Please select your home edition
Edition
upffront 2018 FSE Robline 728x90 1

Top-down and Bottom-up Furling Units: Differences and Options

by Phil Anniss 28 Dec 2018 01:00 PST
Top-down and Bottom-up Furling Units: Differences and Options © upffront.com

What are the key differences between bottom-up and top-down furling units and do I need a dedicated unit for each type of furling? For a definition of the expressions, "top-down" and "bottom-up" furling - please read our related blog article.

Dedicated top-down unit

The primary difference between a bottom-up and a dedicated top-down furling drum is that a top-down drum has the addition of a free floating tack swivel mounted on the furling drum. When the drum is furled, the fork and cable are rotated whilst the tack swivel remains static. This allows the torque to be transmitted along the full length of the cable to the head of the sail where the furl starts. With the free floating gennaker tack, the bottom of the sail is then the last part to be furled around the torsional cable.

A top-down drum is heavier than its bottom-up counterpart due to the addition of this tack swivel. It should be noted that some manufacturers specify a separate working load for the tack swivel. For example: the Karver KSF8 and KSF8R top-down furling units essentially have the same overall Safe Working Load (SWL) of 8T, but they have tack swivel SWL's of 3T and 6T respectively. Having said that, with top-down furling, SWL is rarely an issue because the cable is only tensioned during furling and unfurling and even then, with just enough load to hold the cable straight during the furl rather than under serious tension.

Note: a top-down furler can be used as a standard bottom-up furler, it is just the tack swivel becomes superfluous.

Other options?

Cruising

Furling units are a reasonable investment and so most will be pleased to hear that there are some options, other than buying a dedicated top-down furling drum.

Most common of these, and popular amongst cruising sailors, is to use a top-down adapter. This is a stand-alone tack swivel that has an eye to connect into a standard bottom-up furling drum with an upper fork into which the torsional cable is connected.

The top-down adapter can be set up and left permanently on the sail, with the cable connected and tack lashing in place. With a swivel similarly dedicated and stowed with the sail, when it comes time to hoist your gennaker, simply attach the top-down in the jaw of the drum, attached the halyard to the swivel and hoist out of the bag.

The only disadvantages with the top-down adapter are the significant increase in weight, over a dedicated top-down drum, and a slight decrease in available luff length. However for most cruising sailors the advantages of using a single drum for both their code zero and downwind gennakers outweighs the disadvantages.

Racing

Another, slightly more complicated, option is used on a number of big boats, with the crew and brain-power to pull it off! In reality, the tack of the gennaker can be completely independent to the furling drum. Some boats set up a 2:1 gennaker tack line directly onto a padeye on the deck, close to the drum. For the hoist, the swivel is attached to the halyard, the bottom of the torsional cable to the fork in the drum and then the tack to the line onto the deck.

The advantages of this setup are that it is the lightest option and it allows the crew to quickly and easily adjust the luff tension on the gennaker. The downside is that you do need to ensure the tackline trimmer is paying attention during the furl/unfurl manoeuvres.

Summary of available options:

  • Separate, dedicated bottom-up and top-down furling units
    • Expensive
  • Use a top-down adapter on each of your gennakers together with a single, standard bottom-up furler
    • Heavy, but a very flexible and efficient cruising set-up
  • Use a dedicated top-down furler for both bottom-up and top-down furling
    • Slow sail changes but otherwise perfectly acceptable
  • Use a bottom-up drum with a separate gennaker tack line
    • Need to have experienced crew

To get a complete guide to specifying and purchasing continuous line furling systems please download our Furling System Guide.

Related Articles

One Design PROtect Tapes
A set of cut pieces tailored to your class PROtect Tapes are a broad range of high-quality protection tapes for dinghies, racing, cruising and super yachts. PROtect Tapes provides a pro-active solution to chafe and wear prevention. It enhances performance and ultimately promotes safer sailing. Posted on 10 Oct
Practical tips on cruising halyard locks
Bouncing to avoid damage Halyard locks are almost universally accepted in racing circles and are becoming increasingly popular with long distance cruisers, as they recognise the significant benefits. Posted on 2 Oct
Baby Karver Furler KF 0.9
The smallest furler manufactured by Karver, for boats under 30ft Launched this year, this is the smallest furler manufactured by Karver. With a Safe Working Load (SWL) of 900kg, it is suitable for small cruisers and sportsboats up to a maximum of 30 ft. Posted on 26 Sep
Karver KJ Jammer
Releasable under (low) load combined with the reliability of a high load jammer French hardware manufacturer, Karver has been active in the French offshore sailing scene (IMOCA and offshore multihull) since its inception in 2004. Their reputation is based on developing a range of innovative products. Posted on 18 Sep
What is a top down adapter?
A tack swivel is a popular evolution of the top-down furling system The top-down adapter, also known as a tack swivel, is an increasingly popular evolution of the top-down furling system. This technique provides cruisers and racers alike, simplicity, safety and speed for the handling of loose luff sails. Posted on 12 Sep
Reefing Your Mainsail
Are you onboard with reef hooks? An ingenious addition to their portfolio, Karver's KHR Reef Hook offers an unconventional way to reef your mainsail. Originally designed for ocean racing multihulls, reef hooks are now being adopted by more and more cruising sailors. Posted on 4 Sep
Transform your sailing with a Velocitek Speedpuck
Lightweight, compact speedometer with high accuracy Speedpuck is a responsive, digital speedometer which utilises the same GPS technology as the America's Cup-endorsed Prostart. Although suitable for boats of all sizes, the Speedpuck is known to particularly flourish on dinghies and one-design keelboats. Posted on 29 Aug
Karver's new 3:1 Friction Sheave
An increase in quality with a reduction in both weight and price It's not often that developments in fitting design deliver a significant increase in quality and a reduction in both weight and price - all at the same time. But Karver Systems appears to have achieved the impossible with the new 3:1 Friction Sheave. Posted on 21 Aug
Bjarne Lorenzen interviewed: Furling Your Mainsail
Andy Rice looks at 'in boom' and 'in mast' furling Most of the time we think of furling headsails but as Bjarne Lorenzen of sailmaker Doyle O'leu explains, there are options for mainsails too. In the fifth and final post from this series, Bjarne considers the pros and cons of 'in boom' or 'in mast'. Posted on 7 Aug
Ino-Rope update
The latest in textile block performance In light of the newly updated Ino-Rope product range, we ask you to cast your mind back to 2013: a French duo - experienced offshore Mini Transat 650 sailor Thibault Reinhart and professional rigger Julien Barnet - burst onto the sailing scene. Posted on 3 Aug
MBW newsletters (top)