# Displacement hull and hull speed

> What is hull speed and why can't displacement boats go faster?

- Category: Boat design › Hull types
- Kind: Standard part
- Basis: Design rules and figures from the cited sources; example geometry by Xem Studio
- Page: https://xemstudio.com/objects/displacement-hull/ · JSON: https://xemstudio.com/api/geometry?object=displacement-hull · Plain text: https://xemstudio.com/objects/displacement-hull/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); files Xem Studio Design License (free to use and sell from, not to redistribute as files: https://xemstudio.com/license/)
- Use in every chat: add https://xemstudio.com/mcp as a connector (https://xemstudio.com/use-with-ai/)

**Exact dimensions.** True size, with no printing tolerance added.

## Notes

- A displacement hull is supported by buoyancy. Its bow wave lengthens with speed, and when the wave length equals the waterline length the boat is trapped climbing its own wave, so speed is limited by length (Good Old Boat).
- Hull speed in knots is 1.34 x sqrt(waterline in feet); some designers use 1.4. Doubling length does not double speed.
- Used on: Most large monohull sailboats (Good Old Boat).
- The file is a reference example built by Xem Studio from the numbers above (Length = IOM hull length 1000 mm (onemetre.net); beam and deadrise illustrative.). Sizes the sources do not fix are illustrative; scale the example to your own vehicle.

## Sizes

| parameter | value or range | source |
|---|---|---|
| Hull speed | S (kn) = 1.34 x sqrt(LWL ft) | Good Old Boat |
| Alternative constant | 1.4 | Good Old Boat |
| 20 ft LWL | ~6.0 kn | Good Old Boat |
| 40 ft LWL | ~8.5 kn | Good Old Boat |
| IOM RC yacht hull length | 1000 mm | onemetre.net |

## Where the files are

- Good Old Boat: [Displacement hull speed 101](https://goodoldboat.com/displacement-hull-speed-101/) — web — Publisher's page; dimensions are facts
- onemetre.net: [The IOM class](https://onemetre.net/OtherTopics/IOMclass/IOM.htm) — web — Publisher's page; dimensions are facts

## Free STEP/STL (1 parts, Xem Studio Design License, Xem Studio)

Index: https://xemstudio.com/files/hardware/displacement-hull/index.json · license: https://xemstudio.com/files/hardware/displacement-hull/LICENSE.md

- displacement-hull-hull: [STEP](https://xemstudio.com/files/hardware/displacement-hull/displacement-hull-hull.step) · [STL](https://xemstudio.com/files/hardware/displacement-hull/displacement-hull-hull.stl) — displacement hull, 1000 × 181 mm, deadrise 0° (sections illustrative, scale to your boat)

## Questions

**Hull speed of a 1 m RC yacht?**

LWL ~3.28 ft gives 1.34 x 1.81 = ~2.4 kn (formula from Good Old Boat).

## Fits with

- [Deep-V hull](https://xemstudio.com/objects/deep-v-hull/)
- [Modified-V (semi-V) hull](https://xemstudio.com/objects/modified-v-hull/)
- [Flat-bottom hull](https://xemstudio.com/objects/flat-bottom-hull/)
- [Cathedral (tri-hull)](https://xemstudio.com/objects/cathedral-tri-hull/)
- [Tunnel hull (tunnel catamaran)](https://xemstudio.com/objects/tunnel-hull-catamaran/)
- [Three-point hydroplane](https://xemstudio.com/objects/three-point-hydroplane/)