Air Filtration. Shop dust and even welding fume.

Back during COVID and the wildfires out west, I read of a bargain HEPA air filtration hack that could remove viruses and even smoke from the air. I started testing it out in my basement shop, and these many years later, it is still a full-time staple in the shop. 

Also allergies and home renovation projects. This summer we some guys rip out a bathroom, including tile demo, and this filter kept the dust out of the house.

The Corsi-Rosenthal Box. A doctor and an HVAC engineer went together and designed the simplest possible filter, with the intent of reducing COVID viruses in public spaces. It consists of a cheap ($25) 20-inch box fan and 4-5 20x20x1-inch MERV 13 (good) or MERV 15 (better) filters (Box of 6, about $25 on  Amazon). The filters are taped to the fan to make a 20-inch cube that can change the air in a typical room every 4-5 minutes. Much cheaper than a HEPA filter, many times more capacity, and much cheaper to replace the filters.

 Wikipedia. Corsi-Rosenthal Box.org/wiki/Corsi%E2%80%93Rosenthal_Box

 

 MERV Filters. Air filters are rated for particle removal efficiency according to the above table. MERV 13 and MERV 15 filter are pretty effective below 1 micron. Additionally, the room air is being recirculated, so the multi-pass efficiency will be much better than the above single-pass ratings. Over 20 minutes the air may go through the filter 3-5 times, approximately doubling the removal efficiency. 

 According to the simple table, the filters can remove  most smoke and agglomerated viruses after a few passes. My experience is that MERV 13 filters can remove welding fume and paper smoke after about 2-4 passes. Solvents and volatilized organics (part of the paint and burnt plastic smoke) are not removed. 

 Keep in mind that virus particles, as well as many other particles, often exist as agglomerations. They clump together, and in the case of exhaled particles, are in water mist. They will dry in the air, but still, they are typically much larger than the minimum size. 

 

 

Tweaks. There are a few things you can do to further teak efficiency.

• In my home shop, the box uses 5 filters instead of 4, resting on furing strip spacers that keep it off the floor. This increases the flow rate.
• Position the filter so that the air flows in a pattern (plug flow). In my case, it is located under a shelving unit, near the table saw/sand/drill press area. The exhaust blows through, under the stairs, and into a storage hallway. it then flows back to the work/fan area in a plug-flow pattern.The storage hallway never gets dust in it (clean air), there is no disruptive draft in the work area, and the dust is pulled steadily down and away from the work zone. 
• Fan shroud. Cut a piece of cardboard or thin plywood to match the fan blade diameter, and secure it to the discharge side of the fan. This reduces re-circulation and increases flow about 10-15%. 
• You can add a lightweight wooden internal frame (not visible) to make filter replacement easier and to make it more robust against shop knocks. The filters are still taped in place, making them airtight (to each other, but not to the frame except where they seal to the fan).  
• Remove the intake-side grill; it is not needed, since the filters guard the blades. This reduces turbulence in front of the blades, slightly increaing capacity. In my horizontal instalation, I lay the grill on the top so that tools can rest there, and to resist impacts.
• I made the exit shroud from 1/4-inch plywood and screwed it to the fan. A little more durable.  

This was the first version. This simple, 10-minute masking tape project worked just as well as the later evolution, as far as shop air quality is concerned. It was just a little less robust.

A few notes on the photo.

• The filter is about 3/4-inch off the floor. The underside filter gets equally dirty, as the side filters clog.
• It is on its side, discharging under the stairs into another room. This creates an efficient draft-free circular airflow pattern.   
• The inlet grill re-positioned on the top, provides protection from dropped tools without diminishing airflow; the flow rate on each of the five filters is quite low.
• Measured capacity is about 250 CFM with clean filters.  It's pretty clean at this point, having been cleaned after the last significant project.
• Because the fan switches are on the back side, it is powered by a switched outlet, so I can flip it on with a convenient wall light switch.  

Uses. I've been using variations in my home shop for more than five years. It removes dust in a heartbeat. I can weld and grind without it being noticeable in the house.  The filters last 2-6 months, depending on the number of projects, by which time they have turned brown and accumulated a thick layer of dust. I still use a dust mask for some things, but not as often as before; the air stays clean. 

