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Maximum grade to prevent drag boat trailers

Maximum grade to prevent drag boat trailers

Maximum grade to prevent drag boat trailers

(OP)
I am raising the grade of a rural collector road to improve sight distance at a T intersection with a local road.  I am raising the grade approximately 3.5' and would like to minimize the construction on the local road which dead ends and services an island where every property owner has a boat.  What I need to know is what is the maximum grade that can be used on the local road to prevent a boat trailer from dragging when manuvering through the intersection.  Any help is appreciated.

RE: Maximum grade to prevent drag boat trailers

I'm sure boat trailers vary widely, in terms of tongue length, rear overhang, etc.  Maybe one of the automotive fora might be able to help?

RE: Maximum grade to prevent drag boat trailers

Due to the variety of trailers (weights and lengths) vs pulling vehicle, I would provide a geometry that does not exceed 3% ideally and maximum of 5% grades.  Even 5% may be a little dicey, depending on the intersection geometry.

KRS Services
www.krs-services.com

RE: Maximum grade to prevent drag boat trailers

Is the actual grade the problem in dragging a trailer, or the change in grade?

RE: Maximum grade to prevent drag boat trailers

The change in grade should not be a problem provided there is a suitable length of vertical curve. I would suggest that one way to check the risk of dragging is to talk to a boat dealer and see what sort of maximum length boat trailers can get to. With this information create a template that shows the rear wheels of the car, the trailer geometry (wheels, length heights to various points on the trailer and tow hitch when connected to a car) only select a worst case car/trailer combination (lowest tow point, longest trailer). Draw the template at a suitable scale, draw the intersection grade changes (along the travel surface) and then simply "drive" the car/trailer over the surface.

I know it is a "basic" method but it does work reasonably well for one of issues. I have used this method for similar problems, more often than not it is actually used to assess and modify driveways.



regards
sc

RE: Maximum grade to prevent drag boat trailers

(OP)
Thanks to all of the responses.  What I am proposing is about 250' of construction with reverse 100' vertical curves and a 4.25% grade between the PI's.  I like the idea about making a template and "driving" it through the intersection.  I have since found that my office has addressed a similar problem with horse trailers the same way.  I will approach it from that angle. If anyone else has other suggestions, please let me know.  Thanks again.

RE: Maximum grade to prevent drag boat trailers

I recently researched this issue for "lowboy" trailer problems associated with a raised crosswalk.  I found an article written by a masters candidate at the UWVa who did extensive research on the gometry of potential "hangup" situations for different vehicles - one (group) of which was passenger vehicles and trailers - you can find the PDF document at:

etd.wvu.edu/ETDS/E2391/Clawson_Amy_Thesis_etd.pdf

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