The Sevtec Prospector (see http://members.aol.com/sevtec/sev/props.html) is a 4-5 seat craft similar, but larger, than the Scout and uses a 80HP Subaru engine (same as UH18). It has a higher hover height than the UH18 and is capable of traveling on much rougher water. It has twin lift fans and a 6 foot propeller and can be fitted with a windscreen and hood for use in bad weather.
It has a much roomier cabin than the UH18 but is a lot slower (47mph instead of 74mph). It should be more comfortable for long distance inshore cruising and can carry a good payload.
Here is a partial copy of the first plane page just to give you an idea what the plans look like:
I chose to built an 18 foot version of the Prospector. This should give the best load carrying capability and space. The Prospector has twin lift fans mounted vertically behind the cabin. In the video clips I've seen, the lift fans seem to be noisier than on other Sevtec craft. Because I'm trying to minimize noise, I may use the newer sickle shaped fan blades in this craft - I've still to make a decision. Another alternative would be to fit a centrifugal fan - it would fit nicely into the vertical fan bay with the volute chamber formed by the bay. I will build to plan first before looking at this!
Prospector Specifications (18ft hull)
Hull size: 18ft x 8ft (5.5m x 2.4m)
Empty weight: 1000lbs (454Kg)
Max payload: 1014lb (461Kg)
Cruise speed: 30mph
Top speed: 45mph
Fuel use: 2GPH
Engine: Subaru EA81/82 (max weight 260lb, 118Kg), 72-84HP @ 4000rpm
Propeller: 72inch 2 blade Powerfin consuming 36HP @ 200lb static thrust, 1750rpm max
Fan: 2 x 24in diameter 9 blade 4Z consuming 36HP @ 409CFS and 12PSF, max 3500rpm
Hard hull clearance: 12in (305mm)
Cabin flat area: 4.5ft x 10ft (1.38 x 3.05m)
Bought scrapped Subaru pick up. Found engine was rusted up due to water ingress into the inlet manifold. I stripped all of the useful stuff from it (starter, alternator, distributor, etc) and got the rest taken for scrap.
After looking at various different foam types (PVC, honeycomb, etc) I finally order standard Polyurethane foam! The other foam types, while much stronger and lighter, were over twice the cost of PU foam.
Foam finally arrived! There doesn't look to be very much but it's correct. It was supplied in 1200x1200 (4ft sq) sheets which should make panel construction a bit simpler.
Collected resin (80 litres!) and glass from a local plastics company - cash price! I now need to get some clear pine (at least for the rear engine bay area). It's almost impossible to get clear pine - none of the timber merchants keep it.
Started cutting and glassing panels now I have all of the materials. The floor is HUGE!!! . Friend Peter came and helped me for 1/2 day - we managed to cut and glass 14 panels in one day!
Coamings are full length of craft (18 feet). Above is vertical lift fan panel H1A. As I did with the Scout, I've glassed external surfaces with white pigmented resin.
Bonded main hull floor panels.
I had to fill a couple of gaps with foam to get a good fit on the rear fan bay panel H1A to the raised section of the floor at the rear. The bow fitted together well with minimal adjustment. It's a bit of a pain having to make up foam wedges for the the 1/2" to 1" foam transition joints along the sides and at the bow. I used a couple of vertical lengths of wood tacked to the nose corners to get the height absolutely correct. I also used multiple paint cans to support the sloping sides at the correct angle to get the right width and height. I haven't taped the joints on the underside as the hull is far too bendy at the moment - I'll turn it over once I have all of the top deck panels assembled. The plan is to turn it over, tape the joints and attach the skirt and skids at the same time.
Fitted coamings - quite difficult to get them lined up and at the correct height - they are pretty floppy at 18 foot long! Installed dashboard - I just built it in place to fit the coamings/floor/etc. Fitted side decks - it's very tricky to glass the inside joints at the attach strips - there is almost no room to reach into the sharp internal corners. The other squeeze is in the fan bay - you can't turn around in the bay so you have to work with one hand - much cursing going on! The deck skins at the nose are bedded in filler onto small triangular foam ledges - it's impossible to reach these joints after the panel is in place.
I haven't built the nose or the back end yet as I've just discovered that my garage is 3 inches too short! I forgot to include the internal sliding door when I measured it. I can turn the craft around (just!) to work on it but I don't want to move the hull until it is stiff enough not to twist (just in case the floor isn't perfectly flat in the new location).
Installed front deck panel. Fitted cover panels over fan bay. I used unglassed foam to get it to form to the curve nicely. It's a bit messy glassing the inside top surface without dripping resin all over yourself. I eventually used overlapped 6 inch strips - no one will see it inside the fan bay!
I also glassed the bow and floor joints on the underside - I was going to turn the whole craft over to do this but I wasn't happy with the hull stiffness - you could lift one corner by about 3" before the hull came up. I glassed the underside joints by tipping the hull up a couple of feet along one side, and letting it back down onto plastic sheet before the resin cured
Fitted rear panels (all six of them!). I had glassed both sides of the H10 panels before realising they have to be warped to fit - luckily you can still bend them enough to fit (they only need bent down about 1/2" at one corner). The craft (less 4" bow point) clears the garage door by 4mm! And yes, that is a wood plane on the H11 panel! I use it to smooth the glassed panel edges - it doesn't produce the dust that a sanding block does (the blade gets blunt pretty quick though - it's not really meant to plane glass!)
