Over the last couple of years I have been using spraydecks using a bungee cord system. However a couple of decks using a rand system have found there way into my kit bag. So how do they compare? Who would win in a Bungee Vs Rand contest.
A randed deck uses a rubber band (rand) rather than a thick bungee cord to seal the deck onto the boat. Immersion Research uses a rand that has a couple of ridges/fins that help improve the seal. The two decks (IR Royale and IR Klingon Empire) in the images shown are for the same size cockpit. This highlights one of the key differences between a rand and bungee deck.
To get a really good seal the rand deck uses a much shorter length of rand comapred to the bungee in the corded deck. The rand is tough to stretch, but is stretchy (just not as much as a bungee deck) and gives a superb seal against the cockpit. I personally find them tougher to use.
A bungee corded deck tends to be easier to stretch and will have a level of give and may remain slightly stretched over a period of time. A rand is less likely to be stretched out of shape and will retain its shape/length.
A rand also has more surface area contact than a bungee cord so overall can offer a much better seal. The fin design used by Immersion Research takes this to the next level offering additional barriers for the water to try and get passed. I have found decks using this system (including the Royale) to be the driest I have ever used. This has been the case even on boat with very awkward/shallow cockpit rims.