Technical Ducato Mid section Underbody protection

[CamperDoctor]

I’m exploring options to installing an underbody protection skin beneath a Fiat Ducato campervan. My initial idea is for it to run from just behind the exhaust system to just in front of the rear axle. It would fix up to both the longitudinal structural chassis members. Its purpose is to provide resistance to small load mechanical impacts in a similar concept to engine bay under protection.
It would have a secondary role of reducing road spray and muck from coming into contact with ancillary components such as water tanks.
My initial thoughts are to use folded/structurally formed aluminium alloy to give strength verse weight balance. Obviously the more contact fixing points I can achieve on the vehicle underbody, the more strength I can achieve.

Has anyone already attempted this?

 

[Communicator]

My first thought is, how do you intend to access the handbrake adjustment at the bridle?

 

[theoneandonly]

What is purpose of the shield and what above it. (fiat or ALKO chassis). If its to protect from salt road spray i would avoid Aluminium (sheets too large to anodize). Stainless steel of a thinner gauge would be better but more floppy/ suseptable to impact events. Offroading? for access use windows/hatches and rivnuts. Weight not really mentioned but is fibreglass an option ( lot of work making a semi mould to start with). if traveling in rivers will need to consider drainage.

 

[CamperDoctor]

My first thought is, how do you intend to access the handbrake adjustment at the bridle?

The cover would be removable as per the covers under the engine bay. This would then allow access in to adjust the handbrake but also the many other ancillary systems that would have their access restricted. I agree it wouldn’t be a five minute job to remove the cover but hopefully most of the system it restricts access into won’t need frequent (like every month) attention. It’s a balancing game of the benefit over the extra effort required to access things that were normally quick to reach.
I think my biggest concern in terms of access needs would be the LPG tank. I’m happy there would still be sufficient airflow between the cover and van underfloor, in case of, ok this is a very low risk, but just in case, LPG tank leaks.

 

[CamperDoctor]

What is purpose of the shield and what above it. (fiat or ALKO chassis). If its to protect from salt road spray i would avoid Aluminium (sheets too large to anodize). Stainless steel of a thinner gauge would be better but more floppy/ suseptable to impact events. Offroading? for access use windows/hatches and rivnuts. Weight not really mentioned but is fibreglass an option ( lot of work making a semi mould to start with). if traveling in rivers will need to consider drainage.

Some really good point …. !
It’s a fiat chassis, which is good and bad. The longitudinal legs are further apart but the fiat chassis has better position cross members to supporting the middle of the cover.
It’s purpose is a number of things. Primarily I want to reduce muck being thrown up onto the under floor area, water tanks, LPG tank, wiring and piping. I’d also like to have some form of very lite protection against pipes, wires etc being caught by small stones, branches etc. I’m not even considering full blown off-roading, the van just isn’t designed for that.
Yep good point about the aluminium and treatments, that’s now on the list to give extra thought to.
Stainless is an interesting option but just much less friendly to work with, and pricy. I’d also initially considered adding structural reinforcements by some well positioned folds. I’ve got access to industrial sheet metalwork systems so stiffening it up without adding cross members is totally possible.
Weight is always an issue so yes it does need thinking about. I’ve not yet considered what the budget for weight is but in the back on my mind is, I need to be able to take this cover off with a socket while parked on a campsite to repair things if needed. So if I can’t sensibly lift it then it’s too heavy.
Fibreglass/GRP was one of my first considerations but I’ve never worked with it, and my natural assumption is it’s going to be hard work. I’m also concerned a small ground impact would do disproportionately large damage to a fibreglass cover.…?

Many thanks for some really useful questions

 

[theoneandonly]

Fiat versus Alko i was thinking galvanic action of any fasteners and drilling holes or not.
There are a number of hexagonal holes scattered about the Fiat chassis that are intended/ perfect for hexagonal rivnuts for M8.
concider doing it it a least 3,4 sections for ease of manipulation on a camp site. makes stainless more attractive remember you can run with thinner section than Aly and no treatment required (painting ?). Layingup fibreglass is surprisingly easy (yes ive made simple box structures) but creating moulds for this application with no experiance best to go with metal.

