Friday, December 30, 2022

Why I Have a Motorcycle Lift Table

Not actually Erin.
& is used with permission.
Traditionally, this blog goes on vacation between Christmas and New Year's Day. For that reason I let David off the hook this week, but I wanted to write something because I've made an effort to write more often since November, and also because we just haven't had many posts this year due to Real Life problems with our other writers. 

Anyway, this Christmas I bought a Lift Table using gift cards.

Now, you're probably wondering why I bought a table capable of pneumatically lifting a 300 pound motorcycle, especially since you know I don't own a motorcycle in the first place. This is a fair question, and the short answer is "I need to lift heavy things and I have arthritis in my lower back." Because I'm going to be "over the hill" next year, I thought it would be prudent to have a piece of equipment that can hoist most anything I would need to lift, because I'm only going to get older and my arthritis will never get better. My mother is in her 80s now, and while she can currently move without assistance, in the future she may need help getting up like my father did a few years ago. She weighs much less than 300 lbs, but I like to say that there's no such thing as overkill, just increasingly greater chances of success. 

The longer answer, and I can practically hear the record needle scratch as I say this, is I bought it to lift my Bug Out and Get Home Bags. "But Erin," you are saying right now, "if you need a lift table for your BOB and GHB then they're too heavy!"

They're actually not too heavy for me to lift, and they're definitely not too heavy for me to carry because I'm already regularly walking a mile while wearing them. My goal is to work up to walking two miles, and the reason I need to work up to that is because I'm overweight and out of shape. I stop because I'm tired and out of breath, not because the pack is too heavy. When I get it cinched down, my hips carry most of the weight. 

No, the problem is that the arthritis in my lower back is a stone-cold bastard, and sometimes just picking up a heavier-than-usual grocery bag makes me hurt, and I don't see the point in hurting myself if it's not necessary. Furthermore, this lift table actually makes it more convenient for me to put my bag on and off, meaning that I'm more likely to put it on for exercise. 

So now I have a lift table that will easily raise my bag to waist level so I can easily put on it for walks, and then when I'm done smoothly lower it for storage or bag access/maintenance.

I haven't used it long enough to give a long-term evaluation of it, but here's what I've noticed so far:
  • The wheels easily move on residential carpet. 
  • ... which is good, because it weighs 70.5 lbs. I'm not picking that sucker up unless I absolutely have to. 
  • The table is wide enough for my needs without getting in the way, although the hole in the surface is a bit annoying. 
  • Weights up to 150 lbs rise with no extra effort. I just push the foot pedal down. (I haven't seen a need to put on more weight than that.)
  • The lift pedal seems to raise it about one inch per pedal pump, so I have to pump it about 30-some times. 
  • The lift pedal swings a bit from side to side. This is awkward but doesn't interfere with its function. 
  • The table lowers smoothly and swiftly. 
  • I can easily fit all of my packs onto it. 

So, I have a lift table now. It was expensive, but I'm glad to have it. I'm certain I will find other uses for it; if you read the Amazon reviews you'll see stories of people using it for other purposes, such as installing window sill air conditioners or raising generators to truck bed level. If you find your back constantly hurting from having to lift heavy things, then perhaps the Extreme Max Hydraulic Motorcycle Lift Table is right for you, too.

Friday, December 23, 2022

Prepper's Armory: Scope Mounting

As with iron sights, there's a proper way to mount, adjust, and sight in a scope. Actually, I should say proper ways, because there are a number of variables as well as preferences involved with the process.

Early scopes were externally adjusted, meaning the scope body was solid and the adjustment knobs were located on the scope mounts. Turning these knobs physically changed the angle of the scope tube. Later, the adjustment knobs were moved to the scope body itself, making adjustments simpler. Further developments made the adjustments more consistent and predictable.

The first steps in mounting a scope to a firearm is acquiring a solid rail mount and the proper rings.

Rail mounts come in one- and two-piece configurations and Weaver or Picatinny rail patterns. These days, one-piece Picatinny are the most common; in fact, many firearms come with Picatinny rail either built into the design, or supplied as an optional attachment. Despite the difference in their appearance, they are functionally identical. 