I'm not sure if there are meant to be four flotation compartments at the rear. If you fit the H10 and the extra centre panel it divides into four - I've asked Barry to confirm this.
Barry confirmed there are meant to be four compartments at the back. I'm off to get yet more glass. The plans are also a bit light on the foam needed - I only have enough 1" foam to make 1 1/2 rudders (and there has been very little wastage) and not enough 1/2" to make the bench seat/fuel/battery compartment. A local plastics company uses low density polyurethane foam and I can get some from their stock.
I've asked Barry to confirm the size of the H2 panels at the rear. When I started fitting them I found that there is no way they will fit the hull - there's a 6" gap under between the bottom edge and the H11 panel!
Barry has confirmed there is a problem with the H2 panel size - also the H11 panel is too deep. He increased the flotation compartment sizes by lowering the floor in that area and forget to modify these panel sizes. I've now fitted all of the panels at the rear and the remainder of the front deck (great fun crawling around inside to glass these joints!).
The only glassing left is the underside of the side attach strips, the underside of the small raised section of the rear floor, the engine mount rails and fill panels and the rear bench seat. I now have to sort out a suitable windscreen and cover frames. I will then put hardpoints in for them and the fan/guard frame mount points. It's also time to seriously look for an engine!
Skirt material arrived - I managed to get a 2m (79") wide roll instead of the 60" specified. This means I don't need to splice a 7" strip onto the entire skirt length to get the width of 67" specified on the plans. I intend to make the hood from the same type PVC material - a local company manufactures it in lighter weights.
One thing I meant to mention earlier is that the best tool I've found for cutting the seemingly endless strips of CSM and glass you need for the panel joints, is a rotary cutter (looks like a pizza cutter but has a very sharp blade). Using this tool (I'm still on the original one - bought from a Poundland store!) you can cut though four or more layers of CSM in one swipe.
After an extended "holiday" due to a flu bug I finally got around to working on the Prospector again. I glassed the engine mounts with double payers of CSM and woven. I then fitted the fill panels between the mount frames. I glassed two partitions/supports under the bench seat. It has a battery compartment and two fuel tank areas - I will use boat style plastic tanks that can be removed for re-filling
I lifted the hull onto it's side using a chain hoist - it's even bigger looking when this way up!
I glassed the underside of the outer attach strips, the edges of the fan bay and the rear panel joints. I also added an extra wider layer of glass along the side to bottom joints as per plan. The pic shows white colored resin - it's all I have left - I will probably need about 3 litres more than I have left. I then fitted three plastic pipes from the engine bay, through the lift duct, to under the bench seat to take the fuel electric and control cables. That should be the hull complete (apart from the painting, etc)! I also ordered the fans and the pulleys/belts for the air drive.
Cleaned up the underside by rubbing down the glass edges. Lifted hull onto two table frame to make it easier to work underneath. Belts and pulleys delivered.
Collected shafts and other metalwork from local suppliers. Ordered bearings and a spare plastic fuel tank. Also ordered a waterproof boat style control panel with switches and fuses (and a cigar lighter socket) - should be neater to install. I'll use separate rotary switches for the wipers and lights.
Made lift ducts using the "foam wrapped around a former" technique. I made the duct walls from some off cuts of 1/2" PVC foam for strength. The inlet lip was made from PU foam (it's very hard to sand PVC foam to the radius for the inlet lip). Finished ducts are out of round by only 4mm - easily fixed when I glue them into the hull.
In this pic you can see a foam former still in the lower duct and some of the orange strap is still visible in the outer wall of the upper duct.
Made hubs from the lift fans by machining off the V grooves from a couple of pulleys - drilled and tapped holes to take fan hubs. Bored out pilot hole in fan hubs to take 25mm shaft. Fans and bearings arrived.
Powerfin prop finally arrived - it's a very nice looking bit of gear - the finish is superb. Assembled the fans and cut the blades to length (all 18 of them!) to make 24" diameter fans.
Above is my simple blade marking jig. The pencil is used to mark a line across each blade as it is rotated. I then cut the blades using a jigsaw - the nylon material destroys the edges on the jigsaw blades very quickly. To finish, I sand down to the line using a low speed belt sander. If you uses any high speed tools on this material it just melts and smears rather than cuts.
I've also decided to make the windscreen frame from profiled cedar wood covered with glass/resin. I've spent a great deal of time trying to source suitable window framing with no success. The only types available are PVC house/conservatory framing or aluminium extrusions. the PVC frames are too bulky and the aluminium is too difficult to join at the odd angled corners (nearly all of them are!). Although wood sounds like a lo-tech solution it will allow me to make the entire frame in one piece with no leaks at joints. Being coated with glass should make the wood last a very long time if not forever (after all, the hovercraft has glass coated wood in it's structure). Using wood has the advantage that I will a get good fixing to the top edge of the screen for the hood. The glass will be bonded to a simple ledge in the frame using auto type window adhesive - simple and leak free hopefully! The side sections will be plastic sheet and the two front sections will be toughened glass (to run windscreen wipers on).
