To mount a genie on the rear

reza · Senior Member

To mount a genie on the rear

DeBe · Guru

Hi reza, by the time you add weight of extra framing to suport generator going too be afair bit of weight. dont for get going over humps & dips in the road there will be a fair bit of stress back there. Cheers Daryl

dave06 · Guru

yep 60 kilos is a fair bit hanging off the rear be sure and take it from the chassis members and make the supports go up rather than down for clearance,

the extra weight over the rear will not interfere all that much with the balance of your van just cantilever it a bit with a bit of shuffling of possesions to the front, but not too much

Rolly · Guru

The dynamics of increasing mass at greater distances from the axles, especially to the rear, is now fairly well understood.
Unfortunately, the many of the makers and the sellers of caravans have not yet caught up with the science.

Loads placed away from the centre of rotation(fulcrum) will lower the speed at which a trailer will become unstable and thus reduce safety margins in the case of a need for sudden braking or incident avoidance.

Correct loading of a trailer is most important if one is to avoid the fishtailing and jackknifing that seems to be keeping the emergency services busy.

There is a speed (especially wind speed) at which every trailed box will become unstable.
In the case of a well loaded caravan it is usually in the 110+ Km/hr range.
Badly loaded 'vans may find this happening at metropilitan road speeds.

Dual axle 'vans always feel more stable, but the actual increase in safety margin is not really very great.

The longer and heavier the 'van, the lower the speed at which instability occurs.

A read of Collyn Rivers articles and books will give you a better understanding of the forces involved.

http://www.caravanandmotorhomebooks.com/books/index.htm

Disclaimer: I have no personal nor commercial involvement with Mr. Rivers: He just happens to be a skilled engineer with an ongoing involvement in all things RV.

reza · Senior Member

mmm not much i can do with shuffle the stuff around up front Dave the kitchen there

dave06 · Guru

ok that may in fact work in your favour, have you a Ball weight measure,

there are ways of doing this, on the net, just poke in "Ball weight measure" or "home made ball weight measure"

work out the total weight of the van (loaded) then work out your 10% ball loading

if this exceeds your 10% then the cantilever action of the extra weight of the generator will help bring your ball weight in to the 10% range, try not to go below 10% of the total c/van weight on your ball as this sets up a "pendulum" action where the tail wags the dog (fishtailing)

you may be able to "borrow" a Ball scale from your local c/van reseller

just rough figures here but bear with me

if your van weighs in at say 1800 kilos and your ball weight (with forward kitchen) comes in at 200kg's (20kg's over the 10%),

then you place your 60 kilo genny on the back, which by the way does not give a full 60 kilo effect because of simple mechanics,

given the excess ball weight in the first place, now test the ball weight with genny on rear (even if you only lash it there with ropes for the test), if it falls "roughly" around 180 kilos (10% of total van weight) then you are fine!

this may also be achieved if for instance you mount a spare tyre on the drawbar to "balance" the load if it is found to be under 10%

if however it grossly underweighs the ball weight then I'm afraid you are snookered

this is highly controversial and like tyres there are all sorts of experts out there, but whatever you do you must not go less than the 10% ball loading, this I cant stress enough,

you must "balance" the van with a little extra on the ball!

Rolly · Guru

dave06 wrote:

ok that may in fact work in your favour, have you a Ball weight measure,

there are ways of doing this, on the net, just poke in "Ball weight measure" or "home made ball weight measure"

work out the total weight of the van (loaded) then work out your 10% ball loading

if this exceeds your 10% then the cantilever action of the extra weight of the generator will help bring your ball weight in to the 10% range, try not to go below 10% of the total c/van weight on your ball as this sets up a "pendulum" action where the tail wags the dog (fishtailing)

you may be able to "borrow" a Ball scale from your local c/van reseller

just rough figures here but bear with me

if your van weighs in at say 1800 kilos and your ball weight (with forward kitchen) comes in at 200kg's (20kg's over the 10%),

then you place your 60 kilo genny on the back, which by the way does not give a full 60 kilo effect because of simple mechanics,

given the excess ball weight in the first place, now test the ball weight with genny on rear (even if you only lash it there with ropes for the test), if it falls "roughly" around 180 kilos (10% of total van weight) then you are fine!

this may also be achieved if for instance you mount a spare tyre on the drawbar to "balance" the load if it is found to be under 10%

if however it grossly underweighs the ball weight then I'm afraid you are snookered

this is highly controversial and like tyres there are all sorts of experts out there, but whatever you do you must not go less than the 10% ball loading, this I cant stress enough,

you must "balance" the van with a little extra on the ball!

Dave,

I've read your posting very carefully and I'm afraid that what you have written does not concur with real life science and engineering

The topic is only controversial because persons without the necessary expertise and experience insist that what they think they know is fact, when the reality is they are often mistaken.

I will not enter into a debate with you on this, as you will probably get upset and excessively vociferous.