Weaver (L) and Picatinny (R) rail sections

Scope rings come in diameters for the two most common scope tube sizes, 1" and 30mm. The height of the rings is also important: ideally, the scope is mounted as low as possible but with some clearance between the objective lens and the barrel. If removable lens caps are to be used, their diameter should be taken into consideration when selecting scope ring height.

Mounting Process
If necessary, mount the rail to the firearm. A single drop of blue Loctite can be used to prevent the screws from backing out if they don't come with thread locker already applied. 

Next, attach the ring bases to the rail. Position them so that when the scope is in place they are relatively centered between the adjustment knobs and where the scope tube swells out at either end.

Once the rail and ring bases have been properly mounted to the rifle, place the scope on the rings and determine the best position for optimal eye relief. Keep in mind this can be adjusted in small increments once everything is in place, but try to get it as close as possible. (Proper eye relief is when the shooter can place their head in a comfortable position on the stock and still see the entire field of view through the scope without any fuzzing around the edges.)

Once scope position is determined, install the top half of the rings and loosely screw them down. Don't tighten them all the way yet; scope orientation needs to be checked and confirmed. This can be done by eye, but a better option is to use a leveling tool. Secure the firearm in a soft jaw vice and try to get it as level as possible first, then attach the scope leveling tool and rotate the scope until the reticle is level.

When tightening the scope ring screws, be careful not to overtighten them. Most scope and scope ring manufactures recommend 25 inch-pounds as a maximum. While this can be done by feel, a safer and more precise option is using a torque wrench. This can either be a dedicated tool or an adapter for an existing bit driver.

The screws should also be tightened in a pattern to avoid applying too much pressure to one side and twisting the scope. Since most rings have four screws each, a figure eight pattern is recommended, tightening each screw partially in turn until they're all done. Make sure the reticle remains level throughout the process.

Sighting In
Once the scope is successfully mounted, it's ready to be sighted in, but that's a topic for another article.

Have fun, and safe shooting.

Wednesday, December 21, 2022

Rucksack Night Walking

Not actually Erin.
& is used with permission.
Now that it's become pleasantly cool here in Florida, I've been taking nighttime walks around the neighborhood loop with my camping rucksack. 

As I mentioned back in April, my Bug Out Bag had become too heavy to carry without back pain, and I needed to slim it down. To that end, I tore everything out and rebuilt it from the ground up with the philosophy of "a pack suitable for a three-day camping trip is also a 72-hour BOB". I then supplemented it sparingly with some items that would be useful in a longer-term emergency. 

I think it's safe to say that I've gotten most of the kinks worked out of this bag, and I can carry it without either pain or difficulty. I'm now able to walk the full loop, 1.1 miles, without back pain or getting out of breath. My stamina still needs work because my goal is to be able to do two full miles -- well, 2.2 in reality, because that's two full loops -- and by the time I finish the first loop I'm exhausted and ready for a shower and bed. Still, this is progress that I'm quite proud of, and I know that if I just keep at it I will eventually reach my goal. 

Last night really wore me out, though. I was wearing hiking boots rather than my usual sneakers because it had rained earlier, and they weigh slightly more than I'm used to having on my feet. Around the 3/4ths mark of the walk my feet felt like they were weighed down with sandbags, and I had to concentrate on putting one foot in front of the other. My new rule is that I either walk in boots or with my rucksack, but not both until I'm stronger. 

For those who want to know more about my current 72 hour bag / camping rucksack, it's a High Sierra Long Trail 90L. 

  • 90-liter, expedition-sized backpack with extra cargo capacity.
  • Top-load main compartment with gusseted drawstring closure and adjustable top lid.
  • Drop-bottom sleeping bag compartment with divider.
  • ERGO-FIT shoulder harness, constructed with HEX-VENT mesh and foam padding.
  • Dual, contoured aluminum frame bars
  • Molded foam back panel with AIRFLOW channels.
  • Waist belt, with HEX-VENT mesh and high-density foam padding.
  • Side and bottom compression straps.
  • Internal hydration reservoir sleeve and dual exit ports for tube.
  • Front access to the main compartment.
  • Adjustable sternum strap.
  • Webbing daisy chain for attaching other gear.
  • Soft lashing hardware.
  • Mesh pockets hold water bottles.
  • Tuck-away rain cover also protects pack when checked for air travel.
  • Capacity - 5500 cu. in.
  • Weight: 6.91 lbs.