Finished off fans. Weighed bare hull - it weighs 153Kg (337lbs) - this seemed very light to me as the complete craft should weigh 441Kg (970lbs). I then weighed all of the other bits I have (basically everything apart from the engine, seats and windscreen/dashboard components) and that all came to 86.8Kg. The skirt weighs 25Kg. This gives a grand total of 373.8Kg (822lbs) including 100Kg for the engine - this is under the design weight by nearly 150lbs! There will be "extra" stuff I've haven't allowed for but I would be surprised if it comes to 150lbs!
I bonded the fan ducts into fan bay - I used foam packing sections between the duct and fan bay edges to force each duct to be exactly round.
Fitted fan support cross member to rear fan bay wall. Adjusted fan to duct clearances to about 3mm all round. Made up timber frame used to build engine mount frame. I then discovered I had the wrong length fan belts - ordered longer belts. I can't find a supply for the 1"x2"dia rubber bushes used to mount the engine frame to the rails - after scrounging around I cut some out from a section of horse stable rubber mat (made from chopped recycled car tyres bonded together) - it should be OK as it's built to take the weight of a horse and to withstand outside conditions!
I'm not happy with the weight of the cast iron prop pulley at 13.6Kg (the taper lock bush itself weighs nearly 2Kg!). If I get a pulley made from aluminium and use a Tollok parallel lock bush (the bush isn't taking any torque load as the prop is directly connected to the pulley) it should come in around 5Kg.
Spent some more time trying to source a lighter weight prop pulley - no success. I've had quotes from a couple of pulley companies to make either a plastic composite or aluminium one - unfortunately both quotes were around £350! I have a local machine shop guy who can probably make one for half that price. Ordered 19 foot control cables for throttle and rudders. Longer prop drive belts arrived so I set up the complete drive system ready to make the steel frame..
Spent last few days putting together the engine/prop/fan frame. There's quite a bit of adjustment needed to get everything in place. You start by setting the fans centre in the ducts then getting the fan shafts horizontal and equally spaced front to back (using the horizontal timber support in the pic above). Then a second timber with shaft holes, at the correct spacing for the prop belt, is used to tension the two fan belts equally. This upright timber is adjusted to be vertical. Once this is all aligned you can place the two V frame members in position using the rear fan shaft bearings. These members then have the lower mounts formed on them (I used a flat plate to make a foot at the correct angle together with the tube as per plans). Once both V members are in place you can start with the prop mount. I've chosen to simply use spacers to get the prop belt tensioned - rather than the tilting frame specified on the plans. My experience with V belts has been that you only need to re-tension them once after a couple of hours run-in - the complexity (and weight) of the adjuster isn't really justified in my opinion.
One other thing I've done differently to the plans is to fit an extra support brace to the left hand engine bar pivot tube - it looks a little weak sticking out that far from the frame.
I've still to finish welding it together - it's just tacked enough to hold at the moment.
I also fitted the two fan duct braces onto a short length of angle to transfer the load over a larger area and also to give me something the attach the guard frame to later on.
I used smaller section tube for the two sets of diagonal braces on the V frame (I used 20mmx2mm instead of 25mmx1.6mm).
I got SPA section V belts rather than the 3v type specified (3V belts are not common in the UK). SPA is a slightly larger section belt than 3v so I've gone for individual belts rather than a single banded belt - hopefully that should let the craft continue to operate even if I lose a belt or two!
The engine support bar is 40mmx60mm (the imperial size specified in the plans isn't available in the UK (1"x3" or 25mmx75mm). I also had to use thicker wall section for the 25mmx50mm tube - once again it is impossible to source 1.6mm the lightest available is 2.5mm.
The drawings aren't too clear around the right hand end of the engine support bar. It isn't clear how the bar is clamped to the frame after adjustment - the through bolt is shown but not what it's attached to. I've chosen to fit a small section of 40mm angle beside the adjustment bolt with a 50mm long slot to allow the bar to move up and down). Together with the adjustment screw, which can be locked, this should provide enough force to hold the bar in place.
The drawings have no detail of how the front engine mount bar (shown in above pic) is attached to the engine. Hopefully it will be obvious once I get the engine into place. I'll need to work out how to assemble the engine to the frame as the gaps in the frame are too small to get the engine through!
Finished welding frame. Painted frame. The braces against the rear fan wall aren't quite straight due to the extra welding done after it was removed from the hull - not a structural problem so I'll just leave it as is. Started cutting out skirt sections.
Collected Subaru MV pickup from a farm about 35 miles up in the hills. It had been sitting in a barn for 5 years with a noisy transmission problem. The farmer fitted a battery and it fired up after two revolutions - very impressive and a bargain at £100! He has two other scrap pickup on his farm so I will have to make a couple of return trips I think.
I couldn't resist getting the other Subaru pickups so I went back and collected one today! Cut out more skirt. The front skirt panel vent holes on DWG8 are not dimensioned correctly - if you add up the horizontal dimensions they come to 32.5" but the skirt is only 27". Barry confirmed this error and suggested just making the slots all equal size in the space available - just what I was going to do anyway!
