[HN Gopher] How a yacht works: sailboat physics and design
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How a yacht works: sailboat physics and design
Author : stass
Score : 149 points
Date : 2025-04-15 21:19 UTC (3 days ago)
(HTM) web link (www.onemetre.net)
(TXT) w3m dump (www.onemetre.net)
| stass wrote:
| This site is an absolute treasure trove of technical material on
| sail and hull design, with a focus on model yachts but most of
| the physics scales up. It covers aerofoil theory (momentum,
| circulation, lifting line), sail twist, downwash, planform
| effects, Reynolds number, hull resistance, appendage design, VMG,
| and more.
|
| Lots of spreadsheets and practical calculators too--bulb shape
| optimization, wetted surface area, simple VPP models. If you're
| into sail performance modeling or yacht design, this is one of
| the best resources out there.
| ModernMech wrote:
| Yeah, I miss the days when a higher proportion of this Internet
| was content like this.
| kqr wrote:
| I prefer these days, when the absolute amount of information
| like this is higher, even if there's also higher amounts of
| junk.
|
| I can just not look at the junk today, compared to 25 years
| ago when the information I wanted only existed in a physical
| library in a different country.
| reddit_clone wrote:
| On a related note, I would love to see an animated explanation
| for how sail ships worked.
|
| As a fan of Hornblower series,I suspect most of the relevant
| details went over my head because I didn't understand this.
| jasonpeacock wrote:
| These are good animations for tall ships:
|
| Warship: https://www.youtube.com/watch?v=4Nr1AgIfajI
|
| Explorer: https://www.youtube.com/watch?v=3pYqXrFx6S8
|
| They don't cover the actual physics and processes of sailing a
| tall ship, but they do explain all the parts and pieces and how
| they connect.
| barbs wrote:
| Seems like a good contender for a https://ciechanow.ski/
| interactive article.
| askvictor wrote:
| That's exactly what I was wishing existed when I was looking
| at these walls of text. There's https://ciechanow.ski/naval-
| architecture/ which is interesting, but not quite the same
| WALoeIII wrote:
| Arvel Gentry must be mentioned, he transferred much of the
| aerodynamics research to sailing with an amazing series of
| magazine articles. He debunked a lot of faulty theories, like how
| the slot works, in a meticulous but approachable style.
|
| http://gentrysailing.com/magazines.html
| jp57 wrote:
| I've been getting into sailing, solely for the purpose of
| cruising and sailing for fun with no interest in racing. As I've
| started talking to sailors, I've realized that you need to gauge
| whether you're speaking with a racer or a cruiser. Racers will
| claim these are not mutually exclusive categories, because of
| course racers can also cruise. But racers who cruise will
| ultimately talk to you like racers.
|
| Racers are, as you might expect, fanatical about performance.
| They will go very deep into details about optimizing sail trim
| and shape, and using wildly-named specialized foresails (not
| merely spinnakers, but asymmetric spinnakers, reachers,
| screachers, code-zeroes, etc). It's a bit like talking to an SCCA
| racer about your new pickup truck.
|
| In fact, if you have a good grounding in the basics of sail trim
| ("when in doubt, let it out"), and know how to put a reef in you
| can have a fine time getting between points A and B in a sloop
| with a basic mainsail and jib.
| laluser wrote:
| Isn't that the case with every hobby?
| th0ma5 wrote:
| There's also a specific argument in selling the racing is a
| better way to develop sailing skills because cruising ideally
| may not challenge you.
| mlhpdx wrote:
| I finished my first race Wednesday after a few years sailing
| casually. And, although it's true that whenever there is more
| than one sailboat going the same direction it's a race, being
| in a fleet on a defined course is much faster paced and
| precise. My analogy to driving is that cruising is being able
| to drive on empty roads, and racing is driving in traffic -- it
| becomes about understanding the flow and rules spoken and
| unspoken.
| opwieurposiu wrote:
| The hardest thing for me to get used to is that unlike cars,
| sailboats do not have brakes! Even the "throttle" is under
| your control only indirectly. Out in the ocean with nothing
| to hit this is not much of an issue, anyone can do it.
|
| Close to other boats and rocks and other hazards it takes
| some practice. Pros can to sail into the harbor, luff up and
| grab the buoy without touching the engine.
|
| Having no brakes really teaches you to plan ahead.
| Xylakant wrote:
| My teacher in sailing/motorboat school always said that
| they can spot the accident minutes before it happens.
