We had only two days to spend in London before departing for Northern England. Armed with a long list of sights to be seen, but weary with jet lag, we thought a couple of hours cruising along the River Thames would be a nice easy start to our short visit. But what should have been a pleasant sojourn became an excruciating ordeal that had us contemplating jumping overboard and swimming for it.

No, the weather hadn't gotten rough, and the tiny ship wasn't tossed. We just got to the dock late, neglected to find out the lengths of the dozens of different tours, and got on a boat headed for Hampton Court Palace, which I knew as a nice palace with a neat hedge maze.

For nearly four hours, we were crammed inside a boat that cruised slower than the joggers along the shore. By the time we docked and made our way to the palace's gorgeous gardens, the children were arguing and we were in no mood to tour a castle. The very thought of the return trip sent us scrambling for a pub and a train schedule.

To prevent you from squandering precious vacation hours, here's a primer on the more than 20 different cruises that depart from easily accessible London piers for points along the River Thames.

If you've only got a short time to kill, try these cruises:

City Cruises (telephone 011-44-171-237-5134) leave Westminster Pier, near the Victoria Embankment underground station, and head down river to Tower Pier, close to the Tower of London, Tower Bridge and Riverside Walk, a nice shopping area. The trip takes 30 minutes, operates year-round and leaves every 20 to 30 minutes, starting at 10:20 a.m. During the summer, the cruises extend into the evening. Round-trip cost is about $9.30.

Westminster Circular Cruise (011-44-171-839-2111) goes from Westminster Pier to St. Katharine's Pier, just past Tower Bridge, and back. The one-hour round-trip cruise operates year-round, weekends only in winter, daily April through November, beginning at 11 a.m., and departs every 30 to 80 minutes, depending on the season. Cost is about $9.

If you're in the mood for a longer cruise, but don't want to spend an entire day, try these:

Catamaran Cruises (011-44-171-987-1185) operates boats between Embankment Pier, a few blocks from Charing Cross Pier, to the quaint riverside town of Greenwich, stopping at Tower and St. Katharine's piers. The hour-long cruise operates year-round and leaves every 30 minutes, starting at 10 a.m., with the last boat returning at 5:15 p.m. A round-trip ticket costs about $12.

Westminster Passenger Services Ltd. (011-44-171-930-4097) boats travel from Westminster Pier to Greenwich. The trip, which takes an hour each way, operates year-round; during high season it departs every 30 minutes starting at 10 a.m., with the last boat at 5 p.m. Cost for a round-trip journey is $11.75.

Thames Cruises Ltd. (011-44-171-930-3373) operates cruises that go from Westminster Pier past Greenwich to the Thames Barrier, an engineering marvel built to stop London from flooding. The 75-minute one-way trip operates March to November, with four departures daily during high season and two during low season. Cost is about $11.20 round trip.

If you have time on your hands, here are your choices:

WPSA Upriver Ltd. (011-44-171-930-2062) goes from Westminster to Hampton Court, which takes between three and four hours each way, depending on the tides. Cruises run from Easter through October, leaving daily at 10:30, 11:15 and noon. Cost is about $19.30 round trip.

WPSA also operates service between Westminster and Kew Gardens. The trip, which takes 90 minutes each way, operates from Easter through October, leaving at 10:15, 10:30, 11:15 and 2. Cost is about $16.10 round trip.

If you prefer cruising under the stars, try these:

Several evening cruises depart from Westminster Pier. WPSA boats (see above) leave at 7:45 p.m. on Tuesdays, Thursdays and Saturdays, from May through September, and stop at the Millennium Dome; round-trip cost is about $12.90. On Fridays, the cruise goes to Tower Bridge, leaving at 7:20 and 8:20; cost is about $8. A cabaret dinner cruise, operated by City Cruises (see above) leaves at 7 p.m., returning at 10:30, Wednesday-Sunday from May through October; cost is about $68.

Two evening cruises depart from Embankment Pier. Catamaran Cruisers (see above) operates a daily supper cruise from May through December leaving at 8 p.m and returning at 10:30 p.m.; cost is about $90. Catamaran also operates an hour-long circular cruise year-round with several departures starting at 7:30 p.m.; cost is about $10.50 round trip.

Woods River Cruises (011-44-171-481-2711) operates a three-hour evening dinner cruise that leaves from Savoy Pier, near Westminster Pier, at 8 p.m. Wednesdays, Fridays and Saturdays year-round. Cost is about $86.