Wednesday, March 7, 2012

Explorer build

Here I go again It's the first of March 2012. The last build was a 16' Sevtec Surveyor and took me about 14 months to complete. This time I'm going for something a little bigger a Sevtec Explorer. This craft will have a flying width of 10 foot and it's length is 20 foot. Flying height is 15 inches. The craft on hover should be around 12 1/2 foot wide from the outer edges of the skirt.

I managed to find a workshop to build the craft in just 4 miles down the road from me. The building is a bit worse for wear to put it mildly and has no electricity, but it's under cover and secure, so what more do I need. I have had to do quite a bit of work to get the building inhabitable but after a few days spent boarding up & clearing up the mess that was strewn everywhere I was ready to begin.

It must be my lucky week as I mentioned to a neighbour that I will have to buy a generator for running a glue gun & sander etc and he said I have one in my shed that hasn't been used for a few years, and I was welcome to it it for free if I wanted it. So Monday evening was spent stripping the IC Briggs & Stratton 5hp driving the generator apart. Stripped the carb, washed out the fuel tank, fitted new spark plug, cleaned up the flywheel & magnet, put in a foam scouring pad as a temporary air filter. Put in new fuel and 6 or 7 pulls of the starting rope and it fired into life.  So now I have a 2kw genny.

I decided that because it is such a big craft I would build it on a jig to eliminate any discrepancies from any unevenness in the concrete floor. By Monday lunchtime 5th March I was able to start building the jig. The jig is very simple and made out of 3" X 2". The cross braces are 2.40 metres wide, which gives me a couple inches spare on each side. I have placed the cross braces at strategic points of the hull. I added 2 extra cross braces under the floor as I felt 112" between the front and rear of the floor panel was too large a gap to bridge. The hard hull of the craft will be 90" wide and 240" long

Anyway by Tuesday lunchtime the jig was built and ready to take the foam & GRP panels.

Pictures of the jig below:

Today 7th March 2012 I have ordered the foam core for the hull.  I have decided to use Tricast 6 PU foam.  The plan calls for 4.5lb density foam.  Tricast 6 has a density of 6lb and is approved by Lloyds for marine structual use so should be more than adequate for this application.  The foam has a 7 to 10 day lead time so hopefully it will be here by the end of next week.

I have also emailed several GRP suppliers today with a long list of items including polyester resin & CSM etc.  Last week I managed to buy a 100 metre roll of 200gram fibreglass cloth on ebay at a bargain price of £1 a square metre.

9th of March 2012, I have now placed the order for the GRP materials.  I had quotes back from two of the GRP stockist I emailed for a quote on the list of items I wanted.  There was a difference between the two quotes of over £130 including delivery.

I now have the difficult bit , waiting for all the stuff to arrive so I can start the build of my new toy.

Monday 12th March.  Over the weekend I had doubts to the amount of Tricast 6 foam I had ordered.  I had a funny feeling that I hadn't ordered enough.  I had ordered the amount listed for the explorer on the Amphibious Marines website.  I set about working out how many 25mm thick foam sheets I would need for panels (H6), H8a, side deck stringers H16.  I found that which ever way I cut & joined the foam I was going to be quite a bit short as the rudders used 3 x 600mm x 1200m, then there was the windscreen bolsters which would be approximetely another two 600mm x 1200mm sheets .  I then emailed Ian Speakman to see how many foam sheets he had used in his recent prospector build.  Turned out he had used more 25mm foam than was listed for the exploror and the explorer is a couple of feet longer than the prospector.

I am not going to use foam core for the rudders as I prefer foam/pvc board to make my rudders from.  I used foam/pvc for the rudders on my surveyor and I find they have many advantages over the rudders shown on the plans.  This means I can eliminate three sheets of 600mm x 1200mm tricast, but my order would still be at least 2 sheets short from what is needed.  I decided to order another four 600mm x 1200mm Tricast 6 sheets and four extra 12mm sheets to ensure I had enough for the build.  The postage for the foam to the highlands of Scotland is very expensive at £80 +20% VAT, so I would rather have a little bit too much foam rather than fork out another £96 delivery charge for one or two extra sheets.  I ended up telephoning Julie at Trident foams to increase my foam order by four extra  600mm x 1200mm sheets for the 25mm and the 12mm tricast 6 which is approx another £100 + 20% Vat.  At least I saved having to pay another expensive delivery charge.

