Cylinder mounting types, explained
Once the horsepower question is settled, the kit choice comes down to geometry: where the cylinder lives and how much room it needs. Six mounting styles cover every transom and hull.
Bullhorn (tilt-tube mount)
OBKIT1, OBKIT1-XT, COMKIT1, COMKIT6
540 mm engine-well clearance
Cast horns clamp the tilt tube; the cylinder body moves along a fixed piston rod as you steer.
Hydrive's most popular design — compact, steers through full tilt, suits most modern outboards to 350 hp (XT).
Watch for: Hoses move with the engine, so they're routed with service loops. Some Honda/Mercury cowlings need the brand-specific cylinder variant.
Side mount (tube mount)
OBKIT2, OBKIT3, SPORTKIT, COMKIT2, COMKIT3, COMKIT-SPORT
540 mm balanced (210T) · 330 mm single-ended (210TSE) · 315 mm compact (512T)
Screws onto the tilt tube where a steering cable would — the classic cable-replacement fitting.
Hoses stay stationary; the natural upgrade path from cable steering; single-ended and compact versions for tight wells.
Watch for: Needs side clearance beside the engine; single-ended cylinders need the oil level set rod-retracted.
Front mount (fixed)
OBKIT5, COMKIT5
535.5 mm width mid-stroke
Bolts to the front of most V4/V6 outboards with four bolts and drives the motor's own drag link.
Hoses stationary, simple geometry, no tilt-tube wear point.
Watch for: Needs engine-well width for the piston rod to travel both ways.
Centre mount (double-ended)
OBKIT4
Mounts between the engines
A double-ended cylinder sits between twin outboards under the marlin board, driving both motors through two drag links.
No side clearance needed at all; tidy on twin rigs and outboard cats.
Watch for: Twin installations only.
Sterndrive cylinders
OBKIT2 (cable bracket), MERCRUISERKIT, VOLVOKIT1/2
Per drive
Tube-mount on the drive's cable bracket, or brand-specific cylinders shaped for Mercruiser and Volvo Penta drives.
Purpose-made fits; mid-mount transom-shield options where side clearance is impossible.
Watch for: Power-assisted drives need the dedicated 212T cylinder — tell us what the boat runs.
Inboard (rudder tiller)
COMKIT-IB1/IB2, IBKIT1, HD Series
Inside the hull at the rudder stock
A balanced cylinder drives the rudder's tiller arm; sizing is by rudder torque (KgM), not horsepower.
Scales from 8 m leisure boats to 50 m vessels (HD); feedback helms available for sailors who want rudder feel.
Watch for: Sailboats must use copper, steel or stainless tubing — nylon tubing is not permitted on sailboats.
Clearance figures are Hydrive's published requirements. A few motors (some Honda, Mercury, post-2022 Suzuki DF115B/DF140B, Tohatsu and Yamaha models — Yamaha's 4-stroke 50–70 hp, 80B and 2019 F90LB take the Honda-version cylinder, with transom clamps cut off to clear bullhorn and front-mount cylinders) need brand-specific variants — we confirm the exact cylinder for your engine before anything ships.
The other half: choosing the helm
Wheel feel is set by simple hydraulics — cylinder volume divided by helm displacement equals turns lock-to-lock. The standard 28 cc helm gives about 5.5 turns on the bullhorn kits; stepping up to the 35 cc Model 402 brings that to 4.4 turns with a slightly heavier wheel. Tilting helm versions exist for rake-adjustable consoles, and dual-station boats simply add a second helm into the same circuit.
Admiral and Commander helms have built-in lock valves — non-feedback steering, so the engine can never move the wheel. The HD-series helms for big inboards are deliberately the opposite: full-feedback, giving sailors the feel of mechanical steering with hydraulic muscle.
Mounting FAQs
Which mounting style is most popular?
The bullhorn — Hydrive calls the OBKIT1 its most popular kit design. The cylinder rides on the tilt tube between cast horns, steers smoothly through the full tilt range, and fits most modern outboards. The trade-off is that the hoses move with the engine, so they're routed with service loops.
I'm replacing cable steering — which cylinder reuses my setup?
The side-mount (tube-mount) cylinders. They screw onto the outboard's tilt tube exactly where the old cable ran, which makes kits like OBKIT2 and COMKIT2 the natural cable-to-hydraulic upgrade — same mounting point, stationary hoses, no fabrication.
What if there's no room beside the engine?
Go single-ended or compact: the 210TSE needs just 330 mm of side clearance versus 540 mm for the balanced cylinder, and the compact 512T needs 315 mm. On twin rigs, the centre-mount double-ended cylinder sits between the engines under the marlin board and needs no side room at all.
Do sterndrives and inboards use the same cylinders?
Sterndrives mostly take the tube-mount cylinder on the drive's existing cable bracket, with purpose-made cylinders for Mercruiser (210MERC) and Volvo Penta (210V/216V) — and power-assisted drives need the 212T. Inboards are different: a balanced cylinder mounts inside the hull and drives the rudder's tiller arm, sized by rudder torque rather than horsepower.
Not sure which mounting fits?
Send a photo of your transom or engine well with the engine make and horsepower — we'll pick the cylinder style and the exact kit, first time.