I'll tell you more about my new boots in another post, once I have a bit more experience with walking in them. 

Sunday, December 18, 2022

Guest Post: Waterproofing a Bivy Cover

 by George Groot

George is a member of our Facebook Group and has written for us before.

In the late 1990s I turned in my old olive drab canvas sleeping bag and received a new issue of the Army Modular Sleep System (MSS), which consists of a lightweight summer sleeping bag, a heavier winter bag, and a Gore-tex fabric bivouac (aka bivy) cover. All three items snap together to make a single unit, but you can mix and match the bags as needed; one time I even slept in just the bivy cover during a Texas summer. That old MSS set in woodland camo was turned in years ago as the Army transitioned to the “Let's invade the Moon!” Universal Camouflage Pattern (UCP) before transitioning to the current Operational Camouflage Pattern that looks very similar to MultiCam.

On the surplus market you can find all the parts for an MSS in both woodland and UCP camouflage patters, but for this article I just want to talk about the bivy cover. Generally this is the most expensive part of the MSS since it is made of Gore-Tex, which is generally a dandy fabric for the great outdoors. However -- and I’ve learned this the hard way -- Gore-Tex does not retain its waterproof capability after being run through the washer/dryer in order to get your gear clean for Central Issue Facility (CIF) turn-in. This means that a lot of the bivy covers on the surplus market aren’t very waterproof at all.

However, that doesn’t mean they can’t be made useful again. I recently purchased two UCP pattern bivy covers for my sons, and paired them with a Walmart-brand mummy bag for camping with their Trail Life troop. However, my eldest son woke up in a puddle of water while still inside the tent his first time out. This was a failure of both tent site selection and of the bivy cover, as it offered no protection from the water seeping into the tent. Since the poor judgement of my children isn’t the topic of this article, we’ll focus on getting the bivy cover back up to shape.

Gore-Tex from the factory has a “durable water repellant” (DWR) applied to the fibers. If your bivy cover easily accepts water rather than having water bead off, then it’s likely you need to re-apply a coating or two. The three main types of DWR are fluorocarbon-based, silicone-based, and hydrocarbon-based polymers, and they come in both wash-in and application varieties. There are a lot of “nano-tech” products on the market now, many advertised as “silicone free” but from the reviews I’ve researched and the single product I tested, they come with mixed results.

Wash-in is likely the easiest method, as it lets the washing mashing do all the work. This will generally apply the DWR evenly, inside and out. For something like a bivy cover this should be just fine, but for something like a Gore-Tex jacket with a sewn-in liner, it may not be the best choice as it may change the ability of the liner to wick moisture.

Application, either spritz on or spray on, has the benefit of being a readily available option in most big box stores and sporting goods stores. You’ll see these as various offerings from Scotchguard and Sno-Seal in most chain stores, and specialty stores may also carry NikWax.

However you treat your surplus bivy cover, understand that it isn't waterproof any more, only water repellant now, but just like older canvas bivouac covers it is still an incredible value-add if you have to camp without a tent. If you also have cotton bivy covers, then there are a lot of wax-based fabric treatment options that can really help increase the water resistance, some cheaper than others. (Erin wrote about waterproofing cotton with wax in this article.)

What I did to pep up my son's bivy cover was to spray the outside with Tex-10 water repellent, which turned out to be really expensive and didn’t give the results I wanted. It was difficult to get an even spread/penetration with the spritzer, and so the next day some areas beaded water beautifully, while other areas soaked up water like a sponge. It's not a great value for the performance, so I can’t recommend it. 

For a second treatment I turned the bivy covers inside-out, liberally sprayed them with an Atsko Silicone Water-Guard from Walmart, and let them dry hanging outside overnight. The next morning I tossed them into the dryer and tumbled them on low heat for 20 minutes, and the results were much, much better. The organic solvent provided much easier product distribution through the fabric than the water solvent of the Tex-10, and while the environment might take a hit, better performance for 25% of the price seems like a good thing for us blue collar types.

