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The Blue Lagoon and Coconut Palms
The Blue Lagoon and Coconut Palms
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4wd components Cars: All 4wd vehicles are not equal, each type has its distinct character with attendant pros and cons. Whether you have bought the right vehicle for your purpose will become clear once you have experience in its use. To reach our lodge, the ocean beach, and to return, is within the capability of any 4wd vehicle that is properly driven and has tyres that are correctly deflated (see flotation). For everyday driving on washed-out sand roads, however, requires a special kind of vehicle and most SUV's and 4wd bakkies are not suitable for this purpose because they don't have the suspension travel to give an acceptable ride quality on really bad roads. Cosmetic damage from bush swipes affects the resale values of SUV's to the extent that most owners hesitate to push their vehicles through narrow passages in the bush. Differentials: If you drive your vehicle in a circle on a soft surface you will see 4 different wheel-tracks, each with its own unique radius. Each wheel has therefore traveled a different distance, and turned a different number of times, from its fellows during this maneuver. To allow the two wheels on driving axles to turn independently of each other the axle is driven through a differential. A differential also incorporates a reduction gear called the diff ratio or final drive ratio. Because the front and back axles describe a different arc during a turn it is also necessary to have some sort of differential device between the axles of vehicles in 4wd mode if stresses during the turn are to be avoided. These centre diffs can take several forms but do not incorporate any reduction gears. Vehicles in 4wd mode without a centre diff will encounter drag during a turn and will damage the surface that they are driven over. One of the drawbacks of a differential is that if one of the wheels is allowed to turn freely the other wheel receives no torque. To overcome this problem the locking diff has been developed. When a diff is locked both output shafts are forced to turn at the same rate. Large stresses will will be generated if a vehicle is turned while one or more of its diffs is locked, causing wheels to rip up a soft surface and a lot of drag will be felt, but one wheel will not be able to spin independently of the other. Identical torque will always be delivered to both the output shafts from the diff. A diff may be designed to lock automatically or manually. In the automatic version the diff will lock if it detects one wheel turning while the other remains stationary, or if one wheel turns in the opposite direction from the other. It does this internally and purely mechanically with no input from computers or black boxes and the housing is identical to that of a standard diff, in fact you may not know that your car incorporates an automatic locking diff. The manual, or Detroit locker has an electric, pneumatic or cable actuator that is operated by the driver at his discretion, and can be identified by the control input on the back cover. There will be a push-button on the dashboard to operate the diff locker if it is pneumatic or electric or a T-handle if it is cable controlled. In rare cases a vehicle will be fitted with a diff-locker on the front axle. A front locker will always be manually controlled and locking this diff will render the vehicle virtually incapable of turning. Transfer case A transfer case is a mechanical device that serious 4wd vehicles have attached to the output of the gearbox. A transfer case always incorporates a 2-speed gearbox, which provides the High and Low ratio selectable by the driver, a sideways transfer device which connects to the fore and aft propeller shafts (often through a very expensive chain drive) and either a lockable centre diff or a dog-clutch. If the transfer case contains a diff the vehicle has full-time 4wd capability. When this centre diff is unlocked the vehicle can be driven on any surface without stresses being generated in turns or from unequal wheel sizes. The drawback of this configuration is that if any wheel is allowed to turn freely the other 3 will receive no torque. This is because the centre diff will allow either the front or back prop shaft to turn freely while the other prop shaft receives no torque. Consequently the centre diff is always made lockable, normally by a mechanical lever near the gearshift which will be marked H, L and Diff Lock. Turning the vehicle while any diff is locked will cause one or more wheel to drag, which will do damage to the surface as well as to the tyres. If the transfer case does not have a diff between the fore and aft prop shafts then it must have a dog-clutch to engage the front prop shaft to the power train. The front and rear prop shafts will be forced to turn