How does a mainsail with a jib work

[Bowdrie]

Your question is multifaceted, but this is one example that can be explained in a general manner.
Imagine the mainsail as an aircraft wing, but it has this big pipe along its leading edge, (mast).
If we put a big pipe on the leading edge of a wing it would seriously disrupt the flow over the wing.
The mast has a similar effect, the area of the mainsail directly adjacent to the mast has little positive effect, most of the effective area of the mainsail occurs within ~the 2/3rds section of the middle of the sail.
When an aircraft wing is in a high angle of attack the flow becomes "disconnected" over the wing and the wing loses lift.
Sailboats going to weather are always in a "high angle of attack", (they have high drag and low power).
On an aircraft we can install a "slat(s)" in front of the leading edge to help keep the boundry layer of air over the wing in a "connected" manner that allows the plane to have a higher angle of attack without stalling, (loss of lift).
We do the same with a jib, it, with no mast in front of it, can "capture" the air flow and direct it over the mainsail in a rather smooth flow.
This allows the mainsail to sheet-in a bit tighter without losing lift.
Now this is simplified but kinda shows some of the interaction.
The red slat being the jib, and the wing as the mainsail.

[SailorX]

I want to thank everyone for all the information provided. It helped alot!

I notice there are people here thinking I'm seeking for lessons on this forum but that is certainly not the case. I am here to ask question about the sails...

Yesterday we finally went sailing for the first time and it was amazing.
We had an instructor the first 3 hours and he kinda showed us the basics, explained how the sails work etc.

There wasn't much wind in the morning when the instructor was there but we already had quite some fun. It is a feeling I cannot describe when you pull in the mainsail and you catch wind and gain alot of velocity.

At some point the instructor went away and the real adventure began.
We went out, raised the sail and went for a bit low speed sailing with low to none wind.

Along the route we made a few mistakes we learned from.
When we ran out of drinks we returned to the harbor, it was a very hot day. We kind of forgot that the boat doesnt turn when you have no speed, and there was alot of boats in the harbor with tight space so we used the reverse to brake and almost drifted into another boat. I was able to push us away from the other boat and we slowly motored into the docking spot. We practiced docking a few times after that so we wont have to go through that again. At the end of the day when we returned to the harbor, it went flawless!

We were sailing on a huge lake and noticed a small island with docking options.
We went there and noticed a toilet-house in the middle of the island. We were amazed by it.

The instructor put a reef in our mainsail and explained how it worked.
However when we took the reef out (barely 5 knots of wind), we made the error of detaching the line completely from the sail (I thought this was how it worked. oops). But we had to open the jammer and keep it attached I think? We couldn't really figure that out and the wind started coming up a bit and the sails were flapping so we decided to undo all and continue with the reef.

We also noticed that if the jib is angled in a certain position, the boat would turn to one side, if you steered the other direction the boat would go straight.
This happened like 2 or 3 times and we werent able to replicate it sadly.
I heard people say that you should steer with the sails when sailing, is that what we did unintentionally? I can't really remember the instructor talking about that.

We learned alot yesterday and still have alot to learn, but we haven't had this much fun in a very long time. Worth every penny sofar.

Sadly we forgot anti sunburn so i'm sunburned quite badly.
My muscles really remind me that I'm not the youngest anymore haha

[edexter]

Hi! Lovely boat. We sail a Rhodes 22, fun as heck. Everyone has given you necessary advice, but I will emphasize these:
1. Take classes and get someone experienced to show you how everything works! Money WELL spent. The United States Power Squadron/AMerica's Boating Club has a lot of online and in-person courses from experienced boaters including lots of sailors from chapters all across the country. The commenter who likened going out without training akin to driving without any instruction has it right. See https://www.usps.org/sss-boating-courses.
2. Watch the weather! Wind is your friend but too much of a good thing will ruin your day. We try not to go out if gusts will much exceed 20 knots, but a 10-15 knot wind is sporty. And a thunderstorm can pop up any time during the summer, here on the Chesapeake anyway, figure out in advance what you are going to do if you see a thunderhead building up.
3. If it is getting windy, shorten sail. Your boat has a furling jib, shich can be shortened to any comfortable size using the furling line - it doesn't have to be all the way out all the time! And your main can be partially lowered and tied off as has been described, then you shorten the foresail until it about matches the size of the main and you feel comfortable (can be bigger or smaller depending on which way the wind direction is - if the wind is behind you may want more, etc. - play with it!)
4. Heeling is scary but as it increases your sails will spill more wind. However, a surprise gust CAN knock you down - that;s when you are sideways with the sail in the water. It happened to our boat twice, not with ME at the helm. when a sudden squall hit my spouse when her late husband was helming and they didn't furl the sails in time; but all it meant was they lost some floatables and had to pump out the cockpit, and stuff in the cabin got wet.
5. Most important, wear your lifejacket. Read up on the right size and kind of PFD ("Personal flotation device") and get the right ones: we use self-inflating ones for nice weather, and when it starts to get stiff, we put on the real ones.
6. Practice makes perfect! GO sailing! At first try to find somebody with experience to go with, but consciously trying things, e.g., adjusting the sails, backstay tension, keel setting if it's adjustable, etc., and soon YOU will be experienced. We often try tweaking things, and compare our speed on the GPS to see what works. Nothing more relaxing than the quiet swish of water past the hull.
7. Make sure you have your required safety equipment, it will help prevent a ticket from the authorities, and you might need it. The Coast Guard Auxiliary and the Power Squadron/AMerica's Boating Club have "Vessel Safety Checkers" who are trained authorized to conduct Vessel Safety Checks, to make sure you have th right stuff. Plus they give you a sticker that will tell the marine police that somebody authorized checked your boat that year, might keep you from being pulled over. (Here on the Chesapeake both the Coast Guard and the DNR Marine Police are quite active during the summer months).
Here's a pic of our boat, mighty S/V Certainty, the Terror of Frogmortar Creek. Note that our foresail is only halfway out (it's huge, 170% of the main, which is useful when there isn't much air). Good luck and have fun!

