Motorhome construction - what is best

[peedee]

Prompted by a post on another forum about cracks appearing in bodywork, are manufacturers taking too many short cuts with construction? Some sandwich panels look very flimsy to me and I have heard some are not even bothering to put in frames for doors and windows and are just simply cutting holes in the panels before fitting these. So where is the strength to resist today's pothole strewn roads?

 

It seems to me that the old construction methods of building on a frame and then cladding it is far superior especially with a one piece GRP roof.

 

I assume that the old methods resulted in heavier vehicles and were probably more expensive to build but was it better?

 

Comments please are we going backwards with motorhome construction?

 

peedee

 

[Vernon B]

Good question. Wouldn't be nice to get some "informed" or otherwise response from the industry to posts like this?

[peedee]

It would indeed Vernon. I can only assume by the ominous lack of responses either everyone is watching football :-D or there is much in what I have indicated. Todays bodywork build quality is rubbish! There is certainly no one rushing to its defence.

 

peedee

[W3526602]

Hi,

 

Look at the FREEDOM range of cheapo caravans from Eastern Europe. The shell is made in ONE PIECE, including the floor, from GRP (fibreglass). What can go wrong? No seams to leak! These vans have a MGW which is a smidgen over 750kg, but I believe there is an economy model which doesn't have brakes, so therefore has a MGW under 750kg. My only complaint? The biggest van in the range is only 3 metres long.

 

Subtract 200kg for the wheels and chassis?

 

Unfortunately, a touring caravan shell humped onto the back of a pick-up, never looks "right".

 

602

 

[crinklystarfish]

I personally think that construction quality is generally on the poor side of average, but there are exceptions and some manufacturers / converters are genuinely interested in the quality of workmanship. Some manufacturers also demonstrate a range of approaches where their high end products are splendidly built, whilst their budget stuff is most certainly not. Methods of construction are not as critical as quality of workmanship: some monocoques are horrid, some sandwich panel laminates are superb. 

I suppose when it’s your business to generate huge profit and you are turning out large volumes, then it’s in your interest to make them as quickly and cheaply as possible whilst maintaining a public image of turning out a quality product. 

I don’t think the press help in this regard as superficial observations, assumptions, and the need to secure advertising revenue all play their part in ensuring dubious build quality is, in the main, played down / unreported. 

I’ve seen some very good build quality, but mainly, it’s at best acceptable. It’s just taken me 8 months or so of casual spare time to rebuild a 2007 model of a well known German A class to a state that it should have been in when it left the factory. It doesn’t now rattle, squeak, bits don’t come loose, and the fit and finish of ‘out of sight’ components is sorted. It should, though, have been that way without me having to seemingly constantly roll about upside down swearing with a head torch on. 

While ever we buy them, they’ll continue to spit them out.

[colin]

I've seen panels delaminate, and frames rot, it's not so much which is better it's how well made they are.

[Bill Ord]

Hi,

In general I would expect the Hymer method of construction where the panels are bonded into a monocoque type structure rather than the Rapido method for instance where a wood frame is used to be superior as it would be stiffer and if a leak did occur there is no wood frame to rot. Camping-Car magazine seems to think so and always marks wood framed 'vans down compared to those without.

 

Bill Ord

[peedee]

Many thanks for the inputs.

 

peedee

[Guest JudgeMental]

wood free GRP body. with bonded panels and no screws. constructed like light aircraft. GRP is far more resistant to damage and hail...aluminium skin just to soft IMO

 

http://www.euramobil.de/_technik_gb_2010/

[Vernon B]

Bill Ord - 2010-06-16 11:59 AM

 

Hi,

In general I would expect the Hymer method of construction where the panels are bonded into a monocoque type structure rather than the Rapido method for instance where a wood frame is used to be superior as it would be stiffer and if a leak did occur there is no wood frame to rot. Camping-Car magazine seems to think so and always marks wood framed 'vans down compared to those without.

 

Bill Ord

 

I'm not sure if that's completely true Bill

 

I think I'm right in saying that the term "monocoque" (not sure about that spelling either) was first used to describe a construction method in the automotive industry when steel chassises were replaced by much lighter pressed steel floor pans. Pressed body panels are then welded to that floor to created a strong and rigid box structure.

 

This isn't really the case with coachbuilt motorhomes. Hymer, Rapido and all the others erect a bonded panel structure on a steel chassis of some sort or another.

