Video of Antiroll Tank in Action

 Here is some video and photos of our recording inclinometer to show the effect of the roll tank.  The videos are short because they are size limited by Blogspot.  

We had already crossed the Straight of Juan de Fuca, but no video there.  The next chance to really take advantage of the antiroll tank was encounters with the BC Ferry and other large vessels.  Here is a little video of a BC Ferry passing us (they tend to travel at about 20kt to our 6.5kt).  When they pass, the wake slowly passes us, making for lots of time to build synchronous rolls.  We usually turn and go directly into the wake of large vessels in order to stop building violent rolls.  Not necessary with the antiroll tank. 

Here is what the approaching wake looked like.  A good 10 2' waves to get us violently rocking.  Time to batten the hatches.

The antiroll tank handled it just fine.  We could feel the wake, of course, but the rolling never built above 4 degrees.  It would lean us to one side, but the tank reduced the "snap back" such that the effect of the next wake was again fairly mild.  It was like the tank was frustrating the ability of the wake to really get things rocking.

I later went solo around Cape Caution in order to pick up Beth, who flew home from Bella Bella for a week and was flying back into Refuge Cove.  Here is a little video of "Cape Caution" (which I actually never saw that day.  Very foggy and some long swell coming in from the Pacific.  Nothing the tank couldn't handle.

Oddly enough, the roughest part of my trip this year was from Squirrel Cove, where I spent the night at anchor, across the 3 or 4 miles to Refuge Cove, where Beth was coming in on a float plane at noon.  If I'd had a choice, I probably wouldn't have crossed until later in the day after the tide changed.  This is 20 knot wind against the flood tide and right on my beam.  The ride wasn't pleasant, but also not too uncomfortable once I got used to the fact that the max rolling was all about 10 degrees and seemed fairly mild mannered.  

The inclinometer shows that the maximum roll to port was about 5 degrees more than any roll to starboard.  That is because the wind was coming across the deck from starboard, causing a constant list of about 5 degrees just from just the wind, even if there were no waves.  It was howling pretty good.  So the actual wave induced rolling was about 10 degrees.  About 1/2 of what I would have expected from these conditions without the tank.

My assessment is that the antiroll tank is definitely worth the time and effort.  I still have some experimentation to do with the amount and viscosity of the tank liquid, but even with just a guesstimated amount of tap water, its utility was proven.  If I decide to integrate the tank into the flying bridge structure, it would still be only a $1,000 investment.  From what I've heard, it more effective than bilge keels (at $15,000).  Might be close to being as effective as active fins (at $40K).  Maybe not as effective as a gyro stabilizer (at $60K).  And there are the advantages of no maintenance, nothing to snag crab lines, works at zero speed (at anchor), no need to haul out, no decrease in speed, no increase in fuel usage, no need to run a generator (I've removed mine), etc.  And, as I said in a prior blog, no profit margin for a seller/installer/designer.  The latter is likely the reason that antiroll tanks are rare.

I have read a couple of places where antiroll tanks are claimed to be dangerous in that they might affect the vessel's stability.  Well, yes, that is possible with any system, although probably less likely with a "gravity activated" system as opposed to an "electrically controlled" system.  Gravity is predictable and always "on call."  Other antiroll systems have had their issues, but for some reason don't inspire the same level of criticism (and even fear).  Take for example the effects of an active fin system that gets a bit out of tune.  The fins started rotating the wrong direction, exacerbating the rolls rather than calming them.  Here is a picture of seas similar to what I was in, but the fins got out of sync and the system had to be shut down before it sank the vessel.  Gravity doesn't have glitches.

I know what that feels like.  Here is a picture of my inclinometer taken before I had the antiroll tank operational (going through Race Passage on Johnstone Straight).  This is about what the boat above was doing with active fins. I don't intend to do that again thanks to my antiroll tank.