If I have to do this again, I’ll probably plan ahead and order a NikWax wash-in product, as they have the most consistently positive reviews for treating hard use outdoor gear. NikWax products are also beeswax-based, for those who might prefer that over silicone. 

None of these treatments last forever, so you will end up re-applying as needed to keep performance at an acceptable level. In Alaska that’s probably going to be more often than Arizona or North Carolina.

Stay dry!

Wednesday, December 14, 2022

Prepper's Armory: Scopes, Part 1

When it comes to optics, especially magnified optics, there's a lot of confusion and misinformation out there. One aspect of this type of optic that's not very well understood is the First and Second Focal Plane Reticle.

In variable magnification scopes with a reticle in the First Focal Plane, the reticle will adjust along with the image. This means that any graduations, such as mil-dots or bullet drop compensator markings, will still be useable no matter the zoom level. The downside to this is that at higher magnifications, the reticle itself will appear noticeably thicker and is more likely to obscure part of the sight picture and at the lowest magnification, the reticle may be thinner than preferred. First Focal Plane scopes are also generally more expensive than Second Focal Plane scopes because of the additional manufacturing elements required.

Magnified scopes with Second Focal Plane reticles change the image size, but not the reticle, which means the crosshairs and other aiming marks are always the same size while the view gets bigger or smaller. This can be beneficial for aiming consistency, but if the scope has Mil-Dots, etc. they'll only be reliably usable in a small subset of the full magnification range. This type of scope is generally less expensive than those with First Focal Plane setup.

Scope Anatomy

Image courtesy of The NRA Blog

Starting from the front of the scope and on the right of the illustration is the objective lens, measured in millimeters. It affects both field of view (the width of viewable area at any given zoom level) and the amount of light entering the optic path. The larger the objective lens, the better for both these values.

Moving left and back, the erector tube assembly is next. This element contains the lenses needed for magnification, and may also include the reticle in a First Focal Plane setup. Another part of the erector tube is the focus lens which, as the name implies, helps keep the image crisp and clear. 

Behind the focus lens is the image reversal assembly. When light passes through the series of lenses in a modern scope, it can cause the image to appear upside down, and the image reversal assembly corrects this before it reaches the user's eye.

The magnification lenses move forward and back inside the scope body in a scope with adjustable zoom. When these lenses move forward (away from the ocular lens) magnification increases; when they move rearward (away from the objective lens), magnification decreases. For example, in a 3x9 variable magnification scope, at 9x magnification the erector tube will be closest to the objective lens, and at 3x it will be closest to the ocular lens.

Next is the Second Focal Plane aperture and, if appropriate, the reticle for this type of scope. Finally there is the ocular lens, which collects the light that passes through the scope and presents its image to the shooters eye. Many of these lenses will have coatings to reduce light reflection and improve clarity. 

All the different elements of the scope are sealed with rubber or silicone gaskets to make the scope waterproof, and before final assembly the scope is purged of air and filled with nitrogen (or a similar gas) to prevent fogging of the lenses.

Scope Operation
There are several external adjustment controls on a modern scope. The windage and elevation knobs, located on the top and side of the scope at the middle of the scope body or tube, allow the user to change the position of the reticle for zeroing a scope. These are adjusted in either half- or quarter-minute of angle increments.

If appropriate, there may also be a Bullet Drop Compensator knob. These days it is more likely that the BDC will be incorporated into the reticle.

Zoom adjustment is generally made by means of a collar in front of the ocular lens. Many scopes also have a focus ring at the rear of the eyepiece, used to adjust focus of the reticle for each user.

If the scope has a parallax adjustment, it may have another knob opposite the windage adjustment, or else be changed by rotating the objective end of the scope. This adjusts the reticle focus in relation to the target. If the scope has fixed parallax, it will usually be set at 100 yards in centerfire rifle scopes and 50 yards in rimfire, shotgun, and handgun scopes. This means that at other distances, both the reticle and the target may not be in focus simultaneously.

Another setting is what's called eye relief, the distance between the shooter's eye and the eyepiece of the ocular lens where the entire field of view is visible. Shotgun and handgun scopes have considerably longer eye relief than rifle scopes. While this can usually be adjusted in small increments on the scope itself, it is more coarsely set by the position of the scope on the firearm.

