Design and Construction
The 105 MC rides on hull shapes Smith introduced on the preceding 105M and describes as revolutionary in the multihull industry. Each hull carries a 9:1 length-to-beam ratio and a shallow, fattened teardrop cross-section that Smith likens to a racing monohull, a shape chosen to widen the beam without lengthening the waterline and to carry load without burying the bows. Asymmetric centerboards, built from fiberglass mat, Kevlar, and closed-cell foam, pivot upward and are raised from inside the saloon, enabling shallow-water anchoring without coming on deck.
Construction throughout is solid fiberglass — no coring in the hull itself. Decks and cabintop receive half-inch end-grain balsa only where there are no deck fittings. The lamination schedule uses vinylester resin over a 1.5-oz mat barrier followed by two layers of Cofab mat. The hull-deck joint is a shoebox fit bonded with a chemically cured poly putty that Smith preferred over 3M 5200 for its extended setup time and non-brittle cure, then fastened with stainless steel screws on five-inch centers and capped with a gunwale guard. The result is a serious and strong construction that underpins the model's reputation for longevity.
After a trans-Atlantic passage with his son revealed that production boats were running roughly a thousand pounds over design weight, Smith stripped weight from nonstructural areas — swapping heavier drawer boxes for bins, thinning some plywood panels, and lightening lamination where loads permitted. The goal was increased buoyancy and a more comfortable ride rather than outright speed gains.
Rig and Sailing Performance
The MC's rig represents the most significant step forward from the earlier 105M. The mast stands a foot taller and features a one-foot crane at the top. The mainsail grew from 260 to 340 square feet through a larger roach and full battens, and the headsail is a 350-square-foot furling 150% genoa. An optional screecher of 490 square feet tacks on a curved track spanning both bows and the anchor platform, allowing the tack point to travel athwartships and improving sheeting angles when working upwind; Smith claimed the sail could be driven to within 50 degrees of the apparent wind.
The mast is stepped on deck over the main bulkhead and braced by straight double spreaders, a split backstay with tensioner, and permanent checkstays angled 20 degrees aft. Halyards are internal and led to winches on the mast itself rather than rope clutches on the cabintop — a deliberate choice reflecting that moving forward on a stable platform is not treacherous.
In a test sail in 25-35 knot northeast winds with a reefed main and a flat 90% jib, the 105 MC logged 6.5 to 7 knots closed-hauled, then accelerated to between 7 and 12 knots when cracked off in 17-25 knots of breeze, with very little leeway. Steering was light and the boat was responsive to sudden course changes. The combination of hull and centerboard revisions reportedly required 25% less energy to achieve the same speed as the 3400 predecessor.
Deck Layout and Handling
The cockpit is the social and operational hub of the 105 MC. The sole was lowered slightly to achieve 6'7" of standing headroom beneath the canopy, and a large Lexan window spanning the deck gives the helmsman clear visibility forward. The wheel was moved outboard so the skipper can steer from the rail. Mainsail controls relocated to a thickened transom cap improve both control and crew comfort, and the stern was modified to accommodate swim ladders — small ergonomic details that reflect years of accumulated owner feedback.
Movement forward is straightforward: 14-inch-wide steps, recessed stainless steel handrails, and 10-inch-wide side decks allow safe progress to the foredeck in blustery conditions. A large sundeck forward of the mast provides comfortable lounging under sail, and unlike a lightweight racing cat, the 105 MC's performance is not meaningfully degraded by weight on the foredeck.
The cockpit canopy enclosure — either canvas or rigid panels — distinguishes the MC from the earlier 105M and is the most visible external update the suffix denotes. In bad weather it keeps crew dry, though it complicates mainsheet trim when fully zipped and can create a false sense of protection from the conditions outside.
Accommodations
Step through the companionway into a saloon that shares nothing with a comparable monohull. The 14-foot beam immediately registers as generous space, reinforced by 360-degree portlight visibility and four overhead Bowmar hatches. The centerpiece of the saloon is a C-shaped settee surrounding a solid teak dining table with fold-out leaves that seat six to eight; removed, the table converts to a double berth and the settee becomes a conversation pit.
The master stateroom sits forward on centerline and bridges both hulls, with the queen berth set on an island over open water and backlit by a port spanning the full width. Smoked glass slides aside to give the helmsman a view corridor aft. The head — forward to port — is described as big, bright, and well-ventilated, with a siphon arrangement that flushes fresh water through the toilet to suppress odors. Aft staterooms each offer a 28-by-28-inch dressing area, double berths, opening ports, and standard propane and fume alarms. Minimum headroom anywhere aboard exceeds six feet.
