[todc]

Just thought I'd add to this year-old Post - I have a 2005 3600 Open (Hull # 6) and it has the same issue.  With a full fuel tank, the bottom edge of the swim step is even with the water surface in fresh water.  In salt water the gap is about 3/4 of an inch higher.  Our fuel tank has a tag on it that says "450 gallons" but Tiara has told me it is a 400 gallon tank.  So I'm not really sure.  Over the winter we keep the boat in Lake Washington so I only fill the tank to about 3/4 full.  This keeps the swim step out of the water by about 1.5 inches and small waves don't splash up.  When summer cruising I normally fill it all the way to get the most range.

A related issue is that the fuel gauge does not read accurately at all.  However, I think it is pretty repeatable so I have constructed a graph that assumes the capacity is 400 gallons based on how much fuel it takes to fill the tank at the various fuel gauge level.  It drops down faster than the gauge indicates initially and then levels out.  I'd be glad to send this chart to anyone who is interested.  Just send me a request through the "private message" feature of this forum.

A backup method I use is to estimate how much fuel has been used is to assume fuel consumption is 0.9 gallons per mile at cruise (26 mph).  I get the miles travelled from my Raymarine MFD.  This works pretty good but only for long distance steady cruising at 26 mph.