While on the telephone Julie said that it is looking very likely that my order will be ready to be sent out tomorrow, so I may have my foam by the end of the week.

Friday 16th March 2012.  Today I had two large deliveries.  First one was from Trident foam, a pallet full of Tricast 6.  Not long afterwards a second delivery from Cornish Fibreglass Supplies, of resin & glass matt etc, which weighed in at 172 kilograms.  It has been a busy few days as we have workmen coming to fit external insulation on our house, so I have had to move my large shed, take down a lean to and a fence.  All stuff I could do with out right now.  I am hoping to start marking & cutting out some of the hull panels tomorrow.

Picture below of my two deliveries.  This is what the bare bones of a 20 foot Sevtec Explorer looks like:

Saturday 17th March:  Today I actually feel I have finally started on this build.  I cut out 7 of the panels.  These were H6 (floor), the two hull stringers, H8a & H8b, and two  H16 panels.  Next job is to glue the panels together then start fibreglassing.  I decided to do the longest panels first so I could use the jg to keep them flat while glassing them.   Four of these panels are nearly 20 foot long.  I also knocked up an 11 foot long X 4 foot wide laminating table, so I have somewhere to glass the smaller panels.

I am hoping to have the floor & the 4 longest panels finished before I go back to work on Wednesday.

Sunday 18th March 2012.  I managed to glue the foam together to form panels H8a, H8b & the two hull stringers.  I also cut out the relevent matt & cloth for these panels.  I was hoping to get the panels glassed but I ran out of time.

Monday 19th March was a cold wet & windy day.  I finally started to glass the panels.  I started with H8a & h8b.  I managed to get one side of them glassed before lunch, then I made sure that the two hull stringers were straight and used a few panel pins along their edges to make sure they stayed straight while applying the 200gram  glass cloth.  After lunch I glassed the two stringers on one side then glassed the other side of panels H8a & H8b.  I was hoping to glass the other side of the two stringers, but they were still a bit too green to take a chance on turning them over, so that is a job for tomorrow.

It is now April 6th 2012.

I have made steady progress with making and fibreglassing the panels.  My son had to be admitted for two weeks to a hospital near Edinburgh which is about 220 miles away.  This cost me some building time but he is well and home now which is the main thing.

So far I have finished 10 of the panels and have the two H9 panels glassed on one side ready to have the hard points cut out and filled with a putty made up of 300 grams of resin, 75 grams of 3mm chopped fibres, 30 grams of micro balloons and 4.5 grams of collloidal silica..  The plans show some of the panels have wood inserts along one edge which would be the upper skirt attachment.  I have decided that I am not using wood for this and I will use the hard point putty mix for the skirt attachment.  I will put the panel in place before cutting out these hardpoints, so I can make sure they are in the correct position.

I have been weighing the panels as I have finished them and comparing the weights to what was stated on the plans.  My floor panel came out 7 lbs over weight.  The other panels have either come out with weights as stated or slightly under.  Overall so far I am approx 4 lbs over weight,  which I feel is acceptable.

The floor panel I beefed up a little on the rear edge where the small panel is that the fan panel fits to.  The area is prone to damage if the craft is landed heavily, so I added another two layers of 450 grm CSM under the glass cloth.  This would account for some of the weight increase of the floor panel.

I have also found that since using a resin roller to apply the polyester resin, my panel weights are close to if not lower than weights stated on the plans.  I was using throw away brushes before to apply the resin, but the roller makes a much easier and better job, so worth the extra money. 

This was one of the first panels I had glassed, ready for final trimming & fitting.

Floor panel under construction

Floor panel completed.  This gives an indication of the size of the floor panel

The floor & fan panel (H1).  H1 is 89 inches wide.

Tuesday 1st May 2012.  I have been making steady progress with the build since my last post.  I have made all the lower hull panels in front of panel H1 (lift fan panel) and have started to assemble them.

rather than waffle on about what I have done during the build I shall let the following pictures tell the story to date.

Floor panel, H1 (lift fan panel) and H8 (lower bow panel) in position on the jig.

Panel H8 has been glassed into position.  The wood support frame has been screwed to the jig to ensure the panel stays in the correct position while the other panels are joined to it.

