"Margaritaville"

Construction Details of the 2006 Gemini 105MC

• Hull Construction: The Gemini 105MC’s hulls are hand-laid fiberglass with no core material (solid FRP construction) for strength and simplicity. Tony Smith deliberately avoided cored hulls, preferring the durability of solid fiberglass over the marginal weight savings of foam or balsa cores. Each hull is molded as one piece along with the bridgedeck (no bolted-on crossbeams), creating a rigid structure. A vinylester resin barrier coat is used to prevent osmotic blistering. The two hulls are joined to the deck via a “shoebox” flange joint: bonded with a strong, chemically cured polyether adhesive and through-bolted (stainless steel fasteners on ~4–5″ centers) with a PVC gunwale rubrail covering the seam. This results in a robust hull/deck connection. Each hull has a fine-entry bow and fairly flat bottom, drawing only ~18″ with boards up – ideal for gunkholing in shallow water.

• Deck and Interior Construction: The deck is fiberglass with balsa coring in horizontal surfaces (foredeck, cabin top, cockpit seats) to increase stiffness without excessive weight. High-load areas and where hardware is mounted are kept solid (coring omitted) to prevent compression issues. The Gemini uses extensive molded liners for the interior, which double as structural components. For example, the main cabin liner and furniture bases are molded fiberglass pieces that are glassed and tabbed into the hull before the deck is installed. These liners form the internal cabinetry (dinette, galley, head modules, etc.) and add stiffness to the hull like built-in frames. In the 105MC, the interior was redesigned as a single large molding, improving rigidity and reducing weight compared to earlier models with multiple components.

• Structural Reinforcements & Rig: The 105MC carries a masthead sloop rig with double spreaders and a deck-stepped mast supported by a compression post and bulkhead. To handle rig tension, the chainplates are through-bolted to hefty internal structures, and the rig includes a split backstay plus permanent checkstays for support. The checkstays lead to a stainless rod and plate tie-down in each hull, distributing the load into the structure. These reinforcements allow the Gemini’s sail plan to be powerful while keeping the rig secure. The bridgedeck and hull mold design itself is a major structural element – by molding the bridgedeck integral with the hulls, the boat gains stiffness and avoids the weakness of secondary-bonded crossbeams. Internally, the liners and furniture partition the space and act as additional web frames. The result is a fairly stiff platform for a production cat of this size.

• Centerboards (Keels) and Rudders: Instead of fixed keels, the Gemini 105MC uses twin retractable centerboards housed in each hull. These boards are asymmetrically shaped foils designed to generate lift to windward and reduce leeway. By the 2006 model, the construction of the boards was fiberglass with Kevlar reinforcement around a foam core. The boards pivot up into trunks molded integrally in the hulls, allowing the draft to decrease from ~5′ with boards down to ~18″ with boards up. They can be raised from inside the main saloon via line controls – a convenient feature that lets the crew adjust or retract the boards without going on deck. The boards are designed to kick up if they strike ground, preventing damage.