[GarryD]

Your obviously just about to step onto the near vertical part of the learning curve - straight away book yourself onto an RYA Level 1 DINGHY course. YES DINGHY - you will learn so much in the first hour or so. It'll be money well spent. We went form a Mirror 10 dinghy to a Beneteau First 305. Easy peasy, apart from the parking!


Good luck

[Rumrace]

Reefing by rolling a head sail is a bad plan is the point. Both the UK and Dutch boats have rollers it appears.
The gusts yesterday afternoon were knock down break something gusts. Good fun

[Rumrace]

If you still have your beneteau first hit me up for a key float in a couple months. I’ve developed a Beneteau logo 3D printed in a soft white plastic called TPU. After a year of floating a rusty screw driver I trust it.
Just a silly hobby. I have a Jeanneau so no cool logo to print. I’m using the poop emoji for the pump out float key.
I love the two new Firsts.

[Cynara]

Get a copy of Royce's sailing Illustrated

[rossdv8]

If your boat is the boat in the picture (in your first post), and if you are still planning to sail on the same lake - it previously belonged to a Sailing School.

I am sure that if you took some lessons with that school, they would still remember how your boat works.

A few lessons is all it takes to, as the English saying goes 'Learn the Ropes'. Quite literally. They will also be able to teach you any little safety tricks, many of which people have already posted here.

That yacht used to be rented for 65 Euros for 2 hours. I think that their sailing instruction could be arranged at a sensible price and you would enjoy the time and the money is well worth spending.

Their contact details used to be:

Botentehuur.nl, which is part of BAB NL B.V.
Aambeeldstraat 20
1021 KB Amsterdam
085 - 016 0188
KVK: 85148563

[lestersails]

How do sails work? Don't even ask that question. It is hideously complex and anyone on this forum (or at the bar) who gives you a clear and simple answer has no idea what they are talking about. How sails work is based in the physics of fluid dynamics (air is, in this context, a fluid) and fluid dynamics is one fo the most difficult fields in all of physics.
As they say in New Jersey "fuggedaboudit"*
Follow the advice of the poster who recommended Sailing For Dummies. Simple explanations of the bare bones minimum of how things work. Leave the "why" to the physicists.


*translated to English "forget about it"

[StuM]

Originally Posted by lestersails

How do sails work? Don't even ask that question. It is hideously complex and anyone on this forum (or at the bar) who gives you a clear and simple answer has no idea what they are talking about.

How sails work is based in the physics of fluid dynamics (air is, in this context, a fluid) and fluid dynamics is one fo the most difficult fields in all of physics.

Amazing! I'm so glad to know that I have no idea what I am talking about.
(Or maybe I'm not the clueless person).

Strangely, what I said in Post #2 has served a multitude of students on the courses I conduct well and enabled them to understand the basics of sail trim

Everyone who has ever learnt to fly, myself included understands the concept of air flow over a foil very well without ever hearing the name Bernoulli!

[GrowleyMonster]

First, PLEASE thoroughly learn the Rules of the Road! Otherwise you are literally a menace on the water. Property and LIVES are at stake, even on a small lake, if there are any other vessels present. I will assume you are in the US. Download a copy of both US Inland and also International (COLREGS) for free, or buy a hard copy at Worst Marine or on Amazon. Learn basic safety, including how to keep your boat from sinking or burning, and how to provide first aid and how to operate a Marine VHF and get a distress call out. Learn your legal responsibilities regarding sewage discharge, oil spill, posting required placards, etc. All of this is MUCH MUCH MUCH more important than just learning how to make your boat "go". The actual "going" part is pretty easy. Get a copy of "Sailing For Dummies" and you can learn the basics of using wind, sails, keel, and rudder to make the boat more or less do your bidding and get you from point A to point B, in just a couple of hours.

Classes would be an EXCELLENT way to get your nautical education started. Unless you have a very knowledgeable and sensible mentor able to provide a lot of personal attention, classes are definitely the best way to begin. Well, after downloading Rules and studying them for a few weeks.