Panel H1 (lift fan panel).  The panel is supported by a temporary frame screwed to the jig while it is being bonded with fibreglass matt & tape to the rear of the floor panel.

Panels H1a & H15 can be seen in the background.  H1a has not been trimmed to final shape which will be done when panel has been bonded into position on the hull.

A closer look at the frame supporting H1

One of the 4 screws used to secure panel H1 to the sipport frame.  The two upper screws are within the lift fan duct area, so will be cut out at a later date.  The two lower screw holes will need filling and small glass tape patches bonded over them when the screws are removed.

View of the completed panels at this stage of the build.

H1a now in position and trimmed to final shape.  A support frame was also used as can be seen in the picture.

H8a upper bow panel now joined to H8.  Wood support frame screwed to the jig.

Close up of the framework sipporting H1 & H1a.

Uprights being screwed to the jig.  These will support the hull sides.

The angle pieces of ply screwed to the jig in this picture have two purposes.  Firstly they help keep the iprights verticle and in the correct position.  Secondly they are cut at the correct angle and height to supprt the lower hull side panels. 

Panels H7 are now resting in position on the jig ready for bonding to the floor panel.  No glue or other support was needed to keep them in the correct position.

View from the front of the hull.

View from front after the two bow side panels have been added.  All the lower panels have been bonded in position.

This is the join of the lower side panel to the floor in the lift fan chamber.  I have added extra layers of glass matt here and a layer of 200 gram glass cloth.  I felt this is a potential weak spot, so beefed it up a little.  This added approx 2 lbs to the weight, that I felt was a worthwhile penalty.  The glass cloth is 6 inches wide.

Another view of the lower hull looking from the lift fan chamber.

The two hull sides in position.  Only a few clamps needed to hold the panels in their correct position.  The port side in this picture has already been fibreglassed into position.

The hull deck stringers are put in place ready to be bonded to the hull.
View from the front

Side view of the hull

View of the hull from the rear.  This is as far as I have got with the build to date other than fibreglassing the two stringers into their final position.

Next stage of the build will be to make and fit the helm & bow panels.

Date 15/05/2012.  The past week I have had a lot of hours working on the hovercraft, but it doesn't seem like I have made much progress with the build.  I have ceviated away from the plans slightly by madding four support ribs down either side of the hull.  I feel these will add extra strength to the hull, give extra support to the upper side panel when being walked on.  They are also the starting point for some storage compartments, so the small amount of added weight I feel is well justified.

Upright support ribs

Panel along the bottom of support ribs to form storage compartments.

I have also made and added the deck bolster panels.  I still have to trim them to their final shape.

The metal drum in this picture is 16" high, which will give a good idea of how high the side are on the hull.

I have also started making the rear seat.  I have made & glassed in the rear seat panel and the arm rests.  I still have to round off the top edges of the arm rests then glass them in place. 

 Rear seat panel & arm rests

The arm rests have two main purposes:  Firstly they will add a little extra strength to the hull between the lift fan bay and the deck stringer.  The point just in front of the lift fan bay is a potential weak point as there is a lot of weight at the rear of the craft and again passengers in the front, so this area is a stress point.  I have also added an extra layer of 450 gram glass matt & 200 gram glass cloth to each side of the deck stringers in this area.

Second purpose is that the two fuel tanks will be housed under the rear seat.  As this craft will be fitted with a roof, I need air vents to the outside of the craft from the fuel tank area to stop any build up of petrol fumes, which could be disasterous.  The arn rests will hide the vents on the inside of the craft, but more importantly create chimneys either side of the tank area to guide the fumes to the outside.  To hide the vents on the outside and to stop water coming through the vents to the inside I have made up a plug and then a mould from which I can make two identicle vent covers..

I have also made a 370 round trip to Stonehaven to collect a Subaru Forrester.  The vehicle has done 94000 miles and still has several months tax & MOT left on it.   The engine when new gives out approx 125 brake horse power, so should be fine for the purpose I have in mind for it.  I shall be using the engine & ECU and associated wiring.  The radiator, heater & heater vents ect.  The rest of the vehicle will get scrapped.  I was hoping to use either the front or rear screen from the subaru, but they are too narrow.  The top of the hovercraft deck is 70 inches wide and the widest part of the Subaru screen is 60 inches, so I will have to think again about the craft windscreen.

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