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Old 01 February 2006, 06:08   #11
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Boat name: S.S. Nobstick
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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 maths…. 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 Kg… am I right so far?

Therefore (D/d) X (W-w) is (7000/600) X (100-0) = 1,166 Kg. It’s so close that it looks like it “should” work somehow….any takers? Someone else have a go and try it… JW?
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Old 01 February 2006, 06:28   #12
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Mmmm the trailer Chassis plate, there’s 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 didn’t 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 don’t 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 won’t stamp it up however as if I go with two axles it’ll 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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Quote:
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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