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Ian Brooks

What should I look out for in a craft? New
« on: Feb 18, 2012, 7:46 pm »
What should I look out for in a craft?



(Only joking  ;D)


Safety

Unsurprisingly, safety comes at the top of the list. You will need to look for the obvious, like properly guarded rotating assemblies, adequate buoyancy in case the engine fails on water, good ‘freeboard’ (the height of the sides above the water surface), etc.

There are many other factors in the performance that contribute to a ‘safe’ cruising craft in real life, and these are covered in the sections below. Here you will become familiar with many of the terms that experienced hovercrafters talk about all the time – “plough-in”, “the hump”, to mention just a couple.

Noise

Noise is a critical issue for hovercraft, some are incredibly noisy.

If you own a noisy craft you will be banned, pilloried, have stones thrown at you and generally made to feel unwelcome, wherever you go! There are some craft out there that are so noisy they make a 747 seem like a whisper. You do not want to own one of these!

The HCUK encourages new craft to be quiet in operation – 80dB, or about the noise of a small van passing by, would be considered to be good. The reason is simple – many hovercraft venues have been lost due to excessive noise.

The good news is that newer designs have been evolving that are much better in this respect.

Look out for designs that have twin fans, one for lift and one for thrust. The use of two fans allows the manufacturer to design efficient and quiet systems. These may be driven from one or two engines.

Ask the seller if they have measured the noise. If it is above 87dB, leave it unless you wish to do the work required to bring it within limits. Take advice – older designs may never meet the limit and should be scrapped. But be careful – some manufacturers issue quite misleading noise figures.

Things to avoid:

  • 2 stroke engines
  • Ducts smaller than 900mm
  • Very powerful engines (90hp+)
  • Poor silencers
   
Things to look out for:

  • Separate lift and thrust fans (may be driven from same engine)
  • Efficient silencers
  • 4 stroke engines
  • Low revving engines
  • Large thrust fans/propellers

Reliability

When you are out, miles from anywhere, the last thing you need is to breakdown. There’s no RAC at sea! Recovering a stricken craft can be difficult, so reliability is a big issue.

The reliability of the craft is perhaps the most difficult thing to judge, the best thing to do is ask an experienced Club member. One might expect professionally built craft to be more reliable but that does not necessarily follow – maintenance is the key here. A craft known to Club members will be a known entity, anything else should be viewed with some suspicion.

Things to look for are low stress engines – small industrial engines, car engines or some motorbike engines can be reliable. Don’t buy anything with a 2 stroke engine.

Any craft that has been used in a marine environment (most cruisers have) may well suffer from salt corrosion – often all the controls will require overhaul before reliability can be assured. Likewise, bearings and transmission belts may need replacing.

The good news is that an unreliable craft can usually be made reliable, but it will take considerable effort and plenty of money to do so. So if in doubt, join the HoverClub and ask for advice!


Fuel consumption

Hovercraft can consume huge amounts of fuel. The worst culprits are 2 strokes, a 50 hp 2 stroke can easily consume 5 gallons per hour. 2 strokes should be avoided. On the other hand, a modern twin fan single engine craft can cruise on less than 1.5 gallons per hour, giving a respectable 15 m/gal in good conditions.

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« Last Edit: Oct 31, 2017, 8:33 pm by Ian Brooks »
Ian Brooks
Gloucester, UK