Choose a block by matching four things to the job: sheave diameter to line diameter, bearing type to how the block is loaded and how often it moves, working load to the peak load in that control, and attachment style to the deck or line it lands on. Get those four right and the block runs freely, lasts, and stays safe. This guide covers the selection logic for a 30 to 45 ft cruiser or performance-cruiser, without brand hype and without quoting numbers that only belong on the specific product page.
Written for experienced sailors refitting or upgrading a 30 to 45 ft cruiser or performance-cruiser: people who already know a mainsheet from a vang and want the decision framework, not the basics. We sell across brands and drop-ship much of this catalog, so this is a selection and sizing guide, not a stock report. Always confirm the working load, sheave diameter, and line range on the individual product page before you buy.
Blocks at a glance
| Type | What you'll find / how to choose |
|---|---|
| Single block | One sheave to turn or redirect a line. Choose when you only need to change a line's direction, such as a lead or a turning point. Size the sheave to the line and the working load to the peak pull at that point. |
| Double / triple block | Two or three sheaves stacked to build purchase in mainsheet, vang, or traveler tackle. Match sheave count and diameter to the tackle ratio you need, and rate the block for the loaded, not the hauling, end. |
| Fiddle block | Two different-diameter sheaves in one cheek for compact multi-part purchase, common on vangs and mainsheets. Choose when you want purchase in a low-profile package; still size to line and working load. |
| Ratchet block | A sheave that grips under load to hold the line so the crew can ease and hold by hand. Choose for hand-held sheets, dinghy-style trimming, and control lines you tail by hand. |
| Snatch block | Opens to take the line at the bight, so you rig it without threading a bitter end. Choose for temporary leads, spinnaker gear, and headsail-sheet turning points that must be rigged or cleared quickly under load. |
| Cheek / mast-base block | A block that bolts flat to a surface, cabin top, or mast base to turn a line close to the deck. Choose for low-profile turning points and organized deck leads where a hanging block would foul. |
How do I match sheave diameter to my line?
Size the sheave to the line the block will carry, using the line-diameter range stated on the product page. Too small a sheave forces a tight bend radius that adds friction and shortens line life; too large a sheave wastes deck space and money. Pick the block whose stated line range brackets your actual line diameter, and if you plan to upsize the line later, size for the larger line now.
Ball bearing or plain bearing — which do I need?
Match the bearing to how the block works. Ball-bearing blocks run with low friction and are the choice for dynamic, frequently-adjusted controls such as mainsheets, travelers, and jib sheets where you trim constantly. Plain-bearing (bushing) blocks tolerate high static load better and are the choice for leads and turning points that sit loaded for long periods without moving, such as halyard leads and reefing lines. Roller-bearing blocks sit between the two.
How do I choose the working load?
Work out the peak load the block will actually see at that point, then choose a block whose rated working load covers it with margin. Rate to the loaded side of any tackle, not the light hauling end, because the block near the load carries far more than the line you pull. When your load lands between two sizes, step up to the larger block rather than run a block near its limit — the heavier block runs cooler, lasts longer, and gives you headroom for gusts and shock loading.
How does attachment style change the choice?
The head fitting has to suit both the load and the mounting point. Swivel heads let the block align itself with the load and suit sheets and leads that change angle. Fixed heads hold a set orientation for a consistent lead. Cheek and mast-base blocks bolt flat where a hanging block would foul. Snatch heads open to take the line at the bight for gear you rig and clear quickly. Choose the head that matches the geometry of the job, then confirm the block's working load still covers the point.
Which should I choose?
Start from the job, not the brand. Identify the control (mainsheet, vang, traveler, halyard lead, sheet turning point), estimate the peak load there, and note the line diameter. Then pick the block whose stated line range brackets your line and whose working load covers your peak with margin, choosing ball bearing for anything you trim often and plain bearing for static high-load leads. Where a load falls between two sizes, step up. For a hand-tailed sheet, add a ratchet; for gear you rig under load, choose a snatch block; for a flush turning point, choose a cheek or mast-base block.
Frequently asked questions
Can I use a smaller, lighter block to save weight aloft?
Only within its rating. Weight aloft matters on a performance-cruiser, but never drop below the working load the point actually sees. If two sizes both cover the load, the lighter one is a fair choice; if you are near the limit, step up.
Do I need ball bearings everywhere?
No. Ball bearings pay off where you trim and adjust constantly, because they cut friction under motion. On leads and turning points that sit loaded and rarely move, a plain-bearing block often lasts longer and handles the static load better. Match the bearing to the duty of each specific point rather than fitting one type across the boat.
My line is between two sheave sizes — which way do I go?
Go to the block whose stated line range brackets your line. If your line sits at the top of one block's range and the bottom of the next, prefer the larger sheave: the gentler bend radius reduces friction and line wear. Never force a line above a block's stated maximum diameter.
Do you keep these blocks in stock?
We list blocks across multiple brands and many are drop-shipped, so treat this guide as help with selection and sizing rather than a stock statement. Confirm the current working load, sheave and line range, and availability on the individual product page before you order.