Covid-19

Sometimes I think I’ll emerge from lockdown as a pale, emaciated alcoholic with a dodgy haircut and the social skills of a chair.

At other times I think I might change.

Keep smiling, folks, this too will pass.

I’m retiring this summer!

I’ll be retiring this summer and closing down saltyjohn.com after fifteen years.

As the Metz Communications distributor in UK and Europe we’ve sold thousands of the excellent Metz Manta VHF antenna in that time. A truly great product.

I don’t know who will take over the Metz agency, or what their pricing policy might be, that’s under discussion right now.

We have about forty antennas left in stock and I’ve dropped the price to £49.95 including UK delivery. Delivery to Europe is £19.50. We also have a few cable kits, mounts and other accessories available on the website and some Optolamps, heavily discounted.

So, if you lust after a Metz VHF antenna, now would be a good time to visit saltyjohn.com

I’ll take this opportunity to say “thank you” to our many customers around UK, Europe and the rest of the world for making the last fifteen years such a pleasure. It’s been a fun ride. Not once did I feel the urge to go and get a proper job!

I’ll be keeping this blog going for the foreseeable future.

Fair Winds!

Which cable for my boat antenna?

So, you’ve bought a new marine VHF antenna and you want to buy coaxial cable to connect it to your radio or AIS transceiver. What should you look for?

Here’s the super-quick check-list:

50ohm

Stranded centre conductor

RG58 up to 15m, RG8X up to 25m, RG213 for super-yachts.

Braid coverage over 90%

Tinned copper if you can get it. If not, make sure you seal outside connections to prevent water intrusion using silicone, self-fusing compression tape. In fact, do this even with tinned cable although it isn’t as vital.

When you fit the connectors make sure they aren’t shorted. Use a multi-meter set to 2k ohms. Should read 1 (infinite resistance) between centre pin and outer case of the connector. Do this with the cable disconnected at both ends.

Here’s the slightly longer guide:

First, it has to be 50ohm coaxial cable. Television cable is 75 ohm – forget it, you can’t use that coil left over from your satellite dish installation.

Beyond the requirement for 50ohm resistance you have several choices, determined by how much you’re prepared to spend, the length of the cable run and availability.

To make size selection simple, my advice is that for cable runs over 12m and up to about 25m use RG8X (sometimes called mini8) which is nominally a 7mm diameter cable, in reality a little over 6mm. For runs below 12m it’s ok to use RG58, nominally 6mm diameter, actually closer to 5mm.(With low loss RG58 it is possible to stretch to 15m at which point the loss will be 3dB which is 50%. We don’t recommend more than 50% loss in the cable run).

The next important requirement relates to the construction of the cable. Coaxial cable comprises a central conductor running inside a plastic sleeve (called a dielectric) which is wrapped in a braid sheath, then the outer jacket. The centre conductor can be a single solid wire or a stranded wire. You will want a stranded wire conductor because it is less likely to break due to metal fatigue. Lots of movement on a boat, lots of cable flexing – get a stranded centre conductor. Get braid coverage of more than 90%.

Tinned cable is always the most desirable choice on a boat – exposed to the marine environment, copper turns black and corrodes quickly. If you can’t get tinned coax, make sure your connections are carefully water proofed. Wrap external joints with non-adhesive silicone compression tape. Leave a few centimetres of cable at each end of the run so, if you get corrosion, you can trim the cable back to good clean copper and fit a new connector.

Be aware, tinned coax, particularly RG8X, is difficult to find in the UK and it’s quite expensive because it’s mainly imported from the USA. For some reason white jacketed cable is also rare – I don’t know why – but it should only really be an issue if you’re running cable externally and want to keep it discrete.

When you check you have fitted the PL259 connectors properly, using a multi-meter to test for a short circuit between pin and outer shell, do it with the cable disconnected at both ends. Many antennas show a short circuit to a multi-meter because they are internally grounded as protection against lightning.

There you have it. Check out saltyjohn.com for Metz antennas and marine coaxial cable.

Metz VHF antenna

VHF radio range is line of sight, so height is a very important factor in achieving maximum range. On a sailing boat the most suitable antenna location is, therefore, at the top of the mast. Two boats, each with a masthead antenna 60’ above sea level can theoretically communicate at about 22 miles. (Much greater ranges are possible when atmospheric conditions are right, but this cannot be relied upon). A transmitter at a coast station, perhaps 1000 feet above sea level, could communicate with these same boats at closer to 50 miles. On a power boat you have to do what you can to place the antenna as high as possible above sea level.

A penny in the antenna is worth a pound in the radio. It is important to select the right antenna and install it in such a way that it maximises the performance
of the radio or AIS transceiver to which it is attached.

Selecting an antenna:
For boat applications you would select a 3dBi antenna because it gives a nice fat, round signal pattern and this is important because on a moving boat you want the best chance of some of the signal being directed at the horizon and not the sky or sea.

You can get more focused antennas, 6dBi or 9dBi, but these antennas have a tight disc-like signal pattern and are unsuitable for the constantly moving platform of a masthead located antenna.

Other criteria for selecting a marine antenna, particularly one for masthead mounting, would be:
• Resistance to UV degradation. Clearly all stainless steel construction wins hands down.
• Resistance to bird strikes. Again, a stainless steel whip is less vulnerable than a rigid plastic
one.
• Ability to be removed when the mast is taken down. This is when the antenna is particularly vulnerable and those with factory crimped connections cannot be removed without removing all the cable with them. The connection at the antenna should be an SO239 socket which takes the standard PL259 connector.
• Low weight.
• Sturdy mounting bracket.

