Bad battery connection, corroded wires/terminals, bad ground somewhere. Check out all the wires that connect to the battery, follow them as far as you can making sure connections are clean, tight and corrosion free. Hope this helps. Keep us posted on what you find out.
P.S. congrats on the boat they are very distracting and a great way to waste away the summer ha ha.
2004 WJ Limited (The Phoenix), Addco rear sway bar, CAI, super cool firefighter logo seat covers so my kids don't destroy my leather, sct tune from Flyin Ryan, Fat Bob's Garage 2.5"/2" lift, Treadwright 245/75R16 Pumas.