Houseboat companies usually are booked for the summer by April, so it's advisable to start looking early. Comfort and maximum efficiency of space are important factors in choosing the right houseboat for a trouble-free vacation. Sizes begin at 24 feet (sleeping four) and go up to 40 feet (sleeping 10).

Three companies whose boats we saw frequently on the Rideau and whose appointments were roomy and comfortable enough for a family were:

*Go Vacation Houseboats, Kingston Boat Rentals, Kingston, Ontario, (613) 549-4112: All sizes, berthed in Kingston Harbor on Lake Ontario.

*Summer Magic Houseboats, Port Hope, Ontario, (416) 885-9503: 40-foot houseboats only, berthed in Westport, Ontario, on Big Rideau Lake.

*Big Rideau Rentals, Rideau Ferry, Ontario, (613) 825-3317: 32-foot length boats, berthed in Rideau Ferry, Ontario, between Big Rideau and Lower Rideau Lakes.

The price depends on size and luxury, ranging from $350 to $675 (U.S. dollars) for a week-long rental.

Rental companies usually provide anchors, bumpers, propane gas to run the refrigerator and barbecue, full tanks of gas and water, nautical charts of the Rideau Canal and, sometimes, lock passes. Renters must return boats to their original site with the holding tank pumped out and the gas and water tanks full.

ON-SHORE LODGINGS: Overnight docking at a hotel can be advantageous if you're desperate for a good shower, a laundromat and a meal cooked by someone else. In the busy season, however, reservations are advisable. Places to stay include: Hotel Kenney, Jones Falls, (613) 359-5500; The Opinicon, Chaffeys Locks, (613) 359-5233; Dorothy Alford's Lodge, Chaffeys Locks, (613) 359-5816; Rideau Ferry Inn, Rideau Ferry, (613) 267-2152.

INFORMATION: "Small Craft Guide: Rideau Waterway and Ottawa River" is available for $4.50 (Canadian dollars) from the Canadian Government Publishing Center, Supply and Services Canada, Hull, Quebec, Canada, K1A OS9.