Notes on Design Drawings

These notes have been compiled to assist clients to understand and read the   drawings which are involved in the design of a vessel. These drawings while fundamentally being Engineering Drawings, differ in some ways from such drawings and include some conventions and terms which some clients have found confusing. No apology is made for sticking to the terminology of Naval Architecture, which has lasted and will continue to last, longer than some people who seem keen to introduce house building terms into the rich language of the sea.

Generally I prepare three stages of drawings for my clients, CONCEPT SKETCHES, PRELIMINARY DRAWINGS and WORKING DRAWINGS.

• Concept Sketches are simple sketches drawn to a convenient scale which show the outline of a proposed design. I do not usually make a charge for such sketches, which are prepared to enable the client to understand the concept around which the design will evolve.
• Preliminary Drawings are the next stage in a design and these normally include some of the sheets which will form the basis of the Working Drawings, but some of these at this stage may show little detail. Typical sheets in Preliminary Drawings of a proposed 13 metre yacht might include: 1) Lines 2) Outboard Profile & Sail Plan 3) General Arrangement 4) Deck Plan 5) Port Inboard Profile; and, 6) Joiner Sections or half Sections . For smaller vessels all these sheets may not be necessary. The charge for these Preliminary Drawings is normally agreed to, before the commencement of a design and is payable on completion of the Preliminary Drawings. I have had to commence charging for preliminaries because hours of calculation, and at the drawing board and computer are invested in these drawings, yet this may not be apparent until the design is nearing completion. The charge for Preliminaries is discounted from the charge for the Working Drawings.
• Working Drawings are the full set of drawings used in building the design. Some of these may be preliminaries with additional data drawn in, and checked against other sheets. Additional notes and complete fairing will have been added and Working Drawings are fully dimensioned . Additional sheets such as the Table of Offsets will also be included.

As an example, Working Drawings for a 10 metre cruising sloop could include:-

• Sheet 1. Lines Drawing, Hydrostatic and Dimensional data.
• Sheet 2. Table of Offsets.
• Sheet 3. Outboard Profile and Sail Plan.
• Sheet 4. General Arrangement and Deck Plan.
• Sheet 5. Port Inboard Construction Profile; or in the case of asymmetric layouts both Port and Starboard Profiles may be necessary.
• Sheet 6. Deck Framing, Hull Framing, and Lamination Schedules.
• Sheet 7. Joiner Sections and /or Half Sections
• Sheet 8. Engine, Shaft and Propeller Drawings.
• Sheet 9. Rudder and Ballast Keel and Steering Control Drawings.
• Sheet 10. Mast, Spars, Standing and Running Rigging.
• Sheet 11. Electrical and Plumbing Drawings and Tanks.
• Sheet 12. Stability Curves and Power-to-Carry Sail Curves.

Obviously the number of sheets and the detail included in those sheets, depends on the size and complexity of the design as well as the requirements of the client. Some are skilled boatbuilders and need only some of these sheets to complete the project, such as e.g. Sheets 1,2,3,4,5 and 9 &10. Others wish the design to be completed in more detail for contractual reasons with the builder of their choice. In recent years I have been preparing more designs as Stock Plans mainly for clients building the vessel for their own use; and these have in addition extra sheets and other information which detail the building process in a step by step manner, more appropriate for the DIY person.

When dealing with prospective clients who think there is a possibility that they may wish to purchase a Stock Plan, but require more information on the design, I sometimes use a STUDY PLAN which is information on a design in the form of drawings which give enough detail for them to assess the design but which is inadequate to build from. Depending on the design I sometimes charge for these Study Plans.

Drawings for the exclusive use of one client are drawn in confidence and the original inks of the working drawings are handed over to the client on completion of the design. In such a case we retain no intellectual property rights to the design.

If the design is for a vessel which is to be manufactured in numbers a Royalty Agreement may be drawn up which specifies a lumpsum payment on completion of the design, and a royalty may be payable on the laying of the keel for each boat. Royalties are generally negotiated on the basis of a fixed sum for an initial numbers of boats, or for the first year of production, and royalties at reduced rates for the remainder of the production run. Royalty agreements have not been used much for clients in this country, due to smaller runs in part but mainly due to the difficulty in auditing the numbers of a design which have been built.