Hopefully this article clarifies both components and terminology in the modern scope. Have fun, and safe shooting.

Wednesday, December 7, 2022

Prepper's Armory: Using Iron Sights

Continuing from my previous post, the quality of any sighting system is of little benefit if it isn't applied correctly. The two elements of using iron sights properly are referred to as Sight Alignment and Sight Picture.

Sight Alignment
When your front and rear sight elements are in proper orientation to one another, you have Sight Alignment. With proper sight alignment, aiming is easier, but if sight alignment is not correct and not consistent, then everything is harder.

When using Patridge sights, the top of the front sight blade (or post) should be level with the top of rear sight block, and it should be centered in the rear sight notch. If the front sight protrudes above the rear sight, your bullets will hit higher than you intended; if there is a gap between the top of the front sight and the top of the rear sight, your bullets will hit lower. Similarly, if the front sight is held to one side or the other in the rear sight notch, hits will be to one side or the other on the target. It's also very difficult to hold the sights out of alignment consistently, meaning that your point of impact will wander. 

Tang-mounted or Receiver sights should have the top of the front sight blade (or middle of the crosshairs) centered in the field of view. Tang sights have different sized apertures for different ranges and light conditions.

Image courtesy of the TN Handgun Carry Course

Sight Picture
Looking through properly aligned sights at a target involves dealing with three elements at different distances. Unfortunately, we have a problem in that our eyes can only focus on one element at a time. 
  • If we focus on the target, the rear sight is practically useless
  • If we focus on the rear sight, the target is effectively a blob.
  • Therefore, the general recommendation is to focus on the front sight. The rear sight and target will be slightly out of focus, but will still  be manageable.

Image courtesy of the TN Handgun Carry Course

Proper understanding and use of sights is an essential part of accuracy. As Colonel Townsend Whelen said, "Only accurate rifles are interesting."

In a future post I'll discuss the difference a Red Dot sight can make.

Good luck, and safe shooting.

Saturday, December 3, 2022

Follow-Up Reports

Not actually Erin.
& is used with permission.
Herein is an assortment of further information on topics I've discussed earlier. 

I am pleased to report that using this as an uninterruptible power supply for my CPAP works perfectly. Last month our neighborhood lost power from early morning until about 1 pm, and I didn't experience a change in performance as the Freeman 600 switched from pass-through charging to onboard battery. I am very happy with how this system operates, so unless there are hidden issues with the unit which only crop up after months or years, I consider this experiment a resounding success and recommend the Freeman 600 for all my CPAP-using brethren. 

I haven't yet tested the recharging speed/capabilities of the solar panels. That's on my list of "Things I want to do but first need to find the time to do them."

The Caretras Bunion Splint is doing its job of pulling my toe back into alignment while I work at my desk or watch television. However, the velcro doesn't hold as tightly as it once used to do, despite having been laundered and the hooks free of any lint. However, I have achieved a workaround with something I ordered for a different problem.

This 20-piece set of velcro ties for cable management works a treat for keeping the splint on my foot. The smallest (8" long) wraps around my big toe, and the next smallest (12" long) secures the brace around my instep. I have plenty of each, so if these start to fail I can just use the others, and I still have straps left over to secure the cables I wanted gathered up.

On a related note, I have discovered that wearing these gel toe separators while going for walks or running errands is a useful preventative measure. While they don't prevent my toe from cramping, they reduce the intensity of the discomfort and the time required in the splint to correct it.

Back in 2018 I mentioned using Hickies-brand no-tie shoelaces for my daily shoe and boot usage. As it turns out, while version 2.0 is more durable than version 1.0, they do still experience material fatigue and failure from repeated use. 

However, I have found something better! Lock Laces are a single strand of elastic cord with a spring-loaded lock to gather them tightly into place. This keeps them securely attached to my feet, but with enough "give" that I am able to quickly slip them on and off as needed.

There is even a heavy-duty boot version

I have been using Lock Laces for almost a year now and they continue to stretch and return to form. While I am certain the elastic will eventually fail, they have stood up to daily wear & tear and I am impressed with their durability and performance. I recommend them to anyone who wants to be able to save time putting on or taking off their footwear. 

