Waves, the wind’s assassin

There’s a discussion underway on the YBW forum about rogue waves, wave height and frequency. Here’s my take on the subject from a few years ago…..

It’s been pretty windy around here for the past couple of weeks. We’ve had Force 10 and 11 a couple of times. Off Donegal they measured a wave at 67’ (20.4m), the highest wave recorded in Ireland. The Irish Met Office says the buoy that measured it is 11km off the coast, so it was generated in deep water by the persistently high winds.

I was once in very heavy weather off the east coast of the USA and there was a point at which I didn’t think the boat was going to make it up the face of a particularly steep wave. An illusion, of course, but pretty scary nonetheless.

The probable maximum height of wind waves is around 80% of the wind speed in feet. So, a 50-knot wind blowing over an area of ocean with unlimited fetch would produce a maximum wave height of about 40 feet. This height is achieved after it has been blowing for a day, having doubled in height since the first four or five hours of the storm. Further maximum wave height increase is more subdued, it takes two days to get that wave up to 50 feet in height.

All pretty scary in a small boat.

Check your mast spreaders

Time to remind you to make sure your spreaders are set up properly before embarking on a new season at sea.

Drooping is not usually a good thing. You don’t want drooping bits. You especially don’t want drooping spreaders. Drooping spreaders are a symptom of a rig in distress, a rig on the road to catastrophic failure.

Perky upward pointing spreaders are what you want. Perky spreaders have tips that bisect the angle of the shrouds that pass over them. In this way, the load on the spreader is even and the spreader is disinclined to be pushed up or down and thereby slackening the shroud, threatening the integrity of the whole rig.

Spreaders come in lots of shapes and configurations: The racier boats have spreaders with aerofoil sections, like little aircraft wings, to reduce wind resistance. Cruising boats tend to have longer spreaders to give a broader based rig, sacrificing sheeting angle for better mast support. Old fashioned cruising boats under about 45’ tend to have single spreader rigs, for the sake of simplicity, whilst more modern boats with relatively taller masts adopt multiple spreaders for even relatively small boats. Spreaders can be fixed at the mast or fully articulating and they come with a variety of methods of attaching the shroud to the spreader tip so it doesn’t jump out. But whatever the spreader’s design, drooping must be avoided at all costs – check your spreaders now!

A word of caution: Once you become an aficionado of the perky spreader your marina dock strolls will take on new meaning, your eye will be inexorably drawn aloft in search of droopers with the attendant risk of an early bath or a broken toe.



Smelly heads

You know that stench you get below decks when you return to your boat after a few days away? It is, more often than not, down to the sea toilet.

Most marine toilets are flushed with raw water from sea, lake or river. This flushing water contains living organisms and it’s the demise of these little devils in the pipe work that begins the downward spiral; the resultant bacteria generate that awful sulphurous gas smell which you suck into the boat when you pump. The pipework itself can become contaminated so that no amount of flushing will get rid of the smell.

At one time I handled maintenance for a fleet of charter boats and keeping the heads sweet was a big headache. I was persuaded that a major contributor to the odour was the fact that the translucent sanitation hoses let in sunlight which hastened the demise of the bugs and, thereby, the creation of the bacteria which caused the smell. I wrapped all my pipes in silver foil as a defence but found no real improvement and ended up changing all the pipes at the beginning of each season, and still had to deploy an array of disinfectants on a regular basis.

When I moved onto my boat full time and set off on my three-year modest odyssey the problem was greatly alleviated by frequent and regular flushing. Unless you live aboard you simply can’t keep up the necessary flow.

The only boat of the seven I’ve owned not to suffer the odours was my GB32 trawler which had a fresh water flushing system and in-line deodorizer. But on a long-distance cruising boat you simply can’t afford to flush freshwater down the bog, it’s way too precious for that.

VHF transmission range

For VHF communication the most significant factor in establishing range is your antenna’s height above sea level. This assumes, of course, your system consists of a good antenna with the right size cabling and a properly functioning radio or AIS unit.

Think of radio range as your radio horizon plus the radio horizon of the station you are communicating with. Radio horizon is an invisible circle around your boat, the perimeter of which is the distance to which the radio signal from your antenna will reach. The station with which you are communicating will have its own circle, the extent of which will depend on its antenna’s height above sea level. When the two circles meet you can communicate. This is your range. So, your communicating range varies, depending upon the radio horizon of the station with which you are communicating.

