Follow up on winch project

[Rick Hughes]

A past post has helped decide that I need a winch fitted in my boat shed ... to assist in pulling in of twin axle trailer. Had a number of exchanges .. pointing me to caravan movers - but these ended up in a'dead end' The issue is there is a slight slope on drive before I get trailer into boat shed ... and while I could do this on a single axle trailer - it is impossible to do this on your own with the new twin axle trailer.

The issue is any steering that takes it off straight line, means one axle tends to 'crab' over while one rolls ... huge effort when trying to push manually, if I had winch taking care of the pull, all I would need to do then is steer.

Boat & trailer is 2000Kg, but that is dead weight ... and I am not trying to lift it ...

I have seen 3500Lb winch kits, which I'm hoping will be man enough for the job ..

any view if 3500LB is enough ? .... this is 1590kg .... and I'm assuming this is far more pulling power than I have been able to exert manually.

My thought would be use winch and then split the pull to each corner of trailer with a rope & pulley, allowing me to easily steer from front of trailer while pull applied by winch i.e :

winch did struggle (doubt it) I could turn winch cable back on itself with a snatch block and gain a 2:1 advantage.

I'd weld up a small stand out of 5mm steel, resin bolt that to concrete floor, keeping winch pull level with trailer, and also up off any water.

Comments ?

I'll post a second Q related to battery size needed

[GB]

That's vast overkill - almost enough to lift it vertically, and you say that your drive is on a slight incline. I'm still not quite sure why you don't just use a hand winch or block and tackle.

costs £14.99.

Of course it may 20 mins to do something you can do in 5 with an electric winch, but you save all the trouble with batteries.

[Roger Mills]

I seem to recall - higher up the thread - telling you how to calculate the pull required. Damned if I'm going to do it again!

[Andy Champ]

Nor me. And it's a boat. Don't you have any gear at all? not even an anchor winch?

Andy

[GB]

2tonnes up 'a slight slope' won't be much until the tyres hit an imperfection in the roadway, or a lip going into the boat house. Even then, it won't be much. All this faffing around when a £15 hand winch will be fine. Or at least start with that and upgrade later if needed.

[Dave Liquorice]

IIRC this is one man operation. If he's winding the whinch lever he's not steering... And being a double axle trailer it'll be easyier to steer when it's actually moving compared to stationary.

[Rick Hughes]

I have a 2 tonne one of those winches fitted to my boat anyway ... it is what pulls boat onto the trailer. Unfortunately it's on front of trailer not on rear - so no use for pulling trailer in ... plus boat is in the way.

The reason why I don't want to use a hand-winch or block & tackle is easy .... it is very difficult to push up the slight slope and steer ...it takes a lot of effort to move the twin axle off anything other than straight course.

Therefore trying to operate manual winch or block & tackle while trying to apply a significant sideways effort on steering is just too hard.

A motorized winch running off remote control means I can press button and apply sideways pressure to jockey wheel to steer, no need to apply any rearwards pressure.

I looked at motorized caravan movers (~£900) and even those struggle with twin axle trailers . You can get bolt on axle motors, but 2 things no good here - one they wouldn't last being dunked in saltwater ... and 2 they cost £2.5k

[Rick Hughes]

Nope ... anchor is on a rope, but no winch (it's a ski boat)

[Rick Hughes]

exactly .... that is the key issue.

when there are 2 of us we can push in OK ... on my own I simply can't get the sideways pressure & rearward force enough to move it ... the 2nd axle acts almost as a brake as the tyres crab over .... inherent design flaw in twin axle trailers.

One Caravan company got over this by having a hydraulic system that retracted one axles set of wheels off the floor for 'manhandling'

What would be ideal, is if they had some form of rear steering 'floating/swivel' on the rear axle, that would cure the problem.

I do this to a certain degree by jacking up the front jockey wheel, putting most of weight on raer axle, it makes it easier for 2 of you to move ... but when you are on your own, because of angle of boat you push against the raised bow, and it tends to lift bow up off rollers rather than push trailer backwards.

That 2nd axle really does act like a brake ... for anything other than a straight line.

[Rick Hughes]

On 16/12/2012 20:39, Roger Mills wrote: floor, keeping winch pull level with trailer, and also up off any water.

You said to do it .... but didn't say how to achieve that .......... I have no way I know of to calculate the pull ..that was my original Q.

I know the angle of the drive, weight of boat, trailer, length of pull ... but have no idea of rolling resistance, or friction when one axle is crabbing - so unable to calculate pull required.