That's all for now, but I will update you on any changes. 

Wednesday, November 30, 2022

Prepper's Armory: Iron Sight Types

The earliest firearms were simply pointed rather than aimed, but as technology matured and new concepts were developed, sights started to appear. At first they were similar to what we would think of as shotgun sights today: more of a guide to make sure the shot went in the right general direction than an actual sight for accurate shooting. As rifled arms became more common, however, better sights were needed.

Some of the earlier styles of iron sights are still with us. For example, the Patridge sight (no, not partridge like the bird) was named after 19th century target shooter and inventor E. E. Patridge and consists of a square post front sight and a rectangular notch rear sight (figure B in the illustration below). Nearly every iron sighted pistol, and many rifles, still use this design.

There are also more recent additions to the handgun iron sight family, such as the Steyr Trapezoidal sight  (figure G in the illustration below). Similar to the Patridge system with a front post and rear notch, the difference here is the shape of those two elements. The front sight is pyramidal, while the rear sight has a similarly-shaped cutout.

A selection of open sights, and one aperture sight suitable for use with long eye relief:
A) U-notch and post, B) Patridge, C) V-notch and post, D) Express, E) U-notch and bead,
F) V-notch and bead, G) trapezoid, H) ghost ring. The gray dot represents the target.

The Buckhorn and Semi-Buckhorn are named for the curved elements on the rear sight that extend up and around, containing the view of the front sight. The arms of the Buckhorn come close to meeting at the top, while the semi-Buckhorn is more open. While the former version of this sight has fallen from common use, the latter style is still frequently found on modern production lever action rifles.

For anyone who's ever attended a Cowboy Action match with a long range component, they've probably seen shooters using a tang-mounted aperture sight, sometimes called a Vernier sight. By positioning the rear sight on the wrist of the stock, it gives a much longer sight radius than the usual rear sight location near the chamber of the barrel, and can be removed or folded down when not in use.
It is a precision mechanism, and was one of the earliest finely-adjustable precision rifle sights available.

This sighting system is complemented with the addition of one of a variety of front sights, usually inside a protective tube or hood and frequently combined with a spirit level for consistent levelling of the rifle. This sight is mounted at the traditional location, the muzzle end of the barrel.

Receiver sights were, as the name implies, mounted to the side and top of the rifle's receiver. These sights, also commonly called peep sights, allowed hunters to make accurate "snap shots" relatively quickly, even in low light conditions. As with the tang sights, many receiver sights were also capable of precise adjustments. This style of sight is the conceptual predecessor of our modern Ghost Ring sight.

There have been more sight designs over the years in addition to these. Some withstood the test of time, while others did not.

In my next post I will explain how to look through the sights and put them on the target, aka sight alignment and picture. 

Friday, November 25, 2022

Finding the Angle

Not actually Erin.
& is used with permission.
Special thanks to George Groot for double-checking my math and helping with clarity. 

I realized that my previous post referenced using azimuths to find an angle without explicitly showing how to do that. I will attempt to explain the process, but please understand that math is not my best subject, and I may flail verbally about while trying to make my point. 

Triangulation is a process used in surveying and navigation which uses triangles (hence the name) to determine the coordinates of a point. You need two known angles and one known side length (or distance) to do this, creating a triangle which allows us to use trigonometry to solve for the other angles and distances.

Let us assume that you need to find the distance to the boat in the illustration above. How do you do that without a rangefinder?

1) Starting at point A, shoot an azimuth to the boat and record it. 

2) Using your compass, you turn right 90° and march toward point B. I recommend 10 yards, as it is a short enough distance that your bearing will not vary too much, and it is a nice round number that ought to make math easier. 
How will I know when I've traveled 10 yards? If you're doing land navigation, you should know your pace count per 100 yards, so just divide that by 10 and when you've walked that number of paces, you have arrived. If you don't know your pace count, this article by Lokidude will show you how. 
If the object is quite large, you might need to take more steps; I still suggest you take them in units of 10. 
I am making this slightly more complicated than it strictly needs to be, because you will need to have a straight line (d) coming from the boat that intersects line AB at a right angle. If you don't have a right angle, things will be much more complicated and outside the scope of this article, so I'm having you do a little more work now to save you a lot more grief later. 

