Your VHF radio and your AIS receiver or transceiver operate in the marine VHF band which is 156 to 163Mhz. VHF transmissions are almost entirely restricted to ‘line-of-sight’ which means that from the antenna of a boat at sea the radio waves can travel as far as the horizon. In practice radio waves can see a little further than the horizon, about 20% beyond it. The higher the antenna is located the further away is its horizon and, therefore, the longer the range of transmission.
Communication range is actually the combination of how far your antenna can see and how far the antenna with which you are communicating can see. Imagine that you’re boat is surrounded by a huge circle whose diameter is determined by the height above sea level of your antenna. The higher the antenna is located, the larger will be the diameter of this circle, this radio horizon. Other boats and ships, as well as coastguard land stations, have their own radio horizon depending on the height of their antennae. When your horizon meets another horizon you can communicate, and the distance at which you’re communicating is the combined horizon distance of the two antennas.
I’m going to get a bit nerdy now, just skip to the end if your eyes start to glaze over.
You can calculate your horizon distance with the formula: Horizon in nautical miles is 1.4 x √H1 where H1 is the height of the antenna in feet.
Range is, therefore, 1.4√H1 + 1.4√H2 where H2 is the other fellow’s antenna height in feet. (By the way, that constant, 1.4, takes into account that extra distance the antenna can see over the horizon due to the bending of radio waves).
To give an example, if your mast is 49 feet above sea level your radio horizon distance is 1.4 x 7 = 9.8 nm. You could communicate with a boat having an identical set up at 19.6 nm. If, however, his antenna was on his pushpit at, say, 9’ above sea level, his radio horizon would be reduced to 1.4 x 3, a mere 4.2 nm and you could make contact at 14 nm (9.8 + 4.2). Two small motor boats would struggle to communicate with each other at 10 miles. Coastguard station antenna masts are located high above sea level as are the antenna masts on ships so that a typical sailboat can expect to communicate with them at 30 miles or more.
Now, before you start shouting and waving your arms at me about having made VHF contact at hundreds of miles, I should say that atmospheric conditions can lead to huge VHF communication distances being achieved. A phenomenon known as tropospheric ducting, which typically occurs when there is little wind and high pressure over your area, can lead to very long range communication, hundreds of miles in some cases but more typically 50 or 60 miles. Of course these conditions are not accurately predictable so can’t be relied on to prevail just when you need them.
This all assumes that you have an appropriate antenna, the right size and type of cable and well made connectors – all in good condition. Even the most exquisite VHF radio or AIS transceiver will achieve nothing if the antenna system is defective. So, a penny in the antenna is worth a pound in the radio.
Damage to a gas main in our area has meant that we, along with 1000 other homes, are without gas for a couple of days. As we seek ways to warm the house I’m reminded of Dylan Winter’s short film about using tea candles and flower pots to warm a room:
The film went viral and I had to get on the bandwagon with a couple of cartoons:
Rigging blocks are indispensable on board a sailing boat. They provide mechanical advantage to allow you to move large loads with modest effort and they also redirect the lead of a line to make it more convenient to pull on.
A single block at the masthead with a halyard running through it is a simple one part purchase. It provides no mechanical advantage, but it does redirect the lead of the line to the base of the mast so that you can conveniently haul on it. Without the block you’d have to balance on top of the mast to haul up the sail. This type of ‘turning’ block crops up all over the boat – directing halyards and sheets being the most obvious application.
By combining blocks into sets that work together as a team you gain mechanical advantage. And that’s a lesson for life, if I may wax philosophical.
The most common examples of block combinations on a boat are the systems for controlling the mainsail: the mainsheet, the boom vang and the backstay tensioner.
How much mechanical advantage is gained is known as the ‘purchase’ of a set of blocks – three to one purchase, four to one purchase, and so on – and this is determined by the number and configuration of blocks in the system.
You can tell a four part purchase because the loaded block – the one that moves with the load – has a total of four lines leading to and from it. A three part purchase would have three lines leading to and from it and a six part purchase would have six lines.