 

Certainly there are differences in how manufucturers produce the bonded panels and what materials are used in those processes. And, for that matter, differences in how they joined them together - screws or adhesives. All manufactures make vague claims to the excellence of their particular mix of cocktail but where is the data that tells us which is best - or which is worst?

 

Logic tells us that removing timber frames will eliminate wet rot but can it create other problems? For example I have aluminium frames - lighter than timber, more durable, certainly will not rot. But what about expansion when hot and could that result in stresses within the composite panel? And how is that affected by the material of the outer skin? Is GRP better than Aluminium in these circumstances?

 

I've no doubt that a lot of research has been done in the industry on these things but very little is put in the public demain. And for why? Well as this post appears to demonstrate ... Joe public aint that interested - until something goes wrong.

 

V

 

 

 

[colin]

Vernon B - 2010-06-17 3:30 PM

Logic tells us that removing timber frames will eliminate wet rot but can it create other problems? For example I have aluminium frames - lighter than timber, more durable, certainly will not rot. But what about expansion when hot and could that result in stresses within the composite panel? And how is that affected by the material of the outer skin? Is GRP better than Aluminium in these circumstances?

 

Given the right curcumstances the ali will merrily corrode away.

The grp will expand, maybe not at same rate as ali frame, timber on the otherhand when cold will often get wet and expand but when hot will shrink the opposite of the skin so causing more stress.

[Brian Kirby]

Surely this depends greatly on what objective is sought for "best".  For example, strongest, most durable, or least problematic (and I contest the three are not mutually inclusive, or exclusive :-)).  Strongest, IMO, would be a steel bodied PVC, which has the advantage of having been crash tested.  I accept that Hymer have carried out some "B Class" body crash tests but, so far as I know, these were sample tests, not representative of all Hymer B Class models, nor were they representative of all similar Hymer group A class motorhomes, and are not representative of the latest version of the Hymer B Class bodyshell.  Any extrapolation of the results to other brands/models were, so far as I know, "desk" studies.

Most durable, so far as bodywork is concerned, is surely GRP.  It loses its looks with time but, with reasonable care, is almost indestructible other than by fire or accident.  It is also heaviest and most expensive, being very labour intensive to produce and, in fact, is quite nasty stuff to work with.  However, as Lotus famously discovered years back with the Elite, it should not be continually stressed, because it stress deforms.

That leaves the great majority of "coachbuilt" bodyshells that are usually assembled around a ply floor (now there's a silly idea!) with furniture in place, walls first, then front rear panels, then roof.  Their common weakness is far less what they are made from but, as stated above, how carefully they have been assembled.  The materials used are generally OK, but the design of the joints between panels is virtually non-existent, making good assembly difficult, even before the variability of the man with the mastic gun is taken into account.  There seems to be some variation in the type and quality of the sealants used, I assume on cost grounds, because they are used in very large quantities, and this will affect longevity.

Whether it is preferable to have a timber armature, an aluminium or PVC armature, or a fully bonded stressed skin panel, is rather a moot point.  Where the timber will suffer is if there is leakage at any time, of any magnitude, because by the time the leak is apparent the rot will, in all probability, have commenced.  If the joints are to be expected to fail, timber is a bad choice.  If the joints are well designed and executed, and the timber stays dry, it is as good a material, from a durability standpoint, as any other.  The problem is not so much wood, but keeping it dry.  Eliminate the wood, which is plentiful and fairly cheap, and costs are liable to rise, either investment costs to make the large bonded panels, or materials costs for aly or PVC armatures.  If those cost increases are then recouped by assuming the bodyshell basically rot-proof, and so using cheaper sealants, you get the leak, but not the rotten frame.  The problem then is that although the frame may not rot, the internal lining and finishes are still liable to be damaged by water ingress.

All this is very academic, IMO, since we never get a full specification for what has actually been used in assembling any van.  Manufacturers tell us what they think will impress us, mainly along the lines of "because you're worth it", and we just have to decide, basically blind, where beneficial quality, as opposed to surface bling, lies.  It's a bummer, but I can't see it changing! 

In the end, our best, and virtually the only practical, option, is to favour those makes that have a good reputation for trouble free and durable vans, and avoid like the plague those with reputations for variable quality.  Of course, this only holds good until the accountants get the upper hand at the good firms, and begin cheapening everything down until warranty claims rise to meet the industry average.  How would we know that?  You tell me!  :-D

[Vernon B]

Well done Brian for bringing some substance to the debate.

