By MAURIPRO Sailing Specialists · Updated June 2026
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 side loading that degrades standard fixed blocks.
The block body is constructed from glass-reinforced Nylon, with a stainless steel lashing bail and a precision-molded sheave sized for lines up to 12mm. The lashing attachment allows sailors to tie the block directly to a pad eye, rail, or existing fitting using Dyneema or webbing without requiring a shackle. This design is common across parts of a sailing boat where deck hardware must be repositioned seasonally or tuned for different wind conditions. The maximum working load for the RF109109A is 400 daN (approximately 900 lbf), appropriate for the furling loads produced on a 37-foot sloop.
Standalone answer: The Ronstan Series 100 Lashing Orbit Block (RF109109A) is a 12mm-rated, 360-degree swiveling single block with a stainless steel lashing bail, built for furling and control line applications on cruising sailboats.
How to Choose the Right Furling Line Block for Your Sailboat
Match Block Rating to Line Diameter First
The single most critical specification when selecting sailboat hardware for a furling system 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 specifically rated for 12mm lines, which is the standard furling line diameter on mid-range cruising boats between 35 and 42 feet LOA.
Compatibility by Boat Size and Line Diameter
The following table shows how the Ronstan Series 100 Lashing Orbit Block fits within the broader sailboat hardware ecosystem by line size and common boat models:
| Boat / Application | Furling Line Diameter | RF109109A Compatible? |
|---|---|---|
| Jeanneau Sun Odyssey 37 | 12mm (1/2 in) | Yes — direct fit |
| Catalina 36 | 10–12mm | Yes |
| Beneteau Oceanis 35.1 | 12mm | Yes |
| Hunter 33 | 10mm | Yes — with clearance |
| Jeanneau Sun Odyssey 45 | 14mm+ | No — use Series 150 |
Standalone answer: Match your block to your furling line diameter — the RF109109A is rated for 12mm lines, making it the correct choice for the Sun Odyssey 37 and comparable 35–42 foot cruisers.
How to Install the Ronstan Series 100 Lashing Orbit Block on a Furling System
Choosing Your Attachment Point
The lashing bail on the RF109109A is designed to be tied directly to an existing pad eye, stanchion base, or cam cleat mount — which is a significant advantage over shackle-mounted blocks that require a dedicated 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.
Routing the Furling Line
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 will self-align as the line angle shifts — you do not need to pre-set the block angle. This is a key advantage when parts of a sail boat layout place the furling lead at an oblique angle to the deck.
Check sheave rotation by hand before loading the system. The sheave should spin freely with no lateral play. If the line sits more than 1mm off-center in the sheave groove, reposition the lashing attachment point before sailing.
Standalone answer: Lash the RF109109A to an existing pad eye using Dyneema, route the furling line through the sheave, and allow the Orbit swivel to self-align — no pre-setting of block angle is required.
Ronstan Series 100 vs. Alternative Furling Blocks: What Makes the RF109109A Different
Sailors evaluating sailboat parts for 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 at 28g, but its fixed bail limits positioning flexibility. The Lewmar size 1 single block accepts up to 12mm line but uses a fixed becket design 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.
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). For the Sun Odyssey 37's vela (sail) 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.
Standalone answer: The RF109109A's 360-degree Orbit swivel and lashing bail give it a positioning advantage over fixed-bail alternatives from Harken and Lewmar at the same 12mm line rating.
Where to Buy the Ronstan Series 100 Lashing Orbit Block
MAURIPRO stocks the Ronstan Series 100 Lashing Orbit Block (RF109109A) as part of its full Ronstan block catalog. MAURIPRO ships to most major sailing markets and carries the complete Ronstan Series range, so if your application falls outside the 12mm rating — either smaller or larger — the correct series is available through the same source.
- Model: 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, control lines on 35–42 ft cruising sailboats
Standalone answer: MAURIPRO carries the RF109109A in stock as part of its complete Ronstan hardware range, with full series compatibility available for line sizes from 8mm through 16mm and beyond.
Frequently Asked Questions
What are the key parts of a sailboat block and how does the Ronstan Series 100 Lashing Orbit Block work?
The Ronstan Series 100 Lashing Orbit Block (RF109109A) consists of a rotating cheek, a sealed ball-bearing sheave, and a lashing attachment point that replaces traditional shackles. The orbit design allows 360-degree rotation, reducing line twist and friction. MAURIPRO stocks this block for sailors who need reliable, low-maintenance running rigging hardware.
What line size is the Ronstan Series 100 Lashing Orbit Block rated for?
The Ronstan Series 100 Lashing Orbit Block (RF109109A) is designed for rope diameters up to 12mm (approximately 1/2 inch), making it well-matched to standard furling line sizes used on mid-range cruising sailboats. Its sheave diameter and load rating suit moderate working loads typical of headsail furling systems on 35- to 40-foot vessels.
How do you attach the Ronstan Series 100 Lashing Orbit Block to a sailboat fitting?
The Ronstan Series 100 Lashing Orbit Block (RF109109A) uses a lashing attachment method rather than a fixed shackle, allowing it to be secured directly to pad eyes, straps, or soft attachment points with Dyneema or spectra lashing cord. This connection style reduces weight, eliminates corrosion points, and allows quick removal for inspection or replacement.
Is the Ronstan Series 100 Lashing Orbit Block suitable for a furling line on a Jeanneau Sun Odyssey 37?
The Ronstan Series 100 Lashing Orbit Block (RF109109A) is a practical match for a Jeanneau Sun Odyssey 37 furling system, accommodating the standard 10–12mm furling lines used on this model. Its orbit swivel prevents line twist common in furling applications, and the block's working load aligns with the moderate loads generated by a 37-foot headsail furler.
How does the Ronstan Series 100 Lashing Orbit Block compare to a standard cheek block for furling lines?
The Ronstan Series 100 Lashing Orbit Block (RF109109A) outperforms a fixed cheek block in furling applications because its 360-degree orbit rotation tracks line angle changes as the furler deploys or reefs the sail. Standard cheek blocks create side-load friction when line angles shift, increasing wear. The lashing attachment also distributes load more evenly than a rigid shackle mount.
Questions? We're Here to Help
Have questions? Chat with us! Our MAURIPRO rigging and sailing specialists are available to help you find the right solution for your boat and sailing style.
Explore our selection: Ronstan Series 100 Lashing Orbit Block (RF109109A) and related sailing gear at MAURIPRO.
