Sunday, May 24, 2020

Preventing Holding Tank Collapse

Some time back I wrote a post about filtering the effluent gases coming out the holding tank vent at the stern.  As anyone knows, when the breeze is over the stern, the odor can be truly revolting, thus the need for the activated carbon filter.

It works beautifully, by the way.  Until, that is, the charcoal becomes saturated.

Then you simply discard the old charcoal and pour in a new batch.

But I digress.

While I was installing the filter, it dawned on me that, although I took many precautions to minimize the pressure drop it imposes on the vent line, those could be inadequate in one special circumstance:  When the tank is being pumped.

Holy cow - if the pressure drop was too great, the holding tank could collapse!  I don't want to contemplate what a mess that would be!  And Drew, from whom I got the idea for the filter, mentioned that he had seen circumstances where the charcoal actually reduced the H2S to elemental sulfur, plugging up the granules... even worse!

OK, something needed to be done.

I settled on a lightly spring loaded check valve installed in parallel with the filter.  Installed so that its flow direction was inbound, to allow incoming air to bypass the filter.  Here's what it looks like:

Filter with bypass check valve

I had some difficulty in locating a suitable check valve.  One without some kind of spring to hold it shut would leak holding tank off gases out the stern, rendering the filter essentially ineffective.  But if the spring were too strong, the holding tank would collapse before the valve opened.  I finally hit upon the perfect solution - a check valve designed to be installed in the "bubbler" lines in a hot tub - it opens at 1/4 psi - perfect!


Problem solved.



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Friday, May 22, 2020

Starting The Season Right


Although we use Eolian year round, overnighting at the dock at least once a week, there is that special night - the one that marks the beginning of the boating season.  For us, that was last night.  We are fully provisioned and will leave the dock for 10-14 days tomorrow morning.

And every year, for the first night of the season, it is a tradition aboard Eolian that we watch one of the best sailing movies ever made: Captain Ron.

Tradition satisfied, 2020.

And following on, the next movies will be episodes of Death In Paradise.



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Friday, April 24, 2020

Third And Final Hatch Cover

The first two hatch covers that I built were nearly identical, even sharing two of the three critical dimensions. The final cover, the one that covers our butterfly hatch (called that because when the flaps are open it looks like a perched butterfly, I suppose) is completely different.

This cover has two ends which are vaguely "house" shaped and one long piece that drapes from one side, over the top, and down the other side.  The old cover was in really sad shape - that long piece had shrunk up width-wise from 22" (the width of the hatch) to less than 20", pulling the two end pieces way up.  But I determined that the two end pieces were roughly the correct size and shape, so I disassembled (really easy - the thread was completely rotten) the cover and made a pattern (using Sailrite Duraskrim) from an old end piece.

An end piece pattern is made!
Then, to get the real length of the long center piece (not trusting the shrunken old piece), I simply measured the circumference of the relevant edges of the pattern, allowing an additional 2" for a hem at the bottom of each end.  Then I stitched the whole thing up using my trusty LSZ-1.

Trial fitting
The trial fitting proved satisfactory, so I proceeded with the windows, again using Strataglass.  First it was necessary to layout the location and size of the desired openings, and then add a line 1" away on the outside all the way around to make a "fold-to" mark;  to make a finished edge where the fabric meets the vinyl, I wanted to fold the edge under 1/2" for a hem.

Layout for the windows
After using a hot knife to make the cutouts and the corner notches (to allow the folding under of the hems), the cover lost a lot of its structural integrity - it became very floppy!  I had anticipated this, and so before I made those cutouts, I measured the diagonals from the opening corner marks for future reference.

Floppy!
To make the hems, I pre-creased the edges to the lines and then applied Sailrite's Seamstick basting tape inside the creases to hold the folds in place.  I then made another application of Seamstick to the hems, but left the release paper in place.  I laid the Strataglass over the openings, arranging the canvas so that the Strataglass and canvas were shaped properly...  using those diagonal measurements I took before I made the cutouts.  Then I carefully pulled the release tape out from under the Seamstick, fixing the Strataglass to the cloth and stabilizing the shape (the Seamstick not only serves to hold things in place for stitching, but it also serves as a water seal in the hem).  Then a double round of stitching to make it all permanent.  Lather, rinse, repeat for the other window.

Finally, installation of snaps to match the studs on the hatch completed the project.

Done!


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Thursday, March 26, 2020

Solar, And Temperature

These cool, partly cloudy spring days provided me an opportunity to see the temperature dependence of solar panel energy generation right up close and personally.

In one particular instance, it had been cloudy for at least an hour.  There was a gentle breeze blowing and the temperature was in the high 40s.  Because of the breeze and the shade, my solar panels were cool.

Then the clouds parted and the sun came out, pretty much all at once.

551.6 watts

I know it's a little hard to read, but the blue system monitor at the lower right is showing 551.6 watts.

A few minutes later, the solar panels were still in full sun - that is, no change in energy falling on the panels.  Yet, here is the output:

Later, 532.4 watts

Yup, output has dropped to 532.4 watts as the panels heated up...  that's a drop of 3%.  That is a pretty significant drop.  You folks in the tropics should be able to get a pretty substantial increase in solar output if you can figure out some way too cool your panels...

(FWIW, the biggest reading I saw came later in the day when the sun was higher, and again just after a cloud has passed:  571 watts.  I love seeing that current meter needle buried!)



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