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Old 31 January 2006, 16:59   #1
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Trailer Ponderings

Hi all

I know the only real way to check is on a weighbridge, but Iíve been pondering my trailer today whilst doing a bit of tidying up around the boat.

I brought the used trailer separate to the boat, and have always been a little concerned at the lack of suspension travel, and that the wheels are right up under the arches. But it tows well, as I rebuilt the brakes and have changed the bearings several times.

It has a single axle rated at 1800Kgs which sounds fine until you think about it.

Phoned Ocean and was told to allow 1000Kgs for the RIB itself.
The Suzuki 200 weighs in at over 200Kgs I believe.
A full tank of fuel is around 120Kgs
Plus the anchor/chain etc probably gives me another 50Kgs.

But that does not include the weight of the trailer frame itself, which could take me up over the 1800Kgs.

So as the arms on the suspension units are quite rusty as well now, Iím thinking about going twin axle, which will be a big expense at @£800 minimum for two braked axles and five wheels/tyres and Iíll do the work myself. I canít even use my existing odd size 5 stud 6inch PCD wheels as I'd need to buy two £650 axles to fit them.

And so to my question.
Itís tempting to go for 2 1000Kg axles to save cost, but what happens when you get a puncture? In theory half the load ends up on one 500Kg suspension unit.
Should I be thinking about two 1800Kg axles as a fail safe?
Or am I just paranoid?

By the way I understand Iím letting myself in for 2 x the maintenance costs as well.

What do people think?

Oh and does anyone have two axles, or 4 suspension units, hanging about that arenít being used. Donít mind doing a refurbish job on them.

Nasher.
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Old 31 January 2006, 17:05   #2
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Hi

Ive just been going through the same thing and have decided upon going down the route of two axles having the front one braked but the rear two unbraked. The trailer centre i have bought the parts off has recomended this to me as my real concern was a 6.3 meter rib sitting on one axle and if one new tyre should accidently blow then there would be one shagged tyre holding up the rest!! Not a nice thought!!
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Old 31 January 2006, 17:10   #3
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Simon, my Pacific sits on two 1500kg axles fitted by De Graff for £700 last winter. Why not give Authur a ring just to chat it over with him. Really helpful guy.

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Old 31 January 2006, 17:13   #4
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i have a two wheel and a four wheel trailer

the two wheel is rated at 1800 kg all up and trailer weighs in at 400kg so the load is 1400 kg

the four wheel trailer is 2700kg all up and the trailer weighs in around 750 kg

on the fourwheel item which is a super roller coaster 7 i changed everything, the suspension units never seem to move much on either trailer so if yours dont move i would not worry too much

in the situation where a four wheel trailer has a problem, and 1 wheel goes then you are down to 3 so the load would be spread a bit more evenly. hopefully this wont happen to you. if you are putting on extra axles then they will be new, hopefully more reliable, spreading the load on the trailer better than a single axle, wheels and tyres would be new, etc etc so i would have thought you could get away with 1000kg or 1200kg axles and feel quite comfortable.

the issue with four wheels is it is very difficult to manhandle and the tyres try to rip off when you reverse round tight corners as i have to in some locations, however 4 wheels track better behind the car and the trailer takes less of an ark when cornering

you will indeed increase your costs for wheels and tyres and bearings etc with multiple axles

i have a 4 wheel caravan and the hard boat is 4 wheel but for the rib i wanted a manouverable 2 wheel trailer so personally i would go for another axle of 1800kg if i was in your position and to be honest it tows like a dream, done a lot of miles now with it haha and the boat has not even been near the water yet

if i had gone for a indespension then i would have had to have had 4 wheels cos of the load capacity of hallmark trailers but sbs do a lovely range of high capacity 2 wheel trailers

petes suggestion below for around 700 seems good but on top of that you need wheels and special tyres for the loading. If it gets too expensive then i would consider a new trailer and sell your existing trailer on, perhaps you might be able to do that and it would work out similar to just replacing the axles on yours!!!!

not sure if any of that helps or not but wanted to share in case it does

call me if you want to discuss as i have fully refirbished the indespension one and i can let you know the price i got the sbs for
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Old 31 January 2006, 17:31   #5
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Pete
Spoke to Arthur today and arranged to drop in and see him on my way home from work later this week. the 1500Kg axles would be about right.

Chris
Thanks for all that, I do like the manouverabilty of two wheels but I think my rig is just too heavy. The Ocean625 is a heavy RIB for its size.

Phil
Is only having one axle braked strictly legal?

Nasher.
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Old 31 January 2006, 17:52   #6
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pass but so long as it gets me to the water and back im a happy man!!!
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Old 31 January 2006, 18:39   #7
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Quote:
Phil
Is only having one axle braked strictly legal?
No it's not....all axles must be braked.
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Old 01 February 2006, 04:03   #8
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Nasher

There is a weighbridge at the gravel works (? Marine Aggregates) opposite the Havant tip in Harts Farm Way. They will charge, but I don't think it is much. A trip there may put your mind at rest, or even give you some idea of what you want.
Kendalls on Eastern Way may also be weigh it for you.

Also there should be a plate on the trailer draw bar stating the weight of the unladen trailer, carrying capacity & all up weight. (Not having that plate is also an offence.)
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Old 01 February 2006, 04:56   #9
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if you can find the plate with the unladen weight of the trailer then you can measure the weight of the boat and all its contents using a pretty simple approach and add them together to get the total weight. It was described in PBO 466 (Oct 05) but I will try to decribe it without the pictures - if it makes no sense let me know and I will scan the page.

