How do I adjust mast rake and rig tension on a Beneteau Oceanis 38?
My Beneteau Oceanis 38 has noticeable forestay sag when sailing upwind, and the helm gets heavy as the breeze builds. How should I measure the mast rake and adjust the shrouds without overtightening the rig?
Answer
Centre your Oceanis 38's mast athwartships, set a slight aft rake, then tension the shrouds evenly and check the result under sail. Identify the mast and mainsail arrangement first, as conventional and in-mast furling rigs can need different prebend settings, and no single turnbuckle setting suits every installation.
Inspect and record the rig
Inspect the chainplates, mast heel, spreader roots, wire terminals and turnbuckles before adjusting anything. Tuning cannot correct a moving fitting or damaged standing rigging. Look for broken wire strands, cracked swages, bent threaded studs and distortion around deck attachments.
Identify the mast manufacturer from its plate and obtain the tuning instructions for that installation. Check the boat itself rather than borrowing figures from an Oceanis 38.1 or another model year. Replacement standing rigging may differ from the original specification.
You need a steel tape, a suitable wire-tension gauge, two correctly fitting spanners, replacement split pins and rigging tape. Loos and Spinlock gauges are common choices; choose one that covers your measured wire diameter and construction.
- Photograph every turnbuckle and record exposed thread lengths.
- Measure and record existing shroud tensions before changing anything.
- Check that threaded ends retain adequate engagement throughout adjustment.
Support the mast with a suitably secured halyard before loosening a forestay connection. Never disconnect standing rigging with the mast unsupported.
Centre the mast, measure rake
Work afloat in calm conditions, with normal cruising equipment aboard and the boat sitting level on her intended waterline. Remove obvious sideways loading from the boom and sails.
Use a halyard and steel tape to measure from the same masthead reference to matching port and starboard chainplate positions. Apply equal measuring tension each time. Adjust the cap shrouds until the measurements match, then sight up the mainsail track for sideways bends.
To measure rake, hang a weight from the main halyard just above gooseneck height. Keep it clear of the deck and let it settle. Measure the horizontal distance between the halyard and a clearly recorded reference on the mast.
This establishes a repeatable baseline, not a target. Avoid forward rake. Set the amount of aft rake using the mast instructions and helm balance rather than an arbitrary measurement in millimetres.
Forestay length primarily sets rake, with a corresponding backstay adjustment where fitted. A furling system may conceal the forestay adjustment or restrict access to it. Follow its dismantling instructions and never use the foil or drum as a lever.