A small power catamaran — say 9 to 15 m — is a genuinely buildable project in Lombok, and for day-tour and dive operations it solves problems monohulls cannot: a wide, level deck; stability at anchor that guests feel immediately; shallow draft for beach and reef work; and efficient cruising from modest horsepower. The constraints are equally real: beam that must fit the yard’s slipway and the harbour’s berths, structural engineering in the cross-deck that must be done properly, and a build cost premium of roughly 20–40 percent over a monohull of equal length. This post walks the decisions in the order they actually bite.
Why a catamaran at all
Twin hulls buy three things operators pay for daily. First, deck area: a 12 m catamaran with 5.5 m beam offers usable deck comparable to a much longer monohull — more shaded seating, more gear space, more room for thirty wet snorkellers to move. Second, at-anchor stability: the roll that makes guests queasy at reef stops largely disappears, which is why the platform suits the same missions discussed in glass-bottom and snorkel boats for Gili day trips. Third, efficiency: two slender hulls at displacement and semi-displacement speeds push less water than one fat one, so a cat can hold 15–18 knots on engines that would leave an equivalent monohull short — a different sizing conversation from the one in the Bangsal–Gili fast boat specification guide.
Beam, draft and the slipway problem
Beam is the first hard constraint to check, before any drawing is loved too much. Lombok’s working yards haul boats on beach skids, simple ramps and cradles sized for monohull beams; a 5.5–6.5 m catamaran beam exceeds some of them outright and complicates others. The practical checks the desk runs at concept stage:
- Build site: can the chosen yard frame, join and move a hull of this beam under its roof and down its ramp? Which yards suit which projects is the matching question handled on the yards page.
- Launch path: beach launch of a wide twin hull needs either a purpose-built cradle on rollers or a tide window and a lot of coordinated labour.
- Operating berths: harbour slots at Bangsal and the island jetties price and fit by beam in practice; confirm the berth before you fix the beam.
- Future haul-out: every future antifoul cycle repeats the launch problem in reverse. Design the cradle with the boat, not after it.
Draft, by contrast, is the constraint that flatters catamarans: 0.5–0.8 m loaded is achievable at this size, opening beach stops and shallow reef moorings that deeper monohulls skip.
The cross-deck is the engineering
Two good hulls do not make a good catamaran; the structure joining them does. The cross-deck and its beams carry racking, torsion and slamming loads that have no equivalent in monohull building, and this is where local yard experience is thinnest and where drawings must lead the shed rather than follow it. Key decisions: beam structure (box beams or full bridgedeck), bridgedeck clearance above the water (too little and the boat slams in any chop; at this size meaningful clearance costs windage and weight), and hard structural continuity at the hull-to-beam joints. In fibreglass, that means engineered laminate schedules at the joins; in timber or ply-epoxy, properly sized laminated beams and generous knees. This is a boat class where the desk insists on real naval-architecture drawings before contract — rules of thumb that serve traditional monohulls simply do not extend to cross-deck engineering.
Material and machinery choices
At 9–15 m the realistic constructions are ply-epoxy composite (light, suited to skilled Lombok carpentry, resin-hungry), moulded or one-off fibreglass (repeatable, heavier unless cored, familiar to FRP yards), and — less commonly at the small end — welded aluminium. Weight discipline matters doubly on a cat: payload lives in the bridgedeck, and every excess tonne erodes the efficiency that justified the platform. Machinery is usually a pair of modest outboards (2 × 70–150 hp at this size) or small diesels for displacement work; twin engines widely spaced also give the manoeuvrability that makes these boats easy in crowded anchorages.
Cost, honestly framed
| Configuration | Typical LOA | Indicative band (USD) |
|---|---|---|
| Ply-epoxy day-tour cat, outboards | 9–12 m | 90,000–170,000 |
| FRP tour/dive cat, certified deck | 12–15 m | 150,000–300,000 |
The premium over a monohull comes from two hulls’ worth of surface, the engineered cross-deck, and doubled systems runs. What the premium buys back is capacity per metre and guest comfort per trip. Whether that trade closes for your operation is a numbers exercise, not a taste exercise — run it against the bands on the price and quote page and your seat-revenue model.
How a Lombok cat build runs under the desk
The programme mirrors any supervised commission — specification, drawings, yard matching, contract with milestone payments, staged inspection, sea trial — with three catamaran-specific additions: a drawings package including cross-deck engineering before contract signature; a build-site survey confirming beam handling from lofting through launch; and a trial protocol that tests bridgedeck slamming behaviour into real chop, not just flat-water speed. The general sequence lives on the custom boat build page.
Small power cats reward operators who plan in numbers: seats, fuel per cycle, berth fit, haul-out path. Bring those numbers to the first conversation and the platform decision — cat or monohull — usually makes itself within a week.
Frequently Asked Questions
Can Lombok yards build catamarans?
Yes, within constraints. The hulls themselves suit local timber, ply-epoxy and FRP skills; the discipline the platform demands is engineered cross-deck structure and a build site whose shed, ramp and launch path can handle 5.5–6.5 m of beam. The desk surveys both before contract.
How much more does a catamaran cost than a monohull?
Plan on roughly a 20–40 percent premium at equal length: two hulls’ worth of surface, an engineered cross-deck and doubled systems runs. What the premium buys back is deck area comparable to a much longer monohull, at-anchor stability guests feel immediately, and efficient cruising from modest horsepower.
What is the biggest engineering risk on a small cat?
The cross-deck. Racking, torsion and slamming loads in the bridgedeck structure have no monohull equivalent, and traditional rules of thumb do not extend to them. The desk requires real naval-architecture drawings for the beams, bridgedeck clearance and hull-to-beam joints before any contract is signed.
What draft does a 12 m power catamaran need?
Around 0.5–0.8 m loaded is achievable at this size — one of the platform’s genuine advantages. That opens beach stops and shallow reef moorings that deeper monohulls skip, which is commercially meaningful for snorkel and day-tour operations around the Gilis and Lombok’s south coast.