[John Robertson Posts: 5203 Status: Offline WWW]

70  mph! you must be either very brave or very stupid!!!! I do not think I would be brave enough to try that!

I'm probably a bit of both  .    I always think it's a good idea until the GPS hits 70 - then I start thinking about how I can't turn, what if a boat/bird crosses my path, etc, etc - that's usually followed by a swift reduction in throttle     My Prospector will do 47mph - which I always find amazing as it has the aerodynamics of a shed - and the same puny 70hp engine as the UH18.

The craft only starts to get a bit "floaty" above 70mph - below that it is rock solid stable (look at the shape).  For the last few years, I've been running it with a lower bag skirt pressure to get better comfort - the downside is that the top speed has gone down to only 60mph 

The craft has, what could be called a "soft" plough - you can deliberately plough it in at 60mph and all that happens is that it slows down a bit (the trim wing/elevator lets you deliberately stick the nose into the water, and then lift it back out again when you've slowed down enough - a crude brake!).  It works because the underside of the hull has an upward step all around the inner plough plane and the lift fan can still push lubricating air under the hull even when in the water.  The upward step breaks the water flow and stops the hull sticking itself to the surface (the end result of most bad plough-ins).

None of these things are at all new or innovative (1920's race boats had stepped hulls) and demonstrate that the dreaded hovercraft plough-in is pretty easy to sort (so the obvious question is why hasn't it been?).

[atters]

   I hate you, I so hate you right now. 

[Brian.G.Reynolds]

Thank you John,
 
70  mph! you must be either very brave or very stupid!!!! I do not think I would be brave enough to try that!
 
The foam thing sounds very strange!....
 
very interesting!
 
B.

[John Robertson Posts: 5203 Status: Offline WWW]

The UH18 is supposed to have an 8" hover height but it's more like 6" on a good day.   It's a 19 foot long craft so you can imagine what happens when you try to cross a lump in a field  .  They are not at all suited for land use.

On water it's a whole new ball game.  The low hover height provides massive stability at speed and the pointy nose (no weight up front) lets it handle surprisingly rough water (12-18" waves are near the limit).  I don't use it that much as it can't handle the rough stuff as well as the Prospector but every time I drive it, I am impressed by it's performance.  It's an incredibly efficient hovercraft and will happily cruise all day at 25mph at around 2000-2200 rpm making almost no noise and consuming very little fuel (it uses half the fuel of the Prospector and has the SAME engine!). 

On today's 52 mile trip it only used 9 litres!  If you want some excitement it will also provide that - I've GPS'ed it at 74mph on water a couple of times - seriously scary  .   You can see the hump performance in the video - maybe three seconds from start to finish (Matt had the variable lift control in the wrong position hence the "ball of spray" issue and the fiddling around hafl way through)!  I also timed it at 5.6seconds 0-60mph on water covered sand (took about a mile to stop it again  ).

You might think that it must have a souped-up high horsepower engine but you would be wrong - it has an old overhead valve Subaru flat four engine producing (on a good day!) maybe 71hp.

The construction is a also a bit strange to say the least.  The "hull" (the flat iron shaped bit) is a 6" thick solid lump of polystyrene foam (extruded - not the bead stuff) with a 1/8" plywood sheet bonded to the top.  The hull underside is bare foam!  No glass, resin or anything! I did what I was told like a good boy and built it exactly to the to plans (luckily I didn't think I knew any better at the time  ).  Amazingly the bottom of the hull seems to be almost indestructible - the foam just "dents" and recovers (you get left with some small dents).  It's the kind of lateral thinking that the Bob Windt and Barry Palmer are famous for.

 

[Brian.G.Reynolds]

That looks a fantastic trip! I wish I could be there...
 
A question if I may please, The UH18 does not seem to have much ground clearance, the skirt itself looks only to be a few inches high.
 
How does this effect things? i.e. obstacle clearance?
 
I need educating!
 
B.

[John Robertson Posts: 5203 Status: Offline WWW]

Hover-withdrawal has been setting in for some time so I persuaded Matt to come along with me down to Berwick for some hover-fun (on condition he got to drive the UH18!).

I'd replaced the UH18 exhaust system a few weeks ago as the two year old one had fallen apart over the winter (patching for the Scottish Hoverin had not been a success  ).  The original systems consisted of twin Reliant Robin (I know  ) silencers with an original Subaru combiner box and exited upward tractor-style.  It was very quiet but pretty complicated and heavy so I replaced it with a simple crossover pipe and universal silencer.  The silencer was a straight through type and sounded a bit "fruity" so i was a bit concerned that it may be noisy.

Off we set for the 40 mile drive to the coast.  Weather forecast was one of these "could be anything" ones and, true to form, it poured with rain most of the way there.  We fuelled up, de-trailered and set off upriver.  The wind had picked up a fair bit and was blowing straight downriver for the first part (with some 12-18" chop for the first few miles as the tide was coming in and fighting the river trying to flow out).  After a couple of stops we ended up under the Scottish/English border bridge at Coldstream (about 21 miles from Berwick by river). 

There's a large broken weir under the bridge and, most times, the river flows through a 12 foot wide channel at one end of the weir - the flow rate is pretty impressive!.  The weir is fairly easily crossed with a bit of a run but we decided to go no further as  the upriver bit this time as it tends to be busy with kids., etc on a Sunday.  The UH18 run at the weir was a bit too fast and it ended up teetering over the upriver side!

I watched as Matt set off from the Wier (after a bit of thrust manoeuvring to get the craft off the weir edge) - although you could hear the exhaust noise when a lot of power was applied (sounds like a big V8  ), once at cruise speed the whole craft is very quiet (all but inaudible above the river noises at 50 metres).

Only saw three people walking on the river bank in the 42 mile trip - all of them waved back  .

Stopped at Paxton on the return trip for some human fuel (food!).  When we got back to the dune launch ramp it was occupied by a group of canoeists so we just passed on by and headed out to sea.  There were breakers on the shore but, once further out, it was just a big but slow swell and no real chop.

We travelled down to what we thought was an empty spot on the Beach and parked up for a bit - within 30 seconds a heap of kids appeared from nowhere so, after answering the usual questions we hung around for a bit until they got bored and moved off (the beach has VERY fine sand which blows everywhere).  It was then back to the ramp and trailers.  Covered around 50 miles or so with no issues at all (a good day!).

Hovecraft trip from Berwick