| glitchcrab wrote:
| I've been teaching dinghy sailing since I turned 18 (20
| years now, give or take) as a voluntary position in a youth
| group and whilst the fundamentals of sailing yachts and
| dinghies are much the same, dinghy sailing is a much more
| dynamic and (oftentimes more fun) discipline. For example,
| whilst it's true that there's no brake on a yacht (save for
| backing your motor hard astern), in a dinghy you have the
| ability to do stuff like backing the sail which gives you
| much more control. It's _so_ satisfying when it's blowing
| hard to come steaming up towards a safety RIB then turn
| head to wind at the last moment, back the sail hard
| (literally push the boom over), jump onto the foredeck and
| then step off into the safety boat with the painter in your
| hand.
| oxml wrote:
| Spot on. As a racer, I can say this is mostly true. Although
| for me and many of the other racers I know, it's less about
| going deep into the optimization, sail choices, etc, and more
| about just being competitive. Racers don't always make good
| cruisers because they're always trying to go faster and push
| harder, whereas most cruisers want to slow down and enjoy the
| journey.
| efitz wrote:
| Exactly right. I've known from when I started sailing 35 years
| ago that I was a racer.
|
| Sailboat racing is amazing; it's this incredibly complex
| exercise involving physical boat handling skills, teamwork,
| leadership, communication (in a jargon that itself takes a year
| to internalize), as well as physics, geometry, meteorology, and
| minute observation of effects (that dark patch on the water or
| the flutter of a telltale). All of this feeds into strategic
| decisions on where to position your boat and tactical decisions
| of how to do so.
|
| It looks crazy boring from the outside but if you get into it,
| it's an activity that is intensely mental as well as physical
| and requires a very broad set of skills.
| patagonia wrote:
| I learned to race first and am now learning to cruise. And I'm
| glad I learned in that order. Cruising has a very specific set
| of skills that you'll never learn racing. That stuff will be
| obvious and if you want to cruise, you'll learn those skills.
|
| But what is not obvious to cruisers is that racing teaches you
| how to handle your boat in many different and difficult
| conditions, with confidence. When you race you have to go from
| a specific place to another specific place and you don't get to
| pick the weather. You're often pushing your boat and are in
| high stress situations.
|
| Often, cruisers will go out, when it's nice, and turn on the
| motor when they can't make their boat go the way they want it
| to go.
|
| So, what happens when you're out sailing and an unexpected
| storm rolls in? Because if you sail enough, especially
| offshore, it 100% without a doubt will happen. I'd honestly be
| pretty comfortable handling the boat through all but the worst
| weather, boat breaking weather. And even that, I would be
| confident in my safety gear and ability to contact support for
| a rescue. Because all of that is drilled into you as a seasoned
| racer. And I've been through some bad weather on the race
| course. I've had to make my boat go upwind in horrible sea
| state for hours on end while my crew is throwing up from sea
| sickness.
|
| There are multiple occasions on which I've turned down sailing
| with cruisers because I just don't trust that they have the
| skills or equipment to keep me safe should things go sideways.
| jbs789 wrote:
| Yup - realised the knife wasn't for show when we were out of
| control with a knotted spinnaker halyard headed for some
| rocks.
| _whiteCaps_ wrote:
| If there's more than one sailboat, it's a race :)
| giraffe_lady wrote:
| I've been seeing some modern junk rig refits on the great lakes
| the last few years, which really gives me hope about dedicated
| "get there when we get there" sailors. Those things are
| basically optimized for chilling the fuck out. Easy to sail
| (entire tacking maneuver is basically just throw the rudder
| over and duck), easy to reef, don't heel as hard,
| straightforward to mend the sail or running rigging on the fly.
|
| Only downside is their close haul is like 12o off the wind vs a
| bermuda rig and no one knows how to make them. The east coast
| (esp chesapeake) has some traditional gaff rig setups that have
| similar tradeoffs, like catboats. I would love to see more
| small production boats target this end of the
| "speed/comfort/cost" triangle. Currently it's like if the only
| bicycles available were race-ready track bikes. But sailing is
| already a small niche and new boats even smaller I think.
| boat34189 wrote:
| At the extreme opposite, here's a terrific set of videos on big
| ship architecture, design, engineering, and operations. Like the
| RC model yachts page, much of it's relevant for mid-sized boats
| too.
|
| https://www.youtube.com/@DatawaveMarineSolutions/videos
| mlhpdx wrote:
| The material seems dated. Modern yachts choose to be limited by
| displacement speeds but aren't bound by them. New models that can
| rise on plane (like a speed boat) because of advances in
| materials and manufacturing are starting to proliferate (small
| sail boats known as "dinghies" have been doing this for decades
| but larger boats were limited by their heft). That's not to even
| go into the wide ranging use of foils, which isn't relevant to
| casual sailors but are prolific in high end racing.
