Build the 17 footer and let the wife try it out.

you can try it out, too, of course

If you can find enough water to float the boat, then you sould be able to find enough additional water to use as ballast. Bring along some empty plastic bottles. Milk bottles will do, but the big detergent bottles are stronger and have big spouts for fast filling. They work as bailers, too.

A couple gallons of water placed in the boat as ballast should be all that is needed to get the paddler and cargo combined over that 150 pound "minimum" that everyone is mentioning. Just in case that is still a bit light, I'd suggest you carry 6 to 8 empties, and fill as many as you need, when you need them.

Of course, if you happen to bring along a bottle of drinking water, that works, too.

Figure 8 pounds to a gallon, or 4 pounds to a 2-liter soda bottle.

If you are by sandy beaches those widemouth detergent bottles are rather easy to fill with sand. A gallon of sand weighs more than a gallon of water, so it will take up less space. Pass a line through the handle and this makes a nice anchor for fishing, too. (If you want a more permanent anchor, fill the bottle with some sakcrete concrete mix.)

Obviously, if you bring gear you don't need ballast, so the empty bottles can stay home.

Back to the boat choice: Add and reposition the ballast to the point where the boat is working best for your wife. If it still seems that the boat is too big for her for day tripping, then build the smaller version. If not, then build another of the same type. You'll find the second one goes much faster as you'll be experienced.

You may find that with all the trials, your wife likes this boat and that you have different expectations! In that case, search for a different design for yourself.

the difference in size is not critical in cruising speed. Unless you plan to race for the beach, the faster boater just takes it easier and the two boats can stay close together.

Of course, you could just build an 18 foot double. You have room for it, it would carry your gear, and you'ld be close enough together to hold a conversation. Plus, the cost would be for one boat, not two.

Hope this helps

PGJ