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A guide to superyacht hull design

In this guide to superyacht hull design, we break down the specs, must-know information and outline all of the pros and cons of the typical superyacht hull shapes.

Displacement yacht hull design

  • Fn: up to about 0.42
  • Average power requirement: 5hp/ton
  • Prismatic coefficient: 0.56 – 0.64
  • LCB: 0.50 – 0.54 (54 per cent back from waterline entry)
  • Can be optimised for resistance
  • Capable of doing hull speed
  • High displacement over length
  • Much more forgiving in terms of weight, where the impact on performance is minor
  • Less initial stability, but more dynamic stability, which equals more comfort
  • If you want more speed, you have to increase the length
  • Can carry more fuel, and use less, which equates to more range
  • Offers the most volume at common interior positions
  • Engine room smaller – less power:weight ratio
  • Increase stability by reducing weight (if the centre of gravity remains the same) – a heavy boat is not necessarily more stable
  • Interior materials do not need to be lightweight

Semi-displacement (semi-planing) yacht hull design

  • Fn: 0.6 – 1.1
  • Average power requirement: 10hp/ton – 40hp/ton
  • Prismatic coefficient: 0.63 – 0.68
  • LCB: 0.53 – 0.57 (more volume aft)
  • More buoyancy aft means can keep pushing more power, but this means increased resistance at lower speeds
  • Resistance heavily depends on the frictional component; reducing weight can minimise it
  • Flatter, lighter, sharper forebody – all more suitable for generating hydrodynamic force on the bottom
  • Higher initial stability
  • Larger transom beam means more broaching tendency in a following sea
  • Less flexibility in weight and weight position
  • Wider speed range, so lower speeds mean lower engine loading which is not optimal
  • There is an optimum size – going smaller and smaller makes semi-planing hull harder to achieve, and going larger and larger means the weight increases disproportionately…
  • Much superior seakeeping compared to planing boat
  • Can optimise for higher or lower speeds, but not both
  • Less volume in hull, especially forward part
  • Best of both worlds – lots of possibilities

Planing yacht hull design

  • Fn: 1.1 and above, preferably from 2 and up
  • Average power requirement: 60hp/ton plus
  • Prismatic coefficient: 0.68 – 0.76
  • LCB: 0.58 – 0.64
  • Typically monohedral prismatic aft shape – constant deadrise
  • Light displacement
  • Engine room forms a significant part of hull volume (up to 30-40 per cent)
  • Weight matters – power:weight ratio is critical
  • Usually very sharp entry angles, although Fn 1.2 to 2 favours LCG forward and blunt entry
  • Big beam and little weight mean extreme initial stability
  • Uncomfortable in certain sea conditions
  • Friction significant, so if left in the water for a couple of seasons speed will drop
  • Wavemaking coefficient very low, so frictional resistance is the dominant component
  • Lots of exotic hull shapes, designed to reduce wetted surface and improve comfort in a seaway
  • Little effective volume – foreship, nothing fits; aft ship all engines
  • Dynamic stability is a big factor, and can limit what is possible
  • Speed benefit, and can escape bad weather

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