Collected third pickup - this one has no door or exhaust system or fuel tank. Once home, I got it started by feeding petrol into the fuel line to fill the carb - started first turn! I measured the compression on all of the engines once warmed up. One has 103000 miles, the other 63700 and the third 50500miles. The compression on the highest mileage engine was about 15% lower than the other two, the 50K mile one had one cylinder with about 16% lower compression than the other three and the third one had an oil soaked air filter and ejected about 100mls of oil from the open exhaust port when first turned over (although it ran just fine once started and has been OK since). Maybe it would have been simpler just to get one pickup - then I wouldn't have a choice of engine to use :-)
I cut out the front skirt control vent cover - the drawings show a left and right hand side. I'm assuming this is an error due to the divider skirt that used to be used and it's meant to be a single section (if I'm wrong it would be easy to just cut it in two!). The dimensions look wrong to me also - half the front skirt is 28.3" yet 1/2 the vent cover is 30.6"?
Too cold to work on the engines today, -7C. Completed skirt panel cut out - glued reinforcing strips onto partition skirt and attached drain hole cover. I figured out that the vent panel is meant to be attached to the side panel by it's outboard edge - it looks weird on the flat skirt and doesn't look like it should work - I'll find out later!
Glued together skirt. - only took about two hours. The trick to getting the joints lined up is to make sure the two sections have their outside surfaces facing each other - with the 'tabbed' panel underneath. Then glue the centre section making sure the contact and outboard marks line up with each other. Work out from the centre until the joint is complete.
I've even glued the partition skirt to the side skirts - I will need to hook the skirt over the craft before attaching it as the inside loop area is now smaller than the craft hull!
Finished off some skirt details and checked over all the joints for gaps. Started to strip one of the Subaru pick ups. When I looked at it I discovered that the pickup windscreen is exactly the right width to fit onto the top front deck panel on the Prospector - it's even tilted at the correct 40degree angle! I pushed out the glass and tried it on the hover and it looks great - I'll even be able to use the twin wiper mechanism. I'm not sure if the glass is laminated or just toughened? If it's toughened then I will need to rubber mount the edges - if laminated, I can just bond it to a frame. I have two spare windscreens if I have an "accident".
I stripped out the interior of the pickup - heater fan/radiator/control panel/etc. The dashboard hasn't been chewed by farm dogs and just happens to be the correct width for the Prospector dash so I'm tempted just to use it complete with controls, etc. It is a little heavy but it's mostly foam and thin plastic - the foam is molded onto a sheet metal frame to make it rigid so I could probably remove some of the metal from the inside to reduce the weight. At the end of the day, by the time I fitted brackets and individual dials/switches/wiring/cables/etc there may not be much weight difference. It even has all the air vents, windscreen front and side demisters and a glove box - a bit cheesy for a hovercraft maybe?
Removed engine from pickup and cleaned it up. Did some weighing of the Subaru bits:
Engine = 88.8Kg (195lbs) complete & ready to run with all accessories.
Flywheel on it's own = 10.4Kg (23lbs)
Dashboard = 9.8Kg (19lbs) with all instruments/switches/etc
Instrument cluster on it's own = 2.2Kg (5lbs)
Heating unit & fan = 7.8Kg (17lbs) including all ductwork
Windscreen glass (5mm thick) = 9.4Kg (21lbs)
The windscreen weighs the same as using flat glass so I will definitely fit that (it's even tinted!). Using the dashboard would add roughly 7Kg to the alternative of using the instrument cluster, discreet controls and duct/grillwork so it's not that much extra on a large craft like this. The only real problem is duplicating the horizontal and vertical curves for the windscreen frame and hull joints!
The current plan is to mould foam/glass over the back edge of the windscreen to make a frame - the screen glass will sit against a flat step in the frame, bedded into silicon sealant. I will then seal the outside edge using the same sealant. I need to allow the screen edges to move a bit in case it's toughened rather than laminated glass (if you stress the edges of toughened glass it can shatter).
Positioned windscreen and made frame using the glass as a former. In doing this I realised I had made an error with the position of the step on the front deck - it's too far forward. This wouldn't really be a problem except I want to find windscreen wipers so I need the ledge to be just below the windscreen edge to fit the wiper mechanism. I will move the ledge backwards and make it curved to fit the windscreen bottom edge.
The windscreen frame is made from leftovers! The lower edges are made from sections of 1/2" PU foam, the front uprights are PVC foam and the side diagonals are wood moldings. The top edge has a ledge to fit turn buttons to hold the front edge of the hood - it's also got several layers of glass to make it stiff (the centre wood is just a temporary support to hold the screen in position while I glass the outside of the frame, The side screens will be cut from 4mm all-weather plastic sheet (they curve slightly inwards at the front). I will bed the glass screen onto neoprene window seals on the face and bottom edges and will either bead the outside with sealant or fit small aluminium strips.
Completed glassing windscreen frame. It's now quite stiff, you can only push the top sideways by about 1/4" - with the glass in place it should be very stiff. I cut out the front deck in front of the windscreen and intended to join it flush with the forward deck. I decided to joint it on top of the front deck as the chances of making an invisible joint in a flat deck are remote! There is now a 1/2" step in place of the 2" step - this also places the wiper mechanism in the correct position. Drilled holes for wiper mounts and worked out how to fix them into position.
