What does the Doctor think -August

WHAT DOES THE DOCTOR THINK THIS MONTH?

August 2013

Why do ships have a bulbous bow?

I was doing one of my stints as doctor on a cruise liner and Deannie and I were standing on the bridge chatting to the captain as we left Stockholm, a beautiful city built on many interconnecting islands. We had moored at anchor right by the main old town and it was time to extricate ourselves and sail off to Copenhagen, Looking around at other ships, I was reminded of that horrible great bulge that has appeared on the bow of many ships at, or just below, sea-level. I had always assumed that the bulb was some sort of stabiliser but that is only part of the case. The captain explained that the bulb increases the buoyancy of the front of the ship, thus reducing the pitching of the vessel (important to Deannie and me because our cabin is in the hospital at the front of the ship, at sea-level. More importantly, the bulb modifies the way the water flows around the hull, reducing drag and thus increasing speed, range, fuel efficiency and stability. The fuel saving is between 12% and 15%, a phenomenal amount when you consider that these cruise liners actually spend most of their time travelling. The bulb works best when vessels are longer than 50 feet and cross large volumes of water at a speed somewhere near their maximum speed. Our ships have a maximum speed of about 23 knots and travel most of the time between 18 and 20 knots, so it applies.

I asked how it actually worked and the captain became a bit technical! It is all down to the “form effect”. On a conventionally shaped bow, the bow wave is generated just in front of the bow and it is the bow wave which is the greatest force impeding the vessel's forward motion. A bulb placed in front of the bow and below the water forces water to flow up over the bulb, creating a trough which partially cancels out the bow wave, reducing the wake. The pressure distribution along the hull changes, reducing wave resistance – this is the form effect. Of course, the addition of a bulb does increase the ship's wetted area. As wetted area increases, so does drag. For this reasons, the bulb is only efficient at higher speeds, when the benefit from the reduction of bow wave and the form effect far outweigh the increased drag. In 1935, the French superliner Normandie had a bulb and the Queen Mary did not. Both vessels managed equivalent speeds across the Atlantic but the Normandie did it with 30% less engine power than Queen Mary and with a corresponding reduction in fuel use.

Confusing telephone mumbers – be very careful which you use. Fed up with automated answers?

Are you as confused as I am by all the new telephone numbers? The following will give you an idea of the pricing system. It is a stodgy, but I hope it helps.

Numbers beginning with 01 or 02 are regular geographic numbers (eg Thetford is 01842, Watton is 01953 etc) which will be charged on a local or national basis. These numbers are usually included in bundled (included in the price) minutes on your landline or mobile contracts.

Numbers beginning with 03 are new and are a non-geographical equivalent to the 01 and 02 numbers. They should be charged in the same way as 01 and 02 numbers.

0800 and 0808 numbers are free from a landline. However, from a mobile, they may cost about 20p / minute as they are often not included in the free minutes allowed by your mobile contract. There is often a cheap 01/02 or 03 equivalent for this number – check on the website saynotopremium.co.uk

07 numbers are usually mobile numbers but some ar “follow me”numbers which are extremely expensive to dial and must be avoided.

08 numbers (0870, 0871, 044, 0845) are almost always more expensive to dial than 01/02/02 numbers; some include a revenue which is shared with the person you are calling and these numbers are often excluded from “included minutes” on both landlines and mobiles. Check the above website for alternative01/02.03 numbers

09 numbers are genuinely expensive premium numbers and should be avoided. Another useful website is saynoto0870.com. It will give you all sorts of useful cheaper alternative numbers.

Another tip – look on the back of your credit card. The UK helpline will start with 0845 or 0870 or an equivalent. However, there is also a number you can use when you are abroad. It will start with +44 or 0044. To dial that number from the UK, simply avoid the 44 and put a 0 in front of the remaining numbers to have a cheap call. Eg My Mastercard number +44 1268... becomes 01268...

Many companies now have automated 'phone lines where you can spend many minutes listening to options and pressing buttons. A 53 year old from Kent has devised a system to enable you to bypass all that. Go to the website pleasepress1.com    where you will find all sorts of advice about how to avoid the automated “if you want to  ..….., press 1”  systems.

A man said to his wife “What would you do if I won the Lottery?” Quick as a flash came the reply “I would take half your winnings and leave you”. “Are you sure?” he asked. When she affirmed, he said “OK, I've just won £10. Here's a fiver – now push off”.

Best wishes to you all     Ian Nisbet