Round nose hybrid build

[Chris H.]

Looking good. Have you tried Gunnersens? They list a 3mm marine. http://www.gunnersens.co.nz/products/ma ... ywood.html

[Flatworm]

Thanks Chris. They only seem to have 3mm hoop pine. I was offered this from another supplier and it is heavier and over twice the price of okoume.

[Flatworm]

Have been laminating. Leant the hard way that foam and polyester resin glue like to party - fortunately on a simple panel. Have been struggling with glue choice. Not cheap here, sometimes the glue is as expensive as the ply. Tried a few options on the inside walls, finally bit the bullet on epoxy glue - West system with microfibres. Will try that today.

Was going the PMF way but now that I have 20L of polyester epoxy that I can't use on foam, I might consider fibreglass. Will have a look around the forum to see what is the thinnest anyone uses. I can get 100g (3oz) or 200g (6oz) cloth. As it is going over 4mm ply, it is just a water proof coating rather than structural. I'm mindful of weight but definitely don't want any leaks.

[Flatworm]

[Flatworm]

Good steady progress this weekend. Inside lined, walls and roof on. Front (bent) door kind of installed.

Tomorrow. Kitchen.

Contact and fibreglass guru coming around tomorrow night to give advice.

Planning on installing a continuous hinge for hatch soon then continuing the roof down around the back. Once everything is done, I'm going to rout around a template to cut down from the hinge, around the wall and down at the back. Hopefully this will work as an easy way to make a hatch.

[Flatworm]

Productive day.

Worked on kitchen and cabinets. In the evening, I bribed a local fibreglass guru with beer to give me some advice. He was very positive and told me too whack the 4mm over ply on. He also told me that it would take one of his guys a day to glass the outside using 100g (3oz) cloth and peeler ply. This will give a good finish.

I've done enough fibreglass to know that I don't enjoy it so subbing out this job is an easy decision.

Working today so tomorrow I'll disassemble the whole thing - nothing is glued together, tidy joins up and probably polyurethane the interior. Then I need to reassemble, epoxy it together and prep it for glassing.

Now that will be progress!

So far I'm in for around 50 hours work and about $1500.

Trailer guy coming around this week too.

I know that I'm dreaming but I think that I could be camping in March. If I am, I'll exceed many wildest expectations as although I started in September, I only did a couple of days before I stopped work until January.

[OP827]

Fiberglassed 4mm plywood skin will be very strong, much stronger than many commercial units.
Did you get a quote for glassing work, I can imagine that peel ply is not cheap, but it will sure give a final finish for painting, provided the surface before glassing was prepared.

[Flatworm]

The peel ply is about $3NZD/SQM -$2usd. I only need about $50 worth. The owner of a fibreglass business is going to help me glass - I sold him my bach (holiday house) last year and I'll also teach him how to fly fish. He said that we can do it in three consecutive evenings when I'm ready.

I'm really happy with a deal like that.

[OP827]

That IS a good deal, I'll be watching how this goes, pictures please .

[Flatworm]

Busy afternoon although you wouldn't know it as the caravan looks the same as it did before I started. Disassembled the caravan down to a bare floor, sanded the inside panels, glued and reassembled. Was a bit intense as everything had to be square. Seemed to work well. Tricky part was laminating the rear bend as I had to glue the ply to the walls and to the foam roof panel while bending the rear roof section before the glue set and without getting epoxy over my newly sanded walls or letting the ply sag away from the foam. Maybe should have waited until Claire was around but it worked out well in the end.

I'm very pleased that the round nose section held its shape once I unscrewed it from the base. It spread less than 10 mm and seemed very strong.

Now that everything is glued, the whole caravan is strong. With the front being a pre stressed arc and a bulkhead, and another bulkhead dividing off the kitchen, and a partial arc at the rear, the structure is very solid.

I'm thinking that I might flip it upside down to ply the outside. We'll see.

I'll do a little work this morning and then go fishing.

