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© 2009 Mark Kennett

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Boat plans – Independence 48
Design analysis

Independence on anchor

The Independence 48 is a long-range offshore displacement motor boat, characterised by seaworthiness and excellent fuel economy.

The Independence 48 is a long-range offshore displacement motor boat, characterised by seaworthiness and excellent fuel economy.

The clean, easy lines of this hull are relatively simple to build, with no complex plate rolling required.

The non-critical nature of the weight and loading characteristics of this vessel, and its ability to carry large loads without compromising performance, indicate a versatile design, suitable for a variety of uses.

Simple to build

This boat has a simple, easily built steel hull that is well suited to individual or amateur construction. The hull form is a single hard chine design that is straightforward to plate up.  The only plate that needs to be formed is the small closer plate at the forefoot. This can quite easily be formed using a couple of G cramps, your oxy-acetylene torch and a bit of patience. The hull is built on a heavy flat bar keel and the framing is all straight section flat bar and angle. Wheelhouse and cabins are made from marine ply on a timber frame. This keeps top hamper weight down and makes fitting out easier.

Economical to run

I think it is safe to say that the era of cheap fuel is over. A long-range motor boat needs to travel at moderate speeds and must be easy to drive in order to be economic in today’s high-cost environment. The Independence 48 meets these requirements.

It is powered by a single 100hp heavy-duty diesel engine that is fully capable of bringing the boat to its terminal hull speed of about 9 knots in all sea conditions.

Cruising speed is at a more economical 7.5–8 knots and this results in a typical fuel consumption of about 1.9 imperial gallons (8.6 litres) per hour. With a fuel capacity of 500 imperial gallons (2,273 litres) the boat has an ultimate range of just under 2,000 nautical miles; more if you go slower.

Seaworthy

Independence 48 underwater sections

The simple, attractive lines of this boat contain the elements of seaworthiness. The chine form, reaching to just above the waterline forward, slopes down in a gentle curve to the deepest part of the hull proper. This imposes a sharp, V-shaped forefoot, which makes for easy driving and reduced pitching, and prevents the hull from pounding in a head sea. 

The bottom becomes flat in section at its deepest part, then curves steeply up to a fantail-type run. This serves to distribute the displacement so that the centre of buoyancy is aft of amidships, which eases the motion in a seaway and reduces displacement aft to reduce the danger of broaching in a following sea. The sides of the vessel have a fairly bold outward flare, which helps to dampen rolling and suppress spray. 

The moderate beam combined with the flat sections in the run provide good stiffness without inducing rolling, and reduce squatting under power. The bold sheer makes for a dry boat when driving to windward.

The original boat has proven to be very able and seaworthy in the short and dangerous seas of the North Sea and English Channel, and performed excellently when crossing the Bay of Biscay, in the Atlantic and the Mediterranean.

The boat can also be used in the European canal system and the original voyaged from the Mediterranean to the North Sea by way of the French canals.

Versatile

The hull form is a versatile one. Experienced shipwrights and boatmen can alter the arrangement somewhat but excessive top hamper and windage must be avoided. This design is not suitable for steel superstructures.

The original was built as a long-range cruising/working boat for two people who required a large deck space and hold/storage space for tools and equipment.

It has comfortable, full-size accommodations including a huge double berth, full-size galley, fridge and cooker, adult shower and heads compartment and proper wheelhouse. There is ample storage for personal possessions plus a large quantity of tools and equipment. It has 240 imperial gallons of drinking water. Deck equipment includes a derrick.

This boat could be very useful for adventurous voyagers who need to earn a living as they go. It is capable of carrying heavy loads and has plenty of deck and hold space. Its excellent fuel economy makes long-range operation both economic and practical. Its seaworthiness, ruggedness and the fact that this hull form dries out nearly upright indicate a good performer in a hard-service environment. 

Traditional design

Independence 48 from the quarter

Although this is an original design, the parent hull form was developed for shrimp trawling on the east coast of the United States in the 1920s. This type of hull, constructed in wood or steel, has been built in various sizes ranging from about 25 feet up to about 100 feet, and it is a testament to the type’s utility that it is still in use today.

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