Anti-Roll Tank Pitch and Roll

 Can reducing roll somehow increase pitch?

When going through my pictures from our 2026 cruise, I found a couple videos of interest having to do with the ART.  Down loading from my camera, I had a few videos.  The best video was down loaded somewhere on my computer, but not where I thought, and I haven't located it yet.  Grrrrr.

But here's what I was doing.  Every time a ferry or large ship went by, I positioned my boat so as to maximize the effect of their wake.  I know, that's odd.  I know that my roll period is about 1.5 seconds side-to-side.  So several factors made a difference in how to maximize the effect of a wake.  We are all aware that when a boat is passing and throwing a large wake, we can wait for them to pass and then turn towards the wake.  That allows us to cross the wake at something closer to 45 degrees instead of taking the wake broadside.  It reduces the roll.

Even still, plowing into a wake at 45 degrees at speed might not be the best.  Slowing helps, although slowing too much can actually increase the amount of pitch.  It's sort of a Goldilocks maneuver.  Not too slow, not too fast, not too shallow of an angle.  Except of course, when one want's to maximize the effect, which I admit is seldom the desire.

In this video I was just passed by a boat heading the opposite direction.  That is actually not the wake that generally gives me the largest roll.  Being passed in the same direction usually tosses me around the most.  With an opposite wake, I usually have to turn away from the wake a little (or reduce speed) to get the strongest roll effect.  That's what I did here.  I have my camera sort of pointing to the oncoming wake so that I could see how much roll I could generate.  Not much.  But what I found interesting when reviewing the video was the amount of pitch.

Normally in this situation, it's time to look around the cabin and make sure coffee cups, etc., are secure.  I usually say "wake coming" if I don't think my wife is paying attention to what's happening.  But here, the ART takes care of the roll.  What is interesting is the amount of pitch.  It seems really bouncy.  I have to think that it has always been the case, but because the roll is basically gone, the pitching is what draws attention.  

You can see a little bit of the bow anchor in the lower right of the video.  It does swing a little bit from the rolling, but it looks like nothing in comparison to the pitch.  Interesting.  If you double click on the video it may go full screen.

The other video I'm looking for was a larger wake and the camera was facing straight forward.  To be continued (maybe) . . . .

2026 Cruise to Northern B.C.

I haven't posted too much about our cruising, but I was just going through some photos that I hadn't organized from our 2026 cruise.  I found the pods of Pacific White-sided dolphins fun to watch, so I thought I would share.  Dolphins often will "bow ride" on a boat for awhile, but we seem to attract a lot of them.  Maybe our speed is not too fast, not too slow.  A school will be a mile away, barely visible, and change their course to intersect ours.  

We are usually on the lookout for whales, who sometimes don't change course, so we have to change ours.  One of the things I like to do with whales is get on a parallel course and then count the number of seconds between the spouts.  That way, instead of filming for over a minute to get a good picture, I can tell within a few seconds when and where they will appear again.  In this first video, I'm starting my counting as it is going down.  You can double click to get a full size screen and then hit escape to, well, escape.

I counted 74 seconds until it spouted again.  Then I can count 72 seconds and start filming.

Don't have to do that with dolphins.  Here comes a big pod making a bee line to intersect our course.  No need for a course correction, as they are plenty acrobatic to stay out of the way and join in with us.

I can't imagine that we just happen to be going where they are going.  Some say they like the effect of the boat's bow and makes their swimming easier.  I have a different theory.  They are pack hunters and tend to ambush schools of herring, smelt, etc.  I think the boat makes a nice big disturbance for bait fish and the dolphins just watch what the boat scares up and then chase out to the side to feed.  The boat is effectively a bird dog.  On the other hand, the do seem to find travelling alongside a fun activity.

I think these videos are all the same pod, but this would happen several times a day.  Good fun.

This year, every wolf we saw was "driftwood" colored.  Kind of hard to spot from any distance.