However, for your own wellbeing, and that of those who trust in your judgment, may I respectfully suggest that you study the current knowledge with an open mind.

You say that you don't read much, but this is a topic on which much has been written, with only a small part of it by engineers and researchers.

It's time, I think, to have a read of the material written by the qualified few.

dave06 · Guru

if you take notice of my post I only submit that it is possible, I mention nothing of the construction side of it, this I would see an engineering firm about, I would not personally undertake it, nor do I state anywhere that the original poster should, do try to at least read my post before showing your ignorance of it's content

the engineers employed by an engineering firm would work out the details and it is they that would have the final say

Jock's 18 footer has on it's rear two spare tyres and two jerry cans, given average weights, that would ammount to very roughly 80 kilo's, quite legal and quite safe, I have seen many like this, his addition was accomplished by gobells engineering here

the only thing that would bother me is the depth of the generator and the ability to keep it "upright" with limited bracing ability, not being able to brace it through the van wall! I see as a major drawback

I would not take the job of placing it there but it is in theory quite doable! given the correct calculations, not one for the backyarder!

I dont need to read the material submitted by more knowledgable folk to pass on that which I see out here all the time. I dont have the time or inclination

if I have any doubts about what I am doing then I seek expert help, as we all should.

as I said, experts willing to shout down any input everywhere!

Rolly · Guru

dave06 wrote:
..........as I said, experts willing to shout down any input everywhere!

As they will when information provided is either erroneous or incomplete, which some of yours is.

No further comment, as I dislike your continual demeaning of anyone who cares to suggest that the information that you provide may be in any way less than absolute.

.

dave06 · Guru

you take a shot then hitch up your skirts, drop your lip and run when anyone answers.

the original question was, and still is, "is it possible in theory to mount the genny", I say it is with the correct advice and balance,

I was showing a way to find out if he has the correct balance, merely step one of a multistep procedure to an end result,

if the balance is correct then the next logical step is to seek expert advice from an engineering construction firm!

who will make many calculations, based on knowledge gained by actual observance of the vehicle involved,

as we all know we cant make asumptions, particularly engineering assumptions without seeing the construction method involved,

the findings will then be used to actually construct it by suitably trained personell (my next bit of advice!) because as we know any construction of this kind must come under insurance criteria and would have to be passed and stamped by various authorities anyway

and I guess you calling me "upset and excessively vociferous" is not demeaning, mate take a look at your own posts for insults before you hold yourself up as mr cleanskin!

humpy · Veteran Member

that motorbike ramp you fitted for us on the back of our kimberley kamper in 98 is still onboard Dave along with our motorbike it weighed in at 120 kilos didnt it

PeterD · Guru

dave06 wrote:
I dont need to read the material submitted by more knowledgable folk to pass on that which I see out here all the time. I dont have the time or inclination

if I have any doubts about what I am doing then I seek expert help, as we all should.

as I said, experts willing to shout down any input everywhere!

Well Dave, that's a funny attitude. It sounds like you have no doubts on the subject so you are not going to consult superior experts to see if you are right or not. Not only that you seem to ridicule those who point out you may be wrong.

I know Dave is not going to look at these links but I suggest the rest of you look at them to see if Dave's thoughts are worth considering or not.

http://www.noboundaries.com.au/Safety/caravan_stability.htm

http://www.towingstabilitystudies.co.uk/stability-studies-simulator.php

http://www.towingstabilitystudies.co.uk/stability-studies-game.php

Reza - you say your generator only weighs 59 kg. You are forgetting the weight of the structure needed to support it. Whilst it may not quite double the weight it still will be considerable. Also consider your ball weight as a percentage of your total weight. At the current 180 kg I would say you should not be lightening your ball weight. When you add weight to the ends you will be making your van less stable. In situations where weight is concentrated at the ends you need more ball weight. Play with the 3rd link to see the effects.

Those that were quoted with getting away with extra weight at the ends may come to grief if a good wind gust or road surface upsets their straight line progress. This was amply demonstrated in the second link.

dave06 · Guru

I suggest you do study the links placed in here,

the one by colin rivers I am very familiar with it is only common sense and if you read what I wrote in my first response you will see it backs up what i actually said regarding balance and stability and the ten percent ball weight rule

the second simulation deals with "loading" of the van inside not any mass outside, if you take notice of the weight positions, they are indicitive of internal dimensions of the van, and does not take into account Ball loading

the front weight stays inside an "invisible" front wall marked by a bit of black tape and does not actually proceed to the ball where it could represent the actual "balance" of the van, this simulation is to simulate the loading and not the constant weight of the van, and given the loading relationship of roughly 2/3rds weight at the back and 1/3 to the front of course it will fishtail

I would like to see the same simulation where the weights are of equi distance from the wheels, and a correct ball loading, this outcome would be entirely different

the third one starts off with a van that is inheratantly unstable, it states a total mass of 1000 kg's with a ball weight of 62kgs nowhere near the ten percent needed, even unloaded I managed to gain a speed of 195 kilometres per hour, not bad with an unstable van

I stated that if the van was front heavy with a front kitchen to start off with then there "MAY" be a little room to play with, there may not be as well, thats why I devised a very basic test, all should be well providing the balance is kept

without knowing all variables including distance from wheel to rear and individual wheel loading and a definate ball weight loading then a conclusion to construct or otherwise cannot be made by anybody,

this is why I still say consult an engineer and he/she will take all measurements and make all calculations and why I did not say yep she'll be apples mate go ahead

I notice with a wry smile you left out the other little piece at the end where I said

"if I have any doubts about what I am doing then I seek expert help, as we all should!"

