Overpowering question

[WillieC]

“....roofer...”

With metric shingles, no less.

[dkirsop]

In high school we supposedly became metric. In 1st year university all my science courses were metres, kilograms and seconds. Then I went to engineering school and was told to forget all that and we used kips, ergs, slugs and other strange terms. Eventually I graduated to nods, ferkins and grams - otherwise known as the NFG system!

[WillieC]

I am a master with the NFG system!

[DesertAlbin736]

US military has, since at least Vietnam & probably earlier due to NATO membership talks distances in kilometers, or "klicks" (but aircraft fuel in pounds). In all my discussions involving Canada I try to include things in metric & temps in deg C. Gallons are assumed to be US gallons. The actual US gallon to litre (giving the Canadian spelling here) conversion factor is times 3.7854. Sometimes I've mistakenly used 3.84. dkirsop & ssig, could someone please explain to me what the heck Kilo Pascals are vs millibars vs inches of Hg vs mm of Hg? Also "Humidex" vs dew points & % relative humidity?

The US flirted with going metric back in the 1970s but the idea was a bit too complex and baffling for us. A litre is like a quart but a bit more, a meter (metre?) is like a yard but 3 inches longer. A cm is 2.54 inches. A km is more than a half mile but less than 3/4. Mind boggling! At least we can understand that 1 nautical mile = 1 minute of latitude (but not longitude), handy for scaling distances on a chart.

DSCN4754 (1280x960).jpg

.

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Can't wait to go to Quebec where they don't bother including English translation on signs & websites.

Then I went to engineering school and was told to forget all that and we used kips, ergs, slugs and other strange terms

The only thing I know about slugs is they shrivel up if you sprinkle salt on them

[Bob Noodat]

The metric system (thank you Napoleon Bonaparte) is a truly wonderful system. Eminently logical. You can work between volume, area, mass, liquid volume without a pause. If I need to know how many gallons fall on a twenty acre field if we get 1/2" of rain, that calculation would indeed boggle the mind. Just convert it into metric and you can do it in your head, within a few percent:

20 acres is 8 hectares, which is 80,000 square meters. 1/2" is 12.5mm, or an 80th of a metre, which means that 1000 cubic meters fell, or 1000 x (100cm x 100cm x 100cm) = 1000 million cubic cm which is a million litres, then to get the 3.8 litre per gallon figure, just divide by 4 to get 250, 000, add 5% of that last number, or 12,500, and you have 262,500 gallons.

Do that Imperially!

Of course, you can always just Google it, but where's the satisfaction?

[DesertAlbin736]

Then there's statute miles. 1 mile = 80 survey chains = 5,280 feet. 1 survey chain = 66 feet. 1 acre = 10 square chains = 43,560 sq feet. 1 square mile = 640 acres. 36 sq miles is one township. All very intuitive. Among my many talents I spent the first four of my 25 years long career with Arizona Public Service Company electric utility as a survey instrument man on crews that worked on lines all over the state.

[WillieC]

Quick. About how long is one side of a square acre? 208 feet.

The metric system makes people dumb...or maybe it frees up brain cells. I can't think anymore so I don't know. (That 208 feet is stuck in my head from looking at property back when we had no chance of buying any. I also used to do square roots on paper. It was part of the electrical apprenticeship. We DO need to know square roots, but I told the instructor that if I ever needed to know the square root of a number and I did not have a calculator at hand, I would stop what I was doing, drive to the closest store and buy one for less than ten bucks. I would also do it on company time and STILL save the boss money.)

What is this thread about? My brain is overpowered.

[Bob Noodat]

Thread?
That 208 foot value, like all DA's numbers, just proves the absurdity of the system: you have to memorize a set of values for each parameter, and further memorize values for any conversions between them. The metric system is just an application of logical first principles. In my rainfall example the 1 or 2% inaccuracy comes largely from rounding off the arbitrary and archaic Imperial values, plus a lazy calculation shortcut. If you simply asked "How many litres of water is the product of 12.5mm of rain falling on 8 hectares of land?" then the answer is exact and obtained without effort or memorization.

[Bob Noodat]

So, an attempt to return to the thread theme, with an apology for the digression(s), all my fault as usual. Bats in the belfry or butterflies in the brain.

I came across a little trawler recently with an interesting feature: a controllable, or variable, pitch propeller.  Made by SABB in the 90s, combined with a Mitsubishi 4 cylinder 36hp diesel. The drive always turns the prop in the same direction, but a hydraulically controlled gearing changes the pitch from forward thrust through no thrust to stern thrust seamlessly, with all gradations along the way.  I believe that if the engine is running the prop is turning.  Apparently these are quite commonly found in Europe, because they can save a lot of fuel and fuel is so expensive over there.  I wonder if any European A25s have CP props?

Picture of the prop:

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Original description of function:

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The hydraulic drive:

20200326_100522.jpg

It would seem that with this system it is possible to have your cake and eat it too: the greatest economy when you want it, or the greatest power when you need it.

[WillieC]

The prop system you describe was often and heartily endorsed by George Buehler. RIP good sir.

[Bob Noodat]

The prop system you describe was often and heartily endorsed by George Buehler. RIP good sir.

