Night sailing

When the sun has melted into the horizon like a knob of butter on a hotplate you flick on the navigation lights and prepare for a night at sea.

Night sailing is at times magical, at other times intimidating. Deep water with plenty of sea room, no traffic, a gentle breeze and a big moon are the ingredients for a pleasant night passage.

We enjoyed just such an untroubled passage between Dominican Republic and Puerto Rico on our sloop Adriana. It had been hot and windless during the day but as night fell the breeze came back and the lights of Mayaguez twinkled on the horizon. I set the jib, slacked the mainsheet and cut the engine. Adriana leaned her shoulder into the sea and came alive. The sky grew into deeper shades of night, beset with a million jewels, as we cut a swathe through the boisterous sea.

Other night passages have been less idyllic: Battling to windward along the north coast of Hispaniola under a grim moonless sky, hugging the rocky coastline to stay within the umbra provided by the land, lightning blooming on the horizon – this wasn’t the most relaxing of night watches.

Dawn creeps up with the promise of delight or of dire warning – radiant sunburst or red tinged clouds. Another day at sea begins. What will it bring?

Forestay tension on catamarans

Forestay tension is achieved by tensioning the backstay. On most boats the amount of backstay tension you need to apply is less than the resultant forestay tension because the forestay makes a more acute angle with the mast than does the backstay.

However, on many catamarans the backstay makes a more acute angle than the forestay, as can be seen on this Prout sail plan. This means that for every kilogram of tension needed in the forestay you have to crank on more backstay tension. So, be careful.

A Loos tension gauge is a handy tool for setting up standing rigging.

 

The Metz VHF antenna

To survive in the marine environment your VHF antenna needs to be strongly built of appropriate materials – look for stainless steel components, including both the body and the whip. How the antenna is built internally isn’t so obvious – you’ll need to rely on reputation and a good warranty.

A marine VHF whip antenna depends for its performance on proper design and build-quality. That tin-can at the bottom of the antenna contains the DC shunted coil that must be precisely tuned to the proper resonance. Getting this bit of the design and build right is the difference between an antenna that performs well and one that doesn’t.

The US built Metz antenna is based on a heavy gauge stainless steel shell which encloses the coil wound around a substantial form. The coil assembly is sealed in a solid epoxy compound. This build method allows prolonged transmission without danger of coil distortion as the antenna heats up. It carries a life-time warranty.

The Metz antenna is used by professionals such as UK Search and Rescue organisations, professional fishermen, tour boats and the Clipper Round the World fleet.

Lower quality antennas have fibreglass or mild steel bodies (see picture) enclosing light gauge coils and inadequate forms all sealed in a waxy substance. This flimsy internal construction leads to distortion of the coil as the antenna heats up when transmitting, which changes the antenna characteristics, leading to poor performance.

You don’t need to pay through the nose for top quality construction: the Metz Manta, at £59.95 including UK postage, is no more expensive than ordinary antennas and lower in price than some other stainless bodied antennas. Check it out at the Salty John on-line shop.

Is your propeller a drag?

If you think anchor selection is a controversial subject you should try talking about propellers. I don’t know why these subjects should cause such angst, but they do. So I’ll just dive right in.

The first issue is drag: Under sail with the engine stopped does a fixed propeller create more drag when it’s locked or when it’s allowed to freewheel? You would think the answer would be unequivocal – and it shouldn’t need rocket scientists to work it out. But just to be sure, some rocket scientists, or their marine equivalents, did work it out and their answer is unequivocal: There is less drag when the propeller is allowed to rotate.
Scientists at MIT and at Strathclyde University agree on this. It is fact.

So, we know we get less drag with the propeller rotating but what are the other arguments for and against allowing the prop to turn?

Noise: The rumble from a rotating propeller can be quite intrusive, particularly if you’re off watch in a stern berth. Some people can’t stand the noise whilst others find it interesting; they like to judge the speed of the boat by the level of noise.

Energy recovery: If you want to run a generator off the shaft it has to turn – simple.
Wear: Where there’s motion there’s wear and tear, if not damage, to drive train bearings and seals.

Gearbox damage: Clearly you shouldn’t be risking damage to your gearbox or losing your warranty protection just to get a half a knot of boat speed under sail or to get a good night’s sleep in the quarter berth.

It seems that Yanmar became so concerned at the number of requests they received for clarification on the best practice for their engine/gearbox combinations that they issued a directive: The gearbox must be in neutral when sailing or your warranty will be invalidated. If you want to stop the shaft use a shaft brake, they say, not our gearbox.

I have to admit I sailed for many thousands of miles with my Yanmar 3GM30F in reverse gear to stop the shaft rotating and I never had a moment’s trouble. Just lucky?

If you have a Hurth/ZF gearbox you must not select forward gear when sailing forwards. Or reverse when sailing backwards, obviously. Apart from that, use the gearbox in reverse to lock the shaft or let it run free, it’s up to you.

With a Borg Warner Velvet Drive transmission you can do what you like, it will rotate anyway.

On some gearboxes damage can occur because the engine needs to be running to provide lubrication, with splash lubrication there isn’t usually a problem, so check the manual.

It boils down to this: If you are obsessed with squeezing out the last fraction of a knot under sail you need to let the prop freewheel. You’ll be happy to accept any wear and tear on your cutlass bearing and you’ll issue ear plugs to those that find the noise is keeping them awake.

If you’re worried about wear or can’t stand the noise you’ll want the shaft stopped and whether you do that by using the gearbox or a shaft brake will depend on your gearbox manufacturer’s advice, and whether or not you’re going to obey it.
Simple, really.

Tuning your rig

It’s really important to have a properly set rig to get the best performance from your boat without placing excessive loads on the rig or hull. The best way to achieve this is with a rig tension gauge made by rigging manufacturers Loos & Co, available from Saltyjohn.com here in the UK.

For the average cruising boat, you’ll be aiming to set up your rig like this:

Forestay tension – masthead rig: It is almost always advantageous to set the forestay tension as high as possible within the limits of structural strength. Generally, it is possible to use 15% of the breaking strain of the wire as the forestay tension. The backstay should be adjusted to maintain a straight mast with the desired forestay tension. The backstay tension will usually be less than the forestay tension because the backstay makes a greater angle to the mast than does the forestay – some catamarans are the exception to this rule.
Note that rollerfurling jib tension can only be set by adjusting backstay tension.

Forestay tension – fractional rig: Because the forestay tension cannot be directly balanced by the backstay tension some mast bend is accepted and the sails are cut to accommodate it. Forestay tension of at least 15% of the wire strength is desirable but, if this should result in excessive mast bend, it may be necessary to back off the tension.

Upper and lower shroud tension – masthead rig: The initial rig tension should be high enough that the leeward shrouds do not go slack when sailing close-hauled in a brisk breeze. The proper tension for your boat can be found by a few test-runs under sail and then the Tension Gauge can be used to record and maintain this value.
For many boats, a shroud tension of 10% to 12% of the wire strength is adequate. In some rigs it may be advantageous to carry a bit more tension in the uppers than the lowers.

Upper and lower shroud tension – fractional rig: In most cases the same comments apply as for masthead rigs. However, there is one exception. Where the upper and lower shrouds on a fractional rig lead to chainplates located aft of the mast – swept back spreaders – most of the forestay tension is balanced by the upper shrouds. A shroud tension as high as 20% of the wire strength may be required to achieve the desired forestay tension. Never exceed 25% of the wire breaking strength.

A well-tuned rig and correctly set up spreaders (ban the droop!) will ensure you get the best from your boat and avoid structural damage. The key is the Loos tension gauge.