Here are some good videos I found on casting double hand in the salt. Double hand rods are especially suited for blind casting as it greatly reduces fatigue when you have to fire off cast after cast whole day long. Double hander can also handle wind and distance better. With the advance of Switch rods and modern Spey shooting heads, we no longer have to contend with heavy 15 foot rods that used to dominate the double hand scene not so long ago.
Switches in the 10' - 11' range is especially suited for light saltwater estuary work whereas those handling big surf may opt for rods in the 12' - 13' range. Advancement in graphite rod making technology has also made double hander a lot lighter than it used to.
In this first video, the caster is using a T&T 10 footer 6wt employing snap-C, snake roll and switch cast with good effect.
In this 2nd video, Andrew Moy demonstrate the technique of double hand overhead casting in the salt.
Here is another good video on using Switch rod in the shorline surf and estuary by Jeff Putnam with useful tips on how to time your cast in the surf. For some reason I am not able to embed the video here but you can follow this link to youtube:
Note: You can access all my blog post on saltwater spey by clicking on the "Saltwater Spey" link located on the right hand side under Labels.