|
| Sailing isn't what it used to be.
| creeble wrote:
| Racing isn't what used to be, but sailing very much is.
|
| There are roughly two kinds of sailors: those who care about
| speed, and those who care about comfort. They have almost
| antipodal design requirements, but both kinds are very much
| sailors.
| mmooss wrote:
| Do you know of any good technical / physical comparison of
| the two, or just of the comfort designs?
| creeble wrote:
| Well, there's speed and then there's _speed_. As the OP
| says, very fast designs today are like the Sail Gran Prix
| [1] boats, 15m long foiling catamarans that go 3x the speed
| of the wind, up to around 50 knots.
|
| They bear nothing in common with a typical monohull
| cruiser, or even racer-cruiser like a J-109[2]. Let alone
| compared to a comfortable cruiser like a Hallberg-Rassy[3].
| These are all displacement hulls, whose speed is
| fundamentally limited to waterline-length.
|
| There are monohull sailboats that can plane (most dinghys
| under 20' for example[4]), and there are large catamarans
| that can go much faster for their size than monohulls[5],
| but there are many tradeoffs in cost, dockage availability,
| and (somewhat subjectively) weather comfort.
|
| [1] https://sailgp.com [2]
| https://jboats.com/j109/why-j1093 [3] https://www.hallberg-
| rassy.com/yachts/hallberg-rassy-370 [4]
| https://www.beneteau.com/en-us/first/first-14 [5]
| https://www.catamarans-fountaine-pajot.com/en/sailing-
| catama...
| mlhpdx wrote:
| One recent example (and there are many): The FIRST 30 (former
| Seascape) isn't a race boat, it has a sink and fridge.
| seabit wrote:
| Agreed that these are almost antipodal design requirements,
| but there is also a category in the middle - described as
| either 'performance cruisers' or 'racer/cruisers' designed
| for either dual use, or for sailors like me who believe that
| speed combined with good use of modern forecasting techniques
| are safer at sea than a traditional slow heavy cruising boat.
| Basically, be comfortable enough to be livable, and fast
| enough to avoid the worst weather. The design tradeoffs in
| that category are really interesting IMO. See most X-yachts
| designs, some of the larger J boats (for monohulls) or
| Gunboat, HH, and Outremer in the multihull space
| lasermatts wrote:
| I've been super interested in sailing since moving to San
| Francisco and running around the marinas/Embarcadero.
|
| Did some digging and found a sailing school that I haven't asked
| about classes (yet) https://www.spinnaker-sailing.com
|
| There's even a school that offers boatbuilding lessons in
| Sausalito -- a bit too far/much of a time commitment for me!
| https://www.spauldingcenter.org/current-offerings
| iancmceachern wrote:
| There is an after-school boat building thing that just started
| up in crane cove Park too
|
| There are a ton of opportunities at South Beach Marina
| arnarbi wrote:
| There are many sailing schools around SF, but one that stands
| out is https://www.cal-sailing.org/ - as it's by far the least
| expensive and low-commitment option to get on the water, and
| they have dinghies in which you'll learn very fast (but also
| get wet). Instructors are regular volunteer club members and
| mileage may vary, so make sure to go out with a few different
| ones.
|
| Another good way to get started is to find crewing
| opportunities for casual racing on
| https://www.latitude38.com/crew-list-home/. Many skippers will
| take no-experience folks out for fun. (It may take a couple of
| attempts to find a skipper/crew you enjoy hanging out with)
| clort wrote:
| If you want to learn how to sail and actually how to sail as
| the person in charge, you need to be in a dinghy. Its small
| enough that every thing you do will affect the course and
| speed, you can feel every little difference and nobody else
| will confuse the issue by moving or changing anything without
| you noticing. Sure, having instructors around giving you tips
| is necessary but _you_ are doing it and the feedback is
| immediate.
| jaredhansen wrote:
| Spinnaker might be great - I don't know them - but if you're in
| the market for sailing lessons in SF Bay I can highly, highly
| recommend Club Nautique out of Alameda[1].
|
| The quality of instruction is very high, with a focus on safety
| and building a strong foundation of knowledge. Especially if
| you ever might want to charter in remote locations or sail
| across oceans, it's really an excellent foundation.