The Metz VHF antenna satisfies all these criteria. Its excellent durability as a result of stainless steel construction combined with superb performance makes it the choice of the US Coastguard and UK Search & Rescue services, the Clipper Fleet, many charter companies and thousands of leisure sailors all over the world.

The Beaufort Scale

When Sir Francis Beaufort first devised the scale in 1805 it was simply his assessment of the wind strength, based on the observed sea conditions, so that a mariner could decide how much sail to carry. His scale was intended to describe the conditions under which various amounts of sail could be carried by a man-o-war, the principle warship of the time.

The scale ran from a Force 0, dead calm in which all sail would be flown, to a Force 12 in which the winds were “…. such that no canvas could withstand”.

In 1831, when anemometers had been around a bit, wind speeds were applied to each of Sir Francis’ 13 levels of wind force. A Force 6 was described as a fresh breeze of 22 to 27 knots “or that in which a well-conditioned man-o-war could carry, in chase, full and by, single reefed topsails and top gallant sails”. Very evocative if you know your top gallants from your tam o’shanters.

Over time the scale was further modified and modernised. Wind speeds were added, as I’ve said, and a ‘state of sea card’ was produced bearing photographs of the sea state to be expected for each Beaufort force. Further Forces were added to cover the conditions that might prevail in tropical cyclonic storms. Wave heights are now seen on many versions of the scale.

The wind speeds which were applied to each of the Forces were, presumably, those that most closely related to the conditions that Sir Francis described. For instance, F0, dead calm, is given a wind speed of less than 1 knot, something of a no-brainer, but F5 is 17 to 21 knots – it must have taken some serious debate to arrive at that range of figures.  And, inevitably, the progression of wind speeds up the scale is not linear, reflecting the exponentially increasing force on the sails as the wind speed climbs. F5 is 17 to 21 knots, whilst F10 is 48 to 55 knots – an F10 is not merely twice an F5.

The Beaufort scale is seen as an anachronism by many sailing newbies. There is a temptation to assume the Beaufort scale is simply an illogical grouping of wind speeds with no obvious conversion rate to anything else. Why not, they might think, devise some logical groupings: 0-9 knots, 10-19 knots and so on, if it’s necessary to group wind speeds at all. Such logic is all very well if you think of Beaufort Force as simply another form of wind speed measurement such as knots, miles per hour or meters per second, for which there is a mathematical conversion.

But that isn’t where it came from; it might have been diverted to that use, but what Sir Francis Beaufort devised was a means of establishing the force of the wind by looking at the sea, a reference source to tell mariners how much sail to risk in any given condition.

Funnily enough, merchant ships at sea still determine true wind speed from sea conditions – and they supply this information to the MET office. The reason they do this is that anemometers mounted on large fast moving ships don’t tell the true wind speed, they measure apparent wind speed – the wind speed modified by the ships own, often very high, speed and by the effect of the ships superstructure. To get the true wind speed they rely on their deck officers who are skilled at estimating it from the sea state. Sir Francis Beaufort would be proud of them.

The Misery Wiggles

Actually, it’s the Misere wiggles, a section of the Gulf Intracoastal Waterway (ICW) in the southern USA that passes alongside Little Lake Misere. The ICW carries considerable commercial traffic through this section and the huge triple-wide tows have to negotiate this series of bends, day and night. Normally they do this without incident, warning each other of their location and intentions on channel 13 in a laconic shorthand unique to these long-distance truck drivers of the waterway.

Then we come along in our little yacht, desperately searching for somewhere safe to anchor for the night. Such places are like hen’s teeth on this stretch but we think we’ve struck it lucky: A small cut runs off the main ICW and into Little Lake Misere – it looks an ideal spot until we realize how shallow it is – we nose in as far as we can, drop the hook and then realise that our rear end is sticking out an uncomfortable distance.

The big tows – three barges wide and a thousand feet long – have to take up almost the entire width of the channel to get around the bends and this brings the tug’s sterns perilously close to the bank at the entrance to our little anchorage. Guess why it’s so shallow? Right; each tow pushes tons of mud into the cut as it powers around the corner.

I’m on the radio the whole night, making our position known to each tow as its lights heave into view. Their hugely powerful searchlights seek and find us and I catch glimpses of faces in the cabs high above us as they storm by, powerful diesels thudding.

They’re mainly amused. They tell me not to worry. Ha! That’s easy for them to say. They’ll try to miss us, if they don’t the paperwork will be hell, they joke. They promise they’ll try not to bury us as they swing wide to line up for the next section of the misery wiggles, mighty propellers churning up the mud.

Then the mosquitoes arrive. Millions of them. All hungry. I’m their special treat this hot and sultry night in Louisiana. They seem to relish the mosquito repellent dressing – perhaps it goes well with my succulent Anglo-Saxon blood. My only defence is the fly swat which I wield even as I talk earnestly to the next barge captain in a seemingly never ending procession.

By morning I’m exhausted but I’ve saved the ship and her crew and I can wear my battle scars proudly – hundreds of itching welts over every bit of exposed skin.

The misery wiggles, just another one of the joys of small boat cruising.

Propeller – freewheel or not?

Is it best to allow your propeller to freewheel when sailing, or should you lock it? Here are a few considerations:.

The first issue is drag: Under sail with the engine stopped does the 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 recently 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 that 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.