Chum: A Free Plan for a 15 ft 6 in Jeep-Powered Runabout
William D. Jackson's hydroconic-bottom inboard runabout reaches 30+ mph with a marinized Jeep engine.
Chum is a proper inboard runabout with a gearhead twist. William D. Jackson drew it at 15 ft 6 in (4.7 m) with a 6 ft (1.8 m) beam and a convex hydroconic bottom. The plan suggests a marinized Jeep engine, such as the 60 hp Lehman Econ-o-Power, for 30-plus mph, though any light engine from 25 to 100 hp will do. Choose a single or double cockpit to suit how you boat.
Chum at a glance
| Detail | Chum |
|---|---|
| Type | Inboard runabout |
| Length | 15 ft 6 in (4.72 m) |
| Beam | 6 ft (1.83 m) |
| Construction | 3/8 in. marine plywood over white oak and spruce frame; convex (hydroconic) bottom; single or double cockpit |
| Power | Marinized Jeep engine (e.g. Lehman Econ-o-Power, 60 hp) for 30+ mph; any light 25–100 hp engine |
| Designer | William D. Jackson |
| First published | Boat Builder's Handbook, p. 40 |
| Craft Print | No. 36 |
| Plan sheets | 14 |
A runabout with real engineering
The hydroconic bottom uses developed convex surfaces that plywood can follow cleanly, giving a smooth planing shape without compound bends. Three-eighths marine plywood over a white oak and spruce frame makes a stout, traditional structure. Combining the two woods puts strength where it is needed and keeps weight down elsewhere.
The engine choice is wide, from 25 to 100 hp, so you can work with what you can find. Fourteen sheets show the detail you need for an inboard installation and either cockpit layout. Few runabout plans give this much latitude in choosing a power plant.
The original plan sheets
These are the 14 original sheets, scanned from the magazine (the first 12 are shown here). For building, use the full-size PDF in the download section below.
Who designed it
William D. Jackson drew Chum for the Boat Builder's Handbook, page 40, and it was issued as Craft Print No. 36. Few designers contributed as many home-build plans to the Science and Mechanics series as Jackson.
Before you build
- Pick your engine before building the engine bed so you can match mounts, shaft angle and weight to it.
- Plan bilge ventilation and fuel routing for the inboard from the start, as they are hard to retrofit.
- Decide on the single or double cockpit early, because it changes deck framing and seating.
Download the plan
All fourteen original Chum sheets in one file, covering hull, engine installation and both cockpit layouts.
Download the complete plan (PDF, 14 sheets, 12.3 MB)
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