« Reply #11 on: Apr 26, 2020, 5:25 pm »
 

Hi,


Did you see later in the week of each tech talk there is a zoom interactive meeting where all the stuff in the video can be discussed (Thursday 9pm).  It would have been interesting to bring up the Otter's results then.   I'm sure Keith would have welcome having 3 more craft to add to his Quiet list! 


Also I don't think it's been posted on FB yet but I tuned into last week's zoom discussion on cruising in the North West and the tech talk this coming week is going to be by Owen Ellis of the Australian club about his development of electric craft which should be really interesting.

« Reply #10 on: Apr 25, 2020, 6:46 pm »
 
I sold it to an Oyster farmer down South, who eventually sold it on (via an auction site) for approx the same amount. Ho (hum) :'(
Memories are BETTER than Dreams---"Capn" FLINT

« Reply #9 on: Apr 25, 2020, 11:19 am »
 
So,oo. What happened with the Kingfisher?

« Reply #8 on: Apr 25, 2020, 10:38 am »
 
One EXPENSIVE experiment KingFisher was! :'(
Glad I did undertake the task.


Otters are smaller, (but big enough)
Otters are cheap to run (especially ATM)
Otters are my "Ring of bright water" during the muddy current times.
Sparkle patiently sits and waits for matters to progress and will fire up (on the button)
once we are allowed to enjoy life again, rather than "tolerate life and carry on gardening"  :-X

Memories are BETTER than Dreams---"Capn" FLINT

« Reply #7 on: Apr 24, 2020, 6:42 pm »
 
I’d forgotten about Kingfisher - in that case it 8 :-\
Ian Brooks
Gloucester, UK

« Reply #6 on: Apr 24, 2020, 11:58 am »
 
When I measured KingFisher it was "slightly lower" than Otter noise levels, but presume ATM its VERY (very) quiet, i.e. non operational any more---
Memories are BETTER than Dreams---"Capn" FLINT

« Reply #5 on: Apr 23, 2020, 9:59 pm »
 
I thought Ronnie's Kermit was fairly quiet
It's got a 1.8m prop running at less than 1000rpm - that reduces noise significantly and has the advantage of also increasing efficiency (more thrust for less power).   Most of this stuff is pretty obvious once it's been pointed out (like most things!).   Intake turbulence combined with high tip speed is the main noise producer.  Even the mesh in front of the prop/fan makes noise - actually noticeable even though not quite so measurable.  Keeping the mesh as far in front of the prop (and as far from the tips) as possible helps.   Turbulance is also produced on the duct inlet when it "stalls" as a craft sideslips - keeping the blades tips as close to the duct inlet as possible helps..
 

« Reply #4 on: Apr 23, 2020, 8:54 pm »
 
I thought Ronnie's Kermit was fairly quiet

« Reply #3 on: Apr 23, 2020, 8:25 am »
 
I'm not far behind :)  not as "clean" as the Otter but have unobstructed and prop inlets running slow running fan and prop. Keith had a look and approved, spent a while looking at the drive system.  NExAP's in the shed at the moment for a few minor improvements some to do with noise.
 I don't have noise figures to hand but being able to comfortably  make a phone call at 30kph can't be bad ;)  Had to cancel the take away delivery to the beach as weather conditions were deteriorating.

« Reply #2 on: Apr 22, 2020, 10:22 pm »
 
I have the greatest of respect for Keith Oakley, and he has done remarkable things in creating a quiet integrated hovercraft, not something I would ever have thought possible. I do need to take issue with one thing though, and set the record straight. Keith says that there are now 3 "quiet" hovercraft out there. However, he has not taken into account the Otter!

We launched the first Otter in 2012. It has almost all of the design features that Keith recommends, but of course predates his video by several years. If you look closely you will see:

Rear mounted thrust fan
"Clean" fan inlets, with long shaft drive
500mm obstruction free inlets
Very low fan tip speeds
Low revving engine
   
Plus there are some features that are not mentioned in Keiths article.
   
All these factors were designed in from the start to achieve low noise, and thats what was achieved - in 2012. Since then, the MkII Otter (Nick and Kims) have an improved rear end to further clean up the air flow into the fans, and this has reduced noise once again.

So forgive me for pointing out that there are 7 "quiet" hovercraft in the world  ;)

Here's the noise test data:

[mmg]2963[/mmg]
[mmg]2964[/mmg]
[mmg]2965[/mmg]

And here's the video

Ian Brooks
Gloucester, UK

« Reply #1 on: Apr 15, 2020, 4:23 pm »