After studying the dashboard again, I decided that it would need just about the same amount of work to fix it into position as it would be just to mount the heater and instrument cluster so I've decided to just fit the components individually. I fitted the front and side screen demister vents into position and worked out how to fit the heater control unit (I will fit a vertical 1" foam panel between the front plow plane and the top deck). I will "plumb" the heater in using insulated 15mm domestic water pipe - the pipe is rated to 95C at 3 bar and should be resistant to anti-freeze (it's used in domestic heating systems and is resistant to all of the chemicals added to them). I will also pipe hot air from the unit along the RHS using a plastic drain pipe to exit at the side of the bench seat for the comfort of rear seat passengers!
I don't think I need to use the boat electrical panel I bought as I have enough switches just with the Subaru controls. If I fit the ignition switch in place of the re-circulation control on the heater panel and add an extra switch for the bilge pump in one of the blank positions there will still be one spare switch position for any future updates!
Worked all week on under dashboard area! It took a long time to design and build mounts for the wiper mechanism and all the heater bits. I decided eventually to omit the plastic air pipe to the rear seat as the heat will travel backwards naturally. I am going to install an air intake vent on the side coaming to feed the heater fan with ambient fresh air
I also built a steering unit from a cut down Subaru steering wheel and steering column (weighs only 2Kg in total)
I also made up a throttle lever and the cable connections from an aluminium tube pogo stick that was lying around. I installed the heater water pipes and valve control cable and added reinforcing glass layers where the clips will be attached on the underside of the side decks. I won't bother using insulation on the heater pipes - after all, any heat lost from the pipes will end up in the cabin which is where it's supposed to go anyway!
I got a bit of a shock when I tried to order aluminium to make the flywheel adaptor, top pulley, starter mount and heat shield - the total price was £220 ($385)! Aluminium has shot up in price in the last six months and is now almost double what it was a couple of years ago. After a bit of hunting around I managed to find a company that sells off cuts at a flat rate per Kg so the total price came down to only(!) £98 including the pulley material. I still have to pay another £250 to get the machining done!
I tried to figure out a way of using part of the gearbox bell housing to mount the starter - no way, the bell housing holes in the lower half are at a different distance from the crank centre than the holes in the top half. I will have to make up a plate to connect to the studs on the engine and mount the starter. The good news is that it should be possible to mount the starter the right way up - I won't have to fiddle around making drain holes in different places!
Ordered some nice blue plastic nuts and bolts from ebay to use to attach the flotation foam to the skirt and the hood edges to the hoops. Also ordered fuel line connectors (mercury outboard style) and a battery isolator switch (required by construction regs)
Took apart the Subaru wiring harness and tried to figure out the ignition circuit connections. The Haynes manual I have has about 15 pages of schematics - none of which are the same as the pickup harness! There is some strange wiring in a car! I've decided just to use the Subaru fuse box as I need at least half of the fuses and it can be easily mounted under the dashboard. I made up a proper wiring diagram rather then trying to work it out as I go - always a bad method!
Installed the water pipes, control cables and wiring along the deck sides and finished off under the dash (eventually!). All of the controls and heating system add about 18Kg (40lbs) of weight which is not very significant.
I made up hoops from 20mm PVC conduit for the hood. Once they were mounted I made a hood template from polythene sheet and tape to get the fit and look right. It's quite tricky to get the hood to work properly as It's meant to fold back against the rear bulkhead when not in use. It also has to look right. The only problem I have with the look is that the hood is wider than the top windscreen edge - it needs to be otherwise water would drip right from the hood the cockpit. I will have detachable sides Velcro-ed to the inside of the hood top and attached to the hull using a bungee cord onto hooks. The top will be made from PVC skirt material (I bought too much!) and the sides from a lighter weight tent type nylon.
Cut hood from skirt material using template and glued hoop joints. When I tried it on the craft it was obvious that the material was far too heavy - the hoops deform in the centre allowing the hood to droop. Water will collect in these areas causing a weight build up. I could replace the plastic loops with conduit to make them stiffer but the hood will still droop in the middle. I need to get some lighter weight material I think!
I finally installed the heater block and the fans and wiper motor. I then removed all of the other stuff ready to paint the hull.
I also maneuvered the engine into place - suspended on a chain hoist - to work out the position of the front support bar. I don't have the engine shaft coupling plate yet so I used 1/2" timber in place between the flywheel and front pulley face and shoved the drive shaft into the flywheel centre hole to make sure everything is square. I need to add 3" high spacers to the support bar to pick up the mounting points on the engine block. I will actually only make them 2" to allow the engine to be dropped for belt adjustment - I'll use spacers for now. I can actually fit the original air cleaner onto the engine without fouling anything. I will also use the original radiator mounted at a slight angle above the engine rather then fit it inside the lift duct. The original radiator is a bit large but it doesn't need a header tank so there may not be that much weight increase. Mounting it above the engine means I won't need long hoses (more water = more weight) - I can even use one of the original hoses as is.
