Todays Boating

[ashley needhamParticipant @ashleyneedham69188]

Hmmm..perhaps not rooster tails, however, what’s always missing in a model is the white water frothing you get from a real boat. The HSS should have two frothy white plumes from the 4 water jets at the stern.

Ashley

[ashley needhamParticipant @ashleyneedham69188]

I have put in place wedges and splitter vanes. Test out tomorrow. If no good. I will have to make some sort of rudder arrangement.

It’s a bit nippy, hope it is warmer tomorrow! Ashley

[Richard SimpsonParticipant @richardsimpson88330]

Funny but over the years we tend to modify the way we look at things as our experience broadens our horizons and gives us a better balanced approach.  The way I see people has certainly changed but so has the way I see the wake created by various vessels as they pass through the water.

I remember during our Naval Architecture lessons doing my ticket discussing the behaviour of wake and the way bulbous bows prevented the creation of bow waves and took away from that a very simple bottom line.  The way I see it, the hull that passes through the water with the minimum of disturbance is the more efficient hull.  When I look at modern craft such as lifeboats and many pleasure craft and I see large wakes, huge troughs at the stern as they pass, large piles of foam at the stern and big rooster tails, all I see now when I watch that is wasted energy.  It takes energy to disturb that water, which is therefore not being used to propel the hull.

Just sharing a thought.

[ashley needhamParticipant @ashleyneedham69188]

And it’s a good thought Richard

Pictures of the new carriers sailing in formation with other supply and warships appear to indicate that the carriers have a much reduced wake.

Apparently the Australian Jindalee long range radar ( I believe it was bounced off the ionosphere or something silly) could detect wake patterns in the ocean at massive ranges.

Boating today, or rather not much boating. Massively windy and jolly cold. No point in even trying the HSS as it would have been blown all over the place. I took the two gp hulls and some tops, but again, with the tops not being sealed to the hull it wax too dodgy to put then in the water.

Ashley

[Colin BishopModerator @colinbishop34627]

Richard, that’s a bit of an apples & pears comparison. As I understand it, the maximum economical speed of a vessel is close to its theoretical hull speed which itself depends largely on hull length. Thus the express liners like the old Queen Mary had to be around 1000 feet long to achieve a service speed approaching 30 knots. By comparison the hull speed of a lifeboat operating as a displacement vessel might only be 8 knots or so. (just a guess!). However the lifeboat has to operate at 25 knots which requires far more power to achieve semi planing performance so it is operating very inefficiently from a hydrodynamic viewpoint but you will know a lot more about this than I ever will.

Strangely enough, the bulbous bow is not a post WW2 invention, the Germans used it for their liners Bremen and Europa around 1930 and before that, the Victorians inadvertently invented it with the rams attached to the bows of their battleships.

The effective hull speed can be usefully increased by hull design and refinements such as bulbous bows and anti friction coatings to improve economy. Most modern large ships seem to slip through the water with minimal wave disturbance which is a tribute to their design.

Back in the 1930s the Queen Mary and the Normadie were pretty much neck and neck speed wise with QM having a slight edge but Normandie’s hull was far more efficient and you can see this in aerial photos with QM thrashing along while Normadie is clearly making far less wash. Normadie required far less power to make her service speed than QM despite being turbo electric drive but both ships had a very similar maximum hull speed. Of course it was all a bit more complicated than that as propeller design was also a major factor and both ships had big problems with their initial sets.

Colin

[Richard SimpsonParticipant @richardsimpson88330]

I think we are at crossed purposes Colin.  I wasn’t actually intending making any comparison, all I was saying is that when any hull moves through water, of any size or shape, any amount of displaced water detracts from it’s efficiency.  I know that is a wide and all encompassing thing to say but, as a very general rule, it is true.

I was saying nothing more complex than any displaced water is a waste of energy, whether that is a bow wave, a wake, a wave at the stern, foaming or rooster tails etc..  They are all examples of wasted energy, which detract from the hull’s efficiency.

What makes me smile is things like jet skis, flying around making unbelievable amounts of spray, wash and rooster tails as they try to impress everyone.  All I see is monumental amounts of wasted energy!

