Anti-Roll Bag ver. 2.2.

I took a break in my Anti-Roll Bag research and spent several months cruising in northern B.C.  I did take both my homemade and my store bought anti-roll bags.  As I mentioned in the prior blog, ARB ver 2.1, my store bought bag was lightly made and immediately sprung leaks.  Also, it was longer than the width of my flying bridge and therefor was folded upwards at both ends.  I was wondering if this might effect the timing of the water passing back and forth.  I would say yes, in a bad way.  The end of the bag would "inflate" with water, but then drain back out slowly because of the crease at the end of the bag.  It lost some of it "umph" or slosh effect.  Here is a picture (empty) showing how the bag folded at each end.

The $35 store bought bag with about 1 foot extra at each end.

Just as bad was that the bag end folds and unfolds thousands of times a day as the boat rocks.  The material couldn't handle it and developed leaks.  So I went back to my other DIY bag made of stronger material.  But it developed the same issues.  Little leaks and obvious wear points where the bag folded and unfolded thousands of times.  Plus, the force of the "inflation" slowly opened the end seams.  By the time we reached Race Passage on Johnstone Straight, it had just a bit of water in it and was doing nothing.

Here is the bag shortly after a roll to port.  Basically all 150# of water is resisting the roll back to starboard and damping the motion.  I was hoping that the seam being up against the side wall would reduce the stress.  It probably did, but unfortunately, the force of water opened the end seams after days of this.  The material was also starting to delaminate at the creased areas.  You can see that under the bag end and around the coaming is wet from the small leaks.

For those of you who are unfamiliar with this area of B.C., it is notorious for rough water when the wind runs against the current.  We ran it going north on such a day.  Just as we were getting ready to cross to the west to exit by Current Passage, I was hailed by a cruise ship (still out of sight) and asked if I could stay east on the Kelsey Bay side.  The ship was travelling at about 25 knots, so we slowed and let it pass.  But that 20 minutes changed the wave train considerably.  We crossed over to Earl Ledge and rode a fairly smooth laminar flow at about 3.5 knots.  Until the end.  Then the wave train started.  Steep 6 to 8 foot standing waves that were curling over at the top because of the wind.  Even when slowed down, we were still crashing through.  

I decided to move over close to Hardwicke Island so that we could bail out and retreat a little to anchor in Forward Harbor for the night.  But in order to get out of the mess, I had to take several waves on the beam and miss a powerful eddy.  We had prepared for this and everything was stowed properly.  Still, a couple things went flying.  And I got read the riot act by my wife.  What is important to me is to not frighten her and effect her desire to go cruising.  Also important to survive, of course, which we did.  Here is a photo of my recording inclinometer.  It would have been a good time for testing an anti-roll system, however, I don't expect to repeat this.

That's right.  28 degrees to port and 38 degrees to starboard.  Enough of that.

The ARB was proof of concept, but it looks like an anti-roll tank is required for several reasons.  Although the bag slowed the internal wave/water transfer a little without the use of baffles, a bag has other interference issues.  And vinyl coated polyester (or probably any flexible bag material) simply can't handle being creased and re-creased thousands of times under pressure.  Looks like it is time to build an actual tank.  

I've looked for something off-the-shelf that might be modified, but having no luck it will likely need to be completely fabricated.  The interior of my flying bridge cowling is just under 8 feet side to side so plywood is probably the material for a test tank.  I'm thinking that it would probably be about 18-24 inches wide.  As you can see from the picture of the bag above, although a tank would only need contain 3-4 inches of water, the tank (or at least the ends of the tank) would likely need to be 10-15 inches tall to contain all the water that would be transferred in a larger roll.

To be continued . . .