THE DRAWING SHEETS.

The names and titles for some of the sheets may not be instantly recognisable to clients unused to Naval Architect's drawings, and the following may clarify the mystery.

Lines Drawing . This is a representation in three views of the shape of the vessel. This sheet is the most important of all the sheets and the most time consuming to prepare as it must be done with great accuracy. A fully faired Lines Drawing would take many tedious hours of drawing in the past.

This has been substantially reduced by the use of specialist computer programs. The designer must be careful to design the boat the client wants and ensure he does not design the boat the computer wants. I believe many designers are taking the easy route and letting the computer do all the work. I try to be the master and not the slave of the computer.

Hydrostatic Data is prepared from the Lines Drawing and details mathematically, the manner in which the hull will float at rest and how it will respond to loading, and also provides data to enable Stability and Power-to-Carry Sail curves to be developed. The data also enables judgements to be made about how the hull will perform at design speeds and in differing sea conditions and allow drag and hull resistance parameters to be studied.

Table of Offsets Is a table of measurements to allow builders to loft (or draw) the lines full size or in some cases to build the frames or moulds on the building jig directly from them.

Outboard Profile is a view of the vessel showing the appearance of the hull and superstructure floating on her designed waterline. For a sailing yacht this view generally includes the Sail Plan and the sail maker will use it to quote and make sails.

General Arrangement. This is a view of the layout of the vessel. For larger vessels the general arrangement is often shown with the deck removed or part removed.

Deck Plan. This sheet shows the deck layout in sufficient detail to enable all the deck fittings to be installed.

Inboard Profiles are drawn to show the hull viewed with an imaginary fore and aft vertical cut made along the hull centreline. Sometimes both Port and Starboard Inboard profiles are shown to detail the construction of the vessel if some aspects of the design are not symmetrical. In fibreglass construction this sheet sometimes shows the Lamination Schedule which shows details of the weight of glass and the type of glass used and gives resin details.

Deck and Hull Framing drawings are included for timber steel and aluminium hulls to detail the size and spacing of structural members.

Joiner Sections are drawings to enable the joinery of the vessel to be shown in position. A set of joiner sections or half sections is very important to enable clients to assess the "liveability" of the proposed vessel. Joiner sections do not normally show the construction of a vessel.

Some terms which are used and can cause confusion are:-

Floors are structural members which are fitted to keelson and frames across the boat. i.e."athwartships". Note that you do not walk on the floors when afloat, you walk on the soles or the decks. Generally decks are on the outside of the boat and are curved or cambered while the soles are below and are often flat.

The Topsides are the sides of the hull below deck level. We would all be rich if were given a dollar for every time people think topsides means the structure of the decks, wheelhouses, etc

LWL is the abbreviation for Load Waterline Length . In fact it is the length of the horizontal plane representing the water surface on which the vessel with crew, equipment and stores will float at rest. Some designers and texts sometimes use DWL and Design Waterline for the same thing. LWL is more commonly used.

LOA is the abbreviation for Length Overall and represents the horizontal length of the vessel from stem to stern.

Stations are the spacing of the sections cut through the vessel perpendicular to the Waterline plane and the vessels centreline. They are numbered from bow to stern and convention is to number the station at the forward ending of the waterline as Station 0, and at the aft end Station 10. These ten stations are at equal spacing , so the LWL is divided into ten .Sometimes extra stations are used and they are designated fractionally.

Waterlines are parallel planes to the LWL They can be imagined as horizontal slices or saw cuts parallel to the LWL They are designated in some way to show their position or heights above or below the LWL e.g. WL+600 or Waterline -200 etc

Buttocks represent cuts or slices made this time in vertical planes parallel to the centre line. They show you the shape the hull would show if parallel slices out of it with your knife held vertically and moved fore and aft. Buttocks are very important lines especially aft of midships for faster motor vessels and for sailing yachts.

Diagonals represent inclined planes through the hull at the angles shown on the Lines Drawings. Again they may be imagined to be slices or saw cuts through the hull, from the centreline plane to the topsides and/or hull bottom. You will only be interested in diagonals if you are lofting the vessel full size from the Table of Offsets.

