Ronstan Series 75 Two-speed Mainsheet System 3:1 / 6:1 – Bottom Block Only – RF72700B
The Ronstan Series 75 Two-Speed Mainsheet Bottom Block (RF72700B) is a high-load, cockpit control unit designed as the key working component in a two-speed 3:1 / 6:1 mainsheet system for sports boats and keelboats up to 12m (40ft).
This block manages the output of the continuous mainsheet, featuring twin cam cleats to handle both line tails. One tail operates on the direct 3:1 purchase for fast trimming, while the second engages the full 6:1 purchase for precise load control. This dual-control setup allows sailors to switch seamlessly between speed and power depending on conditions.
In use, one line can remain cleated while the other is adjusted for fine tuning when sailing upwind. During manoeuvres, both tails can be worked together to rapidly ease or trim the mainsail, delivering maximum responsiveness around marks.
With a Safe Working Load of 800kg, this block is engineered to match the loads generated in modern two-speed mainsheet systems. It is designed to pair with the Ronstan Series 75 Two-Speed Top Block (RF72700T) to create a complete system.
Constructed to Ronstan’s Series 75 standard, it incorporates 75mm sheaves suitable for lines up to 12mm, acetal ball bearings for smooth operation, and anodised aluminium cheeks for strength and durability. Ratchet sheaves provide additional holding power, reducing effort on the trimmer under load.
When fitting to traveller cars, ensure adequate support for the bottom block and use a stand-up spring kit (RF324-2) to maintain correct alignment and performance.
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