January 2013 – Salty John : The Blog

Failure of the raw water flow is the most common problem with marine engines and can lead to expensive damage to the engine or wet exhaust system. Blockage of the raw water flow can be caused by debris in the inlet through-hull, a clogged inlet strainer or failure to open the inlet seacock. 

The raw seawater cooling flow takes the heat from the engine cooling water in the heat exchanger and discharges it via the exhaust system. Failure of this flow of raw water will not only lead to overheating of the engine but also overheating of the exhaust system components. And it can occur before the normal engine block mounted temperature sensor detects it.

Our Sentry™ exhaust alarm provides an audio and visual signal should your engine’s raw water cooling flow be interrupted allowing the exhaust hose to overheat. It comprises a non-intrusive band sensor strapped to the exhaust hose at the departure point from the engine’s mixing elbow and this activates the alarm if the preset temperature is exceeded. 

Simple to install, a Sentry exhaust temperature alarm makes good sense. That’s why they’re used by fishing boats in Alaska, tugs in the Panama Canal and pleasure boats everywhere. 

If you have separate VHF radio and AIS antennas you have back-up in case you lose one or other of the antenna systems.

If you mount the AIS antenna on the pushpit rail or radar arch you will even have cover in the case of a dismasting. 

You’ll want to have your radio antenna at the masthead to benefit from the greater range that this will provide, but that’s not essential for AIS – an AIS antenna mounted on the rail at, say, 10 feet off the water will receive data from a ship with an antenna mounted 40 feet above sea level at 12 miles distance. That gives you half an hour to react if the ship’s doing 24 knots, more than adequate to avoid an incident. Bigger ships will have antennas mounted much higher than this so range will be correspondingly greater.

If you were dismasted or your masthead antenna failed for some reason you would hook your AIS antenna to your radio and regain communications.

You need to be sure that the radio cable will reach the AIS unit and the AIS cable will reach the radio. Each cable should have a PL259 plug attached; this fits the SO239 socket in the radio and also some AIS units. Other AIS units use a BNC connector so in this case you need to have a BNC/SO239 adapter so you can connect a PL259 to your AIS engine.

The Metz rail mount bracket shown is an ideal means of securing your AIS antenna at deck level. 

I blogged a while ago about junk rigged boats, the choice of intrepid Arctic cruiser Roger Taylor for his heavily modified Corribee, Mingming. Well, I’ve just been reading in the excellent East Coast Sailing on-line magazine that Roger is preparing a replacement for Mingming. The new boat will again be junk rigged, of course. 

He’s replacing the 21’ Corribee with an Achilles 24 because he needs a slightly higher average speed to allow him to travel that little bit further – just another 15 to 20 miles a day is all he’s looking for. 

The Achilles has the same low freeboard and fine lines that Roger liked in the Corribee and he’s going to make Mingming II watertight and unsinkable as he did with the original. He’s fitting watertight bulkheads and filling the ends with foam. There’ll be an escape hatch up front so he can get at the rig from there as well as the companionway – an advantage over the earlier boat. The Mingmings are boats that are sailed from below decks!

I like this watertight and unsinkable concept for a boat – it’s the same principle that takes Japanese glass fishing floats to beaches all over the world. And flotillas of plastic ducks, for that matter!

I’ve blogged about this before but a recent discussion on a boating forum made me think it was worth re-visiting. 

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 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. 

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

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 inch (25.4mm) 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 a bulkhead or deck. 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. 

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 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. Large commercial VHF antennas often come with an N connector.

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. Sorry.

Do your leeward shrouds droop? Do they swing lazily around as you beat upwind with the lee rail well down? If so they’re way too loose.
Just imagine what happens when you tack. The boat comes up onto the wind, the mast straightens and then as you go through the wind onto the opposite tack it flops over to the new leeward side. Its journey is eventually, and suddenly, arrested by what were the flaccid leeward shrouds. The shock load on the wire, turnbuckles, chain plates and mast connection points is brutal.

The leeward shrouds should lose tension but not become loose – simple as that. Letting them dangle serves no purpose and can be quite damaging to the rig. 

So, get yourself a Loos tension gauge and set the rig properly. You’ll be surprised at the improved performance and at the same time you’ll be reducing the risk of catastrophic shroud failure and prolonging the life of the whole rig.

We have the best prices on Loos tension gauges, we stock the full range and we ship worldwide – the link is over there on the right.

If your mast is down for the winter you’ll want to take the opportunity to check that all is well with your VHF antenna system.

VHF antenna systems comprise an antenna (aerial), a feeder cable and a few connectors. 

Check the antenna for any physical damage to the body or whip and check that the support bracket is in good condition. If your antenna is a Metz Manta it will be fine, unless you’ve hit a bridge or a sizable bird and the whip portion is missing or broken. We can supply replacement whip kits if yours has gone astray. The Metz antenna coil is practically indestructible so that will be OK. 

