What's in a set of Plans for a Modern Multihull?

Header Image for article making plans

We take a look at the drawings and technical information that come with a set of set of plans

When I built my first multihull I had a set of about twelve beautifully hand drawn plans on A1 size sheets (if I remember rightly - that was some time back), a materials list typed on A4 bond, and a set of full size patterns off a plan printer.

Times have changed. Our boats are much more sophisticated. Building methods have evolved, and the the information we provide for the construction has changed a lot too.

So what goes into a set of plans? Only a small fraction of the information that gets developed in the design office gets delivered to the builder, but that information on its own is quite extensive.

 

In this article we take a look at the information we provide, how it's delivered, and a brief outline of why we do it this way.



Our plans are organised into nine different categories, each one of those categories with a "series" number. 

Organising the plans in this way helps us to carry out the design work in a logical progression, making the design work as efficient as possible but also serving to provide the builder with a certain amount of flexibility and deploy electronic machining equipment that is available now and will be increasingly available in the future.

The process we use is also designed to facilitate checking and enable changes to be made with a minimum of reworking to other drawings.

Image for CNC Machining a trimaran hull


SERIES 1. PLANS - GENERAL ARRANGEMENT

The General Arrangement Drawings are at the heart of the design process. They describe the layout of the boat and the location of all the permanent bulkheads, floors, seats and dividing panels. These drawings also provide the location of engines, tanks, batteries, and other heavy items including the rig and the forebeam.

The general arrangement drawings are finalised as much as possible in the early stages of the design process and they serve as a reference point for the construction plans that follow.


General arrangement plan. Hull profiles
General arrangement plan top view


SERIES 2. PLANS. SAIL AND RIG PLANS, DECK LAYOUT AND SAIL CONTROLS

These drawings include the sail plan, the rig plan, the deck layout including the sail controls. The specifications are provided on the sail plan. The deck plan provides a list of deck equipment and recommended winch sizes.


Catamaran Sail and Rig Plan
Catamaran Deck Layout Plan

SERIES 3 PLANS. CONSTRUCTION PLANS


These drawings are at the heart of the build process. They define the components and specify the materials. Normally 30 to 40 sheets of drawings depending on the complexity of the boat and the build method.


Construction Plan-01
Construction Plan - joining Details
Construction Plan for the wingdeck of a cruising catamaran


SERIES 4 PLANS. RUDDERS, DAGGERBOARDS, MINIKEELS

Construction of the Rudder, Daggerboard, Keels. Most of our cruising cats offer the option of daggerboards or mini keels and both options are provided for in the plans as a standard inclusion. 



Rudder Plan-01
Construction Plan-02
Dagger Case Plan-01
Dagger Plan-02


SERIES 5 PLANS. FOREBEAM AND LONGERON OR CATWALK

Construction details for the forebeam and the catwalk or longeron and attachment to the hulls. The reason these drawings, and the rudder/daggerboard drawings are kept in a separate section is so that changes can be made (for example change a longeron for a catwalk, or a daggerboard or a mini keel) with a minimum of changes having to be made to other drawings and cutting files.


Foredeck plan-01
Foredeck plan-02
Foredeck Plan 03


SERIES 6 PLANS. PANEL DEFINITIONS

All of the flat panels are defined on these drawings including datum lines where necessary, panel names or numbers, marking lines for openings and lines that show where panels have been offset for planking thickness or the intersection of another panel. These are the panels that have been unrolled from the model and we keep them in this format for later reference in case there are any changes to the laminate specification, the nestings or the cutting files.

At this stage the panels are given a fill. This ensures that we have a closed polygon with no stray lines and we can move the panels to the later stages of the design documentation process with confidence that the routing software will read the definitions without problems.


Panel definition Plan 1 of 2
Panel Definition Plan 2 of 2


SERIES 7 PLANS. ASSEMBLY DRAWINGS


This is a bit like the assembly instructions you get with a product from Ikea. Every part in the boat is numbered for identification throughout the manufacturing and assembly process.

