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, semi-displacement and planing hull types
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