Next check the connection to the antenna – if it’s a Metz it will have a PL259 connector at the base, other types may have factory-crimped or proprietary connectors. Remove any protective tape and check for corrosion – clean as appropriate. 

Leave the cable disconnected from the antenna and go to the bottom of the mast and check the connector at that end of the cable – clean as appropriate. If there is any obvious sign of corrosion to the cable at the connectors you should cut the cable back to a clean section and replace the connectors. Hopefully there will only be a few inches requiring replacement and enough slack in the cable run to accommodate this.

Now, with the cable disconnected at both ends put a multimeter across the centre pin and body of one of the connectors. With the multimeter set to read ohms you should see a reading of 1, indicating there is no connection between centre core and outer braid. If the reading shows zero, or any reading other than 1, you probably have a short between centre core and outer braid. This could be a badly fitted connector or corrosion or other form of damage to the cable. Unless the cause is obvious and repairable you’ll want to replace the connectors and possibly the cable. 

Note that with the antenna connected to the cable this multimeter test will always show a dead short, a zero reading, so you must disconnect the antenna to check the integrity of the cable.

Reconnect the cable to the antenna and add a few wraps of self amalgamating tape or, better still, non-adhesive silicone compression tape such as ‘Bandit’ tape.

Check and clean any deck plugs and/or in line connectors and test the cable run from here to the radio for integrity with the multimeter as above – both ends of the section of cable you’re checking must be disconnected when testing.

If you need to replace the cable remember that marine quality 50 ohm VHF coaxial cable needs to be tinned copper to resist corrosion and the centre core needs to be stranded so it can flex without breaking. 

In order to keep transmission losses to an acceptable level use RG8X cable for runs up to 25m or so. This is nominally a 7mm cable and gives considerably lower signal loss than RG58 (6mm or less) which is often found factory connected to cheap aerials. For very long runs you’ll need RG8U or RG213, a bit of a devil to work with at 9.5mm diameter.

Hopefully your efforts will be rewarded with a ‘loud and clear’ at your first radio check of the new season. 

When you look at what rigging blocks need to do on a cruising boat it comes down to rugged construction and low friction. All the rest is fluff.

If you’re fitting out a super-competitive racing boat you might have the budget required to buy open design composite blocks with plastic ball bearings to keep weight to a minimum. A single 57mm solid sided and reinforced block with steel ball bearings weighs around 170 grams. A composite block with open side plates and plastic balls will weigh in at a miserly 100 grams. This might be of some significance on a racing boat where the crew saw the handles off their tooth brushes to reduce weight but on a cruising boat it makes an infinitesimal contribution to performance. 

On a cruising boat you want simplicity and durability, but you also want the slippiness of ball bearings because they reduce friction by two thirds compared to sleeve bearing blocks. And for durability you can’t beat stainless steel balls.

The Viadana range of reinforced ball bearing blocks does all you need at a really competitive price. 

When I moved Minnie from the lake to the canal and converted her from a sail boat to a motor boat I seriously considered electric propulsion.

My idea was that we could silently putter up and down the canal, chatting quietly in the cockpit and not disturbing any of the plentiful wildlife. I didn’t fool myself into believing that we would be ‘greener’ this way, the environmental benefits of electrical power are dubious at best, but I was attracted by the smoothness, the  manoeuvrability and, most compellingly, the silence of electric power.

My extensive research led me to conclude that there are three things wrong with pure electric propulsion – range, range and range. 

The range I could get out of any practical size of battery installation was unlikely to exceed 3 or 4 hours at very slow speed, then I would have to recharge. My chosen marina doesn’t have shore power and I didn’t want to have to run a petrol generator on the dock or lug heavy batteries home after each excursion. Anyway, I didn’t want to limit myself to such a short time on the water – I really do like to travel further afield than the pub and back. 

I briefly considered solar charging but then I remembered we live in sun-less Britain – so much for that idea. I considered a diesel electric system or a hybrid system but they looked hugely expensive and didn’t provide the silent running I was seeking.

So, Minnie potters around with her four stroke Honda clamped on the transom bracket and we, and the wildlife, tolerate the noise. And it really isn’t that bad; I can convince myself that a two cylinder Honda outboard running at idle speed is perfectly acceptable. 

But, come on you research engineers; we want the joy of silent running cheaply and conveniently. How hard can it be?

As we step into the great unknown that is 2013 let me wish you happiness and prosperity in this New Year.

This blog enters its fourth year and Salty John Boat Products begins its eighth.

Salty John has managed to grow again – a big “thank you” to all our customers for a fine effort in these challenging times. 

The Metz antenna and accessory business stormed ahead as did Loos tension gauge sales. Another stand-out was the new Viadana rigging block and cam cleat business. Other parts of the Salty John product range didn’t do quite as well and we’ll be looking at why that should be so.

Lets all hope we actually have a summer here in the UK; enough of this rain, already! 

And to all boaters, wherever you are, I wish you fair winds and calm seas.