# Stepped hull

> How does a stepped hull make a boat 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/stepped-hull/ · JSON: https://xemstudio.com/api/geometry?object=stepped-hull · Plain text: https://xemstudio.com/objects/stepped-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

- Steps break the planing bottom into several high-pressure leading edges, reducing wetted area and friction drag. Each step must be ventilated, or the step face stays wet and drag rises (BoatTest).
- Steps can add roughly 8-12% performance but are not worthwhile at low planing speeds, about 35 knots for a 30 ft boat. Poor designs can hook in turns (BoatTest).
- Twin steps tolerate CG variation better than a single step (BoatTest).
- Used on: White Iveco (Fabio Buzzi, 1984).
- 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 |
|---|---|---|
| Performance gain | roughly 8-12% | BoatTest |
| Worthwhile above (30 ft boat) | about 35 knots | BoatTest |
| Early hydro step | 75 mm step, 2/3 aft | Wikipedia (Hydroplane) |

## Where the files are

- BoatTest: [Watch your step (stepped hulls)](https://boattest.com/article/watch-your-step) — web — Publisher's page; dimensions are facts
- Wikipedia: [Hydroplane (boat)](https://en.wikipedia.org/wiki/Hydroplane_(boat)) — web — Publisher's page; dimensions are facts

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

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

- stepped-hull-hull: [STEP](https://xemstudio.com/files/hardware/stepped-hull/stepped-hull-hull.step) · [STL](https://xemstudio.com/files/hardware/stepped-hull/stepped-hull-hull.stl) — stepped hull, 585 × 181 mm, deadrise 22°, 2 steps (sections illustrative, scale to your boat)

## Questions

**Why must steps breathe?**

Without air the step face creates suction and drag rises sharply (BoatTest).

## 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/)