Buoyance and lateral area

[Slowmo]

Buoyance and lateral area. Can someone please explain the terms and how to use them in a sailboat design.

[Robert Gainer]

If you want just a definition, that’s fine. But if you want to know how to use this information you really should get a book on the subject. It’s to complex to describe in just a short note.

Buoyancy, the upward force that a fluid exerts on an object less dense than itself.
Lateral area, the projected area of the under water part of the boat.

[Slowmo]

Originally Posted by Robert Gainer

Lateral area, the projected area of the under water part of the boat.

So the CLA can be either axis X or Y?

If that's so... it's more or less self explaining.

[Robert Gainer]

To find the balance of the sail plan you use the center of the area of the hull in the plan view and compare it to the center of the sail plan in plan view. The difference is the lead and it varies from, lets say 14 to 19 % of the designed water line for sloops. You can compare other boats of a similar type to the one you are designing to get some numbers to use. You need to look at a good book like Skene’s Elements of Yacht Design because other things will affect the balance of the boat. The shape of the edge of the keel is just one thing for instance.

[Slowmo]

Originally Posted by Robert Gainer

/...area of the hull in the plan view and compare it to the center of the sail plan in plan view. The difference is the lead and it varies from, lets say 14 to 19 % of the designed water line for sloops.

14-19% plus AND minus(?), or shall the one allways be in front of the other?

When it comes to smaller boats like open trailer cruisers... are they normaly "good designs" or are they just looking nice ?

[Robert Gainer]

No, the center of effort of the sail plan is always forward of the center of lateral resistance of the boat. By saying more or less I meant that the lead would vary from 14% to 19% depending on the design of the boat. This number will also be different for different types of boats; a ketch or a schooner will have a different lead for the sail plan then the sloop that I used in the example. I don’t understand the rest of your question about small boats.

[sorenfdk]

The center of effort (center of the sail plan) should always be forward of the center of lateral resistance (center of the underwater part of the hull in plan view).

What is "good design"? What is "looking nice"? It all depends... Any yacht that fulfills your needs is a good design and if you think it looks good, then it does.

It sounds as if you are new to all this, so I would advice you to go to your local library and borrow some books on yacht design and sailing. They'll provide you with answers to all your questions. (I don't mean to say that you're not welcome here, because you sure are!)

[Slowmo]

Originally Posted by sorenfdk

What is "good design"? What is "looking nice"? It all depends... Any yacht that fulfills your needs is a good design and if you think it looks good, then it does.

It sounds as if you are new to all this, so I would advice you to go to your local library.../

Good design... If I buy plans, can I realy on that the boat really sails well? You know the opposit to "bad design" or actually no design at all.

Around here we have a modern saying: "You learn as long as you have pupils." ...here I am

[Dutch Peter]

Originally Posted by Slowmo

Good design... If I buy plans, can I realy on that the boat really sails well?

Depends on who're buying from. Known designer (and not buying his first design) I wouldn't be to worried. Local designer, try to find out if it has been build before and sail with it.

[sorenfdk]

Well, Peter said it!

[Dutch Peter]

Originally Posted by sorenfdk

Well, Peter said it!

Just repeating what I have learned on this forum!

[Slowmo]

Honestly.

1. That a person X have made designs before.
2. That plans gone into built boats X
3. That boats been sailed by person X

To judge boats from those points is not really a good ansver, more like a guess or astrology.

Put into the above the words:
1. with the IQ 80
2. by builders with no thumbs
3. who's never sailed nothing more advanced then a air-mathress.

I ment if someone actually know the quality of plans floating around in the market. Are they so good plans that a normal eingineer can't make it better in a month of hard studies!?

[Dutch Peter]

So, what's the question then??

Any design can be improved, if that's what you mean. And as soon as it is improved someone will improve yours.
Normal engineer, one month of hard studies?? In design, I don't think so.
In school and from books you learn the basics/theory, but the "fingerspitzen feeling" comes with the years. I know, I still haven't got it!!

[sorenfdk]

Originally Posted by Slowmo

Honestly.

1. That a person X have made designs before.
2. That plans gone into built boats X
3. That boats been sailed by person X

To judge boats from those points is not really a good ansver, more like a guess or astrology.

Put into the above the words:
1. with the IQ 80
2. by builders with no thumbs
3. who's never sailed nothing more advanced then a air-mathress.

I ment if someone actually know the quality of plans floating around in the market. Are they so good plans that a normal eingineer can't make it better in a month of hard studies!?

Honestly!
Of course, if an idiot designs a lot of boats, that are built by idiots, who sell them to idiots, then that doesn't say much about these boats. But that's not very likely to happen, is it?
If someone designs boats that are built by many different boatbuilders, who sell them to many sailors, then maybe, just maybe, his or her designs can't be way off.
But then again - nothing in this world is 100% sure...

[Slowmo]

Originally Posted by sorenfdk

Honestly!
Of course, if an idiot designs a lot of boats, that are built by idiots, who sell them to idiots, then that doesn't say much about these boats. But that's not very likely to happen, is it?
If someone designs boats that are built by many different boatbuilders, who sell them to many sailors, then maybe, just maybe, his or her designs can't be way off.
But then again - nothing in this world is 100% sure...

1. Psychology tells us that people have a very high preference to "like what they own". When it's sold, they tell you they hated it.

2. Some types of design doesn't attract pro's or even initiated amateurs. In such cases it can take years to uncover "the emperors new clothes".

3. Polish glider sailplanes (flying) allways, of it's own time told to be not as good as German ones.
Basicly every Polish model of gliders have afterwords been accepted as having supreeme performance in comparison. This is a good example from real life how "folklore facts" often is embarising faulty. I can guarantee that the same fairytales, in some areas also goes around among sailers and designers.