Minimus II

(Updated 10-13-2018)

-- Building Minimus II
-- Minimus II model self steering

Since our 2017 sailing voyage to the South Pacific in Minimus, the sailing bug is still biting.  Almost a year to the day that we parted with Minimus in French Polynesia, we began construction on our next boat, a small voyaging catamaran called 'Minimus II'. 




During the past year, we've spent many a pleasant hour thinking about, designing and building models of what we'd like our next boat to be.  Throughout the process, our design criteria have been simple.  They include:

--offshore capable
--as small as possible for two crew and their provisions for 6 weeks at sea
--positive flotation
--quick to build of plywood and epoxy construction using "instant boat" techniques
--junk rigged

Minimus II meets these criteria.  She has a carrying capacity of around 1200 pounds, which is what we figure for ourselves, personal gear, ground tackle, dinghy and food and water for 6 weeks at sea. 

She's 23' 9" long with a 13' 4" beam.  Her hulls are dory style with narrow flat bottoms and V-shaped sides.  The rig will be unusual, with 4 masts, two mounted in each hull.  More below about the advantages we hope such a rig will have. 

The construction isn't of course 'instant', but it's close.  As of this writing, we're just two weeks into the build and the first hull is almost ready for bottom paint.  For more information on the building process, see the link at the top of this page.  Unfortunately we'll soon have to put the project on hold as we leave Oregon and head south to Arizona for the winter.  When we return to Oregon next spring, we expect to finish construction and launch in the summer of 2019.  

Following extensive testing on the Oregon coast next summer, we'll begin to think about another Pacific voyage. 

Below is an explanation of our reasoning for designing Minimus II and a description of her.

First though, a few words about our preference for small boats.  We find sailing small boats across vast expanses of watery wilderness to be a challenge, and one that we do well together.  We also like the more intimate experience a small boat provides.  As we noted in our write up on the original Minimus, the much reduced time and expense of acquiring and outfitting a small boat is also appealing.  Our preference is not for a long-term cruising lifestyle but instead an intensive experience measured in months rather than years, followed by a return to home life.  The size and expense of a boat increase as to the cube of its length, so a small boat means that we can do such an activity for a small fraction of the cost usually associated with offshore sailing.  

When one thinks of sailing offshore in small boats, multihulls don’t typically come to mind, yet my personal experience confirms that they have several advantages over monohulls for offshore sailing. My reasoning is based on experience gained during voyages in a wide variety of small boats. Those include sailing a 14’ (4.3m) monohull from Seattle to Alaska, a 23’ (7m) Wharram designed catamaran from Mexico to Hawaii, a 20’ (6.1m) monohull from Seattle to southern Mexico and more recently, a 25’ (7.6m) monohull from California to Tahiti.

Voyaging in such diverse craft has given me a fairly broad range of experience with small boats offshore.  Of the boats listed above, the catamaran was the best sea boat in my opinion, for reasons I’ll explain below. Interestingly, of all the attributes of multihulls, I value speed the least. In my experience, the most notable features are their safety and comfort at sea.

Regarding safety, it should be noted that catastrophe at sea is unusual for a well found boat and well prepared crew. It’s nonetheless prudent to think about what the potential dangers are and how to mitigate them. Most sailors would no doubt agree that at the top of the list are sinking, capsize, fire, losing someone overboard or being run down by a large commercial vessel.

The advent of AIS has made the latter relatively unlikely. The threat of fire or losing someone overboard applies regardless of vessel size or type. As for falling overboard, Pearl and I have an iron-clad rule that when we're outside the cabin, we're always tethered to the boat.  Capsize in a properly designed cruising multihull is exceedingly unlikely, as shown by the extensive safety record of offshore cruising multihulls with conservative rigs.

In the early 1970's, my friend and boat-building mentor, Thomas Firth Jones and his wife Carol survived an Atlantic hurricane between Bermuda and the mainland in their 23' Wharram designed Hinemoa catamaran.  Tom wrote later that if they ever had to repeat the experience, that's the boat they'd want to do it in.  It's the experience they wouldn't want to repeat. 

That leaves sinking.  As an aside to the story above, a 31' monohull sailing near Tom and Carol's position sank in the same hurricane. While sinking is unlikely, it's nonetheless a growing concern as the number of floating containers at sea continue to increase. Not only was it the subject of a Hollywood movie, but on our last voyage we met the boatless crew of a 45’ (13.7m) monohull that had recently hit a container and sunk near Tahiti. Listening to the “glug, glug, glug” sound the crew made in describing the vessel’s last minutes before sinking was enough to send chills down the spine of any sailor.

My catamaran was the only boat I’ve had that would remain floating if holed. She was built of wood and also had watertight bulkheads.

