Extending a trailer chassis?

[Lobster]

I have a small bespoke box trailer, which was deliberately made quite "stubby" so I could stand it on its rear end inside the garage. However, I now have the need to be able to carry on top of it an inverted sailing dinghy (a Topper for the cogniscenti; to facilitate simultaneous camping and sailing!), but unfortunately the chassis is too short - if I position the dinghy with its centre of gravity above that of the trailer (ie to avoid applying significant forces to the towball) then the dinghy hits the back of the car.

So I'm wondering if I could safely modify the trailer by simply extending its drawbar, to put adequate distance between the car and the trailer body? At present the chassis has a welded triangular steel frame coming forward from the front of the trailer body, with a short stubby length of steel is bolted to the apex of the triangle, on to which is bolted the towing hitch. So if I was to replace the short stubby length with a longer piece, then in theory that should work. But I'm concerned about messing it up, in that will this affect the trailer's safety/stability when towing? What criteria determine this? is there a 'formula' or is it just a case of intuition and/or suck-it-and-see? Presumably it would be better to modify the triangular frame accordingly, but that would mean major surgery which I couldn't DIY...

Thanks David

[.]

I can't see any issues with your proposal, up to a certain length limit but it may be more sensible to extend the chassis in front of the wheels rather than over extend the "short stubby length" bit. should be a simple cut and shut job with a grinder and welder but if you're going to go that far you might be better off buying a larger trailer ?

however, I really would like to see you camping and sailing simultaneously !

[Guy King]

The message from "Lobster" contains these words:

Should be OK, but bear in mind that you need to keep the centre of mass forward f the wheels to keep a positive noseweight on the towball. Quite how much will depend on your boat and your car.

The only other thing that would worry me is the leverage where the extended pole meets the triangular drawbar. I'd be tempted to extend it /both/ ways and add a crossbar so from above it would like like an A with a line through the top to the crossbar. This would stiffen it both vertically and side to side.

[Pete Verdon]

People do do it with various canvas contraptions rigged over large dinghies, but not something I'd fancy. Somebody trying to do the same with a Topper really would be worth seeing.

Pete

[Ronald Raygun]

I have no trailer expertise, but I can see that you'd want its COG, when loaded, to be over the axle, or just forward of it. But that doesn't mean the COG of the *dinghy* needs to be there. Provided you can lash it securely to the trailer, so it won't fall off even if its COG is off the back of it, that should be OK (provided this isn't going to stress the structure of the dinghy too much, or that of the trailer, for that matter).

There is another way of moving the overall COG forward. Just pile on loads of extra weight into the trailer, securing it right up forward. You need enough to counterbalance the weight of the Topper which, let's face it, can't be all that much. A few old car batteries should do the trick (and if they're not too old, they might even come in handy for powering some lamps while camping). Also give some thought to redistributing whatever else you put in the trailer, so that all the heavy stuff goes forward and all the light stuff aft.

Alternatively, keep using the trailer as before, but get a roof rack for the dinghy. I know what you're going to say. There's no room for the dinghy on the roof because that's where the bicycles are. :-(

[Lobster]

I see what you're getting at; however the dimensions are such that with the dinghy positioned over the COG, it's already protruding 1.3m off the back of the trailer; it would need to be about 1.9m off the back to give enough clearance up front, which would be inherently very unstable I think, and would need a hell of a lot of weight up front to balance it.

Almost right.... but actually, that's where the *other* Topper goes!

Thanks David

[Lobster]

Indeed - being very deficient in the welding kit/expertise department I wouldn't be able to do that myself. And I'd rather not lose this trailer anyway as the box part is perfectly sized for me: for a start, my local refuse site has just introduced a new limit on trailer sizes which they'll allow in: it's 1.2m internally. I held my breath when I measured mine to check (remember this is a bespoke trailer) - turns out it's 1.195m. How about that!

David

[Alastair]

Should be no problem as long as the extension is not too flimsy. The longer it is the more stable it will be to tow and the easier to reverse (though there are other limits that come in at some point).

-- Alastair

[TMC]

Get a road trailer for the topper and put the camping gear in it

Tony

[Ronald Raygun]

Bloody hell. Would that you could stack them like soup bowls.

Does the solution favoured by canoeists offer a way out? They have an upright bar welded to the roof rack's cross members, so the canoes sit on their side. Could the Toppers go side by side if you did that?

[TMC]

In principle extending the drawer bar where the balance of the trailer is maintained with say a 25kg nose weight should not of itself cause a problem.

Theoretically with topper mounted keel up on the trailer could it create a lift effect similar to an aircraft wing and remove the noseweight altogether?

The trailer may also become unstable side to side because of the weight of the Topper relative to the width of the trailer and the height above the wheels

Tony

[.]

seems the most sensible option.

[Autolycus]

There are two separate aspects to this, I think: structural (will the drawbar be strong enough) and dynamic (what will it do to the trailer handling).

The structural bit can be checked with BS AU 210 Part 1 or whatever may have succeeded it. This recommends a calculation method for determining loads in drawbars.

As far as trailer towing is concerned, the most important bit is that the vertical load imposed by the trailer on the car should be somewhere between about 25kg (yes, alright, 250N) and whatever is the maximum the car maker recommends (probably 50-75kg (do your own *10 if you really do think in Newtons). Too little, and the trailer will sooner or later snake uncontrollably. A problem with large, light, high loads is that strange can be induced by passing vehicles, which can reduce this nose load for long enough for snaking to get established. So err towards the high end of the range. Lengthening the drawbar will, if anything, help stability when the boat isn't loaded by increasing the nose load.

[Guy King]

The message from Ronald Raygun contains these words:

Or face to face like clamshells. A symmetrical crutch that fits in the bilge of both boats would do to locate them together, and lash round with ratchet straps.

[Lobster]

No *that* is an interesting point actually, which might be the killer. When we first started lugging Toppers about on the roof, we were warned by others that it's really important to ensure the front of the boat - which protrudes over the windscreen almost to the front of the bonnet - needs to be tied to the bumper or similar (I use a towing eye) in addition to the obvious ratchet straps over the roof, to prevent just such an effect.

One bloke was apparently frantically flagged down on the M6 because his dinghy was pointing skyward at about 45 deg...!

David

[R L driver]

Without wanting to get pedantic over calculations if you move the hitch further away from from the main load it will reduce the nose weight not increase it, its why wheel barrows have long handles, think about it.

Steve the grease

[Bob Mannix]

Indeed and we are not talking caravans here - it's a *small* trailer so weight calculations are almost entirely pointless - especially if the OP centres the Topper on the trailer. Narrow wheelbase and light load means it is very unlikely to become unstable because of weight/weight distribution - it will just follow rather than having a mind of its own. The most likely threat to stability is the wind effect on the Topper (bad enough when you are sailing them :o) as I was last year - great fun) - the trailer may be too small and light to cope with this and slipstream from large vehicles may affect it badly. Personally I would prefer to have the Topper on roof bars if the vehicle will take it - and leave the trailer for other stuff - more fuel but more stability.