Minimus II

(Updated 12-15-2018)

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


Since our 2017 sailing voyage to the South Pacific in Minimus, the voyaging bug is still biting.  Almost a year to the day that we parted with Minimus, our Cape Dory 25, in French Polynesia, we began construction on our next boat, a small voyaging catamaran. 

 

 

 

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. We wanted our next boat to be:

--offshore capable
--as small as possible for two crew and their provisions for 4-6 weeks at sea
--unsinkable
--quick and economical to build of plywood and epoxy using "instant boat" techniques
--junk rigged

The craft that has evolved from this process we're calling Minimus II. We enjoy experimenting and in terms of her design, construction materials and rig, Minimus II is no exception.

She's an open deck design, 23' 9" long with a 13' 4" beam, which is about as small as one can go in an ocean-crossing multihull with enough weight-carrying capacity for a crew of two. Her carrying capacity is around 1200 pounds, which is what we figure for ourselves, gear and provisions for 4 to 6 weeks at sea.

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. Side panels are bent around bulkheads to form the basic shape of each hull. The bottom is then attached, bottom paint applied and the hull is turned right-side up to finish the decks and cabin. Just over two weeks into the build, the first hull is almost ready for bottom paint. The project is now on hold for the winter until the weather warms up enough to resume epoxy work in the spring. We expect to finish construction and do extensive sea trials next summer on the Oregon coast.

If sea trails are successful, we'll begin to think about another Pacific voyage.

Below is an explanation of the reasoning behind Minimus II and a description of her.

First though, a few words about our preference for small boats. I’ve always been attracted to the challenge of sailing small boats across vast expanses of watery wilderness. On the voyage of Minimus Pearl and I found that it’s something we share and that we do well together. We both loved the more intimate experience a small boat provides. We’ll never forget for example, the many nights in mid-ocean that we leaned over the edge of the cockpit with flashlights to behold myriad dazzling life forms just two feet away. Later, when we shared our observations with sailors on bigger boats, they weren’t even aware of this incredible spectacle.

Another reason we find small boats appealing is that our preference is not for a long-term cruising lifestyle but instead for an intensive experience measured in months rather than years, followed by a return to home life. The size and expense of a boat increase roughly as to the cube of its length, so by going with a small boat 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 (say under 25'), multihulls don’t typically come to mind, yet my personal experience confirms that they have several advantages over monohulls.  I should note here that my references to monohulls are only to those with iron or lead ballasted keels, rather than form-stable designs. 

I’ve sailed a 14’ monohull from Seattle to Alaska, a 23’ Wharram designed catamaran from Mexico to Hawaii, a 20’ monohull from Seattle to southern Mexico and most recently, a 25’ monohull (Minimus) from California to Tahiti. The catamaran was the best sea boat in my opinion. It was, true to the reputation of multihulls, a somewhat faster boat than any of the others, but of the various attributes of multihulls, I value speed the least. Based on 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 with a well prepared crew. Nonetheless, it’s prudent to think about potential dangers 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 is exceedingly unlikely in a cruising multihull with a modest rig and a crew accustomed to the practice of lying to a drogue in heavy weather.

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 later wrote that although they wouldn’t want to repeat that experience, if it did happen again, that’s the boat they’d want to do it in.

That leaves sinking. As an aside to the story above, a 31' monohull 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 continues 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’ monohull that had recently hit a container and sunk near Tahiti. Listening to the crew describe the “glug, glug, glug” sound the vessel made as she sank 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 life raft 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.

The comfort difference between a multihull and a monohull is also significant and is not only related to the lack of heeling. Multihulls, and catamarans in particular, don't roll.  Immunity to rolling in ocean swell 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 father and son crew made the same voyage at about the same time in a 26’ Folkboat. When we compared passage notes in Hawaii afterward, they reported feeling continually fatigued by the constant rolling motion while running downwind for weeks in the trades. 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’ long, suitable for offshore voyaging is a short one and the subset of multihulls within that list is even shorter. Several 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, it will of course have two hulls, hence Minimus II.

Experienced multihull designers will no doubt question several aspects of the design, including the hard chine hull form, the ‘instant boat’ type construction and of course the unusual rig.

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, our priorities are seaworthiness, comfort, ease of handling and a relatively quick, economical build.

The dory shaped hulls we’re using in Minimus II are probably the easiest multihull form to build. It’s also a seaworthy hull form in having ample reserve buoyancy and good load-carrying ability. The V-shaped sides help to deflect water, making the boat drier than vertical sided hulls. Should a collision occur at sea, her 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 hull form of Minimus II makes concessions to 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 we’re 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.

