The problem:

I have a very expensive, high-end wind generator on my sailing vessel. Unfortunately, it has broken blades. Replacing the blades is prohibitively expensive ($2000). Many sailing vessels utilise hydrogenerators that are dragged behind the vessel under way. I am proposing to remove the hub that holds the blades, couple on a shaft and propellor, and drag the prop behind the boat to create a DIY hydrogenerator. The generator itself would remain in a dry location on deck, driven by a ~2m shaft.

I have a table of the RPM required at the wind generator's shaft to produce a given wattage. I also have a number of spare props lying around. I would like a formula to calculate how fast a given prop would turn the shaft, given its dimensions and particulars (pitch, blades, diameter, rake if necessary).

- I do not need the RPM figure to be very precise, +/- 20% would be fine

- assume there is no friction from the shaft and hub

- ideally I want to achieve something like 900 rpm at 5 knots (5.7mph)

- Example problem using a propellor I have lying around: the diameter is 9.5 inches, the pitch 10 inches, number of blades 3. How fast would this propellor spin when dragged at 5kts through salt water?

Here is the RPM to power table if it helps. It would be ideal if I could achieve 900rpm or higher while travelling at 5 to 7 kts.

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https://preview.redd.it/0av1vbidot3b1.png?width=236&format=png&auto=webp&v=enabled&s=53528e7398376596219440d868396384fb93decd

thank you for your help!

Even with it being /r/science I thought this was worthy of recognition for the effort put in.

Should be about 1L glass, does someone have a corn volume occupancy number?

This question is working under the following parameters

1. Such a building was physically possible
2. Each floor needs to be tall enough to live in (for an adult).

Given that pregnant women will have 4, but that’s offset by some people with no legs, or 1 leg.

Alright, reddit. I'm sick of night and day. I'm sick of morning people and night owls. I want to stop this planet from spinning -- can it be done? From an engineering perspective, what will it take, and how long do I have to keep dealing with these crazies?

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https://preview.redd.it/2d568ohddn3b1.png?width=1348&format=png&auto=webp&v=enabled&s=a30ea5bbb974df275ac5d8863ac22bc14eb402ea

Using the relation between meters, liters and grams in the metric system and this redditor's proposal, how many liters is a deciminute ?

https://physicsworld.com/a/great-gaffe-in-the-sky-the-erroneous-physics-behind-the-dark-side-of-the-moon/

TLDR - The prism shown on the cover of Dark Side of the Moon is not physically possible due to the angles of light coming out. Form over function in this case.

tried to ask ChatGPT, but it kept spewing out different answers

for example, when asked about 77 evenly spaced towers:

CHATGPT Answer 1 (44 km):

If you have 77 towers that are evenly spaced across the Earth's land, we can calculate the distance between each tower.

Assuming the land area of the world is approximately 148.94 million square kilometers, we can divide this by the number of spaces between the towers, which is one less than the number of towers (76 spaces).

Land area between each tower = Land area of the world / Number of spaces = 148.94 million square kilometers / 76 ≈ 1.96 million square kilometers

Now, let's convert the square kilometers to meters by multiplying by 1,000,000.

Land area between each tower = 1.96 million square kilometers * 1,000,000 ≈ 1,960,000,000 square meters

To find the distance between each tower, we take the square root of the land area between each tower.

Distance between each tower = √(1,960,000,000 square meters) ≈ 44,246.81 meters

Therefore, if you have 77 towers evenly spaced across the Earth's land, the distance between each tower would be approximately 44,246.81 meters (or about 44.25 kilometers, 27.49 miles).

CHATGPT, Same Question, Answer 2 (519 km):

If you have 77 towers evenly spaced across the land area of the Earth, we can calculate the average distance between each tower. Assuming that the land area is approximately 148.94 million square kilometers, we can proceed with the calculation.

To determine the average distance between each tower, we divide the circumference of the Earth (at the equator) by the number of towers.

Circumference of the Earth = 40,075 kilometers

Average distance = Circumference / Number of towers = 40,075 kilometers / 77 ≈ 519.48 kilometers

Therefore, if 77 towers were evenly spaced across the land area of the world, they would be approximately 519.48 kilometers (or about 322.61 miles) apart from each other on average.

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So... Which one is it? Maybe neither?

1. Shuffle a deck of 52 cards.
2. Turn over the first card by saying "Ace"
3. If the card is an Ace, you lose.
4. Turn the second card by sayiing "Two"
5. If the card is a 2, you lose.
6. Continue like that counting like that: Ace,2,3,4,5,6,7,8,9,10,J,Q,K,A,2,3,...

What are the chances of passing the whole deck without dying?

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I did some Monte Carlo sims and I get around 1.6%.

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How do you solve that analytically. It just seems too much conditionals and a product of a product with a general term that I'm too lazy to try and resolve...

Edit: (12/13)^52 = 1.557%

My brother is on the hunt for a new car. The one he likes, he was told, has a 9 year waitlist. It is electric, and I know those are in demand, but it just seems nuts to me!

My question- how many cars behind is the factory?!! (Obvs the people on the waitlist may drop off etc) but if it is truly 9 years, how many cars will be made before his name comes up?

Before retiring, my dad worked on the assembly line at Ford, and they put out 1 car every 60 seconds, 24 hours a day. I’m not sure that’s the same for electric- but I’m happy with that as a starting point!!

TIA! We are so curious!

I'm not a smart person and cannot figure this out. I have a wall that is 10 feet wide. I have 4 pictures that are 17.5 inches wide a piece. They all hang from a single point in the center of the picture. I want to hang them spaced evenly from each other. I also want a little bit of a buffer(?) on the left and right side near the edges of the wall making them look centered instead of exactly evenly spaced across the whole wall. I hope this makes sense.

Let's assume that's an early modem where 2400 baud actually means 2,4 kbps. If it's actually 9,6 kbps we'll just divide by 4. Let's factor in possible bottle necks given by poor land-line signal, LAN interface between my C64 and the storage medium, etc. (although I believe the narrowest bandwidth is definitely the modem itself). How many days and hours would it take to download Skyrim from Steam?

Hoping someone can help settle a disagreement on how to calculate the chances of the scenario below and an explanation of why and how:

There is a box with 25 switches

Each switch can only be up or down

You have to get the right combination for only 4 of them to 'win' (in this case triggered a lock to open)

You do not know which 4 switches are the relevant ones

What are the chances that you randomly (not methodically) mess around with the switches and get the right combination?

Also:

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1. does it matter if the action was random versus methodical (e.g. going through one by one)
2. Does it matter if only one person randomly messed around with it or multiple people with the only the last person getting lucky

Does the calculation change if there is also a master switch--a master on/off switch?

Edit: in English with a laser

It's 4AM but I don't need sleep, I need answers.