Custom fuselage geometry: putting the mast where you ride

What is custom

Where the mast meets the fuselage, and the lengths either side of it

Specified by

A overall length · B front wing → middle of mast · C middle of mast → stabilizer

Where to start

The custom fuselage configurator in the Custom Shop

Where it is made

Machined in Portland, Oregon

Why is the mast position the custom variable?

The chassis of a foil is four decisions: where the front wing sits, where the mast sits, where the stabilizer sits, and how hard the stabilizer works. We went through them in why the fuselage decides how your hydrofoil rides.

Three of the four you can already choose by buying a part. Front wing is a wing. Stabilizer position is fuselage length. Stabilizer load is the stabilizer and its shim.

The fourth is not for sale. Mast position is set by the fuselage tooling, so on a stock fuselage it is the same for a 60 kg rider and a 105 kg one, on a 30 litre board and a 120 litre one. That is the number a custom fuselage exists to move.

What are A, B and C?

Three measurements, each between fixed reference points, so every fuselage — stock or custom, any connection — can be compared on the same terms.

• A — overall length. The fuselage end to end. It is the number everyone already quotes.
• B — front of the front wing to the middle of the mast. Where the mast enters the system relative to the lift. This is your balance point: how much of the foil arrives through your front foot and how much through your back one.
• C — middle of the mast to the stabilizer. The lever the stabilizer works on. A longer C damps pitch and holds a line; a shorter one lets the nose move.

One detail that matters: A is not B + C. A runs end to end; B and C run between the wing, the mast and the stabilizer, and those points do not sit at the ends of the fuselage. We keep all three on the spec and never derive one from the others.

The front wing connection you ride changes the hardware, not the datums. That is what lets geometry be compared across connections at all.

Why do two fuselages of the same length ride differently?

Look at the drawing at the top of this page. Same A. The mast moves forward on one and aft on the other, and B and C trade length while the spec-sheet number stays put.

Move the mast aft — longer B, shorter C — and the lift sits further ahead of your feet. The foil asks for more front foot to hold level, and the shorter tail lever lets it rotate more freely.

Move it forward — shorter B, longer C — and the lift sits closer under you. Less front-foot pressure to hold height, and a longer lever damping pitch.

Neither is correct. What is correct is the one that matches your weight, your board and what you are trying to do. A geometry that is wrong for you does not stop working; you compensate for it. That compensation shows up as:

• a sore front leg after a long session, because you are holding the nose down all the way;
• a board track run all the way to one end and still not quite right;
• a stabilizer shim doing the job of a geometry correction rather than fine tuning;
• a foil that pumps well or carves well, but not the one you bought it for.

Get B and C right first and the shim goes back to doing what it is for.

Try it: slide the fuselage

This is the bench from the configurator, live. Grab the fuselage and slide it through the mast — the board and mast stay where they are, the wing and stabilizer ride along — or set B with the slider. Change the length, move the mast in the board's track, and watch where the front wing ends up under your feet. Change the board thickness and the mast and watch the two heights from foil mast height: what are you really riding? move — true foil height stays with the foil, true rider height moves with the board under your feet. Turn it by dragging around it (two fingers on a phone), and explode it to see the parts apart.

The gauge under it reads three things, each from geometry and your weight, not from wing data. Balance: to fly level your weight has to sit a little ahead of where the wing lifts, so the bench splits it between your feet — move the front wing forward and more goes on the front foot. Pitch: the stabilizer's lever, from your weight to the stabilizer, against what you ride now; a longer lever is more damped and slower to answer. Height: what a 2° lean moves your weight over the foil, which is why every centimetre of rider height is leverage. The stabilizer's trim push is a placeholder until the shop measures each one, and the wing and stabilizer are generic shapes, not OXZA sections.

One-piece or two-piece?

A custom fuselage comes two ways.

• One-piece — machined to your geometry from end to end. Length and mast position are both yours, so B, C and A can all move.
• Two-piece — a fixed front section that carries the mast, with interchangeable rear lengths. The mast stays at the standard position; what changes is C and A, the tail lever. One front section, several tails, swapped on the beach.

If what you want to change is where the foil balances under your feet, that is a one-piece build. If it is how the tail damps pitch across conditions, two-piece gets you there with parts you can swap.

Which front wing connections?

Six: T8 (5-bolt), T8C (a chopped 3-bolt T8), KT, Armstrong, OXZA EZ and OX Lock. The connection changes the hardware at the front of the fuselage, not where the datums sit, so the same A, B and C describe every one of them. Compatibility with a specific wing is confirmed before your fuselage is machined.

Measure what you ride now

You do not need us to start. With the foil assembled and a tape measure:

1. B — from the leading edge of the front wing where it meets the fuselage, back to the middle of the mast (half its chord behind the leading edge).
2. C — from the middle of the mast back to the leading edge of the stabilizer where it meets the fuselage.
3. A — the fuselage end to end.

Those tape points are not the exact production datums — those sit on our drawings — but they are repeatable, and they tell us where you are starting from. Measure the setup that feels closest to right, and say what you would change about it.

The board matters too, because B is only half of where the lift meets your feet. Note:

• where the board balances — rest it on a broom handle across the deck and measure from the tail to the balance point;
• where your feet sit — tail to the centre of your front foot and your back foot;
• where the mast sits in the track, and how much track is left either side.

How does the builder work?

The custom fuselage configurator opens on the same 3D bench you just used, and the bench and the form are one thing: slide the fuselage or change the length on the bench and the form follows, fill in a number in the form and the bench redraws. Under it, four short steps, and only the first is required:

1. Build — one-piece or two-piece, front wing connection, length (600, 700, 860 or 1000 mm, or your own), and where you want the mast: B, in millimetres, set by sliding the fuselage on the bench or typing it in. On a two-piece the mast is fixed in the front section.
2. What you ride now — the A, B and C you measured. This is where we start from.
3. Your board — length, volume, balance point, foot positions and how far the mast sits from the tail.
4. What you want it to do — discipline, weight, wings and stabilizer, and what feels wrong now.

The build spec updates as you go, and Request this build sends it to us as one email — with your name, email and, if you like, a phone number.

It does not choose B and C for you, and it says so. Turning your numbers into a mast position is our job, not a form's. For the arithmetic it can do — system load, true rider height (deck to fuselage, not the number on the mast), tail leverage and stabilizer pairing — the Balance Advisor at the end of the build tool reads your setup back to you first.

How do I order a custom fuselage?

1. Spec it. Open the custom fuselage configurator: one-piece or two-piece, front wing connection, length and mast position. Add the A, B and C you measured and the board notes above, then press Request this build — it all goes to us in one email. Riding OXZA already? Start in the build tool, run the Balance Advisor, and take the setup across from its last step: the configurator opens with your parts, weight and board filled in.
2. We scope it with you. We come back with the proposed B, C and A for your fuselage, the connection, and the stabilizer and shim to start on. Nothing is cut until you have agreed the geometry.
3. It is machined in Portland. Custom fuselages are built in a machine shop in Portland, Oregon, an hour down the Gorge from where OXZA rides.
4. Ride it, then tell us. Nose-heavy, balanced or tail-heavy, and roughly where it takes off. That is how a starting geometry becomes your geometry — and how the next rider's starting point gets better.

The goal is not a custom part. It is a setup you can repeat: the same three numbers, on the next fuselage, the next board, the next season.

Questions before you start? Contact us, or go straight to the custom fuselage configurator.