 

These drawings show the sequence for assembly and provide some general comments about the build process.

Sorry but we don't supply the screw drivers.

Assembly Drawing 1 of 3
Assembly drawing 2 of 3
Assembly Drawing 3 of 3


SERIES 8 PLANS. LAMINATE SPECIFICATION

 When the laminates for respective parts of the boat have been determined all of the panels with a common laminate are duplicated from the 6 series drawings and moved to the respective laminate groups in preparation for nesting.

 


Laminate Specification plan 1 of 5
Laminate specification plan 2 of 5
Laminate specification plan 3 of 5
Laminate Specification Plan 4 of 5
Laminate Specification Plan 5 of 5


SERIES 9 PLANS. NESTINGS AND CUTTING FILES


The nesting operation positions the shapes of the panels on the material being used for their manufacture and is used by the operator of the CNC machine to manufacture the panels with a minimum of joins being required and minimal wastage.


Nesting layout Drawing 1 of 2
Laminate nesting drawing 2 of 2

Flat panel kit for TR42 trimaran
Kit of Flat Panel Components for a 42' Trimaran

ABOUT THE BUILDING PLANS


DESIGN OPTIONS

Our cruising catamarans offer various layout options including centre bathrooms, forward berths on the wing deck or in the hull, and a variety of layouts in the saloon.

The helm stations can be aft behind the aft cabins, or forward on the bulkhead. 

The boats can have fixed mini keels or daggerboards.

Some options are provided in the plans with no additional charge, some options may require an additional fee.

ACCESS TO THE PLANS

The plans are made available in a Drop Box folder in pdf and dxf format. 

The drawings are on A1 size sheets: 841mm wide x 594 mm high (33.1” x 23.4”) at 300dpi.

The drawings can be printed in smaller sizes (typically A3) to be convenient for filing in a display book. The text is legible down to A4 size. 

 Dimensions are in metric.

We can also arrange to have the plans printed and posted to you on request.

SHEET LIST AND PLANS UPDATES

From time to time we update drawings or add new drawings to the plans set. This is to make corrections, provide clearer instructions, or update design features. When we update drawings the date of issue will be renewed on the sheet list in your Drop Box Folder.

If it is a new sheet it will be added to the list. Updates are supplied to builders free of charge.

SUPPORT

We encourage questions or suggestions for improving the information we provide in order to make the build process as straight forward as possible.

 In a perfect world the plans will explain everything - but in the real world we're still on the road to that place and probably always will be. There is no charge for asking questions.

CHANGES TO THE DESIGN

If you like our design work but want make some changes please talk to us about your ideas. We are happy to consider customising an existing design or creating a fully custom design to suit your requirements.

Please respect that we have good reasons for creating the designs the way they are. If you change the shape of the boat without our approval  you might find that you are not free to advertise the boat as a Grainger when you come to sell. 

 

 

ENGINEERING OPTIONS

 

 All of our designs are available to be engineered for compliance with the ISO standards. There are four good reasons to include an engineering package in your design program.

 

• Firstly if you are in Europe your boat is required to comply with CE standards. This means that we have to supply you or your builder with plans and specifications that comply with these standards.

ISO compliance is also required for boats doing commercial charter work.

 

•Secondly, if you wish to race offshore overnight it is likely that the race organising body (usually a yacht club) will ask to see a certificate of compliance with engineering standards.

 

• Thirdly, compliance with ISO standards will most likely make it easier for you to negotiate a favourable rate with your insurance company

 

• Fourthly, if your boat has been engineered to ISO or other standards, and built in compliance with those standards this can be a significant advantage when you wish to sell and trade up to a new boat.

 

If you are enthusiastic about racing we can also provide you with an engineering package to optimise the weight and stiffness of the structure including carbon rigs, C foils, T rudders and lifting foils.

 

Note that CE marking (Certification European) requires that the boat be inspected under construction and on completion to verify that the construction complies with the ISO or other approved standard. This is the responsibility of the builder.  We can help to direct you to people who cannot assist you through this process if it is required.