And the grizzley's were all the color of rockweed, also called "old man's firecrackers" if you've ever played with them.  The rockweed, not the grizzleys.

That's our boat in the background.  

Dollars Per Damping Degree

I mentioned in a prior post that I might try a comparison of the various common anti-roll systems.  Something that I would call "Dollar per Damping Degree" ($/D°).  I actually had started doing a comparison of the systems before I decided to experiment with the anti-roll tank (ART).  I knew that the other systems would all cost more time, money, fuel, and some even require a generator, but I didn't know which one would be overall the most cost effective.  While some people might like the idea of roll reduction at any cost, it seemed like getting one's money's worth might be a worthy goal.

The biggest difficulty in doing a comparison is getting accurate numbers.  There are online claims as to what a new roll reduction system "feels like," but actual measured numbers are rare.  The problem with the "feels like" test is that the perceived roll reduction always increases as the weight of the captain's wallet decreases.  It seems that nobody does a simple accurate before and after test, with the "before" being the crucial part.  

The same accuracy problem is true with costs. Most often partial costs are given, leaving out haul out fees, yard fees, etc.  Some systems have annual maintenance requirements, but the costs are vague and most internet searches find customer complaints about the maintenance complexity and expense exceeding what was promised.  Reduced performance (increased fuel burn) is also seldom noted, and when it is, it is dismissed as "what's 1/2 knot slower and an extra $100 a cruise when I spent $25K for the system?" 

I measured the roll reduction of my ART and I have the receipts for the costs, so those are the only actual numbers in my chart.  The numbers for the other systems I pulled from various postings on the web, some of them from end users and some from purveyors.  When a purveyor says that their gyro system (for example) costs $40K, one then has to guesstimate the installation costs.  Same with annual maintenance costs.  Same with haul outs and yard times for the installation of some roll reduction systems.  Those numbers in my $/D° chart are followed by a "?" because they are gleaned from various posts on the web.  If you have accurate numbers for costs, degree reduction, etc., for a system, please post in the comments so that I can update the chart.

My boat is small by trawler standards (32' LOA), so any system would be small (like the gyro at only $40K) and costs would be small (in comparison to larger boats).  Still, some stabilization systems would require the installation of a $10K generator running nonstop (like the gyro), in order to stabilize at anchor.  Other systems, like paravanes, sort of work at anchor, but at a greatly reduced roll attenuation capability.  Because roll reduction both while running and at anchor are important to me, my $/D° calculation takes that into account.  Paravanes are generally claimed as 40-60% degree roll reduction underway (depending on speed and proper installation), while only 10-30% at anchor.  If I average those numbers (50% underway and 20% at anchor), I would then weigh those two numbers equally, coming up with 35% reduction overall.  Dividing overall costs by this average overall reduction produces a cost of $650 per degree of damping. 

The numbers are interesting because the material costs and installation are so little for the ART.  It was within my abilities to build the tank and put it in place.  I'm not sure that I would try DIY with the other systems.  Self-installing the rolling chocks maybe?  It would be 10 times the work involved with the tank, but that would reduce the $/D° even further for chocks.  One of the things left out of the chart is the cost of retaining a naval architect, which might be something many would (should?) add.  There are reports on the web of people adding rolling chocks, for instance, and claiming that they did nothing.  Design issue?  Install issue?  Perception issue?  Expectation issue?

The effectiveness of the ART is easily measured, unlike the other systems.  Drain the tank and measure.  Fill half way and measure.  Reduce the amount and measure.  Add a thickener and measure.  Unlike other systems, vessel speed does not alter the system's efficiency.  For paravanes, slower speeds reduce effectiveness.  For rolling chocks, higher speeds reduce effectiveness (because of the increased boundary layer).

Being as no other system came close to the ART on costs and time, I'm not going to do any further analysis or research on the time, expense, and effectiveness of the other systems.  The green text is sort of the "winner" for that line item in a roll reduction system.  You can cut to the chase and just look at the bottom line $/D°.