November 2013 – Salty John : The Blog

We wish all our American friends a wonderful Thanksgiving  Day!

I tackled this subject a year or so ago and it was quite popular so I’m going to run it again. If you have no interest in vhf connectors you can leave now and I hope you’ll find other blog entries of interest.

Boats use coaxial cable for their radio and AIS systems – here’s a look at the connectors you might encounter when installing or repairing the necessary cable runs:

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 allegedly 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.

The connector was originally called a UHF connector, and still is in some circles, which is odd because it was designed for use at frequencies up to 300 MHz, the VHF band, and not the UHF band which only starts at 300 MHz. Mr Quackenbush probably had nothing to do with the misnaming of his creation. 

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 all about its non-constant impedance but at marine frequencies, around 150 MHz, this doesn’t matter a jot. 

You can find fitting instructions on the Salty John website, under ‘articles and links’.
The PL259 needs to fit cable diameters from 5mm up to 10.4mm. (The various cable types are discussed elsewhere on the blog). Although you can buy 5mm PL259s it’s more usual to use a standard connector with an adapter insert to suit the appropriate size cable. 

I like using an adapter because it grips the coaxial braid firmly and that means you don’t need to solder the braid to the connector body. You still need to solder the centre conductor to the centre pin, of course, but that’s easy.

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 deck you have make 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 all called PL363 barrel connectors and you have to specify the length. 

The PL363 comes with a pair of nuts to secure it through the bulkhead – be that a wall 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.

You could consider fitting a PL259 to your AIS antenna lead and then use an SO239/BNC adapter to connect to the AIS unit – this makes sense because the PL259 is easier to fit than the BNC female connector and, should you lose your masthead VHF antenna, you can simply stick the AIS antenna lead, sans adapter, into the back of your VHF radio and you’re back in business radio-wise. 

Another connector you might encounter on boats is the N connector – named for that serial 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. 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. 

I think I’ve rambled on quite enough for one day – I hope some will have found the foregoing illuminating, and I know that many will have slipped into a coma after the first paragraph or two.

Your mainsail, I mean. Do you stuff it or flake it or both?

I‘ve always found the most efficient way to get the main down and under control is to stuff it, just as I was taught at sailing school. You apply the topping lift, release the halyard, form a ‘bag’ with the first yard of sail and into this stuff the remaining sail as it tumbles down the mast track. You punch the cloth into the bag to get a tight fit, and as each batten arrives you align it fore and aft. You then roll the ‘bag’ onto the top of the boom and secure it with sail ties (or gaskets as they are sometimes known). Job done.

This gives you a secured mainsail in double quick time, but I have to admit that the result looks a bit like a boa constrictor that’s swallowed a family of warthogs. Not pretty, and for some boat owners, unacceptable.

Flaking the sail as you drop it really requires two people; one stands at the mast and encourages slabs of sail cloth to fall to alternate sides like a Roman blind whilst the other stands at the leach and hauls the flakes aft, aligns the battens and pushes the reefing lines into the folds to stop them dropping untidily onto the deck. You then secure with sail ties. After a few years the sail learns where the flakes come and the operation becomes more efficient.

The result can be such a satisfying work of art that you delay the fitting of the sail cover so that others can admire your handiwork.

Many sailors, me included, use a combination of the two methods; stuff it until you’re at the dock or have your anchor down, and then go back and flake it.

Of course, if you have a stack pack or use in-mast or in-boom furling you miss all this fun.

Nelson, the Salty Dog, will pop up every now and again with his take on marina living and topical events.
Here’s a couple of his observations.

Recently a shore power adapter appeared for sale on eBay. On one end of the short cord there was a 13 amp domestic plug and on the other was a caravan/boat type three pin plug. The idea was you could supply your boat or caravan/motor home with 240 volt supply from your house. 

Hopefully most of you will have noticed the fatal flaw in this arrangement. When one end of the adapter was plugged into the domestic supply the plug on the other end would become live and, because the pins on a plug are exposed, anyone touching that end would receive a 240 volt wallop, potentially a fatal wallop.

This was clearly a home-made lash up. All professionally made adapters and power cords have a plug on one end and a female socket on the other. Never, ever do they have a plug at each end.

The shore power socket on a boat is, or should be, a recessed male which accepts the socket on the shore power cord. On the other end of the shore power cord is the plug which goes into the live socket on the dock. This way the operator is never exposed to live and accessible components – unless he’s stupid enough to stick something metal in the socket holes, of course.

Even with the correct set up it’s advisable to connect at the boat first, then the dock and disconnect from the dock first, then the boat. Few people follow this procedure, I suspect, which is why the amateur lash up that was for sale on eBay is so potentially lethal.

Following on from the last post on the tea light/ flower pot method of energy production, I can now reveal that the government has given the green light to build the first of 127 new tea light candle fired flower pot power stations.

As you can see from the drawing this is to be a three pot station. It’s anticipated that this station will produce 2 kw of energy, enough to supply at least one small bungalow. 

Will this be the end of unsightly wind turbines, dangerous nuclear plants and the unfortunately named fracking? Watch this space.

When we needed to turn up the heat in the cabin on those occasional cold nights in the tropics we would put a couple of flower pots over a burner on the gas cooker. They would very effectively disperse the heat and soon the cabin would be quite cosy.

Here’s how Dylan Winter does it with candles – he heats his office and his boat this way:

http://www.youtube.com/watch?v=brHqBcZqNzE

VHF range is considerably enhanced by height above sea level and, therefore, a masthead location provides greatest range, all other things being equal. But there are occasions when a deck level antenna is the best option and, of course, for small power boats it’s the only option. 

For AIS systems the required VHF antenna, or AIS optimised VHF antenna, can be mounted on the stern rail to avoid congestion at the masthead and to provide redundancy should the masthead radio antenna fail or be lost in a dismasting. 

If your antenna shares duty as a radio and AIS antenna don’t choose an AIS optimised version, use a straight vhf antenna to ensure maximum performance for voice communication.

Because AIS signals come from communication towers mounted high up on a ship’s superstructure you’ll get acceptable range to your rail mounted antenna. Typically, a 12 to 14 mile range can be achieved in such circumstances, giving perhaps half an hour to avoid even the fastest moving vessel.

Both the Metz and our AlphaOne antenna have AIS optimised versions and are both available with a rail mount bracket for standard 1” boat rail.

Blog comments:

For years I didn’t solicit comments on my blog entries but always felt as though I should. I was warned that activating comments would lead to a spam avalanche. I tried it last year and, sure enough, the vast majority of comments were spam. I’ve decided to try again – comments welcome. If it gets spammy I’ll just have to close off the option again.

I’ve designed an ultra-shoal-draft modification to the venerable Westerly Centaur for those that like to gunk hole or creek crawl. 

As you can see from the drawing the boat is leg-powered which dramatically reduces fuel consumption whilst protecting the environment from carbon emissions.  

The keel has been dispensed with; this reduces initial stability so the operator has to brace himself in the gusts. Early reefing is recommended. Weighted divers boots can be worn by those intending to sail in areas of stronger prevailing winds. 

For offshore work a set of flippers is fitted over the boots and secured with an adjustable strap. A steady cyclical motion of the legs is recommended rather than a rapid fore and aft motion that can be quite tiring.

So there you have it – another great innovation from the design team at Salty John Research Laboratories. Worldwide patents applied for.