This is the same reason I'm not having you walk until you're at 90° to the boat. What is the likelihood that you'll correctly make a 90° angle the first time? To my mind, this extra step prevents that mistake. 

3) At point B, shoot a second azimuth to the boat and record it. 

4) Shoot a third azimuth to point A and record that. 

5) In a triangle, no single angle can be more than 90°, and we're going to create a 90° angle in a moment, so angle ß cannot be larger than 90°. If it is, then subtract it from 180°. If it isn't, then subtract it from 90°. 

6) You now know angle ß. Record it. (For this example we will say it is 60°.)

7) Halve the distance of line AB to create two right-angle triangles which share a side, d. Side d is the distance you need to determine. 

8) You know the distance from B to D (the halfway point between A and B) is 5 yards. You know the measurement of angle ß. This is all you need, so now let's do some math. 

9) How much do you remember from Geometry?

We need to find the length of d, which in this figure is the Opposite side. The tangent of angle ß is the quotient (the number you get as a result of division) of the Opposite over the Adjacent. 
Side note: if you ever forget, just remember SOH CAH TOA:
  • Sine is the Opposite over the Hypotenuse (SOH)
  • Cosine is the Adjacent over the Hypotenuse (CAH)
  • Tangent is the Opposite over the Adjacent (TOA)
But we don't need to find that angle, because we know it. So we do some math jiggery-pokery:
  • Tangent of Θ = O/A
  • Multiply both sides by A 
  • A times tangent Θ = O
Which is exactly the same formula which David's friend gave us here, just with different names for the sides. 

So going back to the original problem with sailboat distance:

We know the distance from B to D is 5 yards. 

We know the measurement of angle ß is 60°. 

Therefore, 5 times the tangent of 60° will give us the length of line d, the distance to our target. 

The tangent of 60° is 1.73205080757. Shortening that to 1.73 ought to suffice. 

Therefore, d = 5 * 1.73. 

Therefore d -- the straight line distance from shore to boat -- is 8.65 yards.

The Right Angle Theorem says that the length of the side opposite the right angle is the square of the sum of the squares of the other two sides. In other words, the famous A² + B² = C², where C is the side opposite the right angle, also known as the Hypotenuse. 

Therefore, 5² + 8.65² = C². 

Therefore, 25 + 74.8225 = C². 

Therefore, C² = 99.8225. 

Take the square root of both sides. 

C = 9.9911 yards. 

So the distance from your current position at point B to the sailboat is almost 10 yards, or 30 feet. 

This makes good intuitive sense, as solving for all angles shows that we originally had a 60/60/60 equilateral triangle, in which case the distance between A and Boat and B and Boat must be the same as the distance between A and B.
Remember, we know that we have a 90° angle and a 60° angle, and all angles within a triangle must add up to 180°, so 90 + 60 = 150 and 180 - 150 = 30, therefore the remaining angle opposite side DB must be 30°. 

Since this triangle is half of our original one, the other half must be symmetrical and therefore identical. Therefore, the angle opposite side AB is 60°. 

George Groot adds:
We can exploit this feature of angles without using a compass for short distances, such as distance across streams or small rivers, simply by using the bill of a cap to align with the distant shore and  then turning to face a point on land without moving your head. The bill of the cap swung in an arc, and the arc describes the same distance (a radius) from the central point, letting you determine a distance that you can’t walk to by walking to a point on the same arc that you can reach. This is much less math than using triangulation to find the distance, and much quicker to determine things like "Do I have enough rope to make a rope bridge?"

If trigonometric functions are confusing, an alternate way is to use "minute of angle math" to determine the distance. Starting at point A, shoot an azimuth to your unknown distance target. Turn 90 degrees to walk parallel to the target for a known distance and shoot a second azimuth to the target. Subtract the smaller angle from the larger angle to get the "inside angle" of the target to your known distance. 