Built the front engine mount bar. Spent a couple of days working out the exact wiring and control runs around the engine. Fitted the fuel pump, heater valve and coil, etc in final positions and double checked the wiring.
Spent last few days making up rudders. Also changed steering cable attachment as it was pushing instead of pulling! Generally tidying up craft ready to rub down and fill before painting this Sunday (hopefully!).
Attached flotation strips to skirt. Barry Palmer suggested just using a single strip (about 100x10mm) between the contact point and the inner skirt attach point. This makes sense as the only place water can enter the skirt (other than though holes) is the inner attach point as this is under water. I've done it this way so hopefully it will work OK! I used blue plastic number plate screws to attach the ends (and the middle) of the foam as well as the strips glued across it.
I moved the fuel pump from the engine bay back to under the bench seat - it's better protected there.
Stripped the hull of all of the carefully attached hardware ready for painting. Started rubbing down the glass seams and other rough areas. I then skimmed the surface with lightweight filler to fill the glass weave and smooth out some of the rough seam areas. It's never going to have a glass smooth finish as most of the panels aren't dead flat - and I don't have the patience for the weeks of filling and sanding needed!
Filling, sanding, sanding, filling, sanding................................ itching, coughing (in spite of respirator!).....................sanding, filling...........
Finally had enough filling and sanding! Every time I clean up and look again another couple of pits appear as if by magic! Hopefully painting on Sunday.
I then tried to crank the engine just to make sure the starter engaged and disengaged properly. The engine would only make about 1/4 turn then stop dead! I removed the plugs and tried turning the engine using a socket on the crank - it locked solid 1/4 turn in either direction. I checked none of the valves were stuck down. I then looked into the plug holes and saw a 1/4" loose lump of carbon in two of the cylinders - this was stopping the piston as it came up to TDC! I then remembered that I had sprayed carb cleaner down each plug hole after I removed the engine from the pick up (carb cleaner dissolves carbon nicely) as a cheap de-coke. It must have been eating away at the carbon in the cylinders until a lump fell off. I sprayed more carb cleaner into the cylinders which softened the carbon until the engine turned over again. I then cranked the engine for a while using the starter and sprayed WD40 into each plug hole until all of the carbon had been ejected from the exhaust - it should be spotless inside now! I then replaced the oil, filter, plugs and fan belt - I still need to adjust the valve clearances and it will be ready to go.
I also had to make new drain holes (and block the old ones) in the starter motor housing and gear case as it's now upside down and would fill with water otherwise!
Painting at last! Friend Peter did the spraying for me as it's not one of my best skills (in fact I'm useless at it)! Took about five hours - three primer coats and two top coats. I used etch primer to make sure it bonded to any exposed glass fibres and a two pack acrylic top coat.
Primer coat - brown might be a good colour for a hovercraft - it wouldn't show the dirt ;-)
It'll take a couple of days to harden properly as the temperature is very low - it peaks at about 4C at mid day and -6 or so at night. I will paint the floor using boat deck paint once everything is fitted and dry.
Started re-fitting the hardware - I've started under the dash to avoid damaging the still soft paint.
It took me a day and a half to fit the dash hardware and to wire everything up. In the pic above you can see (anti-clockwise starting bottom right), the fuse box, steering column, instrument cluster, cigar lighter, heater controls and on the left, part of the heater module. It's getting pretty crowded under there!
Winched hull onto it's edge again ready to fit skirt. I made up the three skids and fitted the skirt to the inner attach locations only. My garage has an 8ft 1/2" wide doorway and the craft hull is 8ft - if I fit the outer attach strips the craft wouldn't fit the doorway. The centre skid should stop short of the laid-flat partition skirt to prevent the partition skirt being damaged by the skid (it's not clear from the plans).
I carefully rolled the craft outside using a couple of round fence posts running on the skids. I then bonded the glass windscreen into position using E foam strips and flexible acrylic adhesive. I still have to attach the skirt to the outer edge and fit the front vent flaps properly (I also have to make up a foot brake assembly and the side screens).
A night shot showing the lights on the craft (the big green circle is the right side navigation light reflecting off of a wall next to the craft). The orange light under the dash is a side indicator repeater I stuck there just in case I need to work under the the dash at some point!
If I can get the engine adapter and pulley plate tomorrow then I should be able to get the lift fans and engine running this coming weekend there is nothing new to be made, it just needs connected together.
I fitted the outside skirt edges (apart from the front and rear - it started snowing again today). I then fitted the side windscreens - made from 2mm acrylic sheet and glued into position using silicon sealant.
Collected pulley and flywheel adapter plate from machine shop. The pulley weight 5Kg (11lbs) which is significantly better than the nearly 14Kg of the cast iron one!
I assembled the drive pulleys and shaft to the fly wheel plate and put it in the lathe to check it was running true. The outer edge of the plate was fine but the inner surface had a slight wobble (about 0.012"). I shimmed between the pulley and plate to get the plate to run better than 0.003". I then assembled it to the flywheel on the engine and re-checked to run out at the end of the shaft (where the pillow block bearing sits). It had a 0.003" wobble! I then removed the shim (it was still there when this pic was taken) and measured the wobble at 0.001". Bolting the aluminium plate to the flywheel obviously distorts it a bit.
