A mainsheet traveler system is sized by boat length and mainsheet load, not guesswork: MAURIPRO stocks 22mm Small Boat, 27mm Midrange, and 32mm Big Boat car-and-track systems, plus complete Lewmar kits for boats up to 28 ft and 36 ft, so you can match the car, track, and control-line purchase to your boat in one order.
On a 30–45 ft cruiser, the mainsheet traveler is the one control that does the most for the least effort — when it's sized right. Undersize the car and the bearings load up and bind in a breeze; undersize the purchase and the control line takes more muscle than most crews want to give it; mismatch the track profile and the car you bought won't even go on. None of that shows up until the first time you actually need to move the boom under load.
This guide walks through how MAURIPRO's Harken and Lewmar traveler systems are actually sized — by car-and-track family, by control-line purchase ratio, and by whether a complete kit or a component build fits your boat — using the manufacturers' own published specifications, not an invented formula.
Mainsheet traveler systems at a glance
| System | Boat length | Type | MAURIPRO SKU | Price |
|---|---|---|---|---|
| Lewmar Mainsheet System – Size 0 | Up to 28 ft | Complete kit: track, car & controls | LEW29060152BK | $290.00 |
| Lewmar Traveler System – Size 1 | Up to 36 ft LOA | Complete kit, 4:1 purchase, 8mm control line | LEW29461354BK | $645.00 |
| Harken Traveler Car 27mm, 3:1 Purchase (Midrange) | 27–34 ft | Ball-bearing CB car, component build | HART2731B | $301.95 |
| Harken Track 27mm Low-Beam Pinstop, 3.3 ft | Pairs with 27mm Midrange cars | Component track | HARR271M | $92.95 |
| Harken Traveler Car 32mm, 2:1 Purchase (Big Boat) | 32–50 ft (up to 70 ft coupled) | Ball-bearing CB car, component build | HART3221B | $344.95 |
| Harken Control Block Kit, 27mm | Upgrades 1:1 to 4:1 purchase | Add-on purchase kit | HART27KIT | $103.95 |
What does a mainsheet traveler system actually include?
A mainsheet traveler system is three things working together: a track mounted across the cockpit or coachroof, a car that rides the track and carries the mainsheet block, and a control-line purchase that lets you pull the car to windward or ease it to leeward under load. Per Harken's own tech-service guidance, sizing one starts with your mainsail's square footage, whether your boom is mid-boom or end-boom sheeted, whether your track is supported low-beam or unsupported high-beam, and whether you race or cruise — not with boat length alone, though length is a fast first filter.
How do you size the car and track to your boat?
Harken sells its ball-bearing traveler cars in three width families, each rated to a boat-length range per MAURIPRO's own live product data: 22mm Small Boat for the smallest cruisers and dinghies, 27mm Midrange cars built to handle high loads on boats from 27 to 34 ft, and 32mm Big Boat cars for 32 to 50 ft (up to 70 ft when two cars are coupled together). The car and the track it rides on have to be the same width family — a 27mm car will not go on 32mm track, and vice versa.
From our rigging bench: the mismatch we see most often on a haul-out isn't the wrong boat-length rating — it's a car and track from two different width families that a previous owner forced together, or a plain slider car muscled onto ball-bearing track. Read the width stamped on the track (22, 27, or 32mm) before ordering a replacement car, not just the boat's LOA.
Complete kit or build it a la carte — which is right for your boat?
Lewmar sells its smaller systems as a single complete kit rather than separate parts. The Mainsheet System – Size 0 is a complete kit for yachts up to 28 ft, and the Traveler System – Size 1 "contains all the components necessary to assemble a standard traveler system with 4:1 controls" for boats up to 36 ft LOA, sized for 8mm (5/16 in) control lines, per Lewmar's own product specification. One box, one price, everything you need to mount it.
Harken's approach is component-based: buy the car, the track, and (if you want more than the base 1:1 purchase) a control block kit separately, in whatever combination fits your deck layout. That costs more line items up front but lets you mix a higher-load car with a shorter track run, or add a control block kit later instead of buying the whole system again.
What purchase ratio do you actually need for the control line?
Per Harken's own published traveler FAQ, the control-line load you pull is roughly 20% of the load on the car itself, and purchase ratio is what brings that number down to something you can actually handle. Harken's own figures for an 11m (35 ft) boat: a 3:1 purchase can leave as much as 32kg (70 lb) on the control line; a 4:1 purchase brings that down to about 23kg (50 lb); and for most cruisers, Harken recommends enough purchase to get to roughly 16kg (35 lb) of hand load, which on an 11m boat means a 6:1 purchase. Lewmar's Traveler System – Size 1 ships with 4:1 controls built in, which lines up with Harken's own "more common on newer boats" purchase for a boat in that size range.