Your radio horizon in nautical miles is 1.4 x root of antenna height in feet above SL. For example, if your antenna is at the masthead, 49 feet above sea level, your radio horizon will be 1.4 x 7 = 9.8 nm. If you are communicating with an identical boat, your combined range will be twice this figure, about 20 miles. However, if you are communicating with the QE2 where her antenna is nearly 200 feet above sea level, her radio horizon will be about 20 miles so you’ll be able to communicate at closer to 30 miles.

Coastguard stations have powerful transmitters located high up on headlands and have large radio horizons. An antenna at 900 feet above sea level would have a range of 1.4 x 30 = 42 miles, so you could communicate at about 50 miles.

Clearly, the ideal location for your VHF antenna is as high as you can get it and, on a sailing boat, that means the masthead. Nowadays you’ll probably be using AIS and radio so the masthead location can create a problem – how to locate two antennas far enough apart so they don’t interfere with each other. If you can get the antennas over 0.75 meters apart, they should function fine. Some experts say they need to be more than 1m apart but anecdotal evidence seems to suggest the 0.75m figure is good enough. If you can’t get this degree of separation your choices come down to using an active splitter or mounting one of the antennas (AIS) at the next highest location – mizzen mast, radar-arch/pole or the pushpit.

Having a second antenna is a wise choice because it means you aren’t interrupting AIS data when using the radio and the second antenna provides redundancy. Arrange the cabling so that either antenna can be connected to either radio or AIS. Carry an SO239/BNC adapter if the input to your AIS is BNC. Your radio is always PL259.

If you have a combined radio/AIS it will usually be equipped with a splitter – be sure to use a full range VHF antenna, 156 to 163 MHz, so as not to compromise reception.

Fair winds!

Masthead LED Navigation Lights

Masthead LED navigation lights – tri-colour, anchor, a combination of the two – make perfect sense for sailboats. Ultra-low power consumption and long life are the main attractions.

Those advantages are obvious, but what else should you expect from your masthead lights? Rugged reliability, for one thing. We shouldn’t underestimate the vibration and brutal motion at the masthead in a seaway and your navigation light has to cope with all that. So, super-solid construction and a strong fixing system should be on the list.

A reliable photoelectric cell to switch the light on at dusk and when daylight fades in storms and fog, and off again when normal light conditions return, is a big advantage. Also, a tall light as opposed to a squat profile ensures the light won’t be masked from some angles by the mast upon which it’s mounted. If you use a lamp like a hockey puck, it might be a good idea to elevate it somehow.

Another factor, a big issue with LEDs, is interference with VHF radio and AIS reception. When you switch on your masthead light you don’t want to hear crackling on the radio and you don’t want your AIS information to go walkabout. You’ll want a guarantee from the manufacturer that this won’t happen. In my role as a Metz VHF antenna system provider, I’ve been banging on about this for years. Navigation lights and antennas share a tight spot at the top of the mast and they must be compatible. As recently as August 2018 the US Coastguard was warning about the proliferation of difficult or failed VHF radio communications as a direct result of LED interference. It is the voltage regulating circuit that’s the culprit and even expensive LEDs may have the sort of buck regulator that oscillates at a frequency which blocks VHF transmissions. Check yours!

LED navigation lights are a great innovation for the sailor, providing excellent performance and miserly power consumption. There are many brands on the market, be sure to choose wisely.

1 December 2018: Salty John has now concluded a deal with OPTOLAMP to stock their range of LED masthead navigation lights. These excellent lights tick all the boxes. Have a look at saltyjohn.com for more details. Should be in stock by Christmas. Now in stock.

Metz VHF antenna – a thing of beauty.

The superb Metz Manta VHF antenna is a thing of beauty and durability. It also gives exceptional performance. What makes it so special is the precision-wound, heavy-duty coil housed within that stainless-steel can, and the way the coil is properly supported so it doesn’t distort when heat builds during transmission. The coil is sealed with epoxy and has a lifetime warranty. The 34” whip is stainless-steel, of course.

The Metz Manta is used by the US Coastguard, UK lowland Search and Rescue organisations, many charter fleets, several boat manufacturers, and the round-the-world Clipper fleet. And by many, many thousands of individuals – it’s been in continuous manufacture since 1977.

The Metz comes with a stainless L-bracket. Other mounting options include the Metz quick release rail mount and there’s an adapter available so it can be mounted on any 1”, 14 tpi, threaded mount.

Put the Metz Manta together with marine quality coaxial cable of the correct size, use top class connectors and your antenna system will extract the maximum performance from your VHF radio and AIS system.

Get your Metz antenna and accessories from

www.saltyjohn.com, the UK and European distributors.