The galley expanded relative to earlier Gemini models by running countertops on both sides of the passageway and adding drawers and a built-in microwave cavity. Smith candidly described the 105 MC as a couple's boat — honest positioning for a design that has six to eight berths on paper but a single head, a constraint that limits overnight passages with large crews.
Known Issues and Limitations
The single most frequently cited structural concern is wire and hose access. Wiring looms are attached to the interior liner before the liner is bonded into the hull, making them virtually inaccessible after construction. Smith's defense — that the looms were engineered to be foolproof and that spare hoses were pre-run during build to ease retrofits — is only partially reassuring, since any wiring fault after the hull is closed requires either creative fishing or invasive surgery. Twelve-volt runs through PVC conduit reduce heat and chafe, and wires exit the mast into the forward stateroom through an accessible panel between deck and liner, which helps at the spar end.
The capsize screening formula returns 2.8 — above the 2.0 threshold commonly cited for blue-water confidence. This is a characteristic of the wide, light catamaran type rather than a flaw specific to the 105 MC, but it reinforces Smith's own characterization: this is a coastal or near-coastal cruiser, not a platform to push into sustained heavy offshore conditions. The comfort ratio of 11.4 reflects the boat's light displacement and rewards smooth-water use where the cat's speed and stability advantages are most pronounced.
Production eventually ended. Tony Smith retired and sold the company, and the new owners redesigned the boat for Caribbean charter use with deeper fixed keels, a product that did not sell well. The original outdrive leg and Westerbeke/Vire engine combination are no longer manufactured, which means that engine and outdrive service increasingly depends on independent marine mechanics willing to work with obsolete components.
Refits and Upgrades
The lifting outdrive is the highest-priority mechanical consideration for any prospective buyer. The ability to raise the leg clear of the water is integral to the Gemini's shoal-draft mission, but it also means the drive-leg seals, bellows, and mounting hardware must be inspected carefully. Sourcing factory parts is increasingly difficult; the most common solution is a full drivetrain conversion to a small outboard-powered pod or a custom diesel-saildrive arrangement adapted to the existing aperture.
The centerboards' Kevlar-and-foam construction has proven durable, but pivot pins and the lifting mechanisms inside the saloon should be inspected for wear and corrosion on any example that has spent time in tropical waters. Because the boards are raised from the saloon, the pivot hardware is accessible without hauling the boat, which makes routine inspection straightforward.
Electrical upgrades are best planned from the outside in. The inaccessible internal looms are a fixed constraint; the workaround is to treat them as permanent infrastructure and run any new circuits through the pre-installed spare conduit or via external surface runs where the liner allows access. Solar, lithium battery banks, and watermakers are commonly fitted and attach cleanly to the DC bus without disturbing the original looms. Cockpit canopy upgrades from canvas to rigid panels are a popular quality-of-life improvement that also improves windage management at anchor.
The Verdict
The Gemini 105 MC is a purpose-built American cruising cat that succeeds on the terms it sets for itself: maximum liveability in a 33-foot package, effortless shoal-water access, and a build quality that has proven itself over three decades of refinement. It will not compete with modern performance cats on speed or windward ability, and it is not designed to. What it offers a sailing couple is a stable, spacious, genuinely capable coastal cruiser that rewards careful passage-making and makes life aboard uncommonly comfortable.
Pros
- Centerboard twin-hull design gives draft as shallow as 18 inches with boards raised, opening anchorages unavailable to fixed-keel cruising cats
- Saloon, master stateroom, and galley proportioned for extended liveaboard use rather than charter head-counts
- Hull construction and hull-deck joint are robust; production quality was consistently above average for the class
- Fully battened, high-roach mainsail and optional screecher deliver strong performance for a cruising platform; 6.5-7 knots upwind in breeze is respectable
- Extensive owner community and documented refit history across a deep production run
Cons
- Internal wiring looms bonded behind the liner are effectively inaccessible; any fault requires significant interior disassembly or creative external re-routing
- Outdrive leg and original Westerbeke engine are out of production; engine-and-drive servicing depends on finding mechanics comfortable with obsolete components
- Single head is a genuine limitation for crews larger than two
- Capsize screening formula of 2.8 places it outside the conventional blue-water threshold; it is a coastal and near-coastal boat, not an offshore passage-maker
- No factory support, no new spares pipeline, and an ownership transfer that effectively ended the original design lineage