 

Remodeling/home improvement. This summer we had contractors tear a bathroom apart. Place at one end of the hallway, dust throughout the project was minimal. The filters, on the other hand, showed where the dust had gone. While they were demoing the tile, we placed it in the bathroom, greatly improving the working environment.

 

Allergies and the Common Cold. We have smaller HEPA filters we run to keep cat dander under control (I am mildly allergic). But when allergies get bad or if serious cold and the flue come to visit, it is one more tool to reduce the spread.   

 

Boat projects. If you must tent you boat to contain dust, this filter can provide excellent exhaust, while containing the dust.  If working inside the boat, it could be placed under a hatch, providing ventilation without dusting the entire marina.

 

 

My shop gets a lot of use and can generate a lot of dust. This is only about half of it. Crowded, but everything in its place.

 

 

Some Public Docks in Maryland

There are many of these, scattered around Maryland. Although identified as county or public docks (and you are allowed to use them overnight for up to 24 hours), it's always been clear to me that these are loading/unloading areas that support the local fishing industry. Mostly, the crab boats don'teven stay overnight. 

I have stayed at a few overnight, years ago, but I always slide up the side into water so shallow no work boat would go there.  They are often not fender-friendly and they arn't visitor docks, in my interpretation. 

Some towns do have docks for visitors to local watering holes. Chesapeake City comes to mind. But that is different and they look different. 

Never stop a working man. 

  San Domingo Creek, MD

 

 

Rockhold Creek, MD

Chesapeake City Town Dock. A tourist dock.

 

Netanyahu's party claims Israel's election was stolen.

Sound familiar?

An incumbent attempting to establish a false reality through accusations and loud repetition. These people don't get embarrassed.

Unmanned Vessels--Would You See This?

I've been reading forum posts by sailors concerned by the increase in unmanned monitoring vessels. This concerns a collision on Lake Erie. The NTSB has recommendations for improving the safety of such operations. What bothers me is that they assigned no responsibility to the powerboat that ran down what could have been a kayaker. It was daylight, and the drone was transmitting AIS, which the powerboat was not monitoring (not required, but it was a 45' boat moving at 25 mph, which in my mind, increases responsibility).

 Read the report. Reach your own conclusions.

NTSB report 

 ----- 

 A small excerpt from the NTSB report, MIR-26-32.

... While the USV was underway near the WE08 site, the recreational vessel owner
was transiting back to Safe Harbor Toledo Beach on a southwest heading at cruising
speed (about 25 mph). Having owned and operated vessels in the Monroe area for
over 20 years, the operator had a thorough understanding of the area and was
navigating his vessel visually. Although the sun was positioned at a low angle in the
western sky off the starboard side of the vessel, the operator told investigators that
the sun was not impairing his vision. He stated there was about 2–3 miles of visibility.
 

With an overall length of 15.7 feet, the USV had a similar length to a small-sized
recreational vessel such as a kayak, canoe, rowboat, or powered skiff. The USV had a
yellow hull, meant to help make it more visible to other vessel operators. However,
due to the vessel’s design, only about 1 foot of freeboard was visible. Additionally,
most of the main deck was covered with solar paneling, which was dark in color, thus
obscuring the vessel’s yellow coloring and making it blend in with the surrounding
water. At the time of the collision, waves were 3 feet, which would have intermittently
obscured the USV’s hull as it dropped through the troughs of the waves and made it
difficult to discern the USV in the water (figure 15 shows the vessel underway in
similar wave conditions). Further, most of the USV’s hull appeared dark yellow when
viewed from the side, as the vessel’s design cast a shadow on the hull....

Winter is Coming

 I previously posted lead-acid battery voltage vs. temperature and state of charge (SOC).

 

If you have switched to lithium iron phosphate, there is also a relationship between temperature, voltage, and state of charge. The drop is less, but remember that lithium cannot be charged below freezing and the battery management system (BMS) will disconnect the battery from charging below about 35F. Additionally, the BMS will disconnect the battery completely below 11.5 volts (typical setting) until charging current is applied and the battery rises above 11.8 volts (typical).