A craft that will not sink also highlights another benefit. The record shows again and again that in the unlikely event of a catastrophe at sea, abandoning the mother ship for the dubious shelter of a liferaft is seldom a good idea unless the boat actually sinks. A multihull built with a lighter-than-water material like wood won’t sink and thus offers an alternative to the expense and weight of a life raft.  Given the low rig and my practice of lying to a drogue in heavy weather, capsize is exceedingly unlikely.  Just to cover all bases though, we plan to have a sturdy fabric tarp that can be tightly stretched between the hulls as a survival platform.

Aside from safety, the comfort difference between a multihull and a monohull is significant.  I should note here that my references to monohulls are to those with iron or lead ballast, rather than form-stable designs. 

The greater comfort of a multihull is not only related to the lack of heeling. Multihulls, and catamarans in particular, don’t roll. Immunity to rolling is a much more significant comfort issue than is generally acknowledged.  When sailing downwind or waiting out a calm at sea, or anchored where there's exposure to swell, most ballasted monohulls roll in a way that exacerbates crew fatigue. Fatigue is the archenemy of short handed and single-handed sailors, as it can lead to bad decisions.

Decades ago, when I sailed my little Wharram catamaran from Mexico to Hawaii, a 26’ Folkboat with a father and son crew made the same voyage at about the same time. When we compared passage notes in Hawaii afterward, they reported feeling continually fatigued by the constant rolling motion while running downwind in the tradewinds. In contrast, and despite having a smaller boat and being single handed, I arrived comparatively well rested. On later voyages in monohulls, I discovered the discomforts they’d been experiencing.

Given my preference for multihulls, one might ask why most of my boats have been monohulls. That primarily has to do with accessibility. The list of small craft, say under 25’ (7.5m) long, suitable for offshore voyaging is a short one and the subset of multihulls within that list is even shorter. A few of the designs by James Wharram, Richard Woods and Thomas Firth Jones come to mind. The few multihulls that are available are typically expensive.  Minimus II is an attempt to address that issue.

First a few words about the name. The little monohull we sailed from California to French Polynesia in 2017 we named Minimus. The new boat will be the second one we've had together and being a catamaran will of course have two hulls, hence Minimus II.

Minimus II is a small, experimental ocean voyaging catamaran designed for a crew of one or two. The object of the design is twofold. One is to significantly reduce build time and expense through a combination of construction methods and materials unusual in multihull construction. The other is to experiment with a simple design and a radical rig.

Her attributes include seaworthiness, simplicity of build, economy and comfort at sea. She’s an open deck design, 23’ 9” (7.2m) long, with a beam of 13’ 4” (4.1m). She’s also about as small as one can go in an ocean-crossing multihull with enough weight-carrying capacity for two people and the necessary payload of food, water and equipment. As offshore capable multihulls go, Minimus II is unusual for its small size, its relatively quick construction and its radical rig.

Experienced multihull designers will no doubt question various aspects of the design, including the hard chine hull form, the ‘instant boat’ type construction and of course the unusual rig. I’ll address each of these issues below.

Most multihull designers focus on speed and windward ability, both of which are understandable attributes given the demands of their clientele. In a small voyaging boat however, neither windward ability nor ultimate speed are primary considerations. Few voyaging boats of any size sail extensively to windward. Instead, seaworthiness, comfort and a relatively quick, economical build are higher priorities.

Minimus II utilizes a dory type hull design with V-shaped sides and a relatively flat bottom. The dory type hull is probably the easiest multihull shape to build. It’s also a seaworthy hull form in terms of having ample reserve buoyancy and good load-carrying ability. In the event of a collision, the raked bows are more likely to ride up and over flotsam, rather than crushing the bows as would likely happen with the currently fashionable plumb bows seen on most multihulls. The V-shaped sides also help to deflect water, making the boat drier than vertical sided hulls.

The particular hull form of Minimus II makes concessions to ultimate speed in favor of simplified construction. Multihull designers will note that the hull shape will create eddies along the chine since the chine, when viewed in cross section, doesn’t bisect the angle between hull sides and bottom. This is a trade off I’m more than willing to make, given the simplified construction. Her hulls have a waterline length to waterline beam ratio of nearly 10 to 1, making excessive turbulence unlikely at normal cruising speeds.

A potential objection is slamming of the flat bottoms when going to windward.  This is mitigated by the relatively thick (1/2") bottoms which are also narrow.  As noted above, time spent to windward will be minimal given the intended purpose of the design.

The 1/2” (12mm) plywood used for the hulls, deck and bottom is thicker than usual for this size of multihull. This was dictated by both the building method and personal experience. One night while sailing to Hawaii many years ago, my catamaran was hit hard by something. I thought I’d collided with a whale, a log or some other immovable flotsam. Instead, daylight the next morning revealed a large U-shaped row of teeth marks below the waterline amidships, clearly showing that the boat had been attacked by a shark. The hulls were constructed of 1/4” (6mm) plywood and fortunately the bite occurred right at a frame member. Had it been a foot to either side, the shark would likely have gone right through the hull.