in unison when this device is engaged and large stresses will be generated if the vehicle is turned or the wheel sizes are not identical. Vehicles which have a 4H, 4L and 2H selector will have a dog-clutch. Any locking diff or dog-clutch will not unlock if it is under stress. To unlock it if it is jammed you have to turn the steering away from centre and rock the vehicle back and forth by alternately engaging a forward and reverse gear. Ensure that the locked component is unlocked when you approach a hard surface or you might travel some distance with locked axles, which cause rapid tyre wear. Locking Hubs A locking hub allows the associated wheel to be mechanically disconnected from its axle. The hub may lock manually or automatically. Locking hubs when unlocked were thought to improve fuel economy by eliminating the friction of the front axle, diff and prop shaft being turned while the vehicle was in 2wd mode. Locking hubs are, after over-inflated tyres, the most common cause of vehicles becoming stuck. The driver fumbling knee-deep at the front wheel of a vehicle filling with water in the middle of a river is a person who either forgot to lock his hubs or tried to save that last nano-liter of fuel by delaying locking just a little bit longer. If you have locking hubs you should get rid of them as they confer no benefit and contribute to many front axle and diff problems. The problems stem from the stationary front axle components not being adequately lubricated and protected from moisture which enters the axle through the breather every time the atmospheric pressure increases. The result is corrosion on the gears and bearing which then fail just when you need them. Automatic hubs are prone to surreptitious, intermittent failure and they are difficult to check without running yourself over. Manual hubs are never locked when you need them. In any case they save no fuel because the friction in the front axle is negligible. Jack up a front wheel and feel it. Viscous Coupling Some 4wd vehicles do not have a transfer case. Therefore they will not have a High and Low ratio, a centre diff or a dog-clutch. Instead they have a viscous coupling between the fore and aft prop shafts which gives them a quasi-fulltime-4wd capability. The viscous coupling is a stretchy sort of thing that takes out the stresses generated in a turn. Many of the vehicles that have them are actually front wheel drive cars with an auxiliary output to the back axle. There is a inevitable loss of torque in a viscous coupling which means that only 60-70% of the available input power will appear at the output. Locking the viscous coupling produces the same result as locking the centre diff or engaging a dog-clutch between the prop shafts. Hill Descent Control HDC One of the many benefits of a transfer case in Low ratio is that very steep descents can be negotiated flat footed i.e. with engine braking only. To compensate for the lack of a transfer case we have HDC. The vehicle uses parts of the ABS (anti-lock braking system) and the speedometer to keep the vehicle going slow by automatically pulling brake calipers in some sort of sequence. Many accidents have been caused by applying wheel brakes on a steep slippery descent causing the vehicle to yaw and roll over. It seems unwise to allow a black box to apply random asymmetric braking to a vehicle in a radical situation and that is in danger of going out of control. That is probably a good time to disable the system. HDC is also used to control wheel-spin. When the ABS detectors see that one wheel on an axle is turning while the other is standing still it applies the brake on the spinning wheel, thereby forcing the other wheel to turn, and thereby (possibly) getting the vehicle to move. Tyre Pressure Probably the single most significant weapon in the not-getting-stuck campaign and successfully arriving at Villa da Luz is tyre pressure. See flotation. Do not attempt to drive on a beach with tyres inflated to more than 0.5 bar. You will uselessly damage the beach, shorten the life of your vehicle and become an object of interest to your peers. Recovery devices and other toys Wheel spanners, tow bars, snatch straps, tow ropes, jumper cables, tyre pump, tyre deflators, sexy tyres, high-lift jacks, winches and their accessories. Wheel spanner and jack. Your wheel nuts may have been tightened by King Kong's more muscular elder brother. Be sure both you and your wheel spanner are up to the task of undoing them. Carry a length of pipe to extend your leverage if necessary but make sure that your spanner can take the higher torque. Ensure that the least muscular driver can undo the wheel nuts before you leave home. Carry a short plank to place under the jack in sandy conditions. If you are caught without one you can place the blade of the spade under the jack if necessary. Tow bars NB Never un-stick a vehicle using the tow-ball. While the tow-ball and