Her flat bottoms have the potential for slamming when going to windward, though as noted above, time spent to windward will be minimal given the intended purpose of the design. It’s also mitigated by the bottoms being narrow and relatively thick (1/2").

One night while sailing to Hawaii many years ago, my catamaran was hit hard by something. I thought she’d collided with a whale, a log or some other immovable flotsam. Daylight the next morning revealed a large U-shaped row of teeth marks just below the waterline on one of the hulls. Clearly the boat had been attacked by a sizable shark in the darkness. The hulls were constructed of 1/4” plywood and fortunately the bite occurred right at a frame member. Had it been a foot to either side, the shark would almost certainly 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 is being constructed of 1/2” plywood, which is thicker than usual for this size multihull. 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. By bending side panels around bulkheads, each hull takes shape quickly and is also self-aligning. Since the side panels are the full length of the boat, there’s no doubt a practical upper limit to the size of boat this technique can be used for, but for Minimus II two people can easily handle it. Regarding workmanship, it should be noted that quick doesn't mean sloppy. This being the 5th boat I've built, I know well the importance of careful work and attention to detail.

Also in the interest of facilitating construction, all the plywood used is double-sided MDO (medium density overlay). This should not be confused with MDF (medium density fiberboard) which has no place in a boat. MDO is plywood covered with a resin impregnated fiber overlay on either one or both outside faces. It’s also known as sign board and is used for outdoor signs and other weather-exposed applications. Unlike most plywood, MDO doesn't require an additional layer of fiberglass to prevent surface checking. Instead, hulls, deck and cabin tops will simply be covered with 3 coats of epoxy and painted. Only the portion of each hull below the waterline will be fiberglassed for extra abrasion resistance should we want to beach the boat.

I’ve tested numerous 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 fiber overlay, so concerns about the overlay separating from the plywood appear to be allayed.

To further simplify construction, no scarfing of either plywood or lumber is required anywhere in the construction. 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 anywhere in the boat.

Good lumber is increasingly hard to find and expensive when it can be found. The wood required is almost entirely 1” x 2” and 2" x 2" lumber. Decking between the hulls will be either 1”x 6” unfinished cedar boards or 1’ wide planks of 1/2” MDO plywood. We've been able to find all the wood needed quite economically by carefully selecting pieces at local lumber yards and building supply centers.

For a variety of reasons, 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. I used to be a sailmaker and could easily enough make more complex airfoil shaped sails, but part of the object of this design is simplicity.

What makes the rig radical though isn’t that it’s junk rigged, but that it's 4-masted, with 2 free standing masts in each hull. This is of course experimental, but we hope will have several advantages. First, it will likely be self steering. Testing we've done on a 1/12 scale sailing model shows that on downwind or broad reaching courses with the mainsails winged out on opposite sides, the rig is aerodynamically stable and unerringly self correcting.  That is, it sails like it's on rails.

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 as a large windvane to provide self steering. The leeward mizzen will then be used to help balance the rig.

Since the sail area is spread between 4 masts, the load on each mast is minimized and the center of effort in each sail is very low. This has the advantage of allowing the use of relatively inexpensive free standing masts. We'll be experimenting with heavy wall 4” diameter aluminum irrigation pipes. These are available economically in parts of the country where irrigated agriculture is common. A free standing rig will also eliminate the need for expensive metal components such as standing rigging, chainplates, turnbuckles, etc.

Although such a rig won’t go to windward in company with modern rigs, windward ability isn’t a priority for this design.  Any voyages we'd be likely to undertake would be mostly in the trade winds where the vast majority of sailing is on beam reaches, broad reaches or downwind. 

A feature not shown in the sketches at the top of this page is a removable dagger board that will be slotted between the center two deck boards and secured against lateral movement by ropes on each side.  Like any surface-piercing foil, it will be subject to cavitation, but that should be acceptable since its primary function is providing a pivot point to facilitate steering in tight quarters, rather than leeway prevention.  We wouldn't expect to use it much while voyaging. 

Designing and beginning to build Minimus II has been most enjoyable. It’s especially the experimental aspects that engage my mind and make us both excited for sea trials. The nature of experimentation is such that some ideas may work as well or better than expected, and others not as well as we hope. Regardless of what we discover, the process will have been rewarding. We look forward to reporting after sea trials next summer.