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TECHNICAL LIBRARY

GENERAL ITEMS

USING ANCHORS

Using the right anchor with adequate holding can be crucial to the safety of the boat and crew. Often the main question confronting the prudent skipper is what is the nature of the bottom in the intended anchoring area? The other main factors - size of the vessel and weather conditions expected are often more easily established. Therefore an anchor should be chosen that will hold in the worst conditions and in the worst ground.

Forces on the boat will try to drag the anchor along the bottom so for the anchor to hold the flukes must dig-in or grab. Flukes should be broad enough to stop the anchor dragging and not too broad so it will be difficult to get the anchor off the bottom. Stowage space will also be a consideration - especially in small boats. For this reason Kedge anchors will often allow the stock to be moved through the shank and be then stowed parallel to it. Danforth and Plough (CQR) anchors have better holding compared with Admiralty or Stockless types - and therefore can be lighter for the same size boat. A 10M boat would require a Stockless anchor of at least 22Kg but the Plough anchor would need to be a minimum of only 11Kg for the same performance.
The role of the anchor line needs to be understood if the boat is to be anchored safely. Chain, being less prone to chafe damage, is the best line available and the more the better. Some chain is essential to keep the shank parallel or nearly so with the

bottom. When the boat pulls back on the line it will start to lift chain. If sufficient chain is lying on the bottom the force on the anchor will not only be gradual and minimum - it will also pull the anchor horizontally rather than vertically.
Where the bottom is rocky or chafing is likely to occur rope will not last and should not be used. Where rope needs to be used in for the sake of stowage or handling, care has to be taken to use at least the minimum amount of chain. For example a 5-8 metre boat should have about 100-125 M of 10mm rope with at least 6M of 6mm chain. However a chain anchoring line will nearly always give the safest anchoring - particularly in rough and / or extended conditions and where chafing could be a problem.
Allowing enough scope will also give peace of mind - with the guiding principle that too much is much better that 10cm too little. With all chain in quiet protected waters with little on no tidal stream 3 times the maximum depth at high tide will be sufficient. For rope this scope figure is 5. However, in harsher conditions scopes of at least 5 (chain) and 7 (rope) are advisable. In areas where there are likely to be rocks or other potentially anchor snagging hazards an anchor buoy attached to the anchor crown will allow easy anchor retrieval - ensuring that such a buoy has enough line to allow for the highest anticipated tide. Such a buoy should obviously not look like a regular mooring to minimise the risk of another craft using your anchor buoy as a mooring.

ANCHOR CABLE MARKING

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     To remove the guesswork out of how much anchor cable has been played out the anchor cable - whether chain or rope, needs to be suitably marked. Several methods are available.
     Both ropes and chain can be threaded with different coloured tapes at say 10M intervals or same colour tape - using one strand for 10M, 2 strands for 20M and so on. Electrical cable ties are suitable for the latter method. They are especially useful in the dark when they can be felt. There is little danger in fouling either fairleads or winches if they are not made too big.
      Paint colours or bands will also work even though the paint will need replacing more frequently than tape or cable ties. Paint marks can be more easily obscured by mud etc. but with normal care in cleaning anchor cable as it comes on board there will be a useful life to pained marks.

BATTERIES

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     The condition of batteries on a boat is essential for convenience, comfort and perhaps even survival. Most batteries are 12 Volt lead acetate type and are charged from the engine driven alternator or generator. Some boats have a 24 Volt system but the principles of care are the same for both.
     The batteries must be sufficient in number and capacity to supply enough energy for the electrical appliances fitted to the boat. There should be reserve capacity and an electrical system capable of shedding non-essential services in the event of one or more batteries malfunctioning. There should be enough power to run essential services for 6 hours without charging.
     These batteries contain a weak solution of corrosive Sulphuric Acid. With a hydrometer the state of battery charge can be found. When fully charged the Specific Gravity (SG) of the electrolyte will 1.25 and when fully discharged the SG will be around 1.15. The electrolyte level should not fall below the level of the top of the plates. If it does the cells should be topped up with distilled water (best), rain or tap water - but NEVER sea water. A fully sealed battery cannot be checked this way and a voltmeter must be used. A 12 V battery on charge or nearing full charge will measure close to 14 V across the terminals. When charging ceases the voltage will read between 12 & 12.5 V. The battery is discharged when the voltage gets to 10.5 V with a light electrical load applied. For a 24 V battery these voltage numbers are doubled.
     The charging system should be able to charge a fully discharged battery within 16 hours but not at such a rate as to cause the battery to became hot or for it to give off large quantities of gas (hydrogen which is explosive). Battery tops should be kept clean and dry and the terminals kept free from corrosion. Corroded terminals and connections should be cleaned with brush or sandpaper and after reconnection they should be lightly smeared with vaseline or light grease.

To calculate the required battery capacity for a boat the average daily wattage for all electrical components needs to be determined. Assuming a 12 Volt system divide the total wattage by 12 which results in the number of Amphours needed. Double this figure and round up to the nearest standard battery size for the required battery capacity. In the example with 1152 watts being the daily average 96 amphours (1152 / 12) are required. Therefore a 200 Amphour battery is recommended.