[Oeanda]

Stay home. Wear a helmet. Make sure to read the instructions for the helmet, to avoid strangulation…

[KWF]

Some have replied the boat won’t capsize.
I believe that is true due to wind, but suspect very large waves could sink it

[lestersails]

Originally Posted by StuM

Amazing! I'm so glad to know that I have no idea what I am talking about.
(Or maybe I'm not the clueless person).

Strangely, what I said in Post #2 has served a multitude of students on the courses I conduct well and enabled them to understand the basics of sail trim

Everyone who has ever learnt to fly, myself included understands the concept of air flow over a foil very well without ever hearing the name Bernoulli!

No knock on you Stu. My point was not in any way to denigrate any single person's knowledge, but to dissuade the OP from thinking s/he has to truly understand how sails work to sail.

You and I have an adequate working knowledge of a very simplified model of how sails and wings work. Our simplified understanding, adequate for practical purposes of things like sail trim and (in your case, piloting) does not mean that you and I fully understand how an airfoil works. I rather doubt in pilot training that you mastered Munk and Glauerts thin airfoil equations, the Kutta condition, the Biot-Savart law, the Kutta-Jakowski theorem, and can manipulate differential equations and Fourier series. I certainly can't.

And it is also worth saying that a theoretical physicist who does completely understand how an airfoil works would not necessarily make a very good sailor!

Equally important to knowledge is understanding the limits of one's knowledge. I agree with the several posters who commended sailing courses to the OP. They can give you the pragmatic, grossly simplified explanation of how a sail works. But more importantly, a few dozed other much more practical things s/he needs to know to get out on the water on that boat.

[rossdv8]

Sail theory is a good read. Preferably using a book with pictures, and perhaps some YouTube videos about how sails work, and more videos about sailing lessons on small boats.

However none of the theory can actually prepare you for the first time you 'feel' the response of the Jib and mainsail when the boat is sailing.

Go Sailing.

Find someone who will take you out on sensible days with winds and waves that are NOT Scary. Choose someone who will let you steer the boat while they trim the sails and tell you what they are doing and why.

Learn how to tack, and how to go about.
If you have the right conditions, and someone who uses his / her brain, they might even teach you how to park your boat.
Literally stopping the yacht, as if you are parking a car (by what is called backwinding the jib). Learning to 'Heave to' like this is something not taught much these days, but it is a survival skill, much like not running with scissors or with a loaded gun. Or turning your wheels a little towards the kerb when parking your car on a hill.

Something else people seem to fail to teach (or learn these days) is how to sail your boat by jib alone, or by mainsail alone.

All this stuff is really basic and simple. Learning it will probably save you some day.

So While I think there has been some wonderful advice and great suggestions in this post about the theory of how a Mainsail with a Jib works, I still believe the best, most practical way to learn this is to take some basic sailing lessons.

There will be sailing clubs where you want to sail (especially if you are in The Netherlands).

Another source of theory lessons, and please don;t laugh at this out of hand) is to wander down to the local pond and watch people sailing radio controlled sailboats.

These things use their mainsail and jib in exactly the same way.

In fact, one of my yachts was a well known 26 foot racing yacht. I decided I wanted a 1/10 scale model made of it, an the 'experts' told me it would not sail.
I persevered and made a very rough 1:10 scale balsawood and ply model, with a scale sized mast and keel, then I floated it in a friend's swimming pool.

Before I could do any more, I lost the yacht in a cyclone (a typhoon in the northern latitudes).

A friend, who was a yacht builder and keen modeller, acquired the badly damaged hull, and rebuilt her to better than new in her old racing colours, because he had helped build her in the 70s.
At the same time he created a beautiful 1 foot to 1 inch scale model of the hull and rigging, but put a way oversized keel and rudder on.

There are videos of the model sailing on YouTube, and she sails as nicely as the original yacht. I have since modified to rudder back to scale depth, and am working on getting the keel as close as possible.

Sorry - wandering off topic.

What I wanted to point out is, that model yachts are also a great way to learn how a Maisail and Jib work together.

If you are lucky, you might get talking with a local model sailor, who might not only show you how the mainsail and jib work together - but who might even let you try out the controls yourself.
While you cannot 'feel' the boat, you very soon learn what NOT to do, and learn just how these two sails work, because on a model, you are mostly using the two of them 'together'.

You learn what the boat looks like when it is about to be blown flat, you learn how to sail the boat 'Into the Wind'.
You learn why none f us like sailing with the wind Directly behind Us (being blown along and getting seasick from the constant side to side movement).

So, my suggestions?

Jib and Mainsail theory tips in this post.

A book or two on Learning to Sail

Some YouTube videos about Learning to Sail

Some lessons at the local sailing club Just about all local sailing clubs have beginner lessons). Small two person dinghies are great.
- Don;t be disappointed to see 10 year old kids who can sail alone around a course, while you are struggling to work out what rope to pull.

If there is one active - your local radio controlled model yacht club.