The Bug-Out Boat

28 April 2020     Editor    38 Comments.

GALLERY | Click images to enlarge

As I am confined to quarters for the duration, pacing the perimeter of my isolation in endless circles, my imagination is drawn to devices of freedom and escape. Freedom of the seas is a perpetually compelling and romantic idea so here I present a Bug Out Boat for 2020.

The basic concept is millennia old: tie (or ‘catamaran’) a few logs together into a rudimentary raft, build a platform above with some shelter and a device to catch the wind, and get the hell away from here. I grant you that if you were really in such a predicament you could easily buy or steal any number of fiberglass sloops currently glutting the market as your getaway vehicle, but you need to give the blogger his due.

HULL DESIGN

BUG-OUT is designed for 4x8 sheets of plywood. The 8’ long bows and sterns are identical, the center section is 16’, for a total length of 32’, plus rudders. Each hull is built from 8 sheets of plywood, plus bulkheads.

The hulls (really the pontoons) are built 2’x2’ square in section - rotated 45° to create a diamond. The shape is as rudimentary as it gets: there is no rocker or graceful sheer - just a brutal 16 feet of ‘extruded’ plywood. I am tempted to call the style “Polynesian Neo-Brutalism”. Be that as it may, the simple shape hides a number of virtues besides the primary one: it can be constructed with little more than a T-square.

• There are no interior accommodations within the hulls, so they are simple and forgiving to build.
• The V’d diamond section provides a gentle and well-moderated ride in a seaway.
• One nice thing (for a designer) is you are not tempted to make the WL beam “just a bit more” in order to fit in more stuff. BUG OUTs hulls have a 13:1 finesse ratio, and will easily exceed hull speed.
• The hulls also have a high prismatic coefficient, which means they make a good sail carrying platform - not a lot of hobby-horsing in a seaway.
• They are also reasonably wave-piercing at speed, which is why the the crossbeams are elevated above on plywood struts.

Long-time Proafile collaborator James Shanahan (who is working on a proa version of BUG-OUT) has contributed the design of the bows. It is a simple developable surface that remains a consistent diamond section throughout. Yet it has a lovely “boaty” shape that should provide a clean entry and a nice wake.

The platform is constructed of 4 plywood box beams running athwartship, that are lashed to the hull struts. There are twin 2’x1’ section boxes spanning fore and aft across the beams, providing both dry storage and resistance to wracking. Duckboards fill in where needed to make a walking surface that is also permeable to air and water.

THE JUNK RIG

BUG-OUT sports an unconventional rig for a multihull: a Chinese lug, or junk. Specifically, this version is called a split junk rig, or SJR for short. Developed and documented by Slieve McGalliard on the Junk Rig Association site, the clever refinements shows a great deal of promise in overcoming the Achilles heel of the junk, namely, poor windward performance, or L/D ratio. Besides that, the rig offers all the usual junk virtues of bulletproof sturdiness, cheapness in construction and maintenance, and ease of reefing and furling for a small crew. The easy reefing is a big deal for a multihull. It’s nice to carry as much sail as you want, but no more. Most wind-caused capsizes result from not taking in that last reef. This particular SJR design is inspired by Dave Zieger’s Cat Ketch WAYWARD. It includes a crab-claw top panel, so how can I not resist?

Foils: the simple and sturdy skeg rudders are controlled by a linkage borrowed directly from Nathanael Herreshoff’s 1876 Centennial Regatta winning catamaran AMARYLLIS. The daggerboards are angled 45° to provide hydrofoil lift and to counteract heeling force, because that’s just the way I roll.

THE POD

At first I was going with a simple tent shelter on the bridge deck, however I just couldn’t stop. The current pod shelter design employs a V’d bottom shape to permit a lower bridge deck floor without slamming. This gains considerable extra volume and headroom.

Though limited to 8’ in length, the pod includes two outboard berths, comfortable seating for 4 at the dinette, a galley to port and a composting head to starboard, and plenty of stowage. I have included flip-up seat backs in the design in order to add 9” of width to the 24” wide berths when desired.

This pod is just one idea. The variety of pod design and construction is limited only by the imagination and requirements of the builder (oh… and physics).

And that, is basically that: a minimal yet capable cruising catamaran designed to be constructed for little expense in short order by the less skillful of craftsman.

SPECIFICATIONS

LOA: 32’-6”
LWL: 30’-3”
Beam: 18’-10”
Draft: 3’-9”
Draft board’s up: 2’-0”
Disp. Light: 2000 lb.
Disp. Heavy: 3800 lb.
Sail Area: 405 sq. ft.

NOTES

The general rule-of-thumb for free-standing junk masts is a minimum 12:1 bury in the hull. Because a cat is quite a bit stiffer than any mono-junk, 10:1 would be safer. The V-shaped underside of the pod permits an 8:1 bury for the 36’ free-standing mast.  A tabernacle is constructed just forward of the shelter, permitting the mast to be easily lowered. Alternately, The mast can be stepped on the second beam and supported by stays. This would be lighter, cheaper and more efficient (since the mast can be smaller in section than the free-standing variety) however you lose the junk rig’s wonderful 360° trimming ability.

The hydrofoil daggerboards are easily substituted by low-aspect-ratio keels.

Much thanks to James Shanahan, Robert Wise and Dave Zieger for their feedback and encouragement.

 New Designs  Catamarans  Rigs