When examining foil drawings such as drawings of rudders, centreboards and keels, the

Span is the depth or length from top to bottom and the Chord is the section length fore and aft i.e. the length of an horizontal slice.

With respect to rigging there are two kinds, Standing Rigging, which is generally wires which support the mast, such as Shrouds which support the mast athwartships; and Stays which do so fore and aft. e.g. The Forestay is the wire from masthead or hound to stemhead , while the wire from masthead or hound to chainplate on the deck outboard from the mast is the Main Shroud , sometimes if it goes to the masthead called the Cap Shroud. The other kind is Running Rigging , such as the Halyards which are rope lines or wire/rope combinations which run over blocks to haul up the sails and Sheets which are the lines attached to sails to control them. Note that the sheets are lines and not sails e.g. the Mainsheet is the arrangement of rope which is attached to the Mainsail.

It is my hope that these notes will assist you to read the drawings with more understanding, and enable you to share the endless pleasure available from the examination of drawings and illustrations of boats and yachts, which share with seabirds and dolphins, the distinction of being the most graceful things to use the waters of our world as a supporting medium. e terms which are used and can cause confusion are:-

Floors are structural members which are fitted to keelson and frames across the boat. i.e."athwartships". Note that you do not walk on the floors when afloat, you walk on the soles or the decks. Generally decks are on the outside of the boat and are curved or cambered while the soles are below and are often flat.

The Topsides are the sides of the hull below deck level. We would all be rich if were given a dollar for every time people think topsides means the structure of the decks, wheelhouses, etc

LWL is the abbreviation for Load Waterline Length . In fact it is the length of the horizontal plane representing the water surface on which the vessel with crew, equipment and stores will float at rest. Some designers and texts sometimes use DWL and Design Waterline for the same thing. LWL is more commonly used.

LOA is the abbreviation for Length Overall and represents the horizontal length of the vessel from stem to stern.

Stations are the spacing of the sections cut through the vessel perpendicular to the Waterline plane and the vessels centreline. They are numbered from bow to stern and convention is to number the station at the forward ending of the waterline as Station 0, and at the aft end Station 10. These ten stations are at equal spacing , so the LWL is divided into ten .Sometimes extra stations are used and they are designated fractionally.

Waterlines are parallel planes to the LWL They can be imagined as horizontal slices or saw cuts parallel to the LWL They are designated in some way to show their position or heights above or below the LWL e.g. WL+600 or Waterline -200 etc

Buttocks represent cuts or slices made this time in vertical planes parallel to the centre line. They show you the shape the hull would show if parallel slices out of it with your knife held vertically and moved fore and aft. Buttocks are very important lines especially aft of midships for faster motor vessels and for sailing yachts.

Diagonals represent inclined planes through the hull at the angles shown on the Lines Drawings. Again they may be imagined to be slices or saw cuts through the hull, from the centreline plane to the topsides and/or hull bottom. You will only be interested in diagonals if you are lofting the vessel full size from the Table of Offsets.

When examining foil drawings such as drawings of rudders, centreboards and keels, the

Span is the depth or length from top to bottom and the Chord is the section length fore and aft i.e. the length of an horizontal slice.

With respect to rigging there are two kinds, Standing Rigging, which is generally wires which support the mast, such as Shrouds which support the mast athwartships; and Stays which do so fore and aft. e.g. The Forestay is the wire from masthead or hound to stemhead , while the wire from masthead or hound to chainplate on the deck outboard from the mast is the Main Shroud , sometimes if it goes to the masthead called the Cap Shroud. The other kind is Running Rigging , such as the Halyards which are rope lines or wire/rope combinations which run over blocks to haul up the sails and Sheets which are the lines attached to sails to control them. Note that the sheets are lines and not sails e.g. the Mainsheet is the arrangement of rope which is attached to the Mainsail.

It is my hope that these notes will assist you to read the drawings with more understanding, and enable you to share the endless pleasure available from the examination of drawings and illustrations of boats and yachts, which share with seabirds and dolphins, the distinction of being the most graceful things to use the waters of our world as a supporting medium.