What is it?

The Deltaform configuration was developed on the premise that a vessel supported by three hulls configured according to three fundamental principals described below, will have a significantly smoother and more seakindly motion than a conventional monohull, catamaran or trimaran.

The three principles or design elements are;

1. The hull are arranged so their centres of buoyancy are in a formation close to that of an equilateral triangle.

2. The hulls have relatively vertical sides to minimise vertical accelerations from wave action.

3. The hulls be equal or nearly equal in displacement and depth.

 

We refer to the combination of these elements as DeltaForm and as the project has progressed other technologies that complement Deltaform, such as hydrofoils and wave cancellation have been developed in parallel. These are discussed on separate pages.

 

A Traditional Fishing boat in Northern Sumatra
A Traditional Fishing boat in Northern Sumatra

What’s the problem?

 

Ever since man learned to build boats and traverse the earths rivers and oceans boats have evolved in a wide variety of forms particular to various tribes, countries and cultures. Often these forms are very different with very little cross fertilisation in form and construction technology, even where these tribes or cultures live virtually side by side with similar resources at hand and operating in very similar sea conditions. 

 

The outrigger canoes that populated the western Pacific, Melanesia, Polynesia and eventually New Zealand and Easter Island share an ancestry with the  gracious trimarans of the Philippines and the ancient catamarans of Tamil Nadu. And yet in many neighbouring regions of Asia including  Vietnam, Myanmar, Cambodia and Thailand, these craft are virtually unknown. Each has a style of fishing and work boat unique to that country, a style which has remained virtually unchanged for centuries, and even adopting the combustion engine without a change of hull form.

 

It would seem that in many parts of the world the evolution of marine transport has borrowed as much or more from tradition and sticky logic as it has from research and original thinking.

 

A traditional Thai long tail with modern sailing cats in the background. Doug Fuller photo
A traditional Thai long tail with modern sailing cats in the background. Doug Fuller photo

The west has been generally more proactive than developing countries in seeking out new technologies and experimenting with exotic hull forms including hydrofoils, wave piercing hulls, stealth hulls and many other forms.  

However many in the west vehemently resisted the introduction of catamaran and trimaran hull forms for modern sailing boats and motor boats, both commercial and recreational. The arguments were often highly emotional and in many cases quite irrational. Resistance still persists in some quarters.

Are we thinking clearly about the ideal forms for travel at sea? 

 

Traditional outrigger canoe from the Phillipines

 

Conventional motor trimarans employ a main hull that is significantly larger than the floats and the main hull carries most of the displacement at rest. Because the floats are only slightly immersed at rest the craft reacts rapidly to wave action, especially transverse waves, as it is affected by the change in buoyancy distribution. This can create an unpleasant jerky motion is some sea states as one hull rises and then the other hull rapidly cancels the roll action as the reserve buoyancy kicks in.

 

Also because the effective buoyancy of the floats is relatively small and located close the centre of the main hull in the fore and aft plane, the floats provide little damping of pitch motion.

 

Likewise, most power catamarans have a hull shape similar to that of a sailing catamaran. That is, a semicircular or rounded rectangle mid ships section with a rather flat underbody in the aft sections. Sometimes this is combined with a canoe body or keel which terminates forward of the transom; a hull form popularised by Malcolm Tennant in the 1970’s and eighties and still widely used.

 

The problem with this form is that the flat stern sections are located just below the waterline or even on the waterline and in waves, particularly at high speeds, the wave action acting on the flat underbody at the stern can induce a rather violent and unpleasant motion. This motion can be significantly more noticeable on a power cat than a sailing cat because there is no rig pressure to keep the leeward hull pressed in the water and the vessel is free to move with the waves.

And just as important, in the case of the catamaran there is no longitudinal separation of the centres of buoyancy.

 

US Navy Littoral combat ship with trimaran hull configuration
US Navy Littoral combat ship with trimaran hull configuration

The need for research vessels, oil rig supply vessels, some military vessels and other work boats to provide a steady platform in waves has lead to a great deal of research and development in recent decades and one of these avenues is the development of the SWATH, or small wetted area twin hull. The SWATH minimises motion at sea by placing most of the buoyancy under the water on twin submerged torpedo like hulls. The working decks are supported on struts that have very little buoyancy and so do not react violently to the action of the waves on the surface.

 

There is little doubt that SWATHS have a much steadier motion in moderate and high seas, particularly in the larger size range. They are able to maintain course and speed in adverse conditions that would otherwise limit the passage of a convention monohull or catamaran.