I have a lot of doubts on the subject, I personally wouldnt do it because of the overhang and that is why I said Reza should consult an engineer!

I dont mind being shown wrong if it is done in the correct manner I.E. I disagree because........... then rationally list the reasoning, this was not done, I defended what I still see as a correct call

anyway Reza build it, dont build it, but before you do anything consult an engineer in person and make up your own mind from there!

every van is different!

I look forward to you fellows answering future questions about anything technical so we all may study every word and await the inevitable slip up.

I will be very loathe to post in here any more!

yes Mick, yours would be the fifth one I have built, all passed by regency in adelaide and stamped, I hope you enjoy it for a long time to come. see you at xmas! say g'day to Sandy for us!

-- Edited by dave06 on Tuesday 17th of November 2009 01:05:51 PM

Disco Duck · Guru

I have a question here. Does loading a caravan have the same results as loading a truck? On a truck, any weight placed to the rear of the rear axle is in actual fact doubled when that axle is weighed. Does it work like that on a caravan. I am now curious after reading this thread

-- Edited by Disco Duck on Tuesday 17th of November 2009 08:05:14 PM

Peter_n_Margaret · Guru

Disco Duck wrote:

I have a question here. Does loading a caravan have the same results as loading a truck? On a truck, any weight placed to the rear of the rear axle is in actual fact doubled when that axle is weighed. Does it work like that on a caravan. I am now curious after reading this thread

-- Edited by Disco Duck on Tuesday 17th of November 2009 08:05:14 PM

Yes and NO.
With a heavy front kitchechen PLUS a heavy back end you are creating a "dumbell" weight distribution which, as has been said above, is likely to be dangerously unstable, irrespective of ball the weight being correcct.
Good stability requires weight to be concentrated in the centre, over the axles.

Cheers,
Peter

dave06 · Guru

got one out in the block right now with exactly the description you give (forward kitchen rear bed and centre seating) has two off road tyres and two jerries on the back, still on his third time round and no problems to date, it came out of the factory fitted like this, never had a problem

jimricho · Guru

Let's keep it friendly folks.....nothing wrong with a bit of good humoured p1ss taking but let's not get like some other forums I've visited (and left). If we wish to be critical of other's ideas or views there's nothing wrong with that as long as we "play the ball and not the person"

kind regards to all,

Jim

Cruising Granny · Guru

That's why this is a forum. A place to seek input and measure the responses.
I have a split system air conditioner fitted to the back bumper of my 20ft van which has kitchen at the back and bed at the front.
I've never felt any ride altering conditions all the way around the country from Broome to Cairns via the southern states.
The aircon weighs about 60kg installed, and I removed the range hood to fit the aircon outlet.
The roll-out awning weighs more than that, and although it's balanced from front to back, all it's weight is on one side. On my van, the opposite side to the fridge and bathroom.
There is a little more overhang in the rear, but I take it into account when negotiating drains and bumps. So far so good.
There are so many things to consider when fixing more weight on to wherever on these aluminium boxes with staples.
Weight distribution and balance and keep the heaviest lowest - just like a boat.

dave06 · Guru

thank bloody christ for that, someone who has this sort of thing fitted to the rear, (and there are heaps of you that has this type of thing), that is willing to come forward and speak out,

I see hundreds of these when I'm out and about, I get swags of them in here, calling in to say g'day or getting repairs done, I SEE them all the time,

others obviously dont!!!

the external apparatus ranges from spare tyres front/rear, gennies on front/rear or split system air con, front/rear, fuel cannisters front/rear

provided it is done correctly it is fine, not sure about the fuel though, I would not carry fuel out there, better on the back of the vehicle or maybe drawbar where it is a little better protected

but please seek professional advice from an engineering firm or caravan manufacturer first and take the van with you, they wont mind, they need to get all the specs before they can make any decisions,

a pro will not obligate himself/herself without first getting all details

only a fool does this!!!

dont do it without advice from professionals, there are many pitfalls and calculations to be made

ibbo · Guru

I think that this kind of kinky talk about mounting Genies should be censored.Tut Tut.Cheers.Ibbo.

Basil Faulty · Guru

Yeah plus you have to get them out of their bottles first.....

Rolly · Guru

Basil Faulty wrote:

Yeah plus you have to get them out of their bottles first.....

Like this, Bas ?