gooseneck are very strong, the attachments to the vehicle are not. Pulling hard on the tow-ball will detach it and part of the tow-bar from the vehicle possibly convert them into an energy-loaded missile seeking something to destroy. A tow bar is for towing a trailer and nothing else. All cars have towing eyes at strong-points underneath, which can take the huge pull needed to un-stick the car. Identify these points on your car and prepare a bridle of polyester webbing and a pair of shackles to attach it to the tow-eyes. Attach this bridle yourself when it is needed and don't let any 'expert' do it for you. Snatch straps These are long, flat, thick, strong, stretchy webbing belts with stitched loops at each end which allow the towing vehicle to build momentum before yanking the towee out of trouble. Large stresses build up and the strap is deadly if it snaps under load. All spectators should stand well clear when it is in use because it can break, but do carry one because they really work. Also carry two 10ton bow shackles to attach each end to something, and know the attach points on your car. Take responsibility yourself for attaching the strap to your vehicle when you use one, they will rip out anything that is not strongly attached and don't use moving parts like steering rods or the anti-roll bar as an attach point. This is the best device for recovering a vehicle that is stuck in deep, soft sand, but too long for normal towing. Don't be tempted to tie a knot because you won't get it undone. To use it, attach it wisely, close the gap between the vehicles to a meter or two and drive the towing vehicle away at the best speed in a sustainable gear, often 2nd gear low range is best. The stuck vehicle will either pop out of the sand or something will break. If the former happens, take care that the vehicles don't collide in the exuberation over the success of the mission. Tow rope A shorter nylon rope with good quality shackles. Carry one always as well as a shackle wrench to loosen it after use. The cheap orange ones you get in the spares shop are mostly useless because they break at the first snatch after the rope goes accidentally slack. Jumper cables The cheap ones are long on plastic and short on copper. To start a car the copper core needs to be as thick as your little finger (300 amp = 30mm2 = 10mm diameter). Expect to pay substantial money and don't lend them to anyone if you want to have them when you need them. Air pump To go any where it is soft you have to deflate your tyres (down to .6 bar in deep sand). Afterwards you have to re-inflate them to protect the tyres. Spend some extra money on a good pump, or stay on the hard. Tyre deflators Specialist shops sell pre-settable clip-on deflators with which you can deflate all your wheels simultaneously. Pre-set them to .9 bar and relax with a beer while they do the squat-work. Sexy tyres Tyres with huge knobs look great but don't work in sand. At the first hint of wheel-spin they dig a hole which will set the diff on the sand and get you really stuck. Rather pay for long-life tyres such as Michelin or Bridgestone and spend what you thereby save on useful stuff. Hi-lift jacks If you're stuck you need to be pulled out forwards or backwards. To do this you need a tow-buddy or a winch, not a jack. They can be useful when changing a wheel in rough terrain but for much else. Electric winch and accessories The winch The ultimate tool for the independent adventurer. Usually fitted to the front of the vehicle but often needed at the back when it is used for vehicle recovery. At the front it is used for everything from uprooting trees to erecting water towers. To attach it to the back requires a temporary mounting and cable connection that is awkward to use and unsightly. A second battery is not required but keep the engine running at idle whenever the winch is in use and don't try for more than a 20% duty cycle under load, (that is 12 seconds per minute). A winch is of very little use if you are stuck on the beach, firstly because there is nothing to pull against (you can bury your spare wheel to about 2 meters and dig a sloping trench for the wire) and, secondly the soft stretches are long and arduous. Winches are not fully waterproof. If you have immersed your winch open it and clean it before corrosion ruins it. Check your winch for serviceability before you need it to save your vehicle from loss or destruction. Hydraulic winches (trade mark Mile Marker) are, alas, no longer available. If you can get one and you have power steering, don't hesitate ,it's worth more than any electric winch because it uses the powersteering pump hydraulics and has a 100% duty cycle, but get a good man to do the hydraulic couplings as even a slight leak will have you filling the steering pump reservoir with irritating frequency. The warranty on your vehicle may be affected by the interposing of a hydraulic winch in the