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+--- Thread: My boat's at (or over) the upper weight limit for the pilot I want to fit. (/showthread.php?tid=7694)
My boat's at (or over) the upper weight limit for the pilot I want to fit. - Tom - Raymarine - Moderator - 03-19-19 01:53 AM
This is a question that comes up very frequently. People ask:
- I balance my sails well, and/or my helm is very light: why does boat displacement matter?
- What is the problem if my boat is a little bit too heavy?
- Why does it matter more if I am cruising offshore than in-harbour or coastal use?
The key differences between harbour usage and ocean passage-making are the very high duty-cycle, the fact that you're out in all weathers, and the consequences if the pilot can't cope.
So that you can make an informed decision, here are some potential problems you might encounter when using a pilot that's close to its upper specified displacement limit, for long-distance passage-making:
- Greatly accelerated drive wear and likelihood of early failure. If you use a small car to tow a large boat a short distance to the boat ramp occasionally, it'll probably be fine. If you use the same car to tow the boat across the country, it probably won't get to the end of the journey.
- Higher likelihood of failure of the drive FETs in the Actuator Controller (ACU). The FETs in the ACU200 are lower-rated than those in the ACU400 and if they're running at close to the specified maximum current for long periods then they'll get very hot and be much more likely to fail. This would leave you with no drive output (no functional pilot.)
- The drive may stall when you need it most, e.g. when the pilot's trying to prevent a gybe in a following sea. Keeping the sails well balanced helps keep the pilot's load down much of the time, but makes little or no difference when it's a sea that's pushing the stern round and the pilot is trying to force the rudder back the other way. You might not feel all that load at the helm but you have a large mechanical advantage there compared to the drive: for example, the standard Linear drives have a stroke of 300mm whereas your wheel's movement might be 3 turns of perhaps 3.5m circumference to achieve the same rudder movement. Over 4 decades of experience of building pilots has taught us that vessel displacement is the best guide to the maximum loads that the pilot's likely to have to cope with under such circumstances.
- The Actuator Controller (ACU) may reach its peak current and raise a Current Limit alarm, causing the pilot to drop to Standby. Again, this is most likely at times when you least want it to happen.
If you're using a pilot on a boat that's actually over rather than at the maximum specified displacement for the pilot, you can add a further point: no warranty in the event of failure.
We don't like taking support calls from people who've had a failure of an under-specified pilot mid-ocean, so we always recommend leaving a large safety-factor in the choice of pilot to account for offshore sea-states and long-term usage. If you're sailing two-up or solo, it's a very good idea also to at least consider a backup pilot (installed, with an On-Off-On changeover switch, not sitting in a box.) Of course failures shouldn't happen, but what are the consequences if the unlikely does occur?
RAYFAQ#