Coax cable connectors for boats

Here’s a short look at the type of coaxial cable connector you might encounter when installing your radio and AIS antenna systems.

Boats use 50 ohm coaxial cable for their radio and AIS systems – it comes in different sizes but the three you are most likely to encounter are RG58 (nominal size 6mm, but rarely more than 5.5mm), RG8X (nominal size 7mm but usually 6.5mm and the best choice for boats up to super-yacht size) and RG213 (nominally 10mm, actually about 9.5mm – the cable you need for long runs, 30m or more). Coax cable comprises an outer jacket covering a layer of fine mesh or braid, an insulating layer called the dielectric and then the centre conductor. The outer braid and the centre conductor must never meet. Whichever coax size you have you’ll need to join it to the equipment, and to itself, using a variety of connectors:

The PL259 and its female partner the SO239. This connector pair was developed in the late 1930’s by a designer with the fantastic name of E. Clark Quackenbush. He worked for Amphenol at the time and I wouldn’t have mentioned him at all were it not for that magnificent name. Anyway, he designed what was to become the most widely used connector in the amateur radio field.

PL stands for plug and the number, 259, is the inventory number assigned to it by the US military. The socket into which it plugs is given another inventory number, 239, and the prefix SO for socket.

All marine VHF radios have a built-in SO239 antenna socket to accept a PL259. Top quality marine antennas use the same connector, so the antenna cable will have a PL259 at each end, whatever other connectors it has for intermediate joins.

The PL259 is simple, mechanically rugged and relatively easy to fit. That’s why it’s popular on boats. Purist radio techies will tell you about its non-constant impedance but at marine frequencies, around 150 MHz, this doesn’t matter a jot.

Fitting: Most PL259s are the solder type but usually only the centre conductor is actually soldered into the pin, the braid being held mechanically. In some cases the cable is crimped onto the cable, making contact with the braid through the pvc jacket. For this you need an appropriate crimping tool so this type is more popular for industrial application. The leisure sailor is more likely to choose a screw-in-earth type, where the cable is screwed into the threaded inlet of the plug once a section of braid has been exposed, and then the centre conductor is soldered into the pin. Many top quality PL259s are made for the bigger cable size and have an adapter insert to suit the smaller sizes of cable. Using an adapter is convenient because it grips the coaxial braid firmly. I like silver plated connectors because they avoid corrosion and they solder very well – and I’d always have silver or gold plated centre pins for this reason.

You can get PL259s that require no soldering, they are entirely mechanically assembled. The Shakespeare Center-Pin connector is a good example. A little expensive, perhaps, but they are great for solderophobes.

The PL259 is not fully waterproof and the join should be protected with silicone self fusing tape when used outside.

When the cable run on a boat encounters a bulkhead or the deck you have a choice – do you drill a hole and pass the cable through it, continuing the unbroken run, or do you use a bulkhead connector of some sort? I’ll save the debate over the relative merits of deck plugs, deck glands and the various joining methods for another time, but no discussion of the PL259 would be complete without a mention of the barrel connector.

The barrel connector is a double female – you can plug a PL259 into each end and make a mechanically strong connection between two sections of cable. The barrel connector comes in a variety of lengths starting with the small, discontinuously threaded version about 1” long, up to a 12 inch long monster.

The short barrel connector is called a PL258. This shows that the bloke in the spares department in the US military wasn’t on his toes when it came to designating inventory numbers because this is clearly a double socket (SO) and not a plug (PL).

The longer versions are often called PL363 barrel connectors, or bulkhead connectors, or double-females and some other weird designations. You have to specify the length. The PL363 comes with a pair of nuts to secure it through the bulkhead or the deck or a radar arch base. The standard nuts are a bit wimpy but you can buy more substantial ones – the thread is 5/8” 24 tpi.

The BNC connector is a bayonet connector designed for applications where frequent connecting and disconnecting occurs, such as on laboratory oscilloscopes. Despite this it has found its way into applications such as connecting the antenna to an AIS unit, or even for cable to cable connections.

BNC stands for Bayonet Neill Concelman, after its two designers.

Aware that the bayonet design allowed noise to intrude when the cable was subjected to vibration the Neill Concelman partnership came up with a more secure variation, the TNC, for Threaded Neill Concelman.

Both connectors have male and female halves – typically the male bit is attached to the AIS unit and the antenna cable is fitted with the mating female connector. Barrel connectors are also available for cable to cable joins. BNC and TNC connector sets are often chosen as cable to cable connectors when the reliable but chunky PL259/barrel connector/PL259 connection is unworkable.

BNC and TNC connectors are fiddlier to fit to the cable than the good old PL259 but they are high performance connectors, used for frequencies as high as 11 GHz. That’s a gazillion times more critical than the simple 150 MHz of VHF.

