Mr. Hagstrom, On our Buzzards Bay 34, we have a port side water tank (60 gal capacity, removable) and a Jabsco Sensor Max VSD 4.5 GPM. It's a good pump, quiet, reliable, and flows plenty of water for a good shower. If we were building a larger boat like yours, I would probably look at using the same pump, though I might mount two in parallel with isolation valves just in case one fails it does not impact your cruise. Jabsco has a two pumps in one model, the Jabsco Dual VSD, and puts out a claimed 9 GPM. The technical literature describes the pump as self priming, and can be mounted 5' above the water tank. This height would certainly get you up and over the tunnel. I have not installed a system with the pump higher than the tank. It may be worth a phone call to their tech line for additional information. The Jabsco VSD's are a member of the "smart pump" family. This means they can alter their speed according to the pressure drop, keeping up with the demand using as little current, and making as little noise as possible. They are indeed quiet. Good luck on your build! She seems to be a great boat, congratulations. -- Russell Hunt, President Multihull Development, Inc. and Buzzards Bay Catamarans Office #: 508-403-0301 Cell #: 508-759-4111 Email us at: info@MDcats.com Check out our website at : www.BuzzardsBayCats.com http://www.yachtworld.com/multihulldevelopment/