Lightning protection on sailboats is an un-researched area of knowledge.  Most of the information is based on the theoretical physics of lightning coupled with experiential and anecdotal evidence.  This doesn't mean we know nothing about the matter. The articles and links below pretty much cover the ground and I suggest you read them over before deciding the level and complexity of any lightning protection system for you boat.  Two things seem clear:

• You CANNOT make a boat lightning proof, nor even much reduce the chances of a strike.
• You CAN significantly improve the chance you and your equipment will survive a strike.

Read on...

Articles

  Lightning Strikes Onboard  by John Payne(Adobe PDF File, 74.2 KB)

  Marine Grounding Systems  by Stan Honey(Adobe PDF File, 633.7 KB)

  Understanding Lightning Protection  by Bill Laudeman(Adobe PDF File, 170.8 KB)

  Cone Of Protection From Lightning (Adobe PDF File, 76.6 KB)

  The Applicability of Lightning Elimination Deveices to Substations and Power Lines 
  by Abdul M. Mousa, BC Hydro, IEEE Transactions on Power Delivery, Oct 1998.(Adobe PDF File, 1 MB)
  Read this one if you believe lightning eliminators (static dissipaters) really work.

  Boating And Lightning Protection  by William J. Becker. Univ of Florida Extension(Adobe PDF File, 248.3 KB)

  Lightning And Sailboats by Florida Sea Grant  by Ewen M Thomson, Univ. Fla. 1992. Sea Grant Publication(Adobe PDF File, 1.2 MB). Click here for HTML version

  A Critical Assessment of the US Code for Lightning Protection of Boats IEEE  by Ewen M Thomson, Univ. Fla. 1991 IEEE Publication(Adobe PDF File, 727.5 KB)

  A Critical Assessment of the US Code for Lightning Protection of Boats IEEE  by Ewen M Thomson, Univ. Fla. 1991 IEEE Publication(FlashPaper 2 Document, 1.7 MB)

Links

Recommendations for Lightning Protection provided by the American Boat & Yacht Council, Standard E4.  (KP44 website page)

Grounding Your Vessel. Technical articles and links on grounding: on the kp44.org website

Air Terminals (i.e. lightning rods) by Ewen M Thomson, Univ. Fla. Sea Grant. 

Lightning & Sailboats. (i.e. lightning rods) by Ewen M Thomson, Univ. Fla. Sea Grant Publication. 1992. Very good publication. Click here for PDF Version

Lightning and Boats Ewen M. Thomson.  Terrific website for lightning info.  Source for above two articles. He even has a downloadable 23 minute video.

World Wide Opposition to ESE Lightning Rods  from National Lighting Safety Institute, May 13, 2003.  (Article dated 1999, by Abdul Mousa).

Suppliers

Strikeshield Lightning Protection Systems for sailboats and catamarans.  These folks have a system with a clamp and grounding unit that you hang over the side in a lightning storm.  This could be a good idea if you want quick and easy lightning protection.

Forespar "Lightning Master" Static Dissipater.  Supposedly "leaks off lightning causing ground potential".  Mousa, Thomson  (above) and others disagree, saying the ground potential on structures below 300 meters is meaningless in terms of lightning strikes.  

Strikeshield "Air Terminals"  I.e. lightning rods.  Save $70.00 -- go to OnlineMetals.com and buy a length of aluminum for $8.31 and drill it yourself. 

Lightning Master Corporation.  Surge protectors and Dissipaters.  DIssipaters are pretty much shown to be ineffective, but surge protection for onboard electronics is important.