Since one minute of angle is roughly one inch at one hundred yards, if your known distance was 10 feet (120 inches) and your angle was 1 degree (60 minutes) you know that your unknown distance to the target is 200 yards away (60 minutes = 120 inches at 200 yards). This method requires a precise compass, and precise linear measurement, but it does work. 

Thursday, November 24, 2022

Shooting Azimuths

Not actually Erin.
& is used with permission.
Two years ago, David Blackard wrote a post about how to determine the distance to an object in the field without using a rangefinder. This involved knowing the distance and angle to another object and then using a calculator to do some complicated math. 
  1. In the drawing, aligning the start point with the target and then laying out a 90 degree angle for the base is important. 
  2. Measure as accurately as possible along that 90° angle to establish the base, shown as X.
  3. Here is where being able to get good angle measurements is important, since this will give you the vital number that plugs into your distance equation.

This is all very well and good, but in the un-edited version of his post he talked about using a protractor to find that angle. My immediate thought was "Why not just shoot an azimuth using a lensatic compass?" Well, it turns out that David had never heard of azimuths or lensatic compasses at that point, so I sent him some links and considered the matter solved. 

As it turns out the matter is not solved, because today David posted this:

In the comments, a friend said "I have no idea what you're talking about either, but I'd love to find out." I had a bit of time, so I started briefly explaining, and by the time I was done I had a good start on a blog post, which I figured I might as well finish here. 

What is an Azimuth?
Azimuths are used in astronomy and celestial navigation (which is just astronomy with more math) in addition to land navigation, and most explanations will give a complicated answer about three dimensions. Land navigation only uses two dimensions so a simpler application gets a simpler definition. 

Put simply, an azimuth is a compass bearing. Due north is 0°, so east is 90°,  south is 180°, and west is an azimuth of  270°. You get the idea: an azimuth is the angle between north and wherever you're looking.

What is a Lensatic Compass?
You've likely seen a lensatic compass before even if you don't know the name, as it has a very distinctive shape. Rather than describe it, here is a picture with the parts labeled. 

Land Navigation Module 2 Using a Lensatic Compass.

A lensatic compass has a useful feature where you can look through it to precisely align it with a terrain feature, then glance down to see what your azimuth to that feature is. 

Why a terrain feature? Because if you navigate towards a terrain feature instead of a compass bearing, you walk faster and safer, because your eyes are looking at where you're going rather than buried in the compass. Just be sure to check your compass every 100 yards or so to make sure you're still headed in the right direction. 

How to Shoot an Azimuth
Using a compass to find an azimuth is called "shooting", because if you do it properly you hold the compass like a firearm and aim at your target terrain feature. 

There are other ways to do it, but this method, known as the "cheek hold", is the most precise.
  1. Put your thumb through the loop with your forefinger pointing alongside the compass, as shown in the picture.  
  2. Bring your hand up to your cheek with the base of your thumb in the crease between your cheekbone and upper lip. 
  3. Look through the window in the compass cover and find your target terrain feature
  4. Line up the notch (rear sight) with the wire (front sight) and center the feature in the sights the same way you'd aim a gun.
  5. Glance down through the magnifying lens to find your azimuth.

In this example the compass reads 320°, so that is your azimuth. If you want to make your life easier, rotate the bezel ring so that the luminous line is aligned with your compass arrow. With that done, you can quickly check your bearing without having to shoot a new azimuth by aligning the arrow with the line and seeing if the fixed black line is still pointing at your target. If it is, you keep walking. If it's not, something has gone wrong and you need to shoot a new azimuth. 

Back Azimuths
If you need to go back the way you came, you don't need to shoot a new azimuth. Instead, you can calculate a back azimuth:
  • If the original azimuth is less than 180°, you add 180° to get a back azimuth. 
  • If the original azimuth is greater than 180°, you subtract 180° from the original azimuth. 
In the example above, the original azimuth is 320°, which is greater than 180°. Its back azimuth is therefore 320 - 180 = 140°. 

With a quality compass and the knowledge of azimuths, you can make very precise measurements in the field. Combined with the formula above and a calculator with the TAN function, you can quickly determine the distance to an unknown point. 

The Fine Print

This work is licensed under a Creative Commons Attribution- Noncommercial- No Derivative Works 3.0 License.

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