When you "blow the tubes" you're using compressed air to force the water out. The water is the ballast.
"indicated releasing sea water that is held inside the tubes"
"ballast" does indicate a weight keeping a ship or object submerged"
You don't say, clearly I missed that and didn't articulate that point.
"Oh my! An `inflammatory attitude' in alt.flame? Never heard of such a thing..." -- Allen Gwinn, allen@sulaco.Sigma.COM