# Tunnel hull (tunnel catamaran)

> How does a tunnel hull use air to 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/tunnel-hull-catamaran/ · JSON: https://xemstudio.com/api/geometry?object=tunnel-hull-catamaran · Plain text: https://xemstudio.com/objects/tunnel-hull-catamaran/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 tunnel hull has two sponsons joined by a deck whose underside forms a tunnel. The deck and tunnel roof act as a wing in ground effect with the sponsons as endplates, so some of the boat's weight is carried by air (Powerboat & RIB / AeroMarine Research).
- Air lift is cheap: every pound carried by air lets the planing surfaces shrink, cutting water drag. Some tunnel hulls make 30-50% of their lift aerodynamically.
- A lower tunnel improves lift-to-drag; a wider tunnel (higher aspect ratio) is more efficient.
- The file is a reference example built by Xem Studio from the numbers above (Reference RC mono: 585 mm length and 20 deg transom deadrise (SV Design Stealthwake data); 181 mm is an unlabelled width in the same source's deadrise diagram.). Sizes the sources do not fix are illustrative; scale the example to your own vehicle.

## Sizes

| parameter | value or range | source |
|---|---|---|
| Aero share of lift | 30-50% on some tunnel hulls | Powerboat & RIB |
| Sponson deadrise | about 10-15 deg | Powerboat & RIB |
| Typical vee-hull deadrise (comparison) | 18-22 deg | Powerboat & RIB |
| Worked example | 6% air lift cuts water drag ~9% at 50 mph | Powerboat & RIB |

## Where the files are

- Powerboat & RIB (Jim Russell, AeroMarine Research): [High flyers: aerodynamic lift on tunnel hulls](https://powerboatandrib.com/tuition/high-flyers) — web — Publisher's page; dimensions are facts

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

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

- tunnel-hull-catamaran-hull: [STEP](https://xemstudio.com/files/hardware/tunnel-hull-catamaran/tunnel-hull-catamaran-hull.step) · [STL](https://xemstudio.com/files/hardware/tunnel-hull-catamaran/tunnel-hull-catamaran-hull.stl) — Tunnel catamaran: two 12° sponsons, tunnel between, 585 × 181 mm (sections illustrative)

## Questions

**Is lower tunnel better?**

A lower tunnel improves lift-to-drag (AeroMarine Research).

## 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/)
- [Three-point hydroplane](https://xemstudio.com/objects/three-point-hydroplane/)
- [Stepped hull](https://xemstudio.com/objects/stepped-hull/)