powersteering hydraulic circuit. Winch pull capacities are grossly exaggerated (American style), a winch rated at 8000lb (3636kg) does not pull 8000lb. In fact it can pull an 8000lb vehicle up a 15 degree slope on a smooth hard surface if the line is doubled and the drum is pulling in the first layer of wire at an unspecified reel-in rate. The actual single line pull under these conditions is about 420kg (sin 150(3636kg)/2) and the pull of a single wire on the top layer of the drum will be no more than 25% of this figure at that reel-in rate. The torque on the drum will increase as the speed of rotation decreases but there is no telling what the torque will be as the motor approaches stall. You'll have to measure it. Winch Accessories If you're fitting a winch because you think you might need it some day, then you will need an assortment of attachment aids to bring the winch power to bear where it is needed when it is needed. Not having these items to hand will increase the stress of the situation and might tempt you to use unsuitable alternatives, thereby increasing the risk of an accident. Make a point of buying only galvanised couplers. Equipment that is not galvanised will be covered in either oil or rust, and stainless steel is too soft to be useful. Snatch block This is the large-diameter sheave block that you use to double the winch wire. It can be clipped onto the wire by sliding the side-plates apart so you don't need to wrestle with the hook end of the wire. Shackles You need lots of big, strong, galvanised shackles. Only bow-shackles are certified for strength. Chain 2 or three pieces of 10mm galvanised chain long enough to go around a tree or pole. Use high tensile bolts to close the chain loops, shackles of the right size don't go through the chain links. Webbing Bridle Like a broad short version of a snatch strap, for use around a tree you don't want to kill with a chain, or to shackle to chassis hooks or towing eyes Fairleads In practice you will often want to pull to the side of or the rear of the car. To do this you need to run the wire from the winch at the front out to the side or the back, through a snatch block and then back to the rear of the vehicle. To avoid doing damage to the car during this operation you need to pre-plan the points at which the wire will leave and return to the vehicle without touching the soft spots. Folding Spade Essential for digging a hole for the spare wheel. Try to get one that doesn't self-unscrew its handle . Panga You'll need it to get to the tree that you want to tie the block to. Shoes In holiday mode you don't always have them with you. Spare wheel A natural compliment to the winch. Bury the spare wheel and dig a trench for the wire, but expect to dig a huge hole because the wheel will climb out of anything less than a meter deep. Don't forget the spade to do the digging with. A meter of 10mm chain and a shackle are handy for tying the winch wire to the wheel. The chain needs a bolt or a small shackle to make a loop. Tyre repairs kits Tubeless radial tyres are easily repaired with gummy plugs if the holes are small and round. For bigger wounds you will need to fit a tube and a gaiter inside the tyre. Pushing the bead off the rim is often impossible without the right tool. Carry a second spare if you don't have the right stuff. The Art of Getting Stuck Getting a vehicle stuck requires 2 things: a challenging piece of terrain, and poor technique in crossing it. Inadequate planning can get a car stuck, but poor technique in recovering the vehicle often leads to a grossly aggravated situation in which the vehicle can be damaged or even lost. Don't take getting stuck too lightly. Many a fun trip has ended in tragedy. Before you enter an area where you may become stuck ask yourself what the worst is that the situation can deteriorate to, and then weigh the risk of that worst-case becoming a reality. One of the most hazardous places to get stuck is on the ridge of coarse, soft sand at the high water mark of a beach. The driver is tempted onto the hard flat sand that the outgoing tide has left because the going is so easy. An incoming wave then blocks the path and an attempt is made to reach the area of beach above the high tide line. On the way the vehicle bellies down in a place within reach of the incoming tide, and cannot be recovered in time to avoid a total loss. Pulling a vehicle that is axle-deep in sand uphill is very, very difficult for both a winch and a towing car. Backwards would be easier but that's where the sea is getting closer and closer..... There is PC software available that can predict the tide tables for every piece of ocean beach on the planet. If you're going to drive below the high tide line you should have it with you. TideComp 2000 is one such application and is available from www.pangolin.co.nz. There are others that are cheaper.
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