 

However SWATHS do have some noted disadvantages and have not been widely adopted in pleasure vessels or even broadly adopted for use in commercial vessels, despite being extensively researched and tested since the 1960’s and 70’s.

SWATHS have considerably more draft than a conventional catamaran or monohull and this limits their operation in shallow waters. They don’t seem to be too effective at damping motion in the smaller size range (less than about 60’ to 70’). They have a complex and rather cumbersome drive train. They have very little reserve buoyancy and this makes them weight sensitive and  limits their load carrying ability.

Also they are rather ungainly, not all that practical as a pleasure boat, and not very easy or economical to build and maintain. 

 

There is a wealth of research papers on SWATHS available. Most are of a highly technical nature and are full of graphs, theories and mathematical formulas. There’s very little discussion of the human experience of SWATHS and where there is it is usually compared with monohulls and not with catamarans.

Birds and Aircraft use a delta wing formation to achieve equilibrium and maintain stability in flight. A delta shaped configuration of buoyancy distribution can also help seagoing vessels maintain equilibrium without reacting violently to changes in the sea

The DeltaForm project explores efficient hull forms that distribute the buoyancy in a triangular or delta formation designed to minimise pitching and roll to create a smoother and more sea kindly motion in a broad range of conditions.

 

The DeltaForm does this in three ways.

Firstly and primarily by using three hulls of similar displacement arranged in a delta formation with the centres of buoyancy of the hulls positioned to create a stable platform to keep the boat as level as possible in a range of sea states. 

 

Secondly the vertical or near vertical hull sides minimise rolling and pitching action induced by a flared or tapered hull form as the craft encounters waves. Their is no horizontal or broadly angled surface near the interface to induce rapid accelerations.

 

Thirdly by using hulls that are all immersed to a similar level at rest thereby avoiding the rapid jerky movements experienced in a conventional trimaran as the floats roll and pitch in response to the sudden change in buoyancy distribution.

 

 

Monohull yachts have a singular centre of buoyancy and are free to rotate in pitch and roll, limited only by the beam of the hull (roll), asymmetry in the waterplanes (pitch), and the flare in the topsides which can help to dampen the pitching.

 

A catamaran employs two widely spaced centres of buoyancy to limit roll without requiring an exceptionally wide hull that would create significant drag. Pitch resistance is subject to the same forces as the monohull.

 

Conventional trimaran motor yachts may have some longitudinal separation in the centres of buoyancy, but usually not enough to provide any noticeable resistance to pitching and the centre hull usually carries the majority of the displacement.

 

 

The Deltaform configuration separates the centres of buoyancy by similar length and width thereby providing a more stable platform in a range of sea states without creating excessive drag.

The Advantages of Deltaform

The primary goal of the Deltaform concept is to utilise efficient hull forms that distribute the buoyancy in a triangular or delta formation designed to minimise pitching and roll to create a smoother and more sea kindly motion in a broad range of conditions.

The vertical or near vertical hull sides minimise rolling and pitching action induced by a flared or tapered hull form as the craft encounters waves. There is no horizontal or near horizontal surface near the interface to induce rapid accelerations.

By using hulls that are all immersed to a similar level at rest. This significantly reduces the rapid jerky movements as experienced in a conventional trimaran as the floats encounter waves and the boat rolls and pitches in response to the sudden change in buoyancy distribution.

 

However the DeltaForm hull configuration also has a number of secondary benefits.

 

1. Minimal wave resistance and easily driven. The DeltaForm hull configuration allows us to use fine hulls because the buoyancy is evenly distributed across three hull at rest providing good wave penetration. The finer hulls are more easily driven and therefore provide better performance and greater range under power.

 

2. Variable displacement without affecting hull shape. The parallel or near parallel hull sides permit the vessel to rise and fall as displacement changes without affecting the hull shapes. Only the bridge clearance changes.

 

3. Fast and economical to build. The very simple hull shapes can be manufactured and assembled economically from preformed sheets in composite, alloy, or plywood. Some of the designs we have deveped can be built entirely from flat panels.

 

4. Simple and efficient engine installation. Deltaform boats can be fitted with outboard motors or inboard engines in the hulls with a horizontal drive shaft exiting the hull at the transom. The Deltaform is easily adapted to electrical or hybrid pwer systems, inboard or outboard.

 

 

5. Easily adaptable to a variety of performance requirements. For low speed operation (up to about 14 knots) the Deltaform is easily driven and and highly fuel efficient. For high speed operation the Deltaform is readily adapeted to hydrofoils with several possible mounting configurations which include the ability to fully retract the foils at displacement speeds, a feature not easily achievable on most conventional motor yachts.