How do I adjust mast rake and rig tension on a Dehler 34?
I want to check the mast rake and rig tension on my Dehler 34 before the season. She develops quite a lot of weather helm when close-hauled, and the leeward shrouds look loose. What should I measure, and which adjustments should I make first?
Answer
Set your Dehler 34's mast straight athwartships, with slight aft rake, controlled forward pre-bend and enough measured shroud tension to support it under sail. Establish the settings for your particular mast, then refine rake under sail to give light weather helm with roughly 2 to 3 degrees of rudder angle when close-hauled.
Identify your rig
The Dehler 34 name covers several generations, including older Van de Stadt designs and later Judel/Vrolijk boats. No single forestay length or shroud-tension figure suits them all. Replacement masts and standing rigging add further differences.
Check the mast maker's identification plate, rigging arrangement and any existing tuning sheet. Note whether you have swept spreaders, continuous or discontinuous shrouds, and an adjustable backstay. On swept-spreader rigs, cap-shroud tension also provides substantial forestay support.
Before making adjustments, inspect the chainplates, spreader roots, mast step, wire terminals and turnbuckles. Deal with any moving mast support or cracked terminal before tuning. Never disconnect a loaded stay or move the mast heel with the rig under load.
- Borrow a steel measuring tape and a tension gauge suited to the wire's diameter and construction. A Loos gauge is a common choice for wire rigs.
- Record exposed turnbuckle threads, gauge readings and backstay position.
- Mark the current settings so you can return to your starting point.
Centre the mast and set rake
Work afloat in sheltered water, with normal cruising equipment aboard and no pronounced list. Ease the backstay to a repeatable baseline, keeping the mast supported.
- Hoist the steel tape on the main halyard and measure to matching port and starboard chainplate points. Check that the halyard exit and your reference points allow a fair comparison.
- Adjust the cap shrouds until the measurements match, then sight up the mast track to check for sideways bends.
- Measure rake with a weighted main halyard hanging freely beside the mast in calm conditions. Record its distance aft of the mast at a clearly marked height, allowing for the halyard's exit position.
Forestay length is the principal rake adjustment. Lengthening normally increases aft rake; shortening reduces it. A furling drum may conceal the adjuster, and some installations have no readily adjustable forestay. Follow the furler instructions and maintain the specified thread engagement.
Mast-foot position also affects geometry, but it is not a routine first adjustment. On a keel-stepped installation, the relationship between heel and deck partners also affects bend. Follow the mast maker's procedure before changing it.