[HN Gopher] Sail-Trim Simulator
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Sail-Trim Simulator
Author : stass
Score : 136 points
Date : 2025-04-23 18:36 UTC (1 days ago)
(HTM) web link (simulator.atterwind.info)
(TXT) w3m dump (simulator.atterwind.info)
| zeristor wrote:
| I guess I'm not the only person who opened the link from
| yesterday and didn't see anything about sailing.
|
| https://news.ycombinator.com/item?id=43756926
|
| Thank you, you've resolved my despair.
| quaestio wrote:
| Very cool demo...
|
| 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?
| stass wrote:
| Not my demo! But I got inspired by it some time ago to build a
| simulator for monohulls which uses a physics based VPP to
| calculate the boat speed based on input controls like
| mainsheet, jib sheet, travelers, backstay and so on at
| https://www.sailrhythm.com/
|
| 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!
| hadlock wrote:
| What are you using for your physics engine, or how did you go
| about designing your aero model? I've been poking about with
| wing aero for a toy flight simulator and there's not a lot
| written about the design process of modeling this stuff in
| near-real time.
| araes wrote:
| Little confused. So you're mostly giving credit to a demo
| that then inspired your own demo?
|
| 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/
|
| [9] https://en.wikipedia.org/wiki/Land_sailing
|
| [10] https://en.wikipedia.org/wiki/Zephyr_(rover)
| stass wrote:
| If other people are interested in sailboat physics -- this
| resource is a goldmine of information on how sailboat and sails
| work and physics around it:
| https://www.onemetre.net/Design/Design.htm
| philips wrote:
| I am a lake sailer. And without landmarks or anything it is
| impossible for me to perceive the boat as moving.
| derbOac wrote:
| Even some kind of wake or something would help.
| MOARDONGZPLZ wrote:
| I thought I was doing something wrong. It doesn't seem like
| anything I do has any effect, but guess that's just because
| there is no apparent effect.
| reaperman wrote:
| Eventually it made sense that boat-speed only changes the
| "apparent wind", as it's only simulating wind-boat
| interactions, not water-boat interactions.
| sandworm101 wrote:
| But to get the sail-wind interaction you need the movement of
| the boat. To get the movement you then need the hull-water
| interaction. Modeling just a static, vertical, sail doesnt
| really demonstrate anything practical. It is more akin to
| similating a captive foil in a wind tunnel.
|
| 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.
| m_herrlich wrote:
| You can set the wind to 0 and the speed somehow stays at 35
| knots, I don't know much about sailing but that can't be right
| cladopa wrote:
| A great project, but it needs some kind of grid movement and
| rocking, foam or something so you can perceive its movement.
| pomian wrote:
| Here is a fun sailboat race simulator. It's very simple, but
| pretty realistic especially for open ocean racing. You can use
| their default race course, sometimes join a planned regatta, or
| make your own. (It was great during COVID, to try racing across
| the oceans, or around the world. It's in real time, so you might
| not need to change anything for days If you are in the trade
| winds, and open ocean, but then when you get closer to land,
| things get "Western" very quickly - just like with a real boat.
| It's called SailNavSim. (Learned about it from HN.)
|
| 8bitbyte.ca
| 867-5309 wrote:
| why so heavy on the water graphics and light on the sail?
| stass wrote:
| You get water graphics for free from three.js
| chrisrodrigue wrote:
| Pretty awesome if you ask me.
|
| 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?
| ge96 wrote:
| it's hard to tell if you're moving
| gitroom wrote:
| That wake thing would've totally helped me too, felt weird not
| seeing any movement. Glad I wasn't the only one who got thrown
| off.
| api_or_ipa wrote:
| One of the most mind bending facts I tell people, even sailors,
| is that sailboats are not limited to sailing at the true
| windspeed. Sails are wings, not bags. In fact, a boat's top speed
| is directly dictated by its ability to point into the wind
| (assuming, for example, the boat is not physically limited by
| it's displacement hull speed, as in the case of hydrofoils). The
| consequences of this simple truth are manifest.
|
| 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.
| frainfreeze wrote:
| Into the irons/in irons being a dead sailing area, where boat
| is head on into the wind (wind's eye). A lot of people get
| surprised that you can sail upwind as well.
| marktolson wrote:
| I like the idea but I don't get this at all. Shouldn't the speed
| change based on the mainsail trim relative to the heading? I
| pointed the boat dead downwind, eased the mainsail all the way
| out and the speed is 0 kn. I can't even see the value for the
| trim, just speed, but you get speed from correctly trimmed sails.
| inasio wrote:
| It would be great if it would be able to limit the max speed
| based on the heading, right now the slider allows the same max
| speed for any heading. On this boats I suspect max speed is
| achieved going on a beam reach (90 degrees to the wind)
| 0xcb0 wrote:
| Thanks for creating this!
|
| 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
| pmontra wrote:
| The blue cones are probably the wind coming to the boat but there
| is a wall of cones a little further away, visible by zooming out.
| Those cones don't have the same directions of the ones close to
| the boat. It's probably apparent wind (close to the boat) and
| real wind (further away.) It would help to start with a zoom
| level with both winds visible.
|
| 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.
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(page generated 2025-04-24 23:02 UTC)