If you keep your feet on them and restrain the paddles from freewheeling, yes, much more. Rather like dipping your oars in, in a rowing boat and ‘checking’ the boat’s progress.

This would be most pronounced on a traditional peddle boat, with rotary paddle wheels. However, there are some, more innovative craft which use flipper-style paddles, and in the case of this type the effect would be negligible – more akin to a scuba diver resting their flippers.

See this type of boat here, at:

http://www.youtube.com/watch?v=mTlgo-wQlvo&feature=related
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So, the point is that in order to be a good swimmer, you must be able to hold your wrist, hand and fingers flat and those forearm muscles must be strong.

But, I don’t know where you (or anyone else) got the idea that having large/strong forearms would affect your streamline but, that does not happen … not one bit.

So, lift weights to make your forearms strong. A great lift to do is to take a dowel (cylindrical piece of wood) that is about 3-4 cm in diameter. Drill a hole through it in the middle between the ends. The hole should be large enough to thread a piece of rope that is about 2.5 to 3 feet long.

Tie a 5 to 10 pound (2 to 4 or 4.5 kg) weight on the other end of the rope. Now, with your fingers going over the top of the dowel (you can buy one at any home improvement store or most hardware stores) roll the dowel so the rope rolls up. Then, after letting the weight down, turn your palms upward and roll the weight up again.

This is a KILLER exercise and will develop your forearms. We used to call our arms "Popeye" arms … you’ll see and feel why. (If you don’t know who Popeye is, look up "Popeye the Sailor Man" on google and when you find a cartoon, look at his forearms).
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