Hatch support weight question

[Dennis8152]

I need to buy some hatch supports but when I went and looked at them, they were sold by weight or maybe strength. Do I just need to estimate the weight of the hatch and buy something close to that size? I'm sorta confused on this because I've read on this site of people buying 150 lb strength or weight and I know their hatches didn't weigh that much. Please help. Thanks, Dennis8152

[KCStudly]

You need to consider the relative leverage based on the point where the strut is mounted to the hatch.

If your hatch weighs 40 lbs out at the edge, say 4 ft away from the hinge, then the strut must lift 160 lbs if it is mounted one foot away from the hinge (assuming the hatch is horizontal and the strut is pushing straight up); standard lever theory. If the strut and/or hatch are at angles, then there is some trigonometry (or good old Pythagorean theory) involved to figure out how much of the struts available force is actually lifting in the up direction; also known as vector analysis. These are the reasons that so many people get it wrong the first time. The simplest method that I have seen demonstrated here is to work out the mounting geometry for the range of motion of the style and size strut to be used, then use a bathroom scale, and this is important, positioned perpendicular to a mock up strut rod, to directly measure the force. Add 20 or 30 lbs for margin, wind, weakening over time, and that is your number.

You may want to do a mock up to determine the mounting points and hatch angles (using the strut makers extended and compressed dimensions) then contact the maker with your info for a recommendation. Ask them about their exchange policy if their recommendation turns out to be off a little.

My two pennies.

[Dennis8152]

Thank you very much. I'm glad I didn't just guess. With your information, I can figure this out now.
Thanks again...

[KCStudly]

No problem, and good luck.