Phinisi Timber Guide: Ironwood, Teak and Bitti – What Goes Where
A phinisi uses four main timbers: ulin (Borneo ironwood) for the keel and lower planking, bitti for frames and ribs, teak for decks and interiors, and lighter hardwoods such as bayam above the waterline. Each is chosen for density, rot resistance and weight, then sun-seasoned for weeks to months — ironwood sections for up to a year — before it is cut to shape.
- Underwater structure: density and borer resistance win — ulin.
- Internal framing: workability and strength — bitti (Vitex cofassus).
- Deck and joinery: dimensional stability and oil content — teak (Tectona grandis).
- Above the waterline: weight control and a lower centre of gravity — bayam and similar lighter hardwoods.
Timber choice is the part of a phinisi build that owners understand last and pay for first. Two boats of identical length can differ by a wide margin in price and by many years in service life purely on what went into the keel and how long it dried. This guide sets out what goes where, why, and what to ask a yard before you sign.
Which timber goes where on a phinisi?
| Species | Local name | Where it is used | Why |
|---|---|---|---|
| Eusideroxylon zwageri | Ulin / kayu besi (Borneo ironwood) | Keel, stem and sternpost, lower planking | Extremely dense; high natural resistance to rot and marine borers |
| Vitex cofassus | Bitti | Frames, ribs, structure that is not permanently immersed | Strong, workable, holds fastenings well |
| Tectona grandis | Jati (teak) | Decks, superstructure, interior joinery | Dimensional stability and natural oil content |
| Various lighter hardwoods | Bayam and similar | Upper works, non-structural above-water areas | Controls displacement and keeps the centre of gravity low |
Why is ironwood used below the waterline?
Ulin earns its Indonesian nickname — kayu besi, iron wood — honestly. It is dense enough to sink in water when green, and it resists the two things that destroy wooden hulls in the tropics: fungal rot and marine borers. That is why it goes where replacement is hardest and exposure is constant: the keel, the stem and sternpost, and the planking strakes that live permanently underwater.
The trade-offs are real. Ulin is heavy, it is hard on tools and on the carpenters, and it is sourced largely from Kalimantan, which means transport cost and — increasingly — paperwork. Availability is not what it was twenty years ago, and any owner planning a build should treat ironwood supply as a schedule risk rather than an assumption. Legality documentation is covered separately in our guide to SVLK and legal timber sourcing.
What is bitti and why is it used for frames?
Bitti (Vitex cofassus) is the workhorse of the internal structure. It is strong, comparatively easier to shape than ironwood, and it holds dowels and fastenings well — which matters in a hull where frames are fitted after the planking and therefore have to be shaped to the hull rather than the hull to them. Because the frames sit inside a ventilated bilge rather than permanently submerged, the extreme borer resistance of ulin is not needed there, and the weight penalty would be counterproductive.
Where does teak actually belong?
Teak is what buyers picture, but its correct place is above the waterline. Its value is dimensional stability — it moves little with heat and moisture — plus the natural oils that let a deck survive tropical sun and salt with modest maintenance. So it takes the deck, the deckhouse and the visible interior joinery, where movement would open seams and ruin finishes.
Teak is also the biggest discretionary line in a timber budget. A full teak-laid deck on a 35 m hull is a very different number from a painted or composite deck with teak only on the guest areas, and that decision belongs in the specification stage alongside the rest of the interior fit-out and cabin design brief.
How long does phinisi timber need to season?
| Component | Typical seasoning | Risk if rushed |
|---|---|---|
| Heavy ironwood keel and stem sections | Up to about 12 months | Checking and splitting in the highest-load parts of the hull |
| Hull planking | Weeks to several months | Shrinkage, opening seams, early re-caulking |
| Frames and structure | Weeks to months | Warping that pulls the fitted shape out of true |
| Deck and joinery teak | Kiln or air dried to a stable moisture content | Cupping, gapping, failed finishes |
Sun-drying on the beach is the traditional method and it works, but it is slow, and slow is expensive when a yard slot is booked. This is where schedule pressure quietly damages a boat: timber ordered late gets used early. When you review a build programme, check that timber procurement starts before — not with — keel laying. Our custom new-build program treats seasoning as a scheduled activity with its own milestone, not a background task.
How do you verify a yard’s timber claims?
Ask for four things, in writing, before the deposit:
- Species by component — a simple schedule stating what timber goes into keel, planking, frames, deck and joinery.
- Origin and legality paperwork — chain-of-custody documents under Indonesia’s SVLK framework, especially if you have EU-linked buyers, financing or a resale plan.
- Seasoning status — when the timber was cut and how long it has been drying, ideally with dated photos of the stack.
- Scantling sizes — plank and frame dimensions checked against the engineering package, not just against tradition. See naval architecture and stability engineering.
None of this is adversarial. Good yards answer these questions comfortably; the ones that cannot are telling you something useful.
Frequently asked questions
What wood is a phinisi made of?
Primarily ulin (Borneo ironwood) for the keel and lower planking, bitti for frames and ribs, teak for decks and interiors, and lighter hardwoods such as bayam above the waterline. The combination is chosen for rot resistance below and weight control above.
Is ironwood better than teak for a boat hull?
They are not competing for the same job. Ironwood is denser and far more borer-resistant, which is what an underwater structure needs; teak is more stable and better looking, which is what a deck needs. A well-built phinisi uses both, in the right places.
Is ulin endangered or restricted?
Ulin supply is under pressure and increasingly regulated, and legality verification through SVLK is now the practical baseline for sourcing. We do not claim a specific international listing status here — confirm current rules with your yard and, if it matters to your buyers, with a timber-legality consultant.
Can a phinisi be built without ironwood?
Alternative hardwoods are used where ulin is unavailable, and some modern builds use laminates or sheathing in specific areas. Expect a different maintenance and survey profile, and have the substitution reviewed against the scantling package before it is agreed.
How long does the timber last?
A properly seasoned, well-maintained ironwood-keeled hull hauled out annually for inspection, antifouling and caulking checks can serve for decades; re-planking is a major-refit event rather than a routine one. See our wooden hull maintenance calendar for the intervals.
Talk to the team
Komodo Boat Construction is operated by Komodo Luxury, part of Juara Holding Group, active in Komodo marine tourism since 2015. Send us your intended size and finish level and we will put a timber schedule and seasoning programme against it.
WhatsApp: +62 811 3823 875 · Email: sales@komodoluxury.com