Sail Boat Hull Design DIY Smarts Built For Your Needs

Sail boat hull design meant boat strength for us. We wanted a vessel structure that would endure the oceans tests.

Our aluminum boat hull construction is one third the weight, but twice the cost of steel, so they say. And rising at this present time.

Accurate definition of the hull traditional lines drawing is still the common tool. Even though most professional yacht designers use the CAD program.

A sailboat hull is characterized by lines, angles, circles another words geometrical design.

OK, brain freeze like when you eat ice cream...

Deep breath, lets go forward.

Length overall (Loa) Maximum lengthof the hull from the forward most point to the back end. Do not include rudder, bowsprits, spars.

Length of waterline (Lwl) Length of designed waterline (referred to as the DWL) length of boat from bow to stern

Length between perpendiculars (Lpp) Length not used much in yachting, but important for ships. Forward perpendicular (FP) is the forward end of the designed waterline, aft perpendicular (AP) centre of rudder stock.

Rated length most important parameter in any rating rule.

Beam (B or B max) Maximum beam of the hull excluding fittings.

Draft (T) The maximum draft the boat when its floating on the waterline. T, is the draft of the hull without the keel (the canoe body)

Depth (D) The distance between the bottom of the keel; up to the sheer line.

Sheer: lines of a ship toward the bow and the stern upward curves of the deck.

Sheer line: Intersection between deck and the topside.

Boat hull design is a process, important factor is boat displacement. It cannot be determined until lines have been fixed or tried to be drawn. Here is a method to this madness...

Step 1: Main dimensions, research, using information on other hull designs with similar size, designed for similar purposes. With navel architects this is common practice. When you know the size of the yacht, find as much information as possible on other new yachts with the same hull shape.

Drawings of new yachts can be found in boating, sailing magazines. Boat hull designs means you decide dimensions, length overall, draft, displacement, longitudinal centre of buoyancy, ballast ratio, sail area.

Remember all of this is one step at a time...

Step 2: Draw profile, everything centers around the profile.

Midship section: Middle of a boat, waist, creating a constant shape of ribs throughout

Step 3: Draw the midship section, it's important because all other shapes follow its lead.

Step 4: Check displacement, calculate (measure) submerged area just drawn and multiply by the waterline length.

Step 5: Draw the designed waterline, now you know where the mid section is, with the two end points you can make a first attempt at the designed waterline.

Below, sail boat hull design transom is outlined in blue.

Transom means: when you are standing directly behind a boat. It is the flat piece that creates the flat surface. The flat rear end of the boat, the flat, vertical hull section.

Step 6: Draw stations 3, 7 and the transom, waterline is known, and the hull draft and each section should look like (resemble) the midship section. You can draw a ghost transom behind the hull.

Step 7: Draw new waterlines. If you don't like the way they look repeat steps 6 and change.

Steps 8 and 9: Add new sections and waterlines sections 1-9 should be completed and 7-10 waterlines. Make sure you adjust the the body plan so you create a smooth flowing body line.

Step 10: Double check the displacement and the longitudinal centre of buoyancy. Excluding keel and rudder, you can now find the curve of each sectional area to be constructed. If its not right, go back to steps 5 or 6 and make changes.

Step 11: Draw diagonals, check for smoothness, change if needed.

Step 12: Draw buttocks last bot not least, check again for smooth lines.

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