation of stepping down onto one of the benches that run across the boat is made more challenging because the canal boats seem to have the same "docking" procedure that the river boats do: slam into the dock, slide along it for long enough for people to rush on and off the boat, then push off.
(There are English-language signs at the newly renovated river docks which ask you to wait for the boat to come to a complete stop before attempting to board. If you actually do this you will miss your boat. Just follow everyone else. There is no such irony on the canal docks. In fact, most of the canal docks have only a small Thai/English sign identifying them. Some don't even have that.)
We had to slam into the dock three or four times in order for one older man, walking with a cane, to get off the boat. Finally, with the help of one of the boat conductors (a woman), and a middle-aged man on the dock, he managed to make it off without dropping his cane, or falling into the canal.
After you get under way, one of the helmeted canal boat conductors will make their way along the outside railing of the boat, reach in to collect your fare, and hand you a ticket. Fares start at B.5 (about 12 cents, for a fifteen minute ride four stops from Golden Mount terminus to Pratunam pier, about three km.), and go up to B.15 to go all the way to the end of the line, forty or so minutes away.
The conductors/boat handlers also have the job of lowering the roof tarp, which is held up by a folding metal tube frame, so that the boat can make it under some of the lower bridges. They push down the frame and duck. The boat does not slow down. I guess the helmets are more than just decorative.
In fact, the boat slows down only to load and unload as it slaloms around pilings of steel girders dotted along the canal. Makes a better obstacle course, I guess.
If you are sitting in a "designated side-tarp pulley row" you get to pull down on the pulley raising the blue and white plasticized tarps which keep spray from the canal water from splashing the passengers. This is not simply a convenience to riders. Apichet Kittikorncharoen, nicknamed "Big", of the Thai boy band D2B, is currently in a coma after his car went off the road into a canal on July 22nd.
It wasn't the crash that put him into the coma. Instead, it was a fungal infection he contracted after falling into the water, which attacked his brain. At last report he's still in a coma, and doctors don't give him much chance to live. Something to think about as you clutch the clear plastic handle raising the tarp.
Unfortunately between your exceptionally low position in the water (in a fully-loaded boat, you ride with some part of your body at water level. or possibly below) and the height of the protective tarps you don't get much of a view, but it is a fun ride nonetheless.
And it is comparatively fast. The only cross-town ride that as quick is the overhead BTS Skytrain, which is more expensive, less atmospheric, and worst of all doesn't go many places you need it to. Also, it's as cool a ride as you'll get without air-conditioning, since the water, while dangerously polluted, does bring down the temperature in and along the canal.
All in all, I personally am sorry they're gradually getting rid of the canal boats, particularly since what they seem to be replacing them with is more traffic. My first time in Bangkok they were still running boats up Khlong Phadung Krung Kasem, which would've been very convenient. But I guess the future is with the bus system, Skytrain, and the still-long-awaited subway.
If I could only get over my paranoia about getting splashed by khlong water.