|
| [1]https://www.clubnautique.net/school/introduction-to-sailing/
| patagonia wrote:
| My sailing buddies and I are always asking each other, "why is
| sailing dying"? Sailing is a very self selecting sport. People
| generally love it or leave it very quickly. We are in the "love
| it" camp, and we are always super excited to take people that
| are curious about sailing out sailing. I would strongly suggest
| not taking classes. Just get on a boat. It is hilarious how
| easy it is to find a sailor that will take you out. And if you
| enjoy that experience, people are always looking for crew to
| help them sail their boat. So I'd suggest your next step would
| then be that. You'll learn so much faster going out for
| Wednesday night races at your local club. You'll learn both how
| to sail and whether you even enjoy it. A lot of places even
| have a "crew seat" where you literally show up, not knowing
| anyone, and people see you sitting there and ask your
| qualifications and if they have room on their boat and are
| comfortable with the match, take you, a complete newbie and
| stranger, out sailing.
|
| Classes make it easy feel like you've learned "levels" of
| sailing or to feel like you could rent a boat in the Caribbean.
| But, they hide a lot of what sailing is really about.
| Maintenance, rigging, de-rigging, showing up for no wind,
| learning the rules of sailing, etc, etc. They also miss out on
| one of the most amazing aspects of sailing: community. Learning
| from other sailors is key. You'll borrow parts from (and lend
| to) other sailors. You'll help organize races for them and they
| for you.
|
| Sailing is a beautiful, beautiful lifelong endeavor that I wish
| everyone could be exposed to and pursue if they'd like to. Look
| up your local yacht club or Hobie / beach cat fleet or other
| sailing club and just ask if you can get a ride. Show up early,
| listen and do what you're asked, be polite, stay until the boat
| is totally put away, and repeat. Try different boats with
| different clubs and people eventually.
|
| Eventually, maybe take a class (RYA not ASA) to formalize your
| knowledge or fill in the gaps. You'll clearly know what they
| are at that point. Eventually maybe buy your own boat, or do as
| many people do, just keep crewing. Truly good crew are really
| rare and boat owners will love and appreciate you.
|
| I think you'll love it.
| patagonia wrote:
| If you're in Austin, TX, check out Austin Yacht Club or
| austincats.net.
|
| If you're in Charleston, SC, check out Charleston Ocean
| Racing Association (CORA).
|
| Or if you're somewhere else and interested, message me, and
| I'll do my best to find a place and make an introduction. The
| sailing community is a small world.
|
| Maybe I'll see you out there!
| pengaru wrote:
| My buddy has a 36' Pearson in the Berkeley marina, sometimes we
| bring folks out with us.
|
| You can also join the Berkeley Yacht Club (BYC) without a boat,
| it's not too expensive. There's a bar and social events, good
| way to meet sailors with boats in the marina and go sailing on
| a variety of them. They hold races in the bay pretty often, and
| are sometimes desperate for able bodied ballast.
| bee_rider wrote:
| I never ended up on a real-sized sailboat. But, I had fun on a
| little Sunfish as a teenager. They are nice because you can
| reasonably learn to sail them over the course of a couple days,
| and if you flip the boat over you can probably right it without
| too much drama. Just don't bonk your head.
| lasermatts wrote:
| same!
|
| I did some river/lake sailing as a kid on the East Coast but
| now the urge is calling to me! I remember the "righting the
| boat" test being the scariest/most fun part of the experience
| -- super glad I went through that and feel confident on a
| small boat.
|
| Now...I used to remember all the knots we learned but that
| memory is mostly gone
| asimpletune wrote:
| If you have the space the best way to learn how to sail is just
| buy a cheap dinghy and take it out as much as you can. While
| you're looking for a dinghy just read a book on theory.
| Something like a laser is the ideal platform to learn on and
| you can go out in the bay and check out Angel island and other
| fun stuff like that. If you want to get more experience with
| things besides pure sailing then just crew someone's boat for
| free. When you're done, sell your dinghy, get your money back,
| and buy yourself a sloop. This is pretty much how I learned how
| to sail.
|
| School is fine too but you'll realize that you're mainly just
| paying for access to the dinghy anyways. The instructor isn't
| going to teach you anything that's not in a book or that you
| won't learn crewing someone else's boat.
|
| Hope you have fun though with whatever you decide
| reneherse wrote:
| Cal Sailing Club is a great way to start. You'll learn more
| quickly on dinghies than keelboats and the skills will benefit
| your entire sailing career as you move on to bigger boats.
|
| Also check out the Friday night races at Berkeley Yacht Club.
| Skippers always need crew so it's pretty easy to get a ride.
| Just hang out at the gate between 5 and 6pm with your gear and
| say hi!
