Top-Down Adapters: Maximise the value of your furling unit
by Diego Sosa, Upffront 24 Sep 2018 01:00 PDT
Facnor FX 2500 standard bottom-up furling unit with top swivel and top-down adapter © Facnor
Imagine you have a 39 footer and are interested in using the same furling unit for both your code zero and asymmetric spinnaker. We take a look at the furling unit options and discuss the available torsional cables depending on your sailing style and budget.
Furling unit
At 39ft you are really at a cross-over point in terms of unit size.
For bottom-up furling of your code zero you need to be able to create some luff tension. Therefore, a 2500-3000kg Safe Working Load (SWL) unit is advisable. A bigger drum size is also a significant benefit; providing more power to start the furl.
On the other hand, for top-down furling, neither of the above are a benefit. For top-down furling, the working loads are low, as the torsional cable only needs to be under tension during furling/unfurling. For the majority of the time the torsional rope is relatively slack. Also, a smaller drum means greater turning speed which is a benefit for top-down (assuming you can create the required line speed from either your primary winch or your crew!).
In theory therefore, a smaller unit would be appropriate for top-down. Unfortunately, the other key element to effective top-down furling is torsional stiffness from your furling cable and this means they are always bigger diameter than the equivalent bottom-up cable. A larger diameter torisonal cable means wider thimbles which necessitates a larger jaw width on your drum. This often becomes the key factor in the choice of furling unit and forces top-down furling into the next drum size up, regardless of the low working load requirements.
Therefore, an appropriate unit size for both bottom-up and top-down is going to be in the range of 2500-3000kg SWL and your primary options are:
Unfortunately, Ronstan do not have a top-down adapter system. They have either dedicated top-down or bottom-up drums and so if you want to go the "combo" route, that counts the Ronstan out. This is actually a shame because the new Ronstan Gen2 units are very well built and despite having a higher SWL (3000kg), the Series 160 is the lightest unit out of the three. If it was a dedicated Code zero furler you were after, then this would be a strong candidate.
However, at upffront.com we are big believers in the top-down adapter approach which allows you to use the same drum for both bottom-up and top-down furling. It adds some weight but the flexibility benefits, for the majority of cruisers, far outweights the weight penalty. This leaves us with the Facnor and Karver options which both have top-down adapters for their units.
Comparing the two systems (drum + adapter):
- Drum size - The Karver has smaller drum (151mm) which is better for top-down as it generates more speed. But the bigger drum of the Facnor (161mm) might be more important for starting the code zero furl.
- In terms of weight, the Karver package is 6% lighter (drum, swivel and top-down adapter)
- Jaw widths - the Karver and Facnor units have 18mm and 17.5m jaw widths respectively which may/my not have an impact, depending on cable choices - see below.
So in conclusion, from a technical perspective, we would suggest there is little to chose between the Facnor and Karver systems. Karver is slightly lighter but the additional drum size on the Facnor will be useful for your code zero.
Don't forget the furling line for the drum!
Both the Karver and Facnor units require an 8mm furling line. Most clients prefer to furl from the cockpit which means you are looking at a loop length of approx 11m (depending on your deck loyout). There are two quality options:
Like everything in life, "you get what you pay for" and as the plan is to use this drum for both code zero and asymmetric, we would strongly advise investing in the better furling line. The GP line is made from Gottifredi Maffioli Loopline which is a rope that has been specifically designed for this purpose.
Furling Cable options
On the upffront.com website, if you go to the Furling cables category page, it is very easy to see your cable options. Just select your cable length from the filter (black box above the table). We will use 17m - 17.25m to show you the range of options available.
Torsional ropes have improved significantly in recent years but assuming an approx. 17 metre cable length, we are very close to the transition between torsional rope and needing a proper torsional cable. The primary reason for this is that, as torsional loads increase, it is very difficult to terminate the rope around the thimble and stop the thimble twisting out of the cable plus the ends become very bulky.
Torsional performance is directly related to diameter and it is particularly important for top-down furling to have the correct diameter, relative to the cable length, to ensure good furling. A quick review of the options available would suggest that for a 39 footer you should be looking at a 13mm diameter cable for bottom-up and a minimum of 15mm for your top-down furling cable.
The choice of cable then comes down to sailing style, preference and budget!
For a cruising boat, the 13mm Hampidjan rope would be the most cost effective option and perfectly adequate for the code zero. However, if you are looking for a more performance option the Gottifredi Maffioli DM20 cable is specially designed for Bottom-up furling. It is lightweight, a good diameter (not too fat) and reasonably priced. The standard for a GP race campaign is to use a PBO core for Code zero's, to minimise luff sag, but this comes at a price premium.
For the asymmetric top-down cable, there is a problem with the budget 15mm Hampidjan rope option. The thimble to comfortably carry a 15mm rope is too big to fit either the Karver or Facnor units. This is where a custom cable provides more flexibility in terms of optimising thimble widths to suit the drum jaw width.
Therefore, for cruising applications, the Armare K49 cable is an excellent choice. This is a very high quality, custom cable which is reasonably priced. It is the heaviest and largest diameter, but it will be reliable and last for many years. The performance option is Gottifredi Maffioli's specialist top-down cable with a hollow filament "Aircore". This provides the necessary diameter for excellent top-down furling whilst keeping the weight to a minimum.
Summary
- Using the same furling unit for multiple sails is becoming increasingly popular
- The best way to do this is using a standard bottom-up furling unit together with a top-down adapter
- At this size (39ft), both Facnor and Karver provide technically comparible products
- Torsional rope is still a viable option for the code zero but problematic for the top-down asymmetric
- This is a common dilema with top-down: pay for a more expensive custom cable, where the fitting width can be reduced to fit the furler, or buy a bigger unit.
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