On small to midsize boats the mainsail control systems are most commonly four part (4:1) purchases. Another extremely useful four part purchase is the handy-billy. Equipped with snap shackles at each end it can be used for all manner of things: Clipped between boom bale and toe rail as a boomvang it provides the most effective way to hold the boom down when on a run; it can help hoist the dinghy, the outboard or even a MOB. I’ve used my handy-billy to hoist the cooker out of the cabin and the beer supplies in.
To get even greater mechanical advantage you can use one purchase to haul on another purchase – a compound system such as this gives huge mechanical advantage because the efforts of each system are multiplied, not added together: A three part purchase pulling on a four part purchase gives a 12:1 advantage, not merely 7:1. Or you can use a winch to haul on a block system to even greater advantage.
Quick or easy? A downside of block systems is that the higher the purchase the slower the work is done. You have to choose between effort and speed. Very high mechanical advantages involve hauling considerable lengths of line through multiple-sheave blocks, moving the load at a snails pace. For this reason it’s unusual to see individual block systems of higher than 6:1 purchase.
Friction is also a formidable enemy in block systems so choose ball bearing blocks which will keep the loss at each block to less than 3% rather than 10% or more for blocks with sleeve bearings.
There you have it – use blocks to make light work of a tough job.
Let’s recap the displacement hull speed law: As a boat moves through the water it creates a wave. As the boat moves faster the wave increases in length until it eventually reaches the waterline length of the boat. At this point the boat can go no faster without climbing up the face of its own bow wave. Considerable power is required to do this – well beyond that available to the typical sail boat.
The formula for theoretical displacement hull speed is:
Speed (knots) = 1.34 x √LWL in feet
Example: LWL is 25’. Hull speed is 1.34 x 5 = 6.7 knots.
Some lightweight flyers, even if they do have displacement hulls, can slightly exceed this theoretical figure; a constant of 1.4 instead of 1.34 brings these boats into the catchment area, so to speak.
The waterline length on some boats, particularly those with long overhangs, increases as the boat heels, so they go faster heeled that upright.
Monohull boats of the type most of us sail have displacement hulls with sail plans or auxiliary engines of inadequate power to get the boat up onto the plane and so have to conform to the displacement hull speed rule. Planing power boats, of course, are unhindered by the rule and can roar off into the distance leaving we sailors bobbing in their wake.
The well known, perhaps infamous, McGregor 26, a sort of hybrid, a power boat with sails, uses a 60HP motor to get it’s very light weight onto the plane and achieve a speed of 24 knots. (pictured)
But, generally speaking, when someone in the club bar tells you his Slug 22 cruises at 8 knots you’ll know he’s unaware of the displacement speed formula.
Having the correct tension in stays and shrouds is important because a slack rig can impart shock loads to shrouds and chain plates as the mast flops from side to side; a too tight rig can cause structural damage.
A well tuned rig will have equally tensioned shrouds so that the boat will perform well on both tacks, the leeward shrouds won’t dangle flaccidly and the forestay won’t sag. She’ll feel right on all points of sail.
The rig on a cruising boat should be checked regularly to ensure good performance but also because it can be an indicator of something amiss – any unexpected change in a shroud’s tension should be investigated immediately.
Loos & Company makes two different classes of gauge for wire rigging – Standard and Professional. They also make two sizes of gauge for rod rigging.
The Standard range comprises two models, Type A(91M) covering wire sizes 2.5mm, 3mm and 4mm and Type B(90M) for wire sizes 5mm, 6mm and 7mm. These gauges are simple to use and accurate to 5% at mid range.
For more accuracy and convenience choose the Pro models: PT1M for 2.5mm, 3mm and 4mm, the PT2M for 5mm, 6mm and the lower tension end of 7mm and the PT3m for 7mm, 8mm, 9mm and 10mm wire. These gauges are a little more accurate, 3% at mid-range.
The Pro range is more convenient to use because the gauge is left on the wire whilst the turnbuckle adjustment is made whereas the Standard range gauges must be removed whilst the wire is adjusted.
Rod rigging can be accurately tuned with the RT10 and RT11 gauges.
On the Salty John website you’ll find an article on rig tuning using the Loos tension gauge, including suggested wire tension levels:
The full range of metric Loos gauges is available at the lowest prices in Europe from:
A tuned rig is a happy rig!
On my cruising boats I’ve always opted for conventional flushing marine toilets in conjunction 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 I’ve recently come across this article:
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.