Jump-N-Jack: A 1958 Runabout You Build Whole, Then Saw in Two
Berthel Madsen's 1958 Jump-N-Jack is a 9 ft 7 in plywood boat built in one piece and then sawn in two for easy carrying.
Jump-N-Jack has one of the cleverest tricks in small-boat design: you build it complete, then saw it in two. The result is a 9 ft 7 in (2.9 m) boat with a 3 ft 10 1/2 in (1.18 m) beam that breaks into two manageable halves. It takes two people, four in a pinch, and runs on oars or an outboard up to 5 1/2 hp. Berthel Madsen drew it in 1/4 in. exterior plywood with oak framing.
Jump-N-Jack at a glance
| Detail | Jump-N-Jack |
|---|---|
| Type | Take-apart runabout |
| Length | 9 ft 7 in (2.92 m) |
| Beam | 3 ft 10 1/2 in (1.18 m) |
| Capacity | 2 persons (4 in a pinch) |
| Construction | 1/4 in. exterior plywood with oak framing; built whole, then sawn in two |
| Power | Oars or outboard up to 5 1/2 hp |
| Designer | Berthel Madsen |
| First published | Boat Builder's Handbook, Volume 8, 1958, p. 113 |
| Craft Print | No. 192 |
| Plan sheets | 6 |
Why sawing it in half works
Building the hull whole means both halves share exactly the same lines and match perfectly when rejoined. Sawing it in two afterwards turns a 9 ft 7 in (2.9 m) boat into pieces that fit in a car or a small storage space. Oak framing gives the strength needed at the joint, while 1/4 in. exterior plywood keeps weight down. An outboard up to 5 1/2 hp or a pair of oars is plenty for a boat this size.
The original plan sheets
These are the 6 original sheets from 1958, scanned from the magazine. For building, use the full-size PDF in the download section below.
Who designed it
Berthel Madsen designed Jump-N-Jack for the Boat Builder's Handbook, Volume 8, 1958, page 113, where it appeared as Craft Print 192. The six sheets show the oak framing, plywood skin and the cut-and-join method.
Before you build
- Mark the saw line exactly as the plans show before cutting, since accuracy here decides how well the two halves mate.
- Keep any outboard at or below 5 1/2 hp and check the joint hardware every time you assemble the boat.
- Stick to two people for normal use and save the four-person load for flat, calm water.
Download the plan
The complete 1958 Jump-N-Jack plan in one file: six sheets ready to print or open on a tablet in the workshop.
Download the complete plan (PDF, 6 sheets, 4.7 MB)
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