Hatch Gas Spring/Strut Calculator

[Mark Gunter]

I'm trying to use the calculator. My door length is 56" and weight is 60lbs.

Ideal extended strut length, according to calculator, is 33.6"

I find a 30", 100 lb. strut on Amazon. Specs say Extended Length: 30.9", Compressed Length 17.1"

I'm assuming I subtract 17.1 from 30.9 to get the stroke length? If so, that's 13.8"

Bottom line, calculator says I need 33.6" at 90 lb force, and hook it up at 11.73" from hinge ctr pt.

I can get 30.9" at 100 lb force ... should I still be attaching that at 11-3/4" or 12" or so?

[Mark Gunter]

Hmmm, looks like I can get a 35" at 100 lbs. Gonna try that in calculator.

[tony.latham]

I buy my gas springs from McMaster. They have a great selection and if they don't work, you can exchange them.

https://www.mcmaster.com/products/gas-springs

I'm assuming I subtract 17.1 from 30.9 to get the stroke length? If so, that's 13.8"

Yep. McMaster has diagrams of all their gas springs in PDF.

Tony

[Onajourney]

I used this one and they worked great. They are also very price competitive.

https://www.gasspringsshop.com/gas-spring-calculator/

[Mark Gunter]

Thanks Tony & Onajourney!

Man that's a damn fine calculator at gasspringsshop.com, I’m much impressed

[Mark Gunter]

Just an update to say that I went with the gasspringsshop website and calculator and my struts are scheduled to arrive today. Thanks for the tip, Ona

[JP2023]

Hi Dan, thanks for the strut calculator! You have really helped a lot of builders on this forum, and that is awesome!!

I am in the final stages of my build. All I have left to do are the gas struts (saving the best for last!)

I am little nervous that I will place these wrong, since everything that could go wrong has gone wrong with this trailer. Especially since that rear hatch door is my finest carpentry work yet.

When I install the strut using the measurements in the calculator, I will have to compress the strut about 4" to mount it. Does that sound correct? Do I raise the hatch higher in order to attach the strut when it is fully extended? Is there an easy way to compress the spring to install them?

Overall hatch length is 56.25,
Extended length of spring is 32.25
Stroke is 12.5
Hatch Dead Weight is 58 lbs
Spring LBS each- 67lbs

Here are a couple of pics of my rear galley hatch-

[tony.latham]

I will have to compress the strut about 4" to mount it. Does that sound correct?

No, it doesn't. I think you need shorter struts. I can't imagine what it would take to compress those beasts and get them mounted.





Dan's calculator is great, but I couldn't use the suggested spring length because of the configuration of my countertop and stove location. I just went with shorter springs. Also, my 55-pound hatch needed two 90-pounders.

https://youtu.be/5t_Ujc6oEl0?si=dPtmTgyWvuB9ZcLr


Tony

From my book:

During the planning phase of this design, I used an Excel-based calculator that Dan Lott had specifically created for this task –calculating gas strut lengths and weights for teardrop hatches. You weigh the hatch and put that and its length into the calculator. It suggests the ideal attachment points, length, and weight rating for the springs.

If you do a search on the Teardrops and Tiny Travel Trailers forum (http://www.tntt.com) for “Hatch Gas Spring/Strut Calculator” you’ll find the calculator. For this build, the spreadsheet suggested a 27” gas spring. Using Sketchup CAD software, that length put the lower attachment point below the counter and thus wouldn’t work with my stove installation.

The next shorter springs I found have an extended length of 20.12”. Using Sketchup, I could see that they would work by attaching them above the countertop.

If you are not using my profile and galley layout–and if you don’t do CAD– you can use your template along with a hatch-end profile made from scrap to see what will work. Lay the two templates on the floor and use two sticks to mimic the open and closed strut lengths.
Here’s what the struts look like on this build with both the hatch open and closed:

You’ll note that I have room for my 5’ 9” height to access the galley, depending on the trailer frame height. Also note that the hatch is approaching the hinge’s maximum opening of about 95º.

To determine what spring weight you need, weigh and measure your hatch using Dan Lott’s diagram.

My upper attachment point (on the hatch) is 8-3/16” from the center of the hinge. With previous builds, I’ve used blocking built into the hatch frame. For this build, I made a bump-out on the hatch gusset to bolt the strut bracket to.

To find where to place the lower bracket, I drew two circles. The first was a 20.12” (12-1/8”) radius –that’s the extended length of the struts– from the upper attachment point of the open hatch.

The second radius 12.85” (12-7/8”) is drawn with the hatch closed. The compressed strut is 11.85”. To get that 12.85”number, I added an inch to the compressed strut to keep it from bottoming out during closing. Where these two arcs meet is the lower attachment point. Here’s what it looks like:



I hope this helps.

[JP2023]

Thank you Tony! I will take a look at your notes and see how it works!

[pistolriver]

Hello Tony, I cant thank you enough!!! I installed my hatch struts 3 times before I found your Gas Strut Calculator. I wont go into details as to the advice from experts that lead to 3 failure's, but useing your calculator worked the first time I applied my measurements. I cant tell you the relief I felt the first time I closed the hatch. It even helped pull it closed a little right before it is closed. Now my chore is to patch and hide the holes I made, lol. Thanks again, Good Job!!!

[tony.latham]

I installed my hatch struts 3 times before I found your Gas Strut Calculator.

I'm pleased to hear things worked out, but Dan Lott put the calculator together--not me. I even stole (with his permission) his graphic for my book.

Tony

[Steve E]

Used calculator and after getting dead weight of 50 lbs. is each strut 50 lbs. or is dead weight divided by two
for 25 lbs. each strut because I need two. Thanks

[tony.latham]

Used calculator and after getting dead weight of 50 lbs. is each strut 50 lbs. or is dead weight divided by two
for 25 lbs. each strut because I need two. Thanks

Each strut is 50 pounds. But that sounds low. My hatch is 54 pounds, and I have two 90-pounders.

Tony

[Steve E]

Thanks for your info. just something that was brought to my attention.
Have had my trailer for 20 yrs. and am going to make it easier to open hatch..
Thanks Again