 

 

I installed a Li-Time battery (weight savings, price, and the lead was dead) and I have experienced both sorts of cut-offs (very low slow solar through the winter, and charger failure). In both cases, the battery woke up when charging was applied.

 

 

Childs Hill, A Grown-Up's Mountain

 I'm quite sure I will not reach the summit, but I toil on the slope. Sailing. Shop skills. Engineering skills. The view is improving every year. As for understanding people and cultures, I'm not far above the canyon, but at least I know that.

 

 

Trump Aranges Deal for Rusian Diesel

A coward. A corrupt politician trying to sway an election. Un-American. A humiliation to the Republican Party. A humiliation of the Republican Party. Please count the American servicemen's lives that have been spent and lost in the fight against totalitarianism and communism. Trump spits on our brave men. He likes Putin because he is like Putin.

There aren't enough words for a worm like this. Further, the entire Republican Party, every Representative and Senator, has made itself culpable. No blame-shifting allowed, when you support such a man. You are hiding behind such a man.

Keeping the Gasoline Tank Cool (And protected from UV)

By law, above-ground gasoline tanks are ALWAYS painted white or silver. This minimizes solar heating and thus minimizes day/night breathing emissions. I'm a tank inspector from way back. I had a consulting business, and I've been around, over and in thousands of tanks, from 500-10,000,000 gallons. 

 E10 loves to absorb water from the atmosphere. If the water content reaches about 0.5% (more in summer, less in winter), the water will separate, taking the alcohol with it and creating a 15%-by-volume layer that won't burn. Phase separation, as this is called, is very unusual because absorption from the air is a very slow process, taking months. The usual cause, in fact, is a leaking filler cap or vent, not absorption.  It's a slow process, taking months to become important. But prudence requires closing the vent whenever the engine is not in use. Spray can sneak in through the vent.

Water absorption does NOT need to reach phase-separating levels to cause problems. At just a few hundred ppm, sludge generation increases. The gasoline becomes weakly conductive and galvanic corrosion blooms in the carb bowl (brass and aluminum are an active pair). Gasoline also evaporates, and the loss of the most volatile portions can make starting more difficult, and increase gum formation. Better to keep it sealed. 

But a sealed tank builds pressure. Over time, UV damages the tank and the tank becomes weak.  It would be nice to keep it out of the sun. Some people like Sunbrella covers. But on my boat, it would just get grungy with spilled oil, gas, lichens, and algae. 

 Paint is simpler. Since the tank is mostly covered by the seat, there was no need to paint the whole thing. If it was, I might paint the whole thing, leaving only the code stamp exposed (not on a seam).

Simple. The tank is protected from UV and stays cool. It's been seven years, 365 days per year, and the paint is still there.

  

Tiller Pilot Cover

 The leading cause of death for tiller pilots is moisture intrusion in the rain. In the UK they are common on eBay, but not here.

 A few days ago I had to take a 4-hour rainy sail to move my boat between marinas for service. After three years (Total Boat Krypton) the bottom needed anti-fouling paint, and Herrington Harbor North has decided that hauling trimarans scares them, so they won't do it anymore.  

So when the rain started, I pulled out the cover I had made from a scrap of clear vinyl snipped from an old dodger.  No sewing was required. I just folded it, somthing like wrapping a box, and popped a rivet in each of the corners. The bottom is open for ventilation. The tiller pilot stays bone dry, since it produces a small amount of heat in service, sufficient to prevent condensation and evaporate any stray drops.

You can see the buttons and use them right through the vinyl. Very easy. 

You can read the details here: https://www.practical-sailor.com/marine-electronics/no-sew-diy-tiller-pilot-cover/ 

 

Public Service Anouncments in the Election Cycle

No, they are not, Donald. These are taxpayer-funded election ads. 

This is how tyranny starts. He read the tyrant's handbook and memorized it. Please watch this docuseries on Netflix. It is an excellent history of tyrants, starting before Rome, moving through Hitler, Qaddafi, Idi Amin, North Korea, and forward. It is not about current events.

 How to Become a Tyrant, Netflix