HD helm & cylinder selector
Heavy-duty inboard steering is sized in two moves: rudder torque picks the cylinder, then the helm sets how many turns the wheel takes to swing it. This tool works both out from Hydrive's own tables - 107 to 2,651 KgM, vessels to roughly 50 metres.
Outboard, sterndrive or jet? Use the kit selector instead.
What the steering has to move
Rudder torque decides the cylinder. If you have the figure from a naval architect or Hydrive's questionnaire, use it — otherwise start from boat length and treat the answer as a first pass.
The full HD matrix - every cylinder, every helm
Turns lock-to-lock for each pairing. Bold pairings fall in the comfortable manual band (3.5–6.5 turns).
| Cylinder | Torque KgM | Volume cc | Helm 103 | Helm 104 | Helm 105 | Helm 106 | Helm 107 |
|---|---|---|---|---|---|---|---|
| HD150-9 | 107 | 172 | 4.9 | 4 | 2 | 1.4 | 1 |
| HD150-9 ×2 | 215 | 344 | 9.8 | 8 | 4 | 2.8 | 2.1 |
| HD150-12 | 143 | 229 | 6.5 | 5.3 | 2.7 | 1.8 | 1.4 |
| HD150-12 ×2 | 286 | 458 | 13.1 | 10.7 | 5.3 | 3.7 | 2.8 |
| HD175-10 | 185 | 296 | 8.5 | 6.9 | 3.4 | 2.4 | 1.8 |
| HD175-10 ×2 | 369 | 591 | 16.9 | 13.7 | 6.9 | 4.7 | 3.6 |
| HD175-12 | 221 | 355 | 10.1 | 8.3 | 4.1 | 2.8 | 2.2 |
| HD175-12 ×2 | 443 | 709 | 20.3 | 16.5 | 8.2 | 5.7 | 4.3 |
| HD200-12 | 289 | 463 | 13.2 | 10.8 | 5.4 | 3.7 | 2.8 |
| HD200-12 ×2 | 578 | 927 | 26.5 | 21.6 | 10.8 | 7.4 | 5.6 |
| HD200-15 | 362 | 579 | 16.5 | 13.5 | 6.7 | 4.6 | 3.5 |
| HD200-15 ×2 | 723 | 1158 | 33.1 | 26.9 | 13.5 | 9.3 | 7 |
| HD250-12 | 506 | 811 | 23.2 | 18.9 | 9.4 | 6.5 | 4.9 |
| HD250-12 ×2 | 1012 | 1622 | 46.3 | 37.7 | 18.9 | 13 | 9.8 |
| HD250-15 | 633 | 1014 | 29 | 23.6 | 11.8 | 8.1 | 6.1 |
| HD250-15 ×2 | 1265 | 2027 | 57.9 | 47.1 | 23.6 | 16.2 | 12.3 |
| HD400-12 | 1326 | 2124 | 60.7 | 49.4 | 24.7 | 17 | 12.9 |
| HD400-12 ×2 | 2651 | 4247 | 121.3 | 98.8 | 49.4 | 34 | 25.7 |
HD sizing, answered
How are turns lock-to-lock calculated?
Swept cylinder volume divided by helm displacement per revolution. An HD150-9 sweeps 172 cc; a Model 103 helm moves 35 cc per turn of the wheel, so hard-over to hard-over takes about 4.9 turns. Bigger helms cut the turns but make the wheel heavier - that trade-off is the whole helm decision, and it's why the same cylinder is offered with five helm sizes.
What rudder torque does my boat have?
It depends on speed, rudder area, balance ratio and whether the propeller washes over the blade - not just boat length. As working points: around 30 ft commonly lands near the HD150-9's class, 40 ft near the HD175-10. Hydrive sizes precisely from a short questionnaire about the vessel and rudder; we run it with you before anything is ordered.
Do HD helms suit sailing yachts?
Yes - they're the reason many sailors accept hydraulic steering at all. The HD helms' oil-balanced design lets rudder loads be felt back through the wheel, and feedback valve options let you switch that feel on or off, or lock the helm while an autopilot steers.
What about dual steering stations?
HD helms 103-107 don't carry in-built lock valves, so a two-station installation adds the 318C dual lock valve to stop the stations back-driving each other. Tell us the station count and we include the valve set in the kit.
Prefer the full picture first? See the Hydrive range Luxfords stocks