 

V

[Guest JudgeMental]

Euramobil do not use any ply or wood...the floors are a GRP sandwich with aluminium frame, most with double floors. Yes GRP is heavier and more expensive then an Aluminium skin but thats why all the best German manafacturers use it. the roof effectively floats as it is not bonded to sandwich...this stops the GRP cracking and allows it to expand and detract with the heat and cold. I have lost count of the number of "hail damaged" Hymers I see advertised in Germany, and for the life of me dont understand why they dont at least use a GRP roof. Yes aluminium looks nice and smooth when new, But no way is it as tough or resistant to damage as GRP (I have had both so know from experience *-) )

[peedee]

Many thanks once again for some great posts and the food for thought. The focus has been on resilience and damage but little has been said about what is easiest to repair. However, I posted a similar note on another forum and received a nil response so I am wondering why I payed a tenner? Full marks to OAL and its members for the weighty responses.

 

peedee

[Guest JudgeMental]

if you mean something like this the costs would be similar whatever the skin I would think

 

[crinklystarfish]

peedee - 2010-06-18 8:46 AM Many thanks once again for some great posts and the food for thought. The focus has been on resilience and damage but little has been said about what is easiest to repair. However, I posted a similar note on another forum and received a nil response so I am wondering why I payed a tenner? Full marks to OAL and its members for the weighty responses. peedee

I suppose the focus has been on resilience because whether you damage aluminium or grp panels you are looking at specialist repair if you want to return to a ‘pristine former glory finish’. In the field, grp is both more resilient and easier to repair (not easy, but easier). A trip to Halfords and a fibreglass repair kit will see most minor scuffs weatherproof and something like the right panel shape. 

Workmanship being equal, grp monocoque is king; if we are simply talking about the shells of coachbuilt ‘vans. 

You won’t come across many aluminium skinned hulls / topsides on pleasure boats. 

Outside the box, I wonder if we’ll ever see a carbon shelled ‘van. Now that would be light, stiff and strong. You wouldn’t want to ‘gatepost’ it though!

[armstrongpiper]

I wouild recommend a visit to a M/H constructor to see how they do the job. We attended such an event at Autotrail and came away with more confidence in the vehicle we had ordered. Of course, time wil tell......

You can see how everything is made. including the sandwich walls with wood frames etc.

 

 

Neil B

[hallii]

This is all very interesting to me, I purchased a Hymer after much research and many dealer visits.

 

It may or may not be "better" than many other makes but it does have a reputation for being built to last supported, in general, by those who have owned them for many years. Maybe they are now "built to cost" so only time will tell.

 

Mine ( a 522 Van) has aluminium skinned panels and having seen the size of hailstones in Germany I am not surprised that they dent panels, they also break car windscreens!

 

Having driven a few coachbuilts during my research stage I was very aware of the amount of creaking and gentle cracking noises that some makes exhibited whilst on the road. I am not talking about rattles from cupboard doors or blinds etc, these seem to be universal, but more about actual flexing noises. (Or what I perceived to be such.)

 

Could it be that the actual method of construction is not the main factor in the "goodness" of a M/H body, perhaps it is the amount of actual flexing that takes place?

 

If so the base vehicle chassis and it's inherent stiffness would also be a major factor, the best built and stiffest body will surely fail if the chassis is twisting and turning beneath it?

 

Many old caravans were built on heavy and stiff chassis with simple aluminium and wooden structures with nothing more than hardboard on the inside. They seemed to last very well, as is borne out by the amount of them I see still giving good service as garden sheds, chicken coops etc.

 

hallii

[crinklystarfish]

Quite right regarding flex which is why bodies (especially monocoques) designed for use in inhospitable circumstances are isolated from the chassis either by simple rubber / urethane bushes, or, for extreme terrain, fully articulated mounts of frightening complexity. In 'our' case though, the stresses normally aren't enough to flex chassis / beds enough to be a significant issue and don't warrant isolation. Most bodies can stand the minimal amount of flex without falling to bits, but creaking is a consequence. Bonding / sealing products like those from sikkaflex have helped the industry enormously. These allow a bit of movement while keeping the body together.

The truck in the photo would need some form of isolation when put to its intended use.