 

[CamperDoctor]

Fiat versus Alko i was thinking galvanic action of any fasteners and drilling holes or not.
There are a number of hexagonal holes scattered about the Fiat chassis that are intended/ perfect for hexagonal rivnuts for M8.
concider doing it it a least 3,4 sections for ease of manipulation on a camp site. makes stainless more attractive remember you can run with thinner section than Aly and no treatment required (painting ?). Layingup fibreglass is surprisingly easy (yes ive made simple box structures) but creating moulds for this application with no experiance best to go with metal.
View attachment 434551View attachment 434552

This is a long shot but do you know of anybody/anywhere I can get hold of the Ducato under body engineering draws? It would be really useful and interesting to be able to manufacture to a drawing, and then make small adjustments to fit the actual bodyshell.
Out of interest do you have a view as to how much movement/twist I should expect in the longitudinal chassis legs? I’ve heard that the Alko frame on GRP based Motorhomes flexes quite a lot..!! I’m assuming the added rigidity of the Ducato monocoque panel van reduces flex to insignificant levels?
It dawned on me this afternoon as I started planning it out, that there’s potentially a twisting moment on the underbody cover. But my view at present is it will be negligible - do you agree?
yep agree with idea of doing in sections. Also plan in places over the width to put a 20mm offset at 30degrees to the horizontal, pointing up towards the body shell floor, at the front of each section. This will add stiffness and reduce chance of the leading edge catching on the ground.

 

[theoneandonly]

if you have a underslung gas tank has it been properly protected with a thick rubberised paint. anti chip and anti salt. The twisting moment on a van will be a lot less than an alko Motorhome but negligible??
Drawings i doubt it. 5 years ago i looked before i designed my spare wheel hanger. little post 2016 info available from Fiat.
Out of interest do you have a view as to how much movement/twist I should expect in the longitudinal chassis legs?
If i was in work, i know someone who could have, but im not, "unfortunately" i retired in 2019

 

[Reg 65]

The twisting motion of a flat trailer can be enormous. I watched a TV movie of a lorry roll over going round a bend - freeze framing to see what happened. It was an artic with a loaded flat semi-trailer and the back end rolled first - having a higher centre of gravity, springs closer together and no anti-roll bar. The back of the trailer was nearly over before it flipped the tractor unit over with it - nearly 90 degree flex along the length of the vehicle.
But i don't see how a rigid box body like a motorhome can flex at all. To demonstrate how rigid it is take a food container with a tight fitting lid. Grasp the container at each end and flex it with the lid off to see how floppy it is, Then put the lid on and try it again - it doesn't flex at all. If it did the damage to the structure would be so severe it would be obvious.
You would need drain holes whether you are going through rivers or not - water will get in one way or another.
But. frankly, I think this project would be more trouble than its worth.

 

[CamperDoctor]

The twisting motion of a flat trailer can be enormous. I watched a TV movie of a lorry roll over going round a bend - freeze framing to see what happened. It was an artic with a loaded flat semi-trailer and the back end rolled first - having a higher centre of gravity, springs closer together and no anti-roll bar. The back of the trailer was nearly over before it flipped the tractor unit over with it - nearly 90 degree flex along the length of the vehicle.
But i don't see how a rigid box body like a motorhome can flex at all. To demonstrate how rigid it is take a food container with a tight fitting lid. Grasp the container at each end and flex it with the lid off to see how floppy it is, Then put the lid on and try it again - it doesn't flex at all. If it did the damage to the structure would be so severe it would be obvious.
You would need drain holes whether you are going through rivers or not - water will get in one way or another.
But. frankly, I think this project would be more trouble than its worth.

I agree this project is going to be “a lot of trouble” and pretty challenging. But that’s what makes it fun and worth attempting.
Drain holes is an interesting thought. My current design means the underfloor panel will be in probably 3 sections (1-3) running front to back. These sections will have gaps, probably about 20mm between them. Not decided yet if the proceeding panel edge will have a rubber strip to help cover the gap (to stop wind sound effects..!). So water will not gather in the enclosed section. But I had naively forgot that the chassis leg pre drilled holes (that I was intending to use as mounting points) have many purposes ranging from machine holding points during manufacture to drainage. Thanks for the reminder to ensure I keep enough drainage.
FYI I’m not expecting to just go and bolt a bit of metal in place any time soon. This needs the correct level of thought and planning, just as any job like converting a panel van to a campervan involves. Putting the idea out onto a public forum like this is really useful to help identify/decompose the problems that need solving. Ideally I guess somebody might have come back and said “you can buy it here…” but that’s not looking likely at present.

 

[theoneandonly]

“you can buy it here…” but that’s not looking likely at present.

you more likely to get "cant see the point if not off roading"
protecting the LPG tank is worthwhile. I'm protecting my underside by doing as few winter month mileage as possible.