Thus I learned the perils of lightweight construction for offshore sailing. For that reason and to facilitate a quicker build, Minimus II will be constructed of 1/2” (12mm) plywood. Somewhat offsetting the additional weight will be a lack of stringers. Most plywood multihulls are built using a framework of bulkheads and stringers over which the plywood sides are then fastened. I built the Wharram catamaran that way and found it to be a slow, tedious process in which a building base has to be constructed and the various frames and stringers carefully aligned.   

Minimus II will instead be built in the 'instant boat' style pioneered by Dynamite Payson and others.  The hull takes shape quickly and is also self-aligning.  Pre-cut and assembled side panels are bent around bulkheads to form the basic shape of each hull.  The bottom is attached and the hull turned right-side up to finish the decks and cabin.  The second hull will no doubt be even quicker to build.  It should be noted that quick doesn't mean sloppy.  This being the 5th boat I've built, I know the importance of careful work.      

Also in the interest of facilitating construction, only the portion of each hull below the waterline will be covered with a layer of fiberglass.  This will give extra abrasion resistance for beaching the boat.  All the plywood we're using is double-sided MDO (medium density overlay) plywood.  This should not be confused with MDF (medium density fiberboard) which has no place in a boat.  Unlike most plywood, MDO doesn't require an additional layer of fiberglass to prevent surface checking.  Instead, it will be covered with 3 coats of epoxy and painted. 

MDO is plywood covered with a resin impregnated paper outer layer on either one or both outside faces. It’s made for concrete forms, outdoor signs and other weather-exposed applications. I’ve tested pieces of MDO by overlapping and gluing them with an epoxy and wood flour glue mix.  Stressed to the breaking point, the plywood joint invariably breaks within the wood layers, not at the paper to wood join, so concerns about the paper separating from the plywood appear to be allayed.  23 sheets of 1/2” (12mm) plywood are required for the hulls, decks, cabins rudders and leeboard, with 1 additional sheet of 3/4” (18mm) for the 3 cross beams.

To further simplify construction, no scarfing of either plywood or lumber will be required, except perhaps for the cross beams. The plywood panels making up the hull sides, bottom and decks are joined with butt blocks inside and biaxial tape outside.  No lumber longer than 8' is needed.

Good lumber is increasingly hard to find and expensive when it can be found. The wood required for this design will be almost entirely 1” x 2” (25mm x 50mm)  and 2" x 2" (50mm x 50mm) lumber.  We've been able to find all the wood needed quite economically by carefully selecting pieces at local building supply stores.   

Decking between the hulls will be either 1”x6” unfinished cedar boards or 1’ wide planks of 1/2” MDO plywood.

For ease of handling, Minimus II will be junk rigged.  The junk sail is the easiest type of sail to reef and handle, which makes it appealing for short handed crews.  It's also a relatively easy and economical type of sail to make, as it can be sewn from flat panels of cloth, without introducing curves or broadseams.

What makes the rig radical though is that it's 4 masted, with 2 free-standing masts in each hull.  This is of course experimental, but should have several advantages. First, it will likely be self steering.  Testing we've done on a 1/12 scale sailing model shows that with the mainsails winged out on opposite sides, the rig is aerodynamically stable and unerringly self-correcting on downwind and broad reaching courses, as can be seen at the video link above.   

While we haven't tested it yet, the rig should also allow self steering on other than downwind courses by feathering the windward mizzen into the wind and connecting it with double sheets and blocks to the tiller bar.  In this configuration, it will theoretically act like a large windvane to provide self steering.  The leeward mizzen will then be used to help balance the rig. 

Another advantage is that since the sail area is spread between 4 masts, the load on each mast is minimized and the center of effort is very low.  In keeping with the economy of build, this allows the use of relatively inexpensive free standing masts. We'll be experimenting with aluminum irrigation pipes having 4” (10.2cm) outside diameter x 0.072” (1.8mm) sidewall thickness.  These are available in parts of the country where irrigated agriculture is commonly done.  A free standing rig will of course eliminate the need for standing rigging, chainplates, turnbuckles, etc.

Such a rig likely won’t go to windward well and on some courses the windward sails will blanket the leeward sails. As explained above however, windward ability isn’t a priority for this design. The vast majority of the intended sailing will be on a beam reach, a broad reach or downwind. Downwind in light air, when maximum sail area is required, all 4 sails can be used for 298 square feet of sail area. 

As the building process continues, we'll be updating this page and the building page. 

I also hope to put up a page describing a couple small, form-stable, voyaging monohull designs I've been working on.  I'll put a link at the top of this page when it's posted.