Postby jimh » Tue Jul 07, 2020 2:22 pm
Phenolic sheet at 0.375-inch thickness can be tapped for a machine screw fastener.
Typically the downward force on the ladder will be a shear force on the fasteners. The shear strength of stainless steel is extremely high. I would not worry about stainless steel machine screws shearing off.
The concern is most for some force trying to pull the machine screws out of the threaded phenolic sheet.
I do not have any data about the failure load on a machine screw, say a 10-32 thread, in 0.375-inch thick phenolic sheet. Much depends on the phenolic material, which is typically characterized with a series of “G” numbers, like G8 or G10. If you know the actual material its properties can be research to get a better measure of the strength.
Phenolic material is used by Boston Whaler precisely because it has good strength and will hold machine screws in tapped and pre-threaded holes cut with precision.
Based on an undesignated illustration above, there are two hinge brackets with four mounting holes. Eight fasteners will share the load. Assume a 200-lbs swimmer is using the ladder. This load is spread across eight fasteners, which is only 25-lbs per fasteners. However, the bracket and mount may act as a lever and fulcrum, and the forces pulling on the threads could be amplified.
Another analysis: if Boston Whaler embedded phenolic sheet in that location, the sheet may have been intended for just this purpose.