Hi,
Check these guys out, they will be used on the next mega yacht project I am starting now.
http://www.tracplus.co.nz/overview.aspx
Here is an extract from an e mail I got when I first inquired about their equipment, I was asking about the tracking of Jetskis and Tenders just like you are now.
As you may have noticed from our website we basically track anything anywhere and pull it onto the same screen.
We are like the Vodaphone for GPS tracking, in that we are aligned with no particular hardware manufacturer, or carrier so we can use all of them. This means we integrate and assimilate often competing brands of equipment, be it plane, boat,truck or person, and provide the one-stop shop solution. There are several different approaches to this situation and depends entirely on technology infrastructure onboard the ship. First "Active tracking" anywhere / anytime worldwide Simply mixing and matching terminals (GPS devices) on each craft to suit their profile and monitoring them on the boat and on land (if required) via internet on board.
The easiest approach Secondly "Active Tracking" within GRSM Cell phone range only Simply mixing and matching terminals (GPS GRSM devices) on each craft to suit their profile and monitoring them on the boat and on land (if required) via internet on board. Thirdly Wireless network tracking (within a coverage limit) close to ship
Again a mix and match of terminals in a local area fed back into the ship via a remote wireless network
Here is an English Company that I was introduced to when researching something for a client about 6 yrs ago, they were just developing the Wrist Watch Locator at the time. This companies package is used by a couple of large yachts and I have heard no horror stories.
http://www.smltechnologies.com/Conte...s/Products.htm