1. Chock the wheels and level the boat/trailer.
2. Put a pair of bathroom scales under the jockey wheel and record the weight (W).
3. Measure the distance from the jockey wheel to the centre of the wheels/axel. (D)
4. Slide the boat back on the trailer (six inches is probably enough).
5. Measure the distance you have moved the boat backwards (d) - use the same units as for D.
6. Record the new weight on the scales w (it should be less than W).

The weight of the boat, engine and contents is (D/d) x (W-w)

Hope that is useful.

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Old 01 February 2006, 05:38   #10
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Does that work? Let me try and get my head round the maths here..... I'll go and play and see what happens... doesn't sound right to me, but live and learn.. I wish I'd paid more attention in maths classes...
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Old 01 February 2006, 06:08   #11
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My boat has a theoretical weight of 1000Kg, My single axle trailer is 7.0 meters from wheel centre to nose. My trailer is perfectly balanced around the wheel axis when unladen. I.e. there is no weight at all on the nose and all the weight acts through the centre of the wheels. When I put my boat on the trailer, I set her up so that the nose weight is exactly 100KG. From that we can work out that the C of G of the boat is 600mm in front of the wheel centres....feel free to jump in when you see the cock up in my rudimentary mathsÖ. So if I move my boat back exactly 600 mm the C of G of the boat will be above the wheel centre axis and therefore the load on the nose will be 0 KgÖ am I right so far?

Therefore (D/d) X (W-w) is (7000/600) X (100-0) = 1,166 Kg. Itís so close that it looks like it ďshouldĒ work somehowÖ.any takers? Someone else have a go and try itÖ JW?
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Old 01 February 2006, 06:28   #12
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Mmmm the trailer Chassis plate, thereís a bit of a problem.

The chassis plate is on the hitch assembly which I replaced last year, and of course the unladen weight box is empty, as I didnít fill it in, mainly because the old one was un-readable.

Polwart. I think I remember the article, but my copies of PBO get passed on so I donít still have it. So thanks for the explanation. I presume the further you move the boat on the trailer the more accurate the calculation will be.

Looks like I need to work out the boat/engine weight using the PBO method, then get the whole thing down to the weighbridge to find out how much the trailer weighs on top. I wonít stamp it up however as if I go with two axles itíll change again.

Jono. Your calcs look right to me, how did you get the 600mm?

Has anybody else tried it?

Nasher.
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Old 01 February 2006, 06:46   #13
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Quote:
Originally Posted by Nasher

Jono. Your calcs look right to me, how did you get the 600mm?


Nasher.
Ooops... can't read my own scrawl... should be 700mm then it works... doh! Will re-check.. .....Well, I'm blowed..it works! Nice one! You need to "balance" the trailer first though, to make sure it plays no part in the calcs.... or do you?

<edit>.. nope, from another quick calc, trailer has no effect... unless anyone knows differently?
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Old 01 February 2006, 07:39   #14
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Trailer shouldn't have an effect as you've not moved its weight about the pivot point(Axle).

I may be being stupid, by how did you get the 700mm in the first place.

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Old 01 February 2006, 08:26   #15
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Quote:
Originally Posted by Nasher
how did you get the 700mm in the first place.

Nasher.
Sorry... can't sketch it out on here.... and can't work stuff out without a pencil... it's a "moments" calculation. Taking the trailer out of the calc...it's perfectly balanced... . distance between axle centre and nose is 7000 mm and my boat weighs exactly 1000kg.. you will have 900 Kg acting down on the "wheels" and 100Kg acting down at the nose To "counteract" those forces you need 1000 Kg acting "up" at some point. Pick a pivot point, say 1000 mm behind the axle..... and think of the loads as applying torque to that pivot... sorry if this isn't making sense... I'm doing my best.... ...so now we have torque acting Clockwise of 900 X 1000 (distance of pivot point from axle) plus 100 Kg X 8000 (distance of pivot point to nose) Giving a total "torque of 17,000 units. As the trailer is I.e. "equilibrium" I.e. "not moving" this torque must be countered by a "force" of 1000KG (my boat weight) acting anti clockwise at some distance from the pivot. divide 17,000 by 1000 and you come up with 1,700. So the "force" of acts 1,700 from the pivot or, in other words 700mm in front of the axle.... excuse the poor explanation.. but it's the best I can do without a piece of chalk.... If I'm wrong, don't blame me... it's a long time since I tried manual calcs...
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Old 01 February 2006, 08:39   #16
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What did the constipated mathematician do?
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Old 01 February 2006, 08:40   #17
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Worked it out with a pencil...
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Old 01 February 2006, 08:42   #18
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4. Slide the boat back on the trailer (six inches is probably enough).
How the feck am I goin to make 3 tons of boat slide back on the trailer? And then forward again.

I just take it to the weigh bridge. They only charge me if I want a ticket. A couple of kwid in the guy's pocket does it.
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Old 01 February 2006, 09:10   #19
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tie a suitable rope to your house and to the boat, undo the boat on the trailer and drive forward!!

that should do it

Quote:
Originally Posted by jwalker
How the feck am I goin to make 3 tons of boat slide back on the trailer? And then forward again.

I just take it to the weigh bridge. They only charge me if I want a ticket. A couple of kwid in the guy's pocket does it.
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Old 01 February 2006, 10:57   #20
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Quote:
Originally Posted by jwalker
How the feck am I goin to make 3 tons of boat slide back on the trailer? And then forward again.
Have you still got the rest of gArfs tractor? You could use that, if you have.
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