Can you upgrade the purchase ratio without buying a new car?
Often, yes. Harken's Control Block Kits are sold specifically to upgrade an existing 27mm or 32mm car's control blocks from a 1:1 to a 4:1 purchase, per MAURIPRO's own product listings for both kits — a lower-cost fix than replacing the whole car if the car itself is the right size and the purchase is what's underpowered.
Does a mainsheet traveler need a ball-bearing car, or will a T-Track slider work?
Not interchangeably. Per Harken's own FAQ, a ball-bearing car requires its matching CB (captive-bearing) track to let the bearings recirculate — you cannot put a ball-bearing car on plain T-Track, because the balls will skid instead of roll and flatten out. If your existing track is a simple T-Track slider, budget for a matching CB track alongside a ball-bearing car rather than trying to retrofit one onto the other.
What size control line should you run?
Lewmar's Traveler System – Size 1 is specified for 8mm (5/16 in) control lines, per Lewmar's own product data. Beyond a specific kit's spec, Harken's own traveler guidance (published under its Traveler Know-How technical article) is to run the largest-diameter line your car's sheaves are rated for, not the smallest — a thinner line is easier to coil, but it adds friction and grip trouble under load, while the largest line the sheave accepts gives the smoothest, most secure run.
From our rigging bench: the second most common issue we see isn't the purchase ratio at all — it's a fair lead. Even a correctly sized 6:1 system fights you if the control line has to cross another sheave, snag a cam cleat at a bad angle, or chafe against a hatch or winch base on its way to the cockpit. Size the system right, then check the lead before calling it done.
Which should I choose?
If your boat is 28 ft or under and you want one part number that includes everything, Lewmar's Mainsheet System – Size 0 is the direct fit. Up to 36 ft LOA with 4:1 controls already built in, Lewmar's Traveler System – Size 1 covers the same complete-kit approach at a larger size. If you're on a 27–34 ft boat and want to build the system yourself — a specific bearing type, a specific track length, a specific purchase — Harken's 27mm Midrange car, track, and control block kit let you spec each part. Above about 32 ft, or if you're replacing an existing Harken system, the 32mm Big Boat car is the match, with coupled cars available up to 70 ft.
Common mistakes to avoid
Sizing by boat length alone. Length is a fast filter, but Harken's own sizing process also asks about mainsail area, boom sheeting position, and track beam type — get those wrong and a "correctly sized" car can still be under- or over-specified for your actual load.
Mixing car and track width families. A 27mm car will not run on 32mm track or vice versa; confirm the width stamped on your existing track before ordering a replacement car.
Running a ball-bearing car on plain T-Track. Per Harken's own guidance, the bearings will skid instead of roll and flatten out — a ball-bearing car needs its matching CB track.
Frequently asked questions
What's the difference between a mainsheet traveler system and a genoa car and track?
Both use a car-on-track design, but they control different lines: a mainsheet traveler positions the boom and mainsheet attachment point, while a genoa car positions the headsail's sheet lead. The two are sized separately and are not interchangeable parts, even when the track widths look similar.
How much control-line load will I actually feel with a 4:1 purchase?
Per Harken's own published figures, a 4:1 purchase on an 11m (35 ft) boat brings the control-line load down to roughly 23kg (50 lb), compared to about 32kg (70 lb) on the same boat with a 3:1 purchase. Larger or smaller boats scale up or down from there.
Can I use a T-Track slider for my mainsheet traveler?
Only if you're running a non-ball-bearing slider car matched to that same T-Track. A ball-bearing car needs its own CB (captive-bearing) track to let the bearings recirculate; per Harken's own FAQ, forcing a ball-bearing car onto plain T-Track will damage the bearings rather than let the car roll.
Do I need to replace the whole car to change the purchase ratio?
Not necessarily. Harken sells Control Block Kits specifically to upgrade an existing 27mm or 32mm car's controls from 1:1 to 4:1 purchase, which is less expensive than buying a new car if the car's size is already correct.
What control-line diameter fits my traveler system?
Lewmar's Traveler System – Size 1 is specified for 8mm (5/16 in) line. For other systems, Harken's own guidance is to run the largest-diameter line your car's sheaves are rated for, since a too-thin line adds friction and grip problems under load rather than making the system easier to handle.
Is a complete kit missing anything I'd need to buy separately?
Per Lewmar's own product description, the Traveler System – Size 1 "contains all the components necessary to assemble a standard traveler system" — track, car, and 4:1 controls in one part number. Mounting hardware and the control line itself should still be confirmed against your specific deck layout before installing.
See also: How to Use a Mainsheet Traveler on a Sailboat, Harken Traveler Cars: Smooth, Efficient Mainsail Control (Selection Guide), and Which End Stop Do You Need for Your Genoa Car or Traveler Track?.