Ian Nicolson - Boatbuilding: Cold-moulded and Strip-Planked Wood

More titles by Ian Nicolson available from Amberley Publishing:

Alfred Mylne: The Leading Yacht Designer: 18961920
Yacht Designers Sketch Book
The Boat Improvement Guide
The Ian Nicolson Trilogy
Build a Simple Dinghy
Yacht Designers Notebook

First published 2016

Amberley Publishing
The Hill, Stroud
Gloucestershire, GL5 4EP

www.amberley-books.com

Copyright Ian Nicolson 2016

The right of Ian Nicolson to be identified as the Author of this work has been asserted in accordance with the Copyrights, Designs and Patents Act 1988.

All rights reserved. No part of this book may be reprinted or reproduced or utilised in any form or by any electronic, mechanical or other means, now known or hereafter invented, including photocopying and recording, or in any information storage or retrieval system, without the permission in writing from the Publishers.

British Library Cataloguing in Publication Data.
A catalogue record for this book is available from the British Library.

ISBN 9781445651668 (PRINT)
ISBN 9781445651675 (eBOOK)

Typeset in 9pt on 11pt Celeste OT.
Typesetting and Origination by Amberley Publishing.
Printed in the UK.

Why Wood?

Wood has advantages such as a valuable strength-to-weight ratio, resistance to fatigue and shock loads, ability to stand up to different types of damage, also repairability, adaptability, and ease of handling and working. Cold-moulding retains these virtues, and is particularly good in terms of strength/weight and resilience. It is consequently an attractive option for racing craft of all kinds sailing dinghies, powerboats or large offshore racers as well as small tenders, fast launches and rescue boats. Strip-planking is also light in weight and easy to build, but less good in terms of strength and resistance to damage, ease of repair and longevity. For commercial craft, however, the conditions of use tend to favour steel in most cases.

As economic pressures increase there is a tendency to build boats for the widest possible market. Design has gone towards short bow and stern overhangs, ample beam and high topsides because these proportions suit land storage and marinas, (where charges are based on length), and allow maximum accommodation space. When a yacht is wanted that is not short and fat the available choice in fibreglass becomes very small, and this is where cold-moulding becomes especially attractive as it suits such hull shapes and is viable for small production runs. Long, narrow, fast and light launches of the type used on lakes and rivers, where they combine high speed with minimal wave-making wash, are another example, and like rowing shells they have been made in this way for decades.

Both methods particularly suit one-off or custom building, as for racing yachts and dinghies, or short production runs. A set of moulds may be reused for sister ships, are easy to store in between, and compared to a fibreglass mould are much quicker to make and perhaps a quarter the cost. The shape of the moulds can also be altered quite a lot without total rebuilding. This is a unique and valuable asset because racing boats tend to change gradually. When a designer has a successful shape one year, next years boats are likely to be similar and the old moulds can often be modified in a few days.

Wood itself is not a particularly expensive material. Just how its cost should be realistically compared to other boatbuilding materials is much debated. Comparison by weight alone ignores building costs, storage, the density of the material, the cost of buying, handling and working, and so on. Cutting away the forest of prejudices, most experienced people would agree that steel is the cheapest material, with wood and ferro-cement about equal second, then fibreglass, and aluminium the most costly. However these relationships change according to the size of craft involved and the amount of series production. One advantage of cold-moulding is that the cheaper pieces of suitable timber can be used, since long lengths and expensive wide boards are seldom needed. Good quality timber is still necessary, though, and always costs more than rubbish.

Another aspect which makes both cold-moulding and strip-planking attractive to amateurs is that they can be done by people who are short of woodworking skills, and by a small team such as a club or even one person working alone. By careful planning most of the jobs can be handled by semi-skilled labour, and this is also an attraction for professional builders who want to stay in business. Second year apprentices can do much if not all the work, and material stocks do not have to be large.

Anyone worried about his competence should start with a dinghy. Unless the boat is clearly a disaster it will be useful or can be sold, and it will give experience as well as confidence. If building is started but cannot be completed, the materials are not difficult to sell and the experiment will have been cheap.

One disadvantage of all wooden hulls is that they are not impervious to marine borers unless sheathed under water. However the sheathing need not be expensive copper. Cascover, which is a tough nylon cloth embedded in epoxy resin, keeps out worm and is stronger and lighter as well as cheaper. So for the tropics cold-moulding and strip-planking are still attractive, especially as the wooden hull, deck and cabin top make good insulation.

Because wood is an insulator, and above all because it is so attractive, cold-moulded hulls do not need lining provided the interior is well finished, and glue spillages have been minimized, also wiped away before they harden. Furniture is quickly and easily joined to the hull, and given plenty of manpower for laminating the shell a cold-moulded boat can be afloat in a very short time after the design is complete. A fibreglass boat from an existing mould is built quicker, but if the pattern and mould have to be built then the wooden one will be afloat much sooner. So where speed of building matters, cold-moulding is sometimes the best choice.

Finally, a well built cold-moulded boat should last as long as a carvel-planked one, say fifty years.

Cold-moulded Hulls

The term cold-moulding covers a number of related building techniques, but essentially consists of gluing layers of thin wood skins or planks together like a multi-layer sandwich. The result can be considered a composite material, and is very different from traditional wood boatbuilding in which separate pieces are fixed together with metal fastenings (sometimes assisted by glue) so that in use each part can move very slightly in relation to its neighbours. A cold-moulded hull is rather like the shell of a nut; the waterproof outer shell is also the strong structure which makes the nut so tough. If a nuts shell has a weakness it is at the join of the two halves, and in the same way cold-moulded boats (like fibreglass) unless properly designed and built, tend to have less strength at the deck/hull join. The analogy does not hold true, however, in the advanced form of construction seen on some racing boats, where the hull shell is largely to keep out the water and contributes much less to the rigidity and strength of the whole. An internal space-frame takes over much of the structural role as well as linking the stresses from the rig, keel, etc. that would in the conventional version be taken partly by floors, framing, stringers and so on as well as the hull shell. However, a hull built in conjunction with a space-frame structure is still laminated, though more lightly.