I would agree. I think that one issue we saw is that many manufacturers seem to give a hull weight that is on the low side. I noticed that when BWB did their various tests over the years, it was not uncommon to see a 100 pound range for hull weights. And that makes perfect sense to me for any process that has human hands involved. The idea scenario would be as BCB suggests, except that when you pick up the boat new, you fill it up, leave all the crap out (tackle, etc) and get a weight and save it. 10 years later if you think it is getting a bit heavy, you can weight it again.
The problem with the “vacuum” approach is that it is not particularly fast. Of course, running this for an extended period is not going to hurt anything but the vacuum pump itself, but it is not easy to know when you are “done” since truck scales are not very good at weighing 10 pounds or so to see if you have removed another gallon of water or not.
One thing I failed to mention, when you start the process, within an hour the vacuum ought to be at least -15″ or so depending on outside temp, if you don’t get down to that point you most likely have a leak in the bag and you can suck until the cows come home with no effect. Care to guess how I know that?
But note you need to let the pump run an hour before you start watching the vacuum guage. At 5cfm or so (unless you have a big industrial vacuum pump hidden away) it will take quite a while just to get the air out of the boat when you think about the bilge, back end, storage compartments, etc. 5cfm is at sea level pressure, as the vacuum drops so does the volume. Be patient. I suppose you could run the pump output through a dehumidifier and collect the water to see what you are getting, if you are curious, but you have to make sure that outside air is not going thru the thing as well.
All that said, I would not even think about starting the process until you are sure you are overweight and not just either down on power, overloaded with tackle and people, or have a prop that has lost some pitch due to age or abuse. The “faster days” are ahead of us, when we get to the 50 degree dry air (and below).
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2008 Pantera Classic
2014 Mercury Pro XS 200