On the Right Lines


Lateral is a company founded on the practice of naval architecture. Our experience in this field comes from skills, knowledge and insight acquired by our staff over 34 years in the business, from the highest level of management right through to our most recent graduate employees.

In the past, the question of whether a yacht hull was ‘optimised’ was dependent on many factors; the yard, client, cost, schedule. These days Lateral believe that every hull form should be optimised in order to ensure that a yacht will perform to its maximum potential and efficiency. This feature will detail a few of the techniques we use in developing our hullforms to offer unrivalled hydrodynamic performance and efficiency.

As naval architects we are faced with the challenge of producing hydrodynamically efficient hullforms offering sufficient displacement within the given dimensional constraints, whilst maintaining favourable shape coefficients and fair hull lines, that must also achieve the required speed, stability and seakeeping characteristics. To achieve these goals the naval architects at Lateral choose to adopt a methodical approach in developing a hullform, and use optimisation techniques predominantly based on experience, married with an appropriate level of computational analysis through a formal optimisation methodology.

Our hull design process begins with two critical parameters; length and speed. These define the Froude Number which gives an indication of the basic hull type, where to set our goals and how challenging they will be to achieve. Often the speed is not fixed and there will be a number of speeds to optimise against. This is particularly true in motor yacht design where long range cruise speed and maximum sprint speed are often equally important. A principal design speed is generally selected after careful consideration of the vessel’s operating profile, propulsion system concept and close discussions with the Owner’s Team.

The next step is to undertake an assessment of the yacht’s overall design concept. Is the vessel a slender, low volume design or a beamy, high displacement motor yacht? These factors have a critical influence on the direction that we follow, as a yachts displacement in relation to its length is the most influential parameter on resistance. Additionally, there may be special requirements for seakeeping performance which will influence our choice of hull and optimisation process.

At this point we set target values for the optimisation of key form coefficients and parameters including block, prismatic and maximum sectional area coefficients, longitudinal centre of buoyancy and flotation, wetted surface area and immersed transom area. If a bulbous bow is to be used the basic parameters are set down; bulb type, centreline profile shape, sectional area and immersion. Additionally, the effects of appendage and propulsion system integration are considered including propeller diameter, tip clearance and rudder configuration amongst others.

Following these main decisions, a candidate parent hullform is identified; starting from a known and quantified baseline is considered a critical step. Lateral is part of the BMT Group, with its origins in the National Physics Laboratory (NPL) and the British Ship Research Association (BSRA). BMT’s in-house archive of model test data is extensive and spans 65 years of work.

For hullforms requiring more novel solutions we may start from a completely blank sheet of paper, perhaps firstly undertaking a parametric study to investigate optimum dimensions and hull type.

Once the main parameters are set, the next step in our process involves optimisation of the sectional area curve. This is an exercise which is often forgotten but achieving the correct area profile is critical in achieving a set of hull lines which combine the desired characteristics with efficient hydrodynamic performance.

At this stage we must also consider any practical constraints which may limit our ability to achieve the desired sectional area shape, such as stability, integration of the selected propulsion system, stabilisation devices or items within the GA that can impact the hull shape. In the interest of efficient hydrodynamics prevailing, we generally try to manipulate the yacht’s layout such that these do not constrain the hull design adversely.

With the above tasks completed we now have a set of lines optimised to the main parameters. The next step in our process involves more refined consideration of section shapes, waterline shapes and buttocks. Generally, by this stage we will have a clear idea of the mix of characteristics we are looking to incorporate; partial propeller tunnels, return in stern buttocks, trim wedges and forward waterline curvature are all parameters which we optimise at this time. Computational Fluid Dynamics (CFD) is used to make local refinements including improving the pressure wave making characteristics of the hull, and positioning/alignment of appendages such that they follow the hull flow patterns. Taking such an approach in conjunction with final verification by physical model testing, has produced very good results.

As a company, Lateral has a reputation for the development not just of conventional yachts but also those with more novel and specialised hull forms. With experience of SWATHs, semi-SWATHS, catamarans, trimarans, high speed and ultra light weight yachts we have design experience developed specifically to meet a wide range of demanding operating requirements.

Whichever set of requirements we are optimising for, Lateral strongly believe that the emphasis of efficient hullform development and optimisation be focused on the fundamental aspects - get these right and the gains in efficiency can be significant.

Alex Meredith Hardy

Back to the Whitepaper