I then assembled the lift fans and engine frame and fitted the engine. I tensioned the fan belts properly but left the prop belts a bit slack - the fan belts will stretch a bit initially and need the engine lowered again to re-tension them - this will then tension the prop belts properly in theory!
I tied the original Subaru radiator above the engine and fitted an old bit of exhaust and started it up. It ran fine with no real vibration and nothing fell off! It's actually running in the pic below - the wood board on the engine bay is to protect the floor from heat from the leaky exhaust! The rear skirt section isn't attached as you can see so I couldn't get on hover although it was trying!
The tacho isn't reading correctly - I must have knocked the cylinder setup switch when I installed it. The clock second hand is also slightly bent and it jams on the minute hand. Apart from these insignificant problems everything seems to work properly including the heater.
Took apart the instrument cluster to fix tacho and clock. After much fiddling around It turned out that the tacho needle was jamming against the transparent instrument cover - stupid problem!. I re-assembled it and it's fine now. I attached the rear skirt properly and checked the engine again. The craft is on full hover at about 1800rpm even with the front skirt top left unattached!.
Made up spacer/torque tube for prop. It worked out at 206mm long from the pulley to the front of the prop hub. I had holes threaded into the pulley I got made to match the prop hub (6 x M8 on a 75mm PCD). I used long stainless threaded rods screwed into the pulley with 20mm tube spacers and a central anti-torque tube tacked to them.
I discovered a slight problem with using a push-pull cable for the throttle. The choke can't pull the throttle open to the fast idle position against the resistance of the push pull cable. You have to make sure to open the throttle a bit before pulling the choke. I also re-tensioned and re-adjusted the top pulley position to get better alignment with the craft centre line and the engine.
I weighed the craft on my big scales by hovering over the platform and landing on it. I also checked the centre of gravity (Barry told me the 18ft craft should be at 149" - just in front of the fan bay). It was slightly forward at 148" - I have fuel on board and no prop guard so it should move back a bit to the correct place. The craft weighed 438Kg (965lbs) - with about 11Kg (24lbs) of fuel and no prop guard. The target weight is 1000lbs empty so my prop guard can weigh up to 27.5Kg (60lbs) before I reach the target. I have a heater and full windscreen fitted which adds around 20Kg or so of weight so I'm pleased with the result.
Fitted a lighter weight radiator (weighs 3.1Kg instead of the 6.4Kg of the Subaru). I got a plastic/aluminium type from a scrap Nissan Sunny car. I discovered that Nissan (and Kia/Hyundai and other Japanese car makers) don't use pressurised expansion tanks with their radiators - the radiator itself has a pressure cap fitted and the overflow from it just connects to a small unpressurised plastic tank . You don't actually need to use the plastic tank with these radiators resulting in less weight and less to go wrong! I fitted the radiator between the front of the engine and the fan duct in almost the same position it was in the car. About 1/2 of the radiator surface is directly in front of the lift fans - if this isn't enough for cooling I can easily lift it up to expose more area to the fans.
You can also see the air intake pipe snaking it's way from the air cleaner (avoiding the fan shaft) down to the pipe that passes through the fan bay to under the bench seat.
I fitted the front vent flaps. The plans specify that the outboard edge of the flap should be attached to the joint between the forward quarter skirt and the outboard bow skirt - if you do this, the vent flap won't reach across the front and is crumpled at the outer corners. I had to cut the flap away from this joint to allow it to lie evenly on the bow skirt.
Collected conduit to make prop guard. I found a local engineers shop who had a roller bending machine (they actually used to bend 4" box section). They rolled the conduit through the machine to make two perfect circles for the duct - only took about ten minutes and cost me £5 - a bargain compared to the time it would have taken with a lever bender. I decided to make the guard hinge forward over the lift duct to reduce the height for trailering. It's hinged below the prop centre line at the front and jointed just above the top rudder mount at the rear (the highest point). The hinges are 6mm bolts through nylon and conduit - the rear joint and locking mechanism consists of 1/2" conduit inserts welded into the ends on the top half and pinned using R clips to the bottom half once the guard is erected. I tack welded the cross braces and cut out the mesh but my MIG welder decided to pack up and I can't use the stick welder without blowing holes in the thin conduit.
Borrowed a MIG welder and finished the duct including welding the mesh around the outside. It's pretty big on the craft!
The guard is a bit floppy side to side - I don't have the front braces fitted yet. It's not clear whether you need cross braces to the centre of the prop stand or not
While I had the welder I made up a double silencer exhaust from bits of good pipe I found at a local garage - I bought the final stage silencer new, The engine is now very quiet.
I noticed that one of the grub screws that lock the rear pillow block bearing onto the shaft was slack and I suspect that the shaft has moved forwards in the bearing - the fan belts don't look straight and I'm sure I set them up properly? Also the front crankshaft oil seal has started to leak badly so it looks like I'll have to take the engine back out again!!
After messing around with mirrors and lights to try to find the source of the oil leak I eventually discovered it's coming from the sump seal - probably caused by letting the engine sit on the sump after it was removed from the car. I tightened up the sump bolts which made the leak at the front better but produced a new one at the back! I've ordered a new sump gasket as the proper cure.