[Colin BishopModerator @colinbishop34627]

Richard, yes, maybe I went off at a bit of a tangent but you got me thinking! It’s probably also true to say that wasted energy is the price you pay for pushing up the speed beyond economical limits. What make me smile is scale modellers asking about watercooling their motors and ESCs when they are simply addressing the symptoms where the true problem is a mismatched motor/prop combination. Also few people seem to appreciate the advantages of gearing (gears or belts) in bridging the gap between a fast motor and a slow prop to increase the efficiency of the installation and reduce current draw.

Of course water cooling can be needed when it comes to the fast racing boats as the priority is to get maximum speed regardless of the inefficiency consequences.

As an aside to my previous comments I looked up the liner ss United States which achieved 35 knots in service (and more on trials). Despite being roughly only half the displacement of the Queen Mary she needed 240,000HP as against 200,000HP in the QM. She also needed to be only slightly shorter in length than the QM (by 30 feet).

Today’s enormous cruse ships have much lower power plants as they usually cruise at 22 knots or less in service. I think there are always ‘sweet spots’ such as the 20/20 liners of the interwar and post war periods which were 20,000GRT (not displacement) and 20 knots service speed. Bigger vessels tended to have slightly higher service speeds.

Colin

[Richard SimpsonParticipant @richardsimpson88330]

I definitely remember discussions in those Naval Arc lessons about the relationship between speed and the length of the hull.  I always found the explanations a little vague though! I think one of the really interesting aspects that I saw time and time again was the exponential relationship between speed and power required.  Frequently in later years we could be pootling around with only two of the five engines running, one was required for house load so only one would be providing propulsion.  We could still be doing 12 knots or so.  Then, at the other end of the scale if we had four engines going at full load and put the fifth one on line we would probably only get an additional 2-3 knots out of it.  And the fuel difference would be enormous for that extra couple of knots.

Just an interesting snippet while we totally hijack Ashley’s thread, when the QE2 was a steam ship and getting across the Atlantic in five days she used to burn in the region of 700 tons of fuel per day.  She was around 80,000 tons.  Nowadays you can be looking at 120,000 ton ships going significantly slower but using only around 100 tons of fuel per day.  Adjusting itineraries to reduce speeds makes a huge impact on the cost of fuel.

[ashley needhamParticipant @ashleyneedham69188]

Didn’t the ss United States use a battleship propulsion system. Paid for by the government?

The thread is for general discussion. Hijacking totally allowed for interesting and informative discussion,!

I recall that the Island class OPV the RN used to have did about 14 knots on one diesel (it had one shaft) but only 16 when the other was added. The extra power is handy when going uphill of course….

Remember seeing one of the big models in Container house on the South Bank in London, and the bilge keel was curved presumably to match its cruising speed.

Ashley

[Colin BishopModerator @colinbishop34627]

ss United States used a powerplant designed for the new big US aircraft Carriers of the day – possibly the Forrestal class.

Colin

[Richard SimpsonParticipant @richardsimpson88330]

Interestingly that has come full circle as well as now the two new carriers use a diesel electric propulsion system with two turbines and four diesel engines to generate the power for the two main motors.  Almost all new large cruise ships built nowadays are also diesel electric.

[Ray Wood 3Participant @raywood3]

Hello All,

As we are talking things electric !!

My friends son just started running a Polestar electric car, goes like a rocket 🙂

His old diesel powered Merc used £200 of fuel a month for work travel

The new electric car costs him £500 a month to charge to do the same mileage !!

Food for thought, not mentioned in the adverts strangely 🙂

Regards Ray

[The Long BuildParticipant @thelongbuild]

I Just love it on a bank Holiday , cruising up to the Lakes, stopping off at a Service station passing the queue of 40+ Electric cars waiting to charge, the Electric car at the moment is a big white elephant, may improve in the future but at the moment infrastructure is useless an Probably in the long run makes no difference to the overall effect of the environment. Tesla laying of 14k of staff as sales are drastically dropping (according to the news_)..

bit like Model Electric boats, work at home but never at the pond !!

[ashley needhamParticipant @ashleyneedham69188]

Electric cars horribly ungreen from almost any standpoint. I am being green with my 20 year old Suzuki

Still passed ulez emission standard. I have not brought a new car for 15 years so have not ramped up new build or disposal emissions.

ANYWAY. I have a 1,/35 Amati J class yot kit to get rid of for a friend whose husband sadly passed away. Hull started on 20mm mdf build board. All bits in original box appear to be present. The chap who had it was quite meticulous. Pm me any interest.

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