We have been to Bangkok many times, and most recently, this Spring. We learned very quickly to avoid the tourist tuk,tuk, the private boat hires and the organised Tourist Ferry by the Chao Phraya River. These are all too expensive. You can catch the normal express Boat ferry's (orange flag is on the bow of the boat). This is used by the Thai commuters. For 15 bahts (2013 charge), you can travel one ferry stop or 30 of them if you want (the first stop is Central Pier, the 8th stop is the Palace and Wat Arun, the end of the service is at Nonthaburi where there is a very cheap market... clothes, goods, etc). The last ferry that will bring you back to Central Pier (by the Saphan Taksin stop on the BTS Skytrain), is at 4:30 pm from Nonthaburi.
Going the whole length of the service is over 12 miles of sightseeing for 15 bahts (instead of the 200 baht you might pay to use the tourist service). While there is no commentary, if you pick up one of the tourists maps available at all visitor centres in Bangkok, the river is marked with all the stops and all the tourist attractions for you to follow. Each stop has a corresponding number on the shoreside to that on the map so you know when you are at a particular stop of interest, to get off the boat for a look around.
If you only want to do one or two sight-seeng stops on the river during the day... you are still not going to spend more than 60 bahts. You generally don't have enough time to do much more than this so you are wasting 140 bahts on the tourist boat (hop on and off).
The river is busy, with lots of barges and ferries - it is lovely on a sunny day and well worth considering for a cheap day out.
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