The Ronstan Series 100 Lashing Orbit Block (RF109109A) is a single-sheave, 360-degree swiveling block rated for lines up to 12mm (1/2 in) with a stainless steel lashing bail, built for furling lines and control lines on cruising sailboats in the 30-45 foot range. Its Orbit swivel self-aligns with the load angle and the lashing attachment ties directly to existing deck hardware, so you can retrofit it without drilling new holes or adding a shackle.
Ronstan Series 100 Lashing Orbit Block at a glance
| Specification | Ronstan RF109109A |
|---|---|
| Max line diameter | 12mm (1/2 in) |
| Working load | 400 daN (~900 lbf) |
| Attachment | Stainless steel lashing bail |
| Swivel | 360-degree Orbit rotation |
| Body material | Glass-reinforced Nylon with stainless steel components |
| Best application | Furling lines and control lines on 35-42 ft cruisers |
What is the Ronstan Series 100 Lashing Orbit Block?
The Ronstan Series 100 Lashing Orbit Block (RF109109A) is a single-sheave, high-load block designed for furling lines, control lines, and light sheets on cruising sailboats in the 30-45 foot range. Its defining feature is the Orbit swivel system: the sheave housing rotates 360 degrees around the lashing attachment point, automatically aligning with the load angle as the furling line changes direction during tacking or reefing. This eliminates the side loading that degrades standard fixed blocks.
The block body is molded from glass-reinforced Nylon, with a stainless steel lashing bail and a precision sheave sized for lines up to 12mm. The maximum working load is 400 daN (approximately 900 lbf), an appropriate margin for the furling loads produced on a typical 37-foot sloop. Because the block lashes on rather than shackles on, it belongs to a family of Orbit blocks that share the same rotating, self-aligning sheave across a wide range of sizes.
How do I choose the right furling-line block for my sailboat?
The single most critical specification when selecting a furling block is sheave-to-line diameter compatibility. Running a 12mm furling line through a block rated for 8mm lines creates friction, heat, and premature wear on both the line and the sheave. The RF109109A is rated for 12mm lines, the standard furling-line diameter on mid-range cruising boats between 35 and 42 feet LOA.
Within Ronstan's own lineup, the Series 100 sits between the Series 55 (rated for lines to 8mm) and the Series 150 (rated for lines to 16mm and loads to 800 daN). If your headsail furler needs a heavier line, step up a series; if it runs lighter control lines, a smaller Orbit block will serve better. Match the block to the line first, then confirm the working load exceeds your peak furling load with margin to spare.
How do I install the Series 100 on a furling system?
The lashing bail on the RF109109A is designed to be tied directly to an existing pad eye, stanchion base, or cam-cleat mount, a real advantage over shackle-mounted blocks that require a matching pin diameter. Use a 3mm-4mm Dyneema lashing line for the attachment. A simple cow hitch or locked loop knot through the bail provides full load transfer without the risk of a gate failure under shock load.
Once the block is lashed in position, route your 1/2-inch furling line through the sheave with the load direction aligned toward the cockpit clutch or winch. Because the Orbit swivel allows 360-degree rotation, the block self-aligns as the line angle shifts, so you do not need to pre-set the block angle. Check sheave rotation by hand before loading the system: the sheave should spin freely with no lateral play, and if the line sits more than 1mm off-center in the groove, reposition the lashing point before sailing.
How does the RF109109A compare to other furling blocks?
Sailors evaluating a furling upgrade often compare the Ronstan Series 100 against similar single blocks from Harken and Lewmar. The Harken 29mm Carbo Air block handles lines up to 10mm and is lighter, but its fixed bail limits positioning flexibility. The Lewmar size 1 single block accepts up to 12mm line but uses a fixed becket rather than a lashing bail, requiring a dedicated pad eye with a matching shackle pin. The RF109109A's lashing attachment is more versatile for retrofitting on existing deck hardware without additional drilling.
For a 37-foot cruiser's headsail furling system, which typically generates peak furling loads between 200 and 350 daN depending on headsail size, the 400 daN working load of the RF109109A provides an appropriate safety margin without overengineering the installation.
Frequently asked questions
What line size is the Ronstan Series 100 Lashing Orbit Block rated for?
The RF109109A is designed for rope diameters up to 12mm (approximately 1/2 inch), matching standard furling-line sizes on mid-range cruising sailboats of 35 to 42 feet.
What is the working load of the RF109109A?
The maximum working load is 400 daN, roughly 900 lbf, which suits the moderate furling loads produced by a headsail furler on a 37-foot sloop with margin to spare.
How do you attach the Series 100 block to a sailboat fitting?
It uses a lashing attachment rather than a fixed shackle, so it ties directly to pad eyes, straps, or soft attachment points with 3mm-4mm Dyneema. This reduces weight, eliminates a corrosion point, and lets you remove the block quickly for inspection.
Is the RF109109A suitable for a Jeanneau Sun Odyssey 37 furling line?
Yes. It accommodates the standard 10-12mm furling lines used on that model, and its Orbit swivel prevents the line twist common in furling applications.
How does the Orbit block compare to a standard cheek block?
The 360-degree Orbit rotation tracks line-angle changes as the furler deploys or reefs the sail, whereas a fixed cheek block creates side-load friction when angles shift, increasing wear on the line and sheave.
What material is the Series 100 block made from?
The body is glass-reinforced Nylon with stainless steel components, including the lashing bail, for long-term durability under continuous marine furling loads.
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