Forum: Catapult Message Board

It would depend on the load being carried and the quality of the straps that you are using but the ~2inch wide nylon webbing straps that we used to use in the military to strap loads to the top/front/back/sides of our trucks and trailers were rated to several thousand pounds and never even came close to failing from what I could tell regardless of what sort of punishment we put them through. Avoiding sharp edges and ensuring that your load can't shift somehow to loosen the straps during travel are likely your biggest dangers to look out for. The straps aren't going to fail if properly used.

It is also important to make sure that you have the strap threaded through the buckles properly and ensure that nothing is twisted.

Agreed, as long as the straps are properly used and of sufficient size, they won't fail. However, traveling down the road can make the straps vibrate rather a lot due to the wind passing over them. If the strap length is short then it isn't a real problem but for the strap lengths you'll be looking at, for an 'X' layout, it could be a concern. The vibration normally won't hurt the straps but all that vibration gets transmitted to the load and that can get a bit ugly.

ScienceGeek mentioned twists in the straps, which I mostly agree with, but I have put 1 or 2 twists in a long strap and that reduced the vibration greatly.

You might put 'stiffeners' in place. These would be long timbers that can reach from the trailer bed up to some high point on the frame at a slant. Now put a strap on the frame near that high point and anchor the strap to the trailer, not the machine. Tighten down the strap and compress the frame, with the stiffener acting to prevent collapsing the frame. This make a solid unit that, with luck, cannot move up (strap) or down (stiffener).

Catapults are designed for certain loading and we're all pretty good at that sort of construction. Going down the road though presents new stresses and vibrations that are not encountered on the battle field.
We think of supporting a load on the frame in a downward or sideways direction but going down the road those joints also have to help keep the frame from going upward as well. If you can tie the machine down from the upper area well enough, those upward forces are greatly reduce.

I don't think I have access to any straps that heavy-duty... sure would be nice though! What I have is the regular 1" straps sold at walmart. I was thinking two in front, two in back, ratchet them down tight. Maybe I'll just go with the combination of using both the straps and the 2x4s.

Ripcord - I like that idea of twisting the straps to reduce the wind vibration. I'll have to give that a try! As it stands now, there is about 8 feet of strap hanging exposed between the frame. That's a LOT of potential vibrations.

OK, so a few ideas to think about. Once I get the axle supports finished, I'm going to strap it all down and take it for a test drive around the neighborhood. THAT should be quite a site! It'll give me a chance to see how it handles going around turns and through dips and bumps, so I can get an idea of where the stress points will be.

DOT has a habit of looking at the rule book whereas construction folk do not.
Roads get new pavement, the telephone/power poles sink a bit, all kinds of things can change up the amount of clearance between road and overhead obstructions.
Load up the trailer, lightly, then measure to the top of anything that is up there. Brand that number inside your skull (or whatever method allows you to remember it.) I've seen 12'-6" trailers get peeled back under a "14'" foot bridge. So watch yourself. You might even consider making a clearance pole, 1 inch taller than your rig, then when you come up on a "iffy" spot, you can measure it without 'testing' it.

If the rig bounces a lot, check your tire pressure as well but you may wish to modify the suspension (if any) of the trailer. Our 12 foot treb was pretty light and traveled on a single axle, which was bolted directly to the frame. (Talk about odd looking going down the road!) That sucker bounce like mad, I've seen the tires get 2 feet in the air, I kid you not.

Where the straps cross each other, put a bungee cord, duct tape, ACME bubble gum or stout twine around the X. This ties the two straps together and can further reduce vibration.

1" straps? Okay, wrap them several times around and you get multiple straps. True, there is still only one clamp but the strength of the wrapping will be much greater. It even reduces the tension on the clamp.

I had a treb that was eight feet to the throwing arm that I transported on a flatbed trailer with little problem. I removed the weight box and throwing arm for transport.
With 4, 2"ratchet straps from Harbor Freight and all the weight placed forward of the axle, it traveled very well. At 12 feet,though, you'll need to be aware of any low clearances along your route. You should be able to clear them as most things are 14 feet over the roads. Maximum vehicle height is usually regulated to 14 feet as well.

In Orlando, FL, there is a railroad overpass that is marked as 15'9". 12" trailers get hung on it all the time because the road dips under at the center but raises up again on either side. Therefore, longer trailers can be riding on the uphill and down hill slopes at the same time which raises them a few feet and oops.

Get insured.

Walker