Hi again Sweetiepie. This is something we are considering for our Rafiki-37 (kissing cousin to the Tayana-37). We have two black iron tanks
on our boat. We had them cleaned and pressure tested before purchasing
. We found that the smaller fore tank leaked, but the larger aft one tested fine, so we're running with just the one tank now (90 gallons).
I've been investigating the idea of cutting the top off the smaller tank and inserting a diesel
bladder. This would reduce the volume, but other than dealing with chafe issues, I haven't found any reasons not to try.