How a yacht works: sailboat physics and design

https://www.onemetre.net/Design/Design.htm

by stass • 1 year ago

254 76 1 year ago

stass6• 1 year ago

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• 1 year ago

Yeah, I miss the days when a higher proportion of this Internet was content like this.

kqr• 1 year ago

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.

metalman• 1 year ago

Nice to see an enthusiast/engineering site that is putting cutting egde design ideas into the public domain. Grew up with boat builders on the south shore of Nova Scotia, and knew and learned from some of the last people to build and crew working schooners, that were also raced, I a boy, and they proud old men. Also know current builders and restorers of blue water boats. A few years ago I stumbled onto footage of a big hydrofoil cat that was the first boat to break the 50 knot barrier, you could tell that any celebrating was waiting and would largely be to celebrate still bieng alive, big seas, 50+kn, and quite clearly nothing but flinders left if anything broke and they plowed into a wave.,..,........they were standing on deck

reddit_clone• 1 year ago

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• 1 year ago

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• 1 year ago

Seems like a good contender for a https://ciechanow.ski/ interactive article.

askvictor• 1 year ago

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

amelius• 1 year ago

I'd love to have a simulator for a sailboat, preferably running in a browser.

stass6• 1 year ago

I built one recently to mostly help myself visualize how sail trim worked and how various boat controls like mainsheet and backstay affected sail shapes, various forces and boat performance. It uses a physics-based VPP and I calibrated it against Catalina 36 polar charts, so should be pretty precise!

I plan to integrate the simulator with the sail trim guide I'm building to help people learn.

It's a WIP, but accessible at https://www.sailrhythm.com/

Happy to answer any questions!

Lefuz• 1 year ago

There is a modern-ish simulator here: https://thapen.itch.io/painted-ocean

The tutorial level on how to get the ship pointed in the right direction and moving out of the harbour will give you the basics.

WALoeIII• 1 year ago

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

CalChris2• 1 year ago

Ugh. The slot theory lives on. The physics textbook still used at Berkeley, Giancoli, used the slot effect as an example despite … Gentry being a Berkeley grad. I sent a letter. I never got a response. However, the latest edition deleted the slot example and instead uses the Bernoulli principle yet stops short of Runge Kutta circulation.

jp57• 1 year ago

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• 1 year ago

Isn't that the case with every hobby?

th0ma5• 1 year ago

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.

mlhpdx3• 1 year ago

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• 1 year ago

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.

oxml• 1 year ago

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• 1 year ago

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.

adriand• 1 year ago

That sounds like so much fun. How much of a demand does it place on you physically, ie how fit do you need to be to do it well?

patagonia3• 1 year ago

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• 1 year ago

Yup - realised the knife wasn’t for show when we were out of control with a knotted spinnaker halyard headed for some rocks.

cycomanic• 1 year ago

Agreed. I used to race on a one design 34ft boats (steward 34s for the kiwis here). For the Thursday night rum racing they always casually divided up sailors amongst all the available boats and therefore the yacht squadron would refer people in town to them. So naturally we got a lot of cruisers on there around the world trips who wanted to try out racing. The most striking was the lack of urgency. Even though many were quite experienced sailors they were often worse than people who never sailed before. The newbies could be told to which as if your life depends on it and they would go full out, some of the cruisers not so much.

_whiteCaps_• 1 year ago

If there's more than one sailboat, it's a race :)

giraffe_lady2• 1 year ago

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.

jabl• 1 year ago

There's a subset of sailors that are looking for the 'optimal' rig, and are trying out various alternative options. And some people want to be different just for the sake of it.

I'd argue the Bermuda rig is overwhelmingly the dominant choice for a number of good reasons. Yes, upwind performance is one of them, but it can also be a good choice from a simplicity and workload perspective.

Choose a boat without runners or checkstays, install an auto-tacking rail, and you too can tack just by turning the rudder. Various autoreefing systems (rolling jib/main) are likewise common these days.

lillecarl• 1 year ago

I was born into sailing though dad, and I know how he is about performance and ekking every little bit out of what he can (and can afford) (no huge stuff, 21ft). I mean I never let the sails go all out of trim, but I can appreciate putting it on good enough, setting the autopilot and just chill and listen to the sound of sailing, the sound of sailing in a mild summer day is peak life

boat34189• 1 year ago

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

mlhpdx3• 1 year ago

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.

creeble2• 1 year ago

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.

mmooss2• 1 year ago

Do you know of any good technical / physical comparison of the two, or just of the comfort designs?

mlhpdx3• 1 year ago

One recent example (and there are many): The FIRST 30 (former Seascape) isn’t a race boat, it has a sink and fridge.

