Boat Design - First Step - Sheer line and First Chine design

I am trying to understand how to design an chined boat design from zero.

Does First Step is to design the First line ,the sheer line from the TOP VIEW ?

Than Second Step ,we have to create a curve to the First Line ,to the sheer line from the SIDE VIEW.

Is there a rule to design sheer line top and side view ? Is there a need to draw a airfoil at First Step

And what about the Third Step when drawing Second Line - first chine - ?
How to be sure of surface between the sheer line and the first chine is a conic section ? And developable without any problem ?

Thank you very much ,

Umut
Istanbul

Draw the three views of the ship freehand on a piece of paper in pencil. Initially, something similar to other ships and something that you think looks good. Then, little by little, you correct things to make sure "THAT" complies with the SoR.

Step zero, which you've forgotten, is drafting the boat's SoR.

Sheer lines and curves are overrated . Once I was build a rectangular shape bulkheads and transom . Only curves was at the bow : bottom raised to the stringer height . Second curve was from the bow to the windshield base . It looks like boat flipped over.
No waves on the river till you meet one . During storm we dived nose and caught 150l of water going over the windshield .

TANSL said:

Step zero, which you've forgotten, is drafting the boat's SoR.

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This is correct. Without a SoR there is no way to know where and how the chines should be placed, let alone which line to place first.

See this old thread. Lines Plan https://www.boatdesign.net/threads/lines-plan.29882/#post-310553

jehardiman said:

This is correct. Without a SoR there is no way to know where and how the chines should be placed, let alone which line to place first.

See this old thread. Lines Plan https://www.boatdesign.net/threads/lines-plan.29882/#post-310553

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Thank you for the link.
I read there there is FIRST dispacement to lenght curve, SECOND lenght to speed ratio.

I dont know how to draw the first curve and apply to speed lenght ratio.
If I am not wrong , displacement to lenght curve is a sinus curve but someone tried cosine curve. Is there published curves for classical wooden dinghys or chined modern dinghys ?
And for god sake can someone explain what is cosine curve ? How to decide them before the design starts ? I am not designing ships but maximum 4 meters long closed ocean boat and preferably dinghy.

Thank you very much indeed for your time and lessons all,
Umut

MtUmutSarac said:

I am not designing ships but maximum 4 meters long closed ocean boat and preferably dinghy.

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Forum memeber @Dolfiman just posted a spreadsheet (Excel, OpenOffice) calculator for a chined boat.

Gene-Hull Dinghy Chines 3.1 https://www.boatdesign.net/threads/gene-hull-dinghy-chines-3-1.70048/

Sine and cosign curves are not the curves that you would use for laying out the lines of the hull. First things first.................
1. is the boat to be a sailboat or a power boat.
2. If it is to be a power boat, then is it to be a speed boat or a displacement type that is more economical to operate.
3. If it is to be a sailboat, will it be a small dinghy type or a boat that is capable of crossing the med to the Greek islands
..............this is the beginning of what is considered a Statements of requirements, often referred to as SOR. There is more.
4. how much will the boat and all of its cargo weigh. With that question, and the others answered, we can begin to draw some lines and not before we have answered those questions.........but there is more.
5. how many people will be aboard the boat, do we need to plan for accommodations like bunks, toilets, cooking facilities, If it is a cruising boat, we have to have adequate fuel and water tankage.....and more......All that plays into the kind of boat that you will design, the curves that will be appropriate to the kind of boat that it is, and there are still more considerations you must deal with.

There are no absolute specific curves that are appropriate for a boat. The curves and the shape of the sections , the shape of the bow, the shape of the stern and a lot more things to consider before you can realistically design a boat. The mathematics involved is the same math that we have been taught so at least that is a standard design tool.

Tell us what kind of boat you want to draw and perhaps we can provide be a bit more information.

messabout said:

Tell us what kind of boat you want to draw and perhaps we can provide be a bit more information.