Another connector you might encounter on boats is the N connector – named for that prolific connector designer Mr Paul Neill of Bell Labs who designed it in the 1940s. This is another connector set that has high performance, being suitable for frequencies up to 11 GHz. Large commercial VHF antennas often come with an N connector and RG213 cable.

If you have satellite communications on your boat you may encounter the F connector to attach to a remote antenna system and if you want to connect your handheld VHF radio to a fixed antenna you might use an SMA connector, although some manufacturers have their own proprietary antenna connector.

So there you have it, the low down on RF connectors for boats. Have a look at the selection of cable, connectors and other antenna system components at saltyjohn.com

Salty John website redecoration

It’s been a busy couple of weeks on the IT front. We’ve built a new website for the sale of general chandlery items at discount prices, sailorssurplus.com, and we’re working on revamping the Salty John site and taking the opportunity to concentrate on marine antenna systems and rig tension gauges.

 

I must say I’ll miss the old Salty John site, it’s become as comfortable as a well worn pair of deck shoes. But it wouldn’t do any longer; it was too grumpy when visited by the new smart phones and tablets.

We’ve been Metz Communication’s sole agents in Europe for over ten years and that’s the most important part of our business – marine antenna systems. We’ve also offered Loos & Co rig tension gauges for that long, too, and they’re another big chunk of the business. So those two products share their own website, saltyjohn.com

We’ve never wanted to be a general boat chandlery, we simply can’t carry the huge inventory needed to fill that role. What we can do is concentrate on finding bargains to bring to our customers, buying direct from manufacturers and using our low overhead to keep prices ultra-keen. For that we needed a separate site, hence the birth of sailorssurplus.com

 

 

Do your spreaders droop?

With rigs being checked over and re-stepped ready for the new season it might be timely to revisit one of my pet subjects, drooping spreaders:

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, slackening the shroud and 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 at shorter boat lengths. 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 spreaders design, droopiness 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.

So, there you have it. Get your tension gauge working to set your rig just right, re-pin and wrap your turnbuckles, check your spreaders and have a great season.

Heaving-to

When the wind pipes up and the going gets tough heaving-to is a great tactic that lets you stop the world and get off for a while. Or, as Bernard Moitessier says in his classic The Long Way: “….when you no longer know what to do: come about without touching the sheets, put the helm alee, stretch out in the cockpit, eyes closed, and then see things as they are….”.

You can heave-to to have lunch or to weather a storm or, of course, to lie in the cockpit and contemplate. How you do it depends to a large extent on your boat and you should practice the manoeuvre so that you can do it when you need to. For most it’s a matter of tightening up to close hauled and then tacking without releasing the jib sheet. Once the jib is aback, let out the main a little and lash the helm alee. Each boat will behave somewhat differently but the principle of setting the helm and main to drive the boat against the backed jib remains – it’s a matter of finding the right balance for your boat and the prevailing conditions.

In storm conditions you’d be down to storm jib and fully reefed main or trysail but you can heave-to with a fuller sail plan if you just want to stop for lunch or to carry out some task which is best done with the boat still.

Hove-to, the boat should lie about 40º or 50º off the wind and forereach slowly. You are underway so need to act accordingly regarding collision avoidance.

A good skill to acquire is heaving-to.

A head’s up on the marine toilet

On my cruising boats I’ve always opted for conventional flushing marine toilets in Airhead2a1conjunction with a holding tank. On my earlier cruising boat there was a Y-valve to allow waste to be directed to the holding tank or discharged directly overboard, on my later boat all waste went via the holding tank to a dockside pump-out facility or overboard.

These systems were quite satisfactory and I never felt the need to seek alternatives such as on-board waste treatment systems with their complex macerating and chemical treatment paraphernalia.

I did once have a VacuFlush system on a power boat I owned and it was the nearest thing to a home loo I’ve seen on a boat. Step on the foot pedal and whoosh, away it all went. But it used fresh water for flushing and was battery operated thereby consuming two essential resources which excluded it as an option for long term cruising.

A composting toilet is something I’d always thought of as the ideal choice for a cabin in the wilderness rather than on a boat but a couple of years ago I came across this article:

http://www.svsarah.com/Sarah/ewCompostingHeadInstall.htm

It’s a very informative and appropriately lavatorial discourse on the installation of a composting toilet on a boat and makes a good case for such a choice. So, don’t pooh-pooh alternative toilets until you’ve sat down and read it.

Personally I’ll be sticking to my conventional hand flushed marine toilets but I do love the name of the device – the Air Head.