[OP827]

Impressive work, looks great and I like your panels method. What was your method of clamping the internal plywood to the arc surface during the epoxy glueup? I apologize in advance in case I missed to read it in your thread in case you already described it.

[Flatworm]

Good question. When I did most of the panels I weighted where possible but I also screwed down through battens (to minimise the screw hole) into the framing where I needed to. When I did the roof I had a variety of props - brooms, jacks etc holding up the ceiling with a few weights on top as well. I pushed on the foam and where I could feel that there was a gap I put an old piece of ply over the foam and put a screw through it to lift the ply.

I'll have quite a few holes to fill on the inside but I'm not a craftsman.

For the front arc, it was easy to push the ply inside the curve and screw it in place on the frames starting from the middle and working around each side. Also needed to make sure that the top and bottom remained aligned. Not too hard in practice.

Today I partially covered the hatch , added the inside layer of ply and kerfed the foam before I headed out fishing.

This curve is easier in some ways as I'm starting with the interior ply rather than the foam. I'll let you know which method works best when I'm done.

Arranged for the trailer to be built as well. Another friend well come around to help. He thinks that we should be able to knock it off in 4-5 hours. I'm not a sociable person but am humbled by offers from friends on this project.

[OP827]

Thanks, I suspected you would do that. I in my build also drilled holes and used screws with wood or plywood strips on both sides to clamp plywood to curved foam. These holes are not a problem to me, they basically disapper with matching wood putty. I found that PL Premium glue worked good for plywood to foam glueup, so I am using it now with ply to foam panel work instead of epoxy, which I save for glass lamination. PLP is lower viscosity than PL400 construction glue and working time is more than enough for even large panels, much longer than TB2. Lowest cost of all glues (epoxy or TB2) is another bonus. Did you try PLP?

[Flatworm]

Hi OP

I've had the glues blues.

Finding decent, affordable glue has been something that I have grappled with.

Tb2 is hard to get here so I'm using tb3 for a lot of the wood-wood joints. I've also used construction adhesive where I felt that there might be gaps to fill.

Wood-foam. In areas where it seems to be non critical such as holding the sheets to frame I used acrylic filler or tb3..

To glue the laminate up I mostly use epoxy now. I did use some PU glue but it was more expensive than the ply that I was gluing.

Glue is expensive here. I'm settling for epoxy, TB3, and the occasional construction adhesive for small areas where I'm not keen on mixing epoxy.

From my tests, acrylic filler was more than adequate for gluing foam to ply but for these big areas, epoxy is the same price, sets reliably and is more water tolerant.

PU is just too expensive here for me to use lots of it , around $20 per cartridge.

I love your build. Much better craftsmanship than me and an ambitious project.

I lifted one side of mine last night and put it onto the bathroom scales - 75 kg!. Unless my physics is flawed, that makes the whole thing around 150 kg. Still needs another 40 kg of ply, fibreglass, doors and trailer. I haven't been obsessive about weight but figure on between 300 and 400 kg is achievable. No idea really.

TRAILER ADVICE WANTED.
My caravan is very rigid with 2 bulkheads, laminated ply/foam/ply/glass construction and curves in just the right places. I'm planning that the trailer is a simple triangle of pregalvanised box section, reinforced at the joins and torsion axles off the back of the triangle.

I haven't drawn anything up. My engineering friend wants to make quite a heavy trailer but I don't think that one is necessary.

Any thoughts? Box section size and gauge?

Something like this?

[OP827]

Thanks for kind compliments on my build. You are right about glues, it is just the PU glue is cheaper here in North America than epoxy, but I like the strength of epoxy. As for trailer frame, I am also in favor of simple and light A-frame with torsion axle just like you are thinking about, although I have no experience with that. I am thinking of my next (lighter) build with frame like that...

Did you see this board design library for frame ideas:
http://tnttt.com/Design_Library/The%20Ultralight%20Chassis.htm
http://tnttt.com/Design_Library/tear84.htm