|
| https://www.berkeleyyc.org/racing
| mmooss wrote:
| Does anyone know who Lester Gilbert is? I don't see an about
| page.
| philk10 wrote:
| https://www.onemetre.net/OtherTopics/Links/Links.htm
| contingencies wrote:
| If you click 'Home' it is apparent this page is actually about
| radio-controlled racing yachts, which unlike the HN title
| explains the weird scope.
|
| Vessel design goals not mentioned in other comments: cruising
| requires storage space, seaworthiness, living space, will
| generally prioritize stability/safety, may prioritize low draft
| for tropical anchorages, may prioritize single-handed sailing,
| etc. Autonomous vessels which may require visibility, minimum
| height, battery storage, stealth, etc. Multihull vessels are not
| discussed, even though they dominate in many categories because
| they are generally functionally superior in many regards (speed,
| comfort, safety, living/cargo space, low draft) but cost more to
| acquire/maintain. Once you study this stuff enough you realize
| there's a reason why ~nobody cruises on trimarans, people without
| extra money avoid catamarans, people with enough money prefer to
| cruise on catamarans, and large seagoing ferries, military and
| cargo vessels with speed as a design goal are also usually
| catamarans.
|
| Fun fact: IIRC catamaran comes from _kattumaram_ meaning "two
| stick tied together" in Tamil, the ancient Dravidian language of
| southern India. As such it is one of the few Tamil roots that
| entered international English vocabulary. South Indian seafaring
| empires once dominated sea trade as far east as Vietnam. Small
| multihull vessels are the hallmark of the Austronesian peoples,
| who are believed to have spread from Madagascar to Taiwan thence
| taken flight to populate the Pacific Ocean. _Got breadfruit?_
| McNutty wrote:
| Bring back more of this type of internet content!
| Zeetah wrote:
| I know nothing about sailing. I've been on a few sailboats. I
| love the idea of wind power - probably why I like flying remote
| control sailplanes.
|
| I would love to volunteer on someone's race/sail boat to get some
| experience. I'm happy to take the ASA introductory course or ?
| course.
|
| Any advice on how to move forward? I'm in the Seattle area.
| livelaughlove69 wrote:
| I have just started sailing in the UK. I can't recommend it
| enough. It's great time away from the computer in nature but
| still doing really complex technical tasks. The best thing imho
| is to find and join a local club. There are many that aren't
| snooty (having Commodores etc) and it's pretty affordable.
| Members will always be looking for crew. I really wish I had
| done it sooner.
| livelaughlove69 wrote:
| I should say -- better in my experience to find a community
| run organisation run by its members than a commercial
| operation in my experience. A lot of clubs run on the
| enthusiasm of their members and this means lower prices and
| more opportunities to get involved
| glitchcrab wrote:
| Definitely agree here. I've been dinghy sailing for near 20
| years now (in the UK) and most clubs will require you to do
| a couple of days a year as safety boat helm/crew (depending
| on experience) - it's not a lot of time to invest and it
| benefits everyone in the club.
| chaitimes wrote:
| Join a club. There's also facebook groups looking for crews.
| But i guess if you don't have experience, you kind of have to
| provide an incentive like contributing higher towards the
| common costs.
| anon7000 wrote:
| Seattle area recommendations:
|
| - Low-cost: If you volunteer at the Center for Wooden Boats
| (helping around the docks, helping with rentals, etc.), you get
| 1hr of boat rental for 3hr of volunteer, and you get free
| sailing lessons after 45hr of volunteering. Really friendly
| bunch! Great way to learn in smaller boats for free. Plus you
| pick up some skills while you're volunteering. Or you can buy
| lessons and become a member -- boat rental is relatively cheap
| here. There's also Sail Sand Point, which gets you out on lake
| washington on little lasers.
|
| - If you want to get out on the sound, Seattle Sailing Club
| (SSC) has great instructors and friendly people. They offer
| most ASA courses (e.g. ASA101 over a weekend is a great
| introduction to sailing). This approach is more expensive, but
| good if your long-term goal is more "serious" sailing on the
| sound in bigger boats. You'll have more classroom time, a
| textbook, quiz, etc., and probably pick up more knowledge
| overall.
|
| You can also look into Puget Sound Sailing Institute, which is
| a bit cheaper than SSC, but not as community oriented. More
| locations outside of Seattle though.
| zardo wrote:
| Start with dinghy sailing, there are few places in the area you
| can take a class, rent boats, and race. You'll meet people, and
| become a better pick for a crew member.
| sailfast wrote:
| Reporting for duty. Just wanted to say you are doing god's work.
| Everyone should have a chance to experience sailing.
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