ITEM	Wattage	Hours	Total Wattage
Light 1	8	6	48
Light 2	16	6	96
Pumps	72	2	144
Refrigerator	48	18	864

Average Daily Watts 1152

SIMPLE OUTBOARD MAINTENANCE

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To prolong the life of the Outboard follow this check list after every use. Some items won't need attention every time. These steps properly done will improve reliability - often crucial in a single engine boat.
When out in the boat carry a bag with suitable engine spares and a few tools such as Spare Plugs, Shear Pin, Starter Cord, Fuel Line, Circlamps, Shackles, Shifting Spanner(s), Pliers, Screw Drivers (Blade & Phillips) & Signalling Device(s).

HOISTING CLEAT

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To go up the mast the easiest way is to have one of the crew winch another up. Where there is no one to do the winching mast steps are needed or a few blocks with 12mm rope are needed to winch oneself up. To avoid having to drill holes in the mast for steps it could be easier to make up a simple Hoist Cleat to make the job relatively easy - such a device will reduce rope tangling, chafing, & friction; it will also eliminate the need for knots while performing the job.
To make one use a piece of aluminium 8-10 mm thick and about 120mm square. A smaller piece will be OK if a suitable size cleat can be found to bolt to the main piece. Stainless steel would also be suitable but it will be more difficult

to cut and smooth. All edges need to be rounded off - especially in the area of the cleat. The fittings are attached as shown with the bottom pulley having a swivel lock in place.
The top block is taken to the mast top with the main halyard. When the chair is at the work site line 4 is firmly secured to the cleat with a locking turn. On descent one turn around the cleat is enough for fingertip control

A Hoist Cleat at 50% size.
From Aluminium 8mm thick

FORCES ON SAILS

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A sail works exactly the same way that an aircraft wing produces a lifting force - by forcing the airflow passing across the surface to follow two separate paths, one of which is longer than the other. The air speeding up on the longer path causes a reduction in pressure and across the whole surface (wing or sail) an aerodynamic lifting force is generated. The airflow needs to be close to laminar flow to produce this force and if the airflow becomes turbulent the lift force will dramatically reduce. If the airflow breaks away from the surface with the longest path (on the right in the diagrams) the surface enters a stalled state and the "lifting" force becomes very small approaching zero.

The force produced (L for Lift) has the relationship shown to the other factors in the formula. CL, Density & Sail Area are all linear so that if any of them doubles the L force also doubles & vice versa. However, the wind is a squared function and any change in wind has a relatively huge effect on the L force. For example if the wind speed doubles the L force increases by four times (2 squared). This has a direct bearing on reefing in strong wind.
For all practical purposes density can be ignored - except to point out that a boat will sail faster in winter - when the air is colder and more dense, than in summer . The wind speed is beyond the control of most sailors and so the only available adjustments or control measures are the sail area and what is known aerodynamically as the Coefficient of Lift - which is adjusted by the sail quality, shape and setting. Sail quality is the smoothness of the sail material; Sail shape is the sum of the camber shapes from top to bottom - where camber can be taken as the shape of a sail section parallel to the boom or fore / aft axis of the deck from luff to leach. Sail setting will also affect sail shape but its main impact is to control the average angle that the sail meets the wind. If this angle is too low the sail will not generate much lift because there is not much differential pressure on the separate sides of the sail - the sail luffs. If the angle is too great the sail will be stalled - also leading to a reduction in lift. In this case there will be no easy-to-see results. Furthermore what inefficient lift is being developed will be directed laterally more than it need be with consequent drop in forward force and loss in boat speed.

With a properly set sail, the result of lift will always give a component driving the boat forward and one driving sideways.The relative size of these two components depends on the sail setting - which is dependent on the apparent wind direction. These are the primary resultants of the lift force.

With optimum sail setting it can be seen that with a beam wind the driving force is quite large when compared with the lateral force. However, with the wind about 45° off the bow the driving force has become much smaller and the lateral force is now greater. It follows as a general rule that, the further out the sail the greater the driving force - assuming of course that the sail does not luff. In other words the aim is to align the lift force as close as possible to the direction in which the boat is travelling. Thus when sailing close hauled and the lateral force being relatively large leeway will be near the maximum.

Where more than one sail is set there will usually be an interaction between the sails as well as the individual effects. In the case of a main and foresail each sail not only develops its own forces according to each sail setting - the foresail also has added effects on the main. It changes the apparent wind direction between the sails compared with the apparent wind free of sail influence and a slot is created between the sails. In the slot the air is further compressed and speeded up if both sails are properly set. This gives a dramatic increase of force coming from the mainsail.

There is a place where all the resultant lift forces of all the sails aloft, together with other wind forces acting on the rest of the boat, exerts a force. This place is called the Centre of Effort (CE). Against this there is another force consisting of the sum of all the forces resisting the CE - called the Centre of Lateral Resistance (CLR). The relationship of these two forces in both the horizontal and vertical planes needs to be understood.

Fig 1

In the horizontal plane (Fig 1) the relative size and distance apart of the CLR & CE causes a turning moment - unless they both act through the same point. The designer usually ensures that with "normal" sail settings that there is a small resultant moment turning the vessel into wind - called weather helm. The greater amount of sail carried behind the CLR the greater is the weather helm. Conversely less sail behind the CLR reduces weather helm and,where most sail is carried forward of the CLR, lee helm may result. If the vessel is badly trimmed in the fore / aft axis the CLR will shift (rearwards with too much weight aft) and weather helm might become lee helm.
In the vertical plane (Fig2) the relationship of the CE & CLR determines how much the vessel will heel. Therefore any sail plan which lowers the CE will reduce the heeling moment.

Fig 2

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