[Rick Hughes]

I have explained why this is not an option.

[Andy Champ]

That's not a boat :P

More seriously, how about two tackles, one to each side?

Andy

[Onetap]

Me, too, can't be arsed reading it all. Couple of pulley blocks with karab= iners to hook onto either side, cleats to hold the rope and a length of 3x2= to alter direction. The arrangement served the navy for centuries running = out guns of several tons. You can remove the rope and pulleys for use elsew= here when you're not pulling boats around.

[GB]

Thanks for explaining.

I'm delighted that you are not going to be between the boat and the electric winch. Elfin safety will approve of your not being so liable to be run over.

The remote for the winch looks like it's IR, will the boat be in the way? Apart from that minor problem, the winch you have chosen should be vastly more than equal to the job.

Batteries are marketed as XX ah. So a 60 ah one (theoretically) can supply 60 amps for 1 hour, or 120 amps for 30 mins, or 1 amp for 60 hours.

Your 1.2 hp winch will use about 75 amps when working flat out, but that will be for less than 5 minutes, and most of that time it won't be flat out. Just when starting, the winch will use more current.

In theory, then, a rather small battery should be sufficient. In practice, you should get a fairly meaty car battery.

I see that Eurocarparts are doing a Bosch 43 ah battery for £36 and a rather bigger one for £48. Cheap as chips! Given that, I wouldn't bother messing around with dud batteries from breaker's yards.

What you might do is replace your car battery with a new one, and use your working car battery for the winch. What's in your car?

[Roger Mills]

What part of this didn't you understand?

"To pull a trailer up a slope you need a horizontal(ish) force equal to the rolling resistance plus the component of the trailer/boat weight acting along the slope (weight multiplied by the sine of the angle which the slope makes with the horizontal)

You measure the first of these by pulling the trailer along a horizontal surface by means of a spring balance. You can calculate the second.

For example, if the all-up weight of the boat plus trailer is 2000Kg, I would expect the rolling resistance to be around 25Kg. If you pull it up a 5 degree slope (approx 1 in 12) the component of the weight along the slope will be about 175Kg - i.e. 200Kg in all.

When the hoist is laid on its side, it should be able to exert a similar horizontal pull to its rated vertical lift when used normally. So 250Kg should be ok for a 5 degree slope. If it's steeper than that, you might have a problem - so make your own measurements and do your own calculations with the actual data."

As I said, you'll need to measure rolling resistance by pulling it on a level surface with a spring balance. But, from memory (going back 40+ years!) when doing performance calculations on motor vehicles with radial tyres (cross-ply were higher) we used to use 13 lbs per 1000 lbs of weight - hence my guess at 25 (26) Kg for a trailer weighing 2000 Kg.

Then you'll need to measure the angle which the slope makes with the horizontal, and multiply the weight of the trailer by the sine of that angle in order to calculate the component of the weight acting down the slope and then add that to the rolling resistance to find the total pull required.

The rolling resistance will be a bit higher if the tyres are scrubbing, but you - not the winch - will be providing the side (steering) force.

[meow2222]

Don't overlook the one gotcha in this. If there's even a quarter inch lip along the tow path, then for a short distance the winch is effectively pulling the load up a much steeper angle there.

NT

[Roger Mills]

along the tow path, then for a short distance the winch is effectively pulling the load up a much steeper angle there.

Steeper, yes - but not *much* steeper because the tyres would even it out. Also, if you'd got a bit of momentum going, you'd hardly notice a small step.

[GB]

Whilst the maths is impeccable, isn't this 200Kg figure somewhat spuriously accurate? There's only got to be a rut in the drive, a pebble in the way, or a lip into the garage for the required pull to go up significantly. He'd probably want to double that figure.

In practice, he's getting a winch which is capable of far more, but it's only £100, which seems incredibly cheap to me.

[Roger Mills]

There may well be other factors, but following my method of calculation will at least give the right order of magnitude - and you can can add whatever safety factor you choose. The OP claimed not to have a clue as to where to start - so I sought to point him in the right direction, if only to dispel any myth about the required pull being anything approaching the dead weight of the trailer.

[meow2222]

along the tow path, then for a short distance the winch is effectively pulling the load up a much steeper angle there.

My experience of pushing things about by hand is that such tiny obstacles make the required push several times as hard.

Theres close to no inertia with a slow crawling load, it just doesnt have enough speed for any ineertia to be noticed.

But its not a huge issue in that a) any of the suggested cables can provide far more current than they do within the calculated specs b) the hoist is capable of pulling 2 tonnes straight upward.

NT