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Propeller nut fastening

26 March, 2017

The end of the prop shaft is normally tapered and has a keyway in it as well to transmit the torque from the shaft to the propeller. Retaining the propeller on the shaft is done by lock nut.

The lock nut can occasionally come loose when the shaft rotates in the opposite direction to the thread. This can result in the loss of an expensive propeller and all drive!

There are many different ways of securing the propeller nut including; castellated nuts with split pins; drilled nut with split pin; cone nut with lock bolt; a tab washer bent over or; locks nuts.

Lock nuts are not so common in the UK but its worth noting that when fitted, the half nut (the thinner nut) should be fitted first with the full nut last. This seems counter intuitive but actually splits the load correctly between the two nuts.

Each method has its advantages but should never be overlooked when refitting a propeller and should always be checked when the vessel is lifted for any maintenance. Also check for play in the keyway by turning the prop by hand.

Beware of chafe

19 March, 2017

Chafe is well known as a problem for running rigging and sails but it can also affect other parts of a vessel. The photo above shows a fuel hose that was resting on a cutout through a bulkhead in the engine space. As the engine vibrated during normal running the hose gently chafed away unseen.

This one I picked up on an insurance survey and was only evident when lifting the hose to inspect the underside. The owners had completely missed it and were preparing for an offshore passage. Had the line chafed through it was positioned ready to leak fuel over the hot engine. On the same survey I found the exhaust hose was similarly worn through where it was sitting on top of a stud retaining the SailDrive ring.

Inspect the clamping and securing of your hoses or electrical lines to ensure they do not chafe either through engine vibration of movement when underway. Inspecting the hose and cable runs when running the engine on the berth should give a clue, if you see a hose or wire vibrating then its worth securing it with a saddle clamp or cable tie to prevent it wearing through and spilling its contents or shorting a circuit. Placing sheathing around the hose can help but doesn't stop the chafe, it only delays it.

Flexible gas hose

12 March, 2017

Rubber gas hose from the regulator to the bulkhead connector should be rated for LPG and marked as BS3212:1991 and also have the manufacture’s name and date on it. Many boats I come across have old pipes that are cracked and damaged such as the one in the photograph from a boat surveyed recently.

Remember to;

  • Keep the hose away from bight sunlight to avoid UV damage, damp and mechanical abrasion. They are in a harsh environment and can degrade faster is abused.
  • Check for damage to the hose such as cuts, cracks, swelling or abrasion and replace the hose if damaged.
  • The useful life for regulators and hoses is approximately 5 years and they should be replaced after this time.

Regulators cost around £20 and the hose is around £3/m. We all know gas onboard boats can be dangerous so it is worth checking and replacing these relatively inexpensive items.

Redundant seacocks

5 March, 2017

Old and redundant seacocks are often found left in-situ with a short length of hose in the bilge and a soft wooden bung pushed in and hose clipped. This is not a secure way to seal an old seacock.

Remember, wooden taper plugs are supposed to be temporary fixe not a permanent solution. Wood can rot, shrink and split so you need to do more than leave a short length of hose with a softwood plug in a damp bilge to secure your vessel.

Best practice is to remove the old seacock and fully repair the opening in the hull. Understandably many owners are unwilling to do this due to cost, time and the fact that they may want to reinstall the fitting at some time in the future.

If leaving the seacock in place, unscrew the hose tail and fit a proper blanking plug to the thread. These are readily available from chandleries but do make sure the cap is marine grade bronze and not brass.

If you can’t remove the hose tail or get a blanking cap you should as minimum take the hose length as high as possible so that the end is well above the water line even when heeled over and then plug the end. This way if the seacock does leak the hose end will be above sea level and will not flood the boat.

Fuel tank sight gauges

27 February, 2017

Sight glasses in tanks to measure the fuel level are wonderfully simple and clear and do not need electrics which is always a bonus on boats. However they are often poorly installed making them a safety hazard.

A poor installation often consists of a length of nylon pipe or PVC hose coupled directly to the tank top and bottom as shown in the picture at the top.

Normally the pipe is not fuel grade and will become cloudy as the fuel degrades it. If the tube is damaged and broken by a knock from loose objects in the locker it will empty your tank and leave you with a dead engine. In the worse case scenario, a fire melts the tube and continues to feed the fire with the contents of your tank and there is nothing you can do to stop it. In the tank on above, that’s 157litres of fuel in the bilges.

To correctly install a sight glass it should be fitted with a self closing valve at the bottom and top so that in the event of the tube breaking - or melting - the fuel will not empty from the tank. The self closing valve in the bottom picture was reasonable cost from Aquafax and simple to install. The sight glass is protected by a metal cover and still clear after 3 years in use.

Just remember push the button each time you need to check the fuel level as it will continue to indicate the last reading.

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