seabit• 1 year ago

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

lasermatts2• 1 year ago

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• 1 year ago

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• 1 year ago

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• 1 year ago

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.

floren• 1 year ago

I found CSC friendly but basically the boating equivalent of opening the encyclopedia at random and reading -- whichever instructor I ended up with would just decide what he wanted to teach/do that day, no structured curriculum. Presumably one could eventually learn enough to pass the test and be able to take dinghies out yourself, but I didn't have the patience--I bought my own and learned more in 30 minutes than I ever did at CSC

jaredhansen• 1 year ago

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/

patagonia3• 1 year ago

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.

patagonia3• 1 year ago

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• 1 year ago

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• 1 year ago

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.

lasermatts2• 1 year ago

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• 1 year ago

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• 1 year ago

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

CalChris2• 1 year ago

Cal Sailing is a good way to get on the water and learn the basics. You can learn dinghies, keel boats and windsurfing. After you're comfortable with basic keel boat crewing, you can probably get a ride on a boat in the Friday night beer races at the BYC. I started at Cal Sailing and eventually raced at the Rolex Big Boat Series at the St. Francis.

Larry Ellison started at Cal Sailing and Lowell North was dinghy chair in its previous incarnation as a UC Berkeley club.

Goofy fun place.

OldManAndTheCpp3• 1 year ago

Other people have echoed the same advice, I’ll add to it.

Take enough of a learn to sail class that you understand the basic theory —- I took one at my local yacht club.

Then, find a racing fleet! Racing boats need crew weight to help the boat sail towards the wind (so you can be useful while you are still learning), and not all the jobs require as much sailing knowledge as others (my first job was to pull the free end of the line while someone was winching in the sail).

Skippers value consistency —- the boat can’t race without a crew, so literally just reliably showing up is a valuable thing.

stass6• 1 year ago

There is a great school called Modern Sailing School in Sausalito. I highly recommend taking a class from them. I took one in the past and they are great!

Will help you figure out if you are into sailing or not.

mmooss2• 1 year ago

Does anyone know who Lester Gilbert is? I don't see an about page.

philk10• 1 year ago

https://www.onemetre.net/OtherTopics/Links/Links.htm

contingencies• 1 year ago

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• 1 year ago

Bring back more of this type of internet content!

stass6• 1 year ago

Please!

Zeetah• 1 year ago

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.

livelaughlove692• 1 year ago

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.

livelaughlove692• 1 year ago

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

chaitimes• 1 year ago

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• 1 year ago

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• 1 year ago

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.

OldManAndTheCpp3• 1 year ago

I own (half of) a racing boat on the Great Lakes.

Buying a boat brings with it dreams of freedom, winning races, beautiful summer days.

The reality is that you need crew! Serious racers will refer to their boat as their “program”, and are always looking for careful, reliable crew.

I’d say look for a “learn to sail” program at whatever yacht club is nearest you, then see if they have a club racing scene. Most clubs have both.

stass6• 1 year ago

Definitely recommend taking an introductory ASA 101/102/103 classes from a local school! Will help you decide if you are into it while having some fun.

This is how I started.

sailfast• 1 year ago

Reporting for duty. Just wanted to say you are doing god’s work. Everyone should have a chance to experience sailing.

mendeza• 1 year ago

This is amazing, is there something like this about how a guitar works?! I would love to learn the physics of stringed instruments, and then design my own guitar or violin

serkandurusoy2• 1 year ago

I haven't noticed many startups working on bringing modern tech to recreational sailing and cruising.

Systems aboard a typical 35-50 foot sailboat produce interesting data streams, but the data don't seem to be used innovatively or interestingly.

This makes me wonder if the market is too small compared to the unicorn-level valuations most seem to aim/hope for.

Kind of putting this out there because I'm a liveaboard sailor looking out for startup ideas and it would be amazing if it were in the marine-tech space. So any feedback/suggestions would be more than welcome.

ianburrell• 1 year ago

The market is small, there are existing competitors, and things change slowly. I also suspect that there isn't much value that startup could bring. I bet there are fancy products for fancy yachts.

There is a lot of open source going on. There is OpenCPN chart plotter. There is also NMEA OneNet which uses Ethernet so should support things that radars, plus make wiring easier.

serkandurusoy2• 1 year ago

Thanks, yes, I agree with all of those points.

Perhaps still a big enough space for a bootstrapped indie business, for lack of VC scale.

NMEA is quite interesting, though. Coupled with Czone for digital switching and power readings, I bet there is some interesting insight waiting to be discovered, one that can be monetized.

How a yacht works: sailboat physics and design

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