That name was new to me. Not the NFL lineman, I decided, nor the lawyer in Pasadena. Must be this chap:
https://www.passagemaker.com/trawler-ne ... dead-at-69
Supported an old dogs home, so a man after my own heart there.
But I bet he never put a CP prop in an A25.

[DesertAlbin736]

A bit like a sailboat's two blade folding prop. Actually that SAAB prop would be good for an A25 set up with sail rig if it had an option to feather. Which is another reason the sail rig on an A25 is iffy, the drag of the big prop if purely under sail & not motor-sailing.

Fun fact, getting back into the weeds on measuring units (hey, we're all stuck at home with nothing better to do), I mentioned chains as a unit of land survey distance measurements. Way, way, way back in the day, maybe as far back as when George Washington was dabbling in land surveying, distances were measured using physical chains. But not the kind you think of like the one attached to your anchor. It was called the "Gunter's chain" and it looked like this:

aaagunterchain.jpg

It had 100 links, the nearest it came to being anything remotely resembling decimal. Each "link" was 0.66 feet or 7.92 inches. Don't ask how they came up with the idea of one chain being 66 feet other than it's 1/80th of a mile and maybe practical in terms of a limit on how much weight 'chain men' had to schlep around. In frontier days as western territories were surveyed into the township-range-section system long distances were often measured by means of revolution counting "odometers" on wagon wheels. The one mile square sections were "nominal" dimensions east-west and north-south, and where ever the section corner and quarter corner monuments were set, some times just a pile of stones, sometimes a brass cap on top of a pipe set in the ground, that was the legal basis of property lines regardless of actual distances. Of course chains were superceded by tape measures which in turn were mostly supplanted by laser EDM's (electronic distance measurements). I've been away from surveying for 30 years now, and I'm guessing GPS has taken over a lot of that stuff since then. Another fun fact to make things even more confusing, in surveying while the basic unit is the foot, inches are not used, but instead decimals of a foot in 1/100ths. So 1/10th of a foot is close to an inch, but 1/10th is not 1/12th. Just like with an engineer's scale that may be 12 inches long, gradations can be in tenths, twentieths, thirtieths, fortieths, fiftieths, or sixtieths of an inch.

Even more confusing, from my survey course textbook:

Poles. Early surveyors struggled with braced timber panels and wood and metal poles. These devices resulted in the term pole as a unit of measure. It's length was 16 1/2 feet, the same as the rod.

Then there was an "Engineer's chain", 100 feet long with 100 links, each 1 foot long.

Even using a "modern" steel tape could be complicated & requires some skill with a two person team. Distances are measured on the horizontal, not on a slope. Temperatures had to be noted & corrected for to account for expansion and contraction of the steel tape. For long distances "range pins" were used to help count the number of full tape distances, for example with a 100 foot tape. Otherwise a "traverse", a series of angles accurately measured with a transit & distances to get around sight obstacles and back to the starting point would not "close" within geometric accuracy tolerances. The lead guy with the tape reel would have a set of pins and at each 100 foot interval would stick a pin in the ground at the 100 foot mark & move forward. The guy at the zero end would use that pin to mark the start of the next 100 foot segment, then pick up the pin & move forward. At the end of the line he would count up the number of pins he had for total distance.

More crazy trivia, highway curves are calculated and staked differently than railroad curves, the former calculated with pi formulas based on radius, ie "1000 ft curve" or "1500m curve", the latter with formulas based on trig functions and chord definition (distance from center of circle to center of chord).

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I should say the decision to take up surveying after being a truck driver was a pivotal moment at age 34 that changed the arc of my life forever. It led to being hired by the power company which in turn led to job security (after the first four years in the field I transitioned into old style pen and ink map drafting and then later in to CAD drafting and computer based load modeling studies). That led to a comfortable retirement in which we can do all this boating stuff without financial worries.

[DesertAlbin736]

The prop system you describe was often and heartily endorsed by George Buehler. RIP good sir.

Buehler?

https://www.youtube.com/watch?v=NP0mQeLWCCo

[WillieC]

A couple books to look up:

Buehler's Backyard Boatbuilding and The Troller Yacht.

When I was younger, I almost thought I could build a boat in my backyard. Then I thought, WTH, I could WELD a boat! How hard could that be?

We came to our senses and the Starfleet Commander saw an A25 we should go look at. It was made of congealed snot and I was reluctant, being a theoretical purist, the best kind BTW.

It was Buehler, whom we first learned about talking to a guy in a Port Orchard marina who was living on a converted tug boat, who actually convinced us to quit looking and dreaming and get an affordable boat. A normal person ought to be able to afford a boat! Do it!

Buehler wrote of an older period, where lumber yards actually sold seaworthy lumber and skilled craftsmen populated our subdivisions. Sabb engines with feathering props could be had for a few hunnert. When 'Murka was great...

Buehler planted the idea and here we are. Thanks, George!

[motthediesel]

Re: Variable pitch props. Watermota in England used to make a similar small unit. They are now even harder to find than the Norwegian Sabb product. Somebody linked to a A25 for sale here a while ago that had a Sabb engine, but I don’t know if it was equipped with the VP stern gear too. That would be a glorious outfit.

Variable pitch props are more common on ships than boats. My maritime cadet nephew served on a lake freighter so equipped like that last year — The Ojibway.