A ratchet block has a toothed, one-way sheave that grips the line under load — giving 10:1 to 20:1 holding power so you can hold a heavily loaded sheet by hand — while a plain block spins freely in both directions. Reach for a ratchet on any line you tail and hold by hand: mainsheets, jib and genoa sheets, spinnaker sheets, and vangs. Use plain blocks for turning blocks, low-load leads, and the internal sheaves of a purchase system, where free running matters more than grip.
This guide is written for the owner of a 28–45 ft cruiser or cruiser-racer deciding where a ratchet earns its keep and where it just adds friction. Get it wrong in one direction and a loaded sheet rips through your hand; get it wrong in the other and you fight needless drag on every trim. Below we explain how ratchet blocks work, when holding power matters, the difference between manual and automatic ratchets, and which real MAURIPRO products fit each job.
Ratchet vs plain blocks at a glance
| Model | SKU | Sheave | Ratchet type | Holding power | Best for |
|---|---|---|---|---|---|
| Selden 45 Ball Bearing, Automatic Ratchet | SEL40440101R | 45 mm | Automatic (load-activated) | Engages as load rises | Dinghy & small-boat control lines |
| Barton Marine Ratchet Block 55mm | BAM-90500 | 55 mm | Single ratchet | Fixed grip | General-purpose sheet handling |
| Harken 57mm Ratchet, Swivel (Black) | HAR2135 | 57 mm | Manual on/off (both sides) | 10:1 | Sheets in medium to light air |
| Lewmar 60mm Control Block, Single Ratchet | LEW29901661BK | 60 mm | Manual, stainless ball race | Ratchet grip | Cruiser sheets & control lines |
| Ronstan Series 60 Ratchet, Single | RON-RF62100 | 60 mm | Manual on/off (both sides) | Up to 20:1 | High-load sheets, maximum grip |
Drop-ship note: availability is confirmed at checkout; the figures above are the manufacturers' published specifications.
How does a ratchet block work?
Inside a ratchet block, the sheave carries teeth and rides against a spring-loaded pawl. In one direction the sheave spins almost freely, like a plain block. In the other — the loaded direction — the pawl catches the teeth so the sheave ratchets instead of spinning, and the friction it adds multiplies the grip your hand has on the tail. That is why a crew can hold a loaded sheet with two fingers on a ratchet that would tear free on a plain block.
On manual blocks such as the Harken 57mm Ratchet (HAR2135) and the Ronstan Series 60 (RON-RF62100), an on/off switch — fitted to both sides on both models — lets you turn the ratchet action off for free running when you want to ease quickly, then back on when the load builds.
Ratchet or plain: when do you actually need holding power?
A plain block spins freely in both directions and has the lowest friction of any block. That makes it the right choice where you never grip the line by hand — turning blocks at the base of the mast, deck-organizer leads, and the moving sheaves inside a mainsheet or vang purchase, where every bit of drag costs you purchase.
You need a ratchet the moment you tail and hold a line by hand under real load. On a 28–45 ft boat that means the mainsheet, the jib and genoa sheets, the spinnaker sheet, and often the vang. The rule of thumb: if a line loads up enough to slip through your hand or a cam cleat under gust, and you trim it live rather than winching it, put a ratchet under it.
Manual or automatic ratchet — which switching do I want?
Manual ratchets let you choose. With the Harken 57mm (HAR2135) or the Ronstan Series 60 (RON-RF62100) you flip the switch off to run free upwind, then on to grip when you crack off and the sheet loads up. That control is why manual on/off blocks dominate keelboat sheets.
Automatic ratchets decide for you. The Selden 45 Ball Bearing Automatic Ratchet (SEL40440101R) runs on smooth 5 mm Delrin ball bearings until the load rises past a set point, at which the ratchet engages on its own; the switch-over point is adjustable with an allen key. That set-and-forget behavior suits dinghies and small-boat control lines where you cannot spare a hand to flip a switch mid-maneuver. If you want a deeper look at automatic, load-sensing designs, see our Harken Ratchet vs. Ratchamatic guide.
How much holding power do I need — 10:1 or 20:1?
Holding power is the ratio of the load you can hold to the effort your hand supplies, and it varies by design. The Harken 57mm Ratchet delivers a 10:1 holding-power ratio with its standard grip, which Harken positions for medium to light air — enough control for most cruising sheets without making the line hard to ease. The Ronstan Series 60 pushes that further: its patented extruded-hole sheave and matched groove profile give up to 20:1 holding power, so you can hold a higher load by hand.
More grip is not automatically better. A high-grip ratchet holds more but is harder to ease smoothly and can add drag you do not want in drifting conditions. Match the grip to your typical load and wind: lighter air and smaller boats favor the lower ratios and automatic engagement; bigger sheet loads reward the 20:1 designs.
How do I size a ratchet block?
Start with sheave diameter and line diameter, then check the bearing. Match the sheave to the rope so the line seats without pinching — the blocks here run 45 mm (Selden), 55 mm (Barton), 57 mm (Harken), and 60 mm (Lewmar and Ronstan), a spread that covers the sheet and control lines on most 28–45 ft boats. Then look at the bearing system, because it sets how the block runs when the ratchet is off: the Ronstan Series 60 uses a Torlon ratchet pawl with a machined-alloy sheave on Acetal hubs and bearings, the Lewmar 60mm runs a stainless-steel central race and balls in an open, self-flushing body, and the Selden 45 rides on 5 mm Delrin ball bearings. Confirm the block's rated load clears your peak working load with margin before you commit.
Which ratchet block should I choose?
Dinghy and small-boat control lines: the Selden 45 Automatic Ratchet engages itself as load builds, so there is no switch to remember.
Cruising sheets in medium to light air: the Harken 57mm Ratchet gives a controllable 10:1 grip with an on/off switch on both sides.
Everyday cruiser sheets and control lines: the Lewmar 60mm Control Block pairs a stainless ball race with an open, salt-flushing body for low maintenance.
High-load sheets that need maximum hand grip: the Ronstan Series 60 delivers up to 20:1 holding power.
General-purpose sheet handling: the Barton 55mm single ratchet is a straightforward, robust option.
Frequently asked questions
What is the difference between a ratchet block and a plain block?
A plain block spins freely in both directions for the lowest friction. A ratchet block adds a toothed sheave and a pawl that grips the line in the loaded direction, multiplying your hand's holding power so you can hold a loaded sheet without a winch or cleat.
Do I need a ratchet block for my mainsheet?
On most 28–45 ft boats, yes. The mainsheet loads up enough that holding it by hand on a plain block is difficult; a ratchet lets you trim and hold it with control. Use plain blocks for the turning and lead functions where you never grip the line.
What does 10:1 or 20:1 holding power mean?
It is the ratio of the load the block will hold to the effort your hand has to supply. A 10:1 block lets you hold roughly ten times the load you pull against; a 20:1 design grips harder still, which helps on higher-load sheets but makes smooth easing a little more work.
What is the difference between a manual and an automatic ratchet?
A manual ratchet has an on/off switch you flip yourself, so you choose free running or grip. An automatic ratchet, like the Selden 45, engages on its own once the load passes an adjustable set point — convenient on dinghies where you cannot spare a hand.
What size ratchet block do I need?
Match the sheave diameter to your line so the rope seats cleanly, then confirm the rated load clears your peak working load with margin. The blocks in this guide span 45 to 60 mm sheaves, covering the sheets and control lines on most cruising and cruiser-racer boats.