I painted the guard and fitted it to the craft with braces to the lift duct. I also added cross braces using PVC pipe to the centre of the A frame. I haven't installed the long brace from the top of the lift duct to the top of the guard - it seems plenty stiff enough without it and it would interfere with the folding mechanism.
I then installed the rudders using nylon bushes. One problem is that the distance from the rudder pivot to the push/pull rod is isn't correct on the plans (at 3.5") - it needs to be 1.96" to get the full +/-50degree movement from a 3" travel cable.
I moved the craft to level ground and trimmed the bow and partition skirts. On a big machine like this it is virtually impossible to block the back end up to the correct height so I just put it on full hover and loaded the front to get the bow height correct (34.6"). The bow skirt is easy enough to trim but the partition skirt is a real stretch as it's so far back under the flat bottom - you can just reach to mark most of it but you need to jack the craft up to be able to trim it. I'd moved the radiator to above the engine temporarily while I was looking for the oil leak and the engine started to overheat a bit. I stupidly let one of the hoses get too near the alternator pulley and it's rubbed half way through the hose.
Collected fish net from a local factory - £5 for 20m2. I fitted the top brace to the guard as it's needed to support the mesh. I've made it fold in two so I can lower the top of the duct. There is only one set of lengths possible for each section as the two end pivot points are not in the same plane.
Duct fully up..................................................duct folded down
I also made up a pedal assembly for the vent brake. I made it from a single length of 10mm diameter aluminium bar bent to shape both the crank and the pedal itself. I used long upright arms to pull the two vent flap cords (instead of a double pulley to combine both cords) and attached the whole assembly to the floor using PVC saddle clamps. I call it a hovercraft part - simple, lightweight and reliable!
Collected material to built a Sevtec style roller open frame trailer. I built the trailer today and couldn't resist trying it out! It's very hard work winching the craft onto the trailer. Once the first 2-3 feet are up onto the trailer you lose hover and you are pulling a dead weight up a (small) hill. It's also a pain having to tie up the skirt all around the edges and I have my doubts whether it would be good enough for traveling at speed in gusty conditions. Unloading the craft was a bit of a nightmare!! You are supposed to push the craft backwards until the back ends tips onto the ground then pull the trailer out from under it. The first problem is that it's pretty difficult to push a 1000lb hovercraft backwards - even on rollers! More importantly, the partition skirt (and bow skirt to to some extent) gets snagged on the rollers as it moves backwards. All in all, I'm not very impressed with this design! I'll need to try and come up with something a bit better.
The good news is that I moved the craft on the trailer to a nearby sloped field so I could try the craft out properly. After a couple of stops and starts and circles, I set off down the field (about a 10degree slope). As expected, you pick up speed quickly downhill!. I managed to stop and turn on the slope OK and the craft had enough power to get started from a stop on the hill (about 3500rpm seemed to be enough). The rudder control started to play up - I couldn't get full left rudder - so I called it a day. The thrust performance was much better than I was expecting - you could get up to about 25-30mph going up hill which is pretty close to my UH18's performance.
Spent the last few days re-making the trailer. It's now a flat (ish) deck tilt bed.
Trailer frame before decking - the drawbar is a separate part and is hinged at the centre of the axle to let the whole bed tilt up. The front is lifted about 20" or so and lowers the back deck to 3" from the ground (on a flat surface)
The small sides hinge up to extend the deck to about 10 feet wide - outside of the skirt contact area. The theory is that it should prevent the skirt "falling off" the edge of the trailer. In the UK trailers towed by vehicles under 3.5tonnes are limited to 2.3m wide (7ft 6") 0 a bit of a problem for an 8ft wide Prospector! Luckily, the load on a trailer (the hovercraft) is allowed to hang over the sides by 305mm (1ft)! One thing I hadn't anticipated was the greater hover height - the cushion contact point is at the top edge of the sloped sides you can see above. This lifts the hover height from the flat deck to about 20"! I also need to fit a couple of bungee cords to stop the rear skirt from flapping and hitting the ground.
I still need to figure out how to hold the sides up in the extended position, I have fitted a section of 50mm exhaust pipe with a 10mm slot along the entire length to the rear edge - this is slid over the sides and down the slope to the flat deck and locks the sides up and the rounded surface helps prevent the skirt snagging on the deck edge.
The trailer weighed in at 262Kg (572lbs), combined with the hovercraft (including some "extras") the towing weight should be around 715Kg - under the 750Kg limit for fitting brakes in the UK!
Designed and fitted supports for the trailer sides. I used some sections of U channel to hold the back end and a length of angle with a wood block for half way along - I don't support the front end as there is much less pressure there.
I also fitted the fish net to the front of the guard. It's a bit of a hassle trying to get all the wrinkles out of it but once it's on and tight it's very strong. I made a mistake in putting the fish net over the top of the top guard brace - the net stops the brace folding forward to lower the guard. I need to move the brace to outside of the net (easier then moving the net to inside the brace!)
I stuck some anti slip deck tape in a nice chevron pattern over both side decks where I want people to stand when entering the craft.
That's it - all done!