Chesapeake Bay seasons

I have a particular fondness for sailing on Chesapeake Bay where I was lucky enough to keep a boat for five years. Here’s a taste of the seasons on the Bay:

In spring the sailing on Chesapeake Bay is grand, the air fresh, winds reliable. The weather’s changeable, though; tee shirt or foul weather jacket, you never know. Most times you need both in the same weekend. Spring marks the beginning of a season that stretches before us, a blank page to be filled with familiar landfalls and new destinations. Before we can sail, though, we have to prepare; anti-foul the hull, drain the antifreeze from the water system, flush it and top up, change the engine oil, check the rig tension and load the sails back on the boat. Let the season begin.
The summer winds are fickle. A tiny breeze, a mere zephyr, tickles the surface. This is more frustrating than a dead calm. In a dead calm I’d give up, drop the sails, secure the boom and settle down with a good book. Or crank up the engine and be off to my destination. But where there’s a whiff there’s a way; the temptation to try is irresistible. I hoist the main and my lightest jib, use the topping lift to take some of the weight of the boom, go easy on the halyard tension. I know that attempting to move downwind in this tiny breeze is hopeless so I work her onto the wind, a tad below close hauled. I tell the others to keep still, whispering so as not to scare the wind-gods. Is she moving? I watch the wake, toss bits of lint into the water, and stare up at the sails willing the jib to be caressed into shape by this hint of a breath of a breeze. Eventually the tell-tails flutter into life, the boat begins to make way. This movement conspires with the true wind to create an apparent wind and that brings more movement. Yes! We’re sailing. Now let’s just keep her going – a tweak here, a tweak there.

Summer afternoons often bring thunderstorms and we try to get the hook down in a snug anchorage or settle into a marina berth before they let loose their venom. Once in a while, in September and October, hurricanes threaten the Bay; they’re born in the tropics, grow in size and intensity as they move across the Atlantic and many will re-curve when they reach the US, some heading up the coast and reaching Chesapeake Bay as vicious maelstroms threatening the coastal communities with high winds and huge tidal surges.

By the end of October the hurricanes are gone. Autumn is in the air, a magical time on Chesapeake Bay. The breezes are back after the stultifying heat and calms of summer, the trees are starting to acquire what will become a magical mantel of golds and reds and yellows and browns, and delta-flights of honking Canada geese arrive for the winter. I step onto a dew covered deck at dawn and watch the mist rising like steam; all is quiet except for the occasional slap and roil of a fish taking its prey. The first hint of the sun shows itself through the trees on the eastern shore, a promise of another fine day for sailing. But sailing comes later, when the wind arrives; for now I finish my coffee and slip below for another hour in the snugness of a still warm sleeping bag.

Chesapeake Bay – one of my favourite sailing grounds.

Metz marine VHF antenna

An aerial is an aerial is an aerial. No it isn’t. Not by a long chalk.

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 Metz range is based on a heavy gauge stainless steel shell which encloses the 16 AWG 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.

Lower quality antennas have fibreglass bodies 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 and even damage to the radio.

To survive in the marine environment the 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.

You don’t need to pay through the nose for top quality construction: the Metz Manta is similar in price to ordinary fibreglass bodied antennas and substantially lower in price than some other stainless bodied antennas. And it carries a lifetime coil warranty. Check it out at the Salty John on-line shop

Setting off

The sun was still low in the east, just peeking through the tops of the trees. The wind hadn’t got up yet and the surface of the small bay was a mirror. The reflection of the water disturbed by my oars dappled Adriana’s hull. I marveled again at her lines; that sweeping sheer, the elegant transom, the curve of her bow. Carol appeared from the cabin and looked for me, shielding her eyes; she found me and waved. The dinghy nudged the sand and I shipped the oars, Henry jumped ashore, darted here and there, sniffed, pissed against a felled tree trunk and then stood rigid, looking back at me, tail wagging, anticipating. I stepped out and pulled the dinghy a little way up the shore, found a piece of driftwood, an old tree branch, and hurled it along the beach. Henry dashed after it, snatched it up, dropped it, savaged it and then ran back to me with it in his mouth. I tried to take it from him but he wanted to fight over it. I grabbed one end of the branch and lifted, he wouldn’t let go, his little legs pedalled wildly in the air but his jaws were firmly clamped. I lowered him back to the ground, released my grip on his branch and he dashed off with it, triumphant.

I looked out at Adriana now bathed in the morning sun and was a swirl of emotions; happiness, pride, trepidation. Today we would set sail on an adventure, an odyssey. Our course would take us from this small anchorage in a creek on Chesapeake Bay to points south; to Florida and then to the Bahamas, Hispaniola and the Caribbean.

A journey of a thousand miles begins with a single step – Lao Tzu