First off the problem …. My new boat on its trailer – Monterey 194FS weighs in at 2.2T, and while the twin axle Indespension Super Roller Coaster trailer tows beautifully in a straight line, it suffers from the twin axle issue.
This means when you try to steer it off a straight line, you end up with one pair of wheels trying to go in one direction and other wheel at a different angle, they can’t change angle this means you end up with one wheel going where you are pushing the other ‘crabs’ and almost a full drag as it tries to push sideways rather than roll.
There is one German trailer manufacture that produces axles which can allow rear wheels to turn a few degrees either way and reduces loads considerably.
The loading at the tow hitch is very significant ……. You have a car attached – OK put the power on- and just get tyre scuff marks on floor but power of car overcomes it. If you have a DMF flywheel clutch you will incur clutch slip & burn issues.
In my case I have to take trailer off car as it will not reverse into boat store on the tow hitch as screen would foul the 1.8m height limit.
Trying to manoeuver the rig by hand, as there is a slight uphill slope to my drive it is simply not physically possible … even with 2 people as you apply more force it tends to lift bow rather then roll backwards.
Once it is in boat shed and on flat smooth concrete it rolls fine.
Did look at some options …
#1 Manual moving dolly ..
Great on the flat or for single axle .. not much help on twin axles on a gradient.
#2 Caravan moving Dolly
There is a well known battery version “Mr Shifta 2” but the manufacturer no longer makes these, and they are around £300 second hand.
They are not really suitable for twin axles, these units rely on weight of trailer pressing down onto hitch forcing friction onto drive wheels, as a twin axle moves load onto different axles when reversing, the drive wheels tend to lose grip, especially on an inclined drive.
In my case once trailer starts transition from slope to flat almost all weight would come off the traction wheels – at a key point
They also cannot be used with tow hitches that swivel …. You would have to bolt on a device to prevent rotation
#3 Motorized drive motors on trailer axles.
While these exist for caravans, a ribbed roller is lowered down onto the trailer wheel and it drives the wheel that way. There is a shortage of units that can take being immersed in salt water ……. And the 2 big names in this have now withdrawn the boat versions from sale – speaks volumes about reliability.
In addition it was around £2,500 for a twin axle trailer.
#4 ‘Possible’ solution
Came across plans for this version overseas … now this looks with its chunky wheels that it could be suitable …….. still worried about wheel traction.
However I decided to go my own route – a DIY project
To overcome the issues I made some design decisions up front
• Use 12V starter battery – high current, easily kept charge
• Mains motor not really an option.
• Have Winch permanently fixed to solid base
• Arrange height of pull – centre line of winch to match trailer axle.
• Use a 4x4 winch as they are obtained economically (~£80)
• Have radio remote control to make easy to ‘drive’ from hitch end.
• Boat will be ‘reversed in’ so easy attach to rear trailer cross beam
OK so after looking at overall loading … decided to get 3500Lb capacity winch .. the next size down was suitable, but decided to over engineer and should never have a failure, this would have pull to spare.
The unit I decided on was this one from Winch-IT
Description: 12 volt Power in and out and freespool
Specification: 1.2 Hp motor , Twin wireless remotes and wired switch 3 stage Gearbox, complete with Rollers 12.2m Steel cable Dynamic brake
Came with all battery leads, connectors, relay box & remotes.
Next after calculating winch height needed to look at how to ensure when under load the ‘stand’ would not collapse.
Bit of basic mechanical design showed that while I had a dead load down through back vertical section, when under ‘pull’ load this would tend to rotate forward, result with either frame failing or it pulling out fixing bolts.
So what I looked at was a larger base plate and angles struts so that when under load the force would be in a line following angle of these struts ..so no collapse on forward load.
Likewise the trailer will change its pull angle as it is steered into store, so again to provide maximum structural strength made these front struts at same angle sideway as there are front to back.
The resulting design is as shown in the drawing… all made from steel plate & box section.
The base & top plate are made of 9mm steel.
All material came from scrap bin of local fabricator, cost me £2 … I took it away, cut the angles, drilled fixing holes etc. …. Tacked it up with my welder … and then took it back to fabricator for professional weld up and to galvanized … cost £10 for both.
The resulting frame … was very substantial …
Fixing is worth thinking about …. First off there will be a reasonably high load … and rawl bolts tend to crack concrete.
So instead I resin fixed in 2 x M16 stainless studs … resin fixing puts no stress load on concrete, and is vastly superior to rawl bolts.
There is another consideration … if you bolt down at 2 points .. any unevenness under plate of on the concrete results in point loading & fractures.
Here are the 2 x M16 studs – after fixing:
The pucker way to bolt equipment to concrete, is to grout them in.
I made a small frame 25mm thick, temp stuck down with silicone, (also prevents leakage of grout.)
Adjust winch stand so top of frame is level with top of base plate ..I used nuts on the studs and some packers to achieve this.
Then temporarily bolt down, so it is in final position, level & plumb …. Then pour underneath an expanding structural grout. This pours into all gaps, and slightly expands on setting, ensuring 100% load transfer to concrete floor, and has incredible strength in compression.
48Hrs after pouring grout … fitted lock washers and then torqued down nuts to 213Nm, and then bolted on the winch.
The Result:
Power - I used a standard 12V starter battery, in fact took the one off my boat although only a year old, no idea now it had been treated, and put a new one on the boat.
The cabling up is simple as all cables pre-terminated.
The battery is covered with a small wooden box, to keep it clean, and same for winch.
For keeping charged there really is only one way to do this … and that is a multi state Smart charger… just putting 12 V dumb charger across the battery is not good enough, it will never get to maximum capacity, and will fail early.
A smart charger measures the battery terminal voltage and applies the correct voltage to overcome this to get battery to 100% full state.
To charge correctly Lead acid batteries should be charged in three stages:
1. constant-current charge, supplies bulk of the charge, about 50% of charge time
2. topping charge, continues at a lower charge current until saturation recahed
3. float charge. Compensates for self discharge – and can be left on permanently.
This can be taken further making use of microprocessor technology and provides several stages:
1. First off a conditioning charge – preps battery for charging
2. Then a full current charge to about 80%
3. Slow charge to 100%
5. Maintenance analysis
6. Float charge – keeps at 100% capacity, without overheating or gassing off of cells.
7. Maintenance check & reverse pulse to prevent sulfation …. Which causes early life battery capacity reduction.
The one I went for has a great reputation ……… the CTEK msx 5
So in use …
I connect an endless loop lifting strap, by passing over the rear trailer beam,
I feed the leading end through the end loop, and that then gives me a ‘soft’ loop to which I attach the metal winch hook.
The reason for this is to avoid looping steel rope around trailer – which would cause damage to beam and kink the galvanised wire rope.
Conclusion
This makes putting boat away a breeze … also means I can pull the boat out any time without wondering who I can find to help me put it away.
Means I can easily pull it out into the sun for drying for example.
Absolutely 100% fit for the job, and very pleased with result.