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Hello,
sailboats , no engines , single purpose carry one safe from a to b.
two boats , one from plywood , one skin on frame.
no different than sleeping bags, no different than astronauts cabins.
boat internal lenght is 170 cms , internal height is around 45 cms. beam is around 73 cms. double ender and closed to all elements with vieving acrylic bulb.
It will have chines and made from 8mm think marine grade plywood laser cut. And it will be sealed to elements with 600 grams sq meter glass fiber rowing and polyester , single layer.
I think it will be stitch and glue. Plywood sheet size is 170X220.It must use least amount of plywood

Second boat will be skin on frame boat , same dimensions. Skin on frame boat posts can be cut from 18mm thick normal plywood , it would be strong and cheaper than above plywood boat.
Dont tell me these are crazy , this dimensions are a must . must.
Thank you,
Umut

The Design Spiral in The Principles of Yacht Design by Lars Larsson, Rolf Eliasson, Michal Orych is the first illustration in Chapter 1.
It can be a aid in the design process and correct things that you may not have thought of at first.

Umut, your boat is very small if it is only 170 cm long. Let us suppose that you and the boat weigh 100kg. That means that the boat must displace 100kgs of water if it is to float.

Playing around with the numbers it appears that the boat will float and sink about 15 cm into the water. You could start with the first curve which we can call the keel curve. Draw a straight horizontal line about 200 cm long. Let that be the base line. Now erect some vertical lines spaced 170 cm apart. That will be the bow and stern location of your boat drawing. At the front make a marker dot on the vertical line 14 cm above the base line. At the other vertical line, the stern of the boat, make a dot about 16 to 18 cm above the base line. Find a location at about the middle of the base line, make a dot there. use a very limber stick about 250 cm long and bend it so that it touches the front dot, the middle dot, and the stern dot. Trace a line where the stick (called a spline) lies on the paper that you will use as a plan. ..............................Now we have a tentative curve that represents the keel line of the boat.

The keel line might very well be described by some obscure mathematical equation but that is of no interest to the designer of little boats. The spline will do the job of describing the curvatures very nicely. The first line that we have drawn is part of the "profile" or side view of the boat. You also need to draw a plan view of the boat which you may think of as the birds eye view. Use the spline in a similar way to draw the sheer line of the boat. First lay down another straight line which will represent the centerline of the boat as viewed from the top birds eye view. It is not necessary to draw curves on both sides of the center line.............if the boat is to be symmetrical.

There is a lot more to do before you have done the complete design but perhaps this will get you started with the curves. As you manipulate the spline, you will notice that the curves can be made into slightly different shapes by moving the maximum camber of the curve to slightly different locations along the base line or centerline. That is where experience comes into play. It all depends on the particular purpose that the boat is to serve.

After you have done the major curves, you must decide, judiciously, how to shape the sections. Sections are the shape of the boat cross sections if you sliced it into segments similar to the way a loaf of bread is sliced. The shape of the sections will determine whether or not the boat will float at a certain height in the water, the sections will also largely determine how stable the boat is. In your case, the 73 cm beam that you will use, the boat is going to be a bit shakey or as the boat guys say,"tender".

In any case, a boat with these dimensions will not be very stable and may very well be dangerous in any water other than a swimming pool.

The link below is from Eric W. Sponberg Naval Architect. (retired)
THE DESIGN RATIOS A Naval Architect’s Dozen (or thereabouts) A primer on some basic principles of naval architecture for small craft. As first published on BoatDesign.net, January – March, 2010. By Eric W. Sponberg Naval Architect BSE, PE (CT) CEng (UK)
Home https://www.ericwsponberg.com/
https://www.ericwsponberg.com/wp-content/uploads/2021/09/THE-DESIGN-RATIOS.pdf

The "cheapest" boat i built that i could sleep on, was a Gentry Chautaqua. Chautauqua.

With a fabric cover for the open cockpit, it will take on no water. Otherwise for solid ply, Bolger Tortoise.

Both good in their respective duties and within the limitations.

MtUmutSarac said:

And for god sake can someone explain what is cosine curve ? How to decide them before the design starts ? I am not designing ships but maximum 4 meters long closed ocean boat and preferably dinghy.

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MtUmutSarac said:

boat internal lenght is 170 cms , internal height is around 45 cms. beam is around 73 cms

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MtUmutSarac said:

Dont tell me these are crazy , this dimensions are a must . must

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I would never call a troll crazy. You should epoxy coat a sleeping bag to make it ocean worthy. A second option is to use fabric printed with nautical themes like anchors and mermaids.