Sail-Trim Simulator(simulator.atterwind.info) |
Sail-Trim Simulator(simulator.atterwind.info) |
8bitbyte.ca
The obvious next step would be to calculate the cog and tilt the entire rig in response to sail forces, which sheds wind until a balance point is reached, or the boat flips.
First, consider the edge case where the sail is acting as a bag when you're sailing downwind. As the boatspeed approaches the true windspeed, the apparent windspeed falls to 0 and the sail will luff. In this specific case, the boat can not go faster than the wind.
Now consider the boat cutting across the wind at a 90 angle. When the boat starts moving, the wind comes 90 degrees off the bow. As the boat increases speed, the apparent wind shifts closer to the bow. Apparent wind is just vector addition of true wind and boat wind. If the boat achieves the same speed as the true wind, then the apparent wind is sqrt(2) ~ 1.4x faster than the true wind. More wind means more power, so with that additional wind, it can go faster. Continuing the example, as the apparent wind increases, it appears closer and closer to the bow. Eventually the sail will stall and produce less lift. This is the point where the boat will go no faster.
The slowest point of sail is directly downwind. In a race, it is often much faster to gybe back and forth rather than ever go directly downwind. When a boat goes directly downwind, their boat speed cancels out the true wind. In the strangest case, if a high performance boat going faster than the speed of wind (say, on a broadreach) goes directly downwind, the apparent wind will appear to be coming head on. They've effectively gone 'into irons', yet they're facing 180 degrees off true wind.
If you ever get the chance, you should see the SailGP boats race. Their sails are almost always hauled fully in, even downwind. The other thing is that they gybe downwind because to go directly downwind would be to stall. In effect, these boats can achieve multiple times the true wind speed, but so long as they aren't pointed directly into, nor directly away from the wind.
Most yachts have polar charts, and the speed is a function of sail area, heading, wind speed and direction amongst other things. Are you considering calculating estimated boat speed based on given conditions and controllable variables?
The biggest problem that is puzzling everybody is that speed never changes. I eventually decided that this is because the app calculates the setup of the mainsail to get the desired boat heading and speed given the wind. If you keep the heading constant and change the boat speed you see that the sail rotates around the mast.
It's the opposite of what we do when sailing: we set the sail to a shape and direction (let me use these terms) to go somewhere. In this simulator we do it backwards and adjust the wind to get the sail into a shape and direction.
I am still learning and would love to use this, so I can validate my thoughts :D What would be great: - change model. I sail mono hull and would love to have - like others stated. Som kind of indicator that we are moving - or clouds
Why even use Unity if this exists? Why even install an app if you could feasibly run a full-blown game with 3D physics in the browser on your iPhone at 60 FPS? Where in the world are all the browser-based games?
https://news.ycombinator.com/item?id=43756926
Thank you, you’ve resolved my despair.
It uses Catalina 36 Tall Rig as a base model for sailboat parameters and was calibrated to match ORC-published polars for it within 1-5% on both close, beam and broad reaches.
Mostly built it for myself to help me understand how less common control affect the sail shapes, angles of attack and boat heel and behavior in a visual way.
It's still WIP, but you might find it useful for yacht-specific stuff!
Either way, both demos are fairly interesting, especially since there's so little exploration of sailing and the physics involved most of the time.
The second sailrhythm demo seems rather high quality and a better representation of the physics involved. Not sure if you're planning to work on it further, yet putting the rudder heading up near the top would be helpful, maybe with a circular dial you can select like the compass or broad reach displays. Kinda weird when the boat flips completely around to head left.
Some kind of visual representation on the Boom Vang, Cunningham, Outhaul, Backstay, and Jib Lead would also be helpful, since it's really difficult to tell if they're actually doing anything. Maybe a transparent deformation magnified overlay showing the sail profile surface deformation extended away from the actual sail in extreme distortion. Otherwise the changes are so minute its challenging to perceive.
Otherwise, it's a cool demo, and seems to be (from a not especially experienced sailor) relatively realistic of the forces involved. Suggested extension would be showing the wind flowing off the sails and how the forces transition. Also, showing other boats, particularly something complicated like a Windjammer [1], Full-Rigged Ship [2] or Schooner [3] varieties.
Also cool, simply because so few submissions seem to deal with sailing, boats, and generally water transport principles. Lots of possible VC ideas related to sails and sailboats. MarineTraffic [4] is currently tracking 300,000 ships out on the world oceans, and surprisingly small number use any form of sail based propulsion. Route planning and "this much cargo to this area with this speed of delivery" estimation relative to money spent on oil and fuel for a normal ship would likely be possible. From this Quora answer (suggested by Google) a small container ship (something with 15000 kW, 2000-3000 TEU capacity, maybe a Feedermax ship) might use 2000 tons of fuel crossing the Pacific (maybe $500,000 to $1,000,000 of fuel) [5]. This paper [6] has a much more complicated breakdown if you're interested in those types of calculations.
Also quite a bit with drones, and automated sailing. [7][8] Even a decent amount with land propulsion [9] that's been explored occasionally and there's even a tiny amount with space probes and planetary rovers as concepts [10].
[1] https://en.wikipedia.org/wiki/Windjammer
[2] https://en.wikipedia.org/wiki/Full-rigged_ship
[3] https://en.wikipedia.org/wiki/Schooner
[4] https://www.marinetraffic.com
[5] https://www.quora.com/How-much-does-it-cost-to-fuel-a-cargo-...
[6] https://www.man-es.com/docs/default-source/document-sync/pro...
[7] https://en.wikipedia.org/wiki/Unmanned_surface_vehicle
[8] https://www.saildrone.com/
Thank you so much for the detailed feedback. I do have plans to implement wind flow visualization and have a way to visualize forces as well. Controls a bit tricky to do, but this is definitely something I've been pondering. As you said, at certain headings the changes sometimes are too small to perceive.
Another thought of (if there's actually further interest in this kind of software) would be middleware like SpeedTree (https://en.wikipedia.org/wiki/SpeedTree). Seems like sailing games have been pretty popular lately (Sea of Thieves (40m player base), Assassin Creed IV (15m)) so there's probably at least some market for modestly priced middleware that handles sailing physics.