What is your boat made of? If it is plastic, is it regular Royalex or R-84 Royalite? Nova Craft tends to call Royalite "Royalex", and regular Royalex "Royalex Plus".
It might make a difference in deciding what type of adhesive to use for securing anchors.
Second, how do you intend to use the boat? Are you just going to be paddling it tandem?
If you are going tandem and don't anticipate any heavy, duty whitewater usage, a pair of Gaia tandem end bags may suffice: http://www.gaiasports.com/product.php?productid=16324&cat=359&page=1
These are quite light. There should be plenty of room in the front stem of the canoe (even it the bow person is sitting) and behind the stern seat for these.
If you just want the boat to float reasonably well in the event of a capsize, just the tandem end bags may suffice. If you anticipate paddling serious whitewater you may want more floatation. You would certainly have room for a Gaia center bag: http://www.gaiasports.com/product.php?productid=16328&cat=359&page=1
You could also go with the standard vinyl coated nylon Gaia center bag of the same size which costs less but is significantly heavier. The specs indicate dimensions of 50" x 36" but that is for the flattened, uninflated bag and both dimensions will shorten as the bag is inflated. The inflated bag will probably be no more than 44-46" in length so if placed in the center it will occupy less than 2 feet in front of and 2 feet in back of the center thwart.
You will also need at least 4 anchors for "keeper straps" to keep the bags tucked up into the stems of the boat and to keep the center bag from sliding forward or back. These don't have to be real heavy duty. I usually use 1" stainless steel D rings on vinyl patches or just 1" nylon webbing loops on vinyl patches. For keeper straps you can use just about anything. I like 1" wide flat nylon or polypropylene webbing but you could use 3/4" wide flat webbing, or tubular webbing, or polyester webbing or even accessory cord for this purpose.
For bag lacing I like to use 3 mm diameter nylon accessory cord. Nylon cord stretches a bit when wet but it really doesn't make any difference. You could go with 2 mm cord or heavier cord. I drill holes in the boat just below the gunwales. I like to space them about 4" apart but no more than 6" apart. Drill with a bit just big enough to allow the cord to pass. On a Royalex boat I sometimes drill the holes very slightly undersized, then use a warm scratch awl to ream the hole just a little bigger to allow the cord to pass. The Royalex will then sort of settle back around the cord.
I just lace the cord in a straight across, back and forth pattern but you can use any pattern you like. A keeper strap can be secured around a carry thwart near the stem, or a fastener secured under the deck plate, or to a hole drilled through the hull at the stem just below the deck plate. The other end of the keeper straps securing the end backs attaches to an anchor bonded to the hull floor. The center bag keeper strap can just attach to a floor anchor at each end.
Run your lacing and put your bags in the boat and inflate them to see just where the ends of the bags will wind up when it comes time to mark the position of your anchors. Vinyl D ring patches can usually be bonded to normal Royalex boats (which have an inner vinyl layer) with a vinyl adhesive like Vynabond. Royalite boats can pose a problem since vinyl adhesive often doesn't bond well, or does not result in a durable bond.
Some folks use contact cement (like DAP Weldwood) to secure bag anchors but if the anchor is submitted to much tension it might work loose. Another option is to use West System G Flex epoxy to secure vinyl anchor patches which should work with both Royalex or Royalite. The G Flex does not result in an instant "stick" like with contact adhesive or vinyl adhesive so you have to tape the anchors in place with duct tape to keep the from sliding around, and lightly weight them with something like a sand bag or water filled bag while the epoxy cures.
For composite boats if you have any epoxy and fiberglass handy you can 'glass in nylon webbing loop anchors more cheaply. Fray the ends of a short length of webbing, make a loop out of it and cover the frayed ends with several layers of fiberglass.
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