Another Engineering Question

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Jones
Posts: 81
Joined: Mon Nov 17, 2003 11:22 am
Location: Idaho

Another Engineering Question

Post by Jones »

Just an observation:

When I loaded the BoJest onto the trailer and started working out the axle location (they're on a movable sub-frame) to adjust tongue weight, I noticed that the trailer exhibited some "spring". With a plumb hanging from the bow eye, I noticed I could get about 1/4" deflection with an additional 300 pounds of weight between hitch and leading axle.

After performing our most recently discussed strength calculations (hey, thanks Bill!) the figure came out to 2200 pounds, which is pretty much equal to the boat's weight.

Questions: What are your thoughts on the addition of stiffeners... are they needed or is the flex in the steel a good thing, acting as cushion in travel?

Could this become a source of chafing/abrasion as the boat and trailer are in motion?

If stiffeners are added to the main rails, which is more effective... compression (top installed) or tension (bottom installed)?
Avoid Haste.

FDMSIV
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Post by FDMSIV »

How long is your trailer (or the distance between the axle and jack stand)?

When you tested everything, was the boat strapped to the trailer as it would be in transit? The hull will act as a stiffener once it is strapped down.

I think you want some flex in the trailer to absorb shock. This isn't really a problem if it is a steel trailer, could cause some issues if the trailer is aluminum. If you do want to stiffen the trailer I would suggest you try to keep the stiffeners in tension. The tensile strength of steel is much higher than the bucking load (compressive load).

Jones
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Joined: Mon Nov 17, 2003 11:22 am
Location: Idaho

Post by Jones »

Let me clarify:

Only a part of the trailer is showing much flex, specifically the unreinforced span of C4*5.4(x2) main rails from the most forward cross member (shall we call it station 4) and the cross member whereby the tongue is attached. The span is 72".

It's as per design, just happened to notice the flex. It may be a good thing.

p.s. - I always wondered about folks using 1/2" rod in compression for a stiffener... seems it would buckle easily?
Avoid Haste.

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Bill Edmundson
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Post by Bill Edmundson »

If I'm understanding correctly, I'd put the stiffener at the 36" point between the compression flanges (top). This will go a long way to prevent buckling. But, it will not limit the vertical deflection. I feel like some flex is needed. That flex is shock not going to your boat when you hit that pothole.

Bill
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Jones
Posts: 81
Joined: Mon Nov 17, 2003 11:22 am
Location: Idaho

Post by Jones »

Bill Edmundson wrote:That flex is shock not going to your boat when you hit that pothole.

Bill
Agreed, it does look "comfy" for the boat... not to mention that I dropped down to 1500# springs on both axles. They give some, but are predictable.
Avoid Haste.

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