HURRICANE HINGE & GAS STRUT PROBLEM

[Tom&Shelly]

Are your brackets aluminum Todd?

As he mentioned, I've seen them. They're hell-for-stout steel. And his welds don't look like my turkey-dropping globs.

Tony

Wow! 1/8" steel bent by the struts!

Tom

[Aguyfromohio]

That's a nice build it's a shame to see it damaged.
I have only built two hatches with gas struts, but I offer these thoughts.

first, your gas struts seem pretty high force. One of ours has 60 lb struts, the other has 90 lb struts. Yours are 160 lb.
If you move your attach point back from the hinge even a couple inches you may be able to reduce strut forces. Run the spreadsheet again a couple inches back to check.

second, #8 screws seem small. Larger diameter screws like #10, #12, or 1/4 inch have much higher pull out strength.
looking at this table https://www.zillarac.com/Portals/0/Documents/PDF/Screw%20Pull-out.pdf

we see that going up from #10 to 3/8 screws more than doubles pull out strength. Those little #8 screws may be in the wrong weight class for this fight.

Theoretically if you use more screws but smaller screws the system should have equal strength, but real life does not cooperate. Even though ten screws at 100 lbs should be the same as five screws at 200 lbs, the small screws will fail sooner in real life. The phenomenon is called a "zipper failure" (progressive structural failure). One of those screws will fail first because it is in a soft spot, or it's out on the end, or whatever. When it lets go (pop!) the load goes up on all the others remaining, and soon enough the second weakest screw pops. Loads go up one the rest. pop. wait. pop. wait. pop-pop-pop-bang. Like a zipper running down the line. So using bigger screws prevents that first one from letting go. No zipper failure.

There is good reason to stay hopeful and try again. It lasted for while, so you must be pretty close to the failure point, just a bit over the line.
If you can reduce the loads a little and increase the strength a little you will likely move out of that danger zone.

[DWT77]

Thanks everyone for the replies!!!

I will read these a couple of times and look at the teardrop and study which ideas will work out the best.

I feel like it is a combination of a few different things. From re-enforcing the brackets, moving them back further from the hinge pivot point and bigger/stronger screws in the hurricane hinge.

Again thanks for the help

[aggie79]

The discussion was in a post a long time ago, and I can't find it now, but the poster brought up that the traditional orientation of the gas struts causes upward pressure on the hinge, particularly with the hatch in the closed position. If I recall correctly, it was in response to hinge failures/detachments similar to your situation or perhaps it was the hatch lifting up near the hinge when the hatch was closed.

The poster suggested a reverse strut orientation where the mounting point of the strut closest to the bulkhead was on the sidewall instead of the hatch, and the mounting point of the strut farthest from the bulkhead was on the hatch instead of the sidewall. With the hatch closed, this reverse orientation pushes down on the hatch rather than pushing up on the hinge. This seemed to make sense, so it is how I did my struts.

Here's a picture of my galley showing the strut locations/orientation:



As always, there are some trade-offs with design changes. The downsides of the reverse orientation are: (1) when first lifting the hatch, the struts don't "engage" or assist lift until the hatch is partially open, and (2) the longer struts cause more interference with galley cabinets. It's hard to see in the picture, but I had to inset my the upper portion of my upper cabinets to provide clearance for the struts in a closed position.

[danlott]

Since my teardrop is 5' tall my hatch came out to be 65" and 100 lbs for the dead weight. Spreadsheet said I needed 39" springs at 162 lbs of force each (Total 324 lbs). I was able to find 36" springs at 160 lbs so I gave them a shot. (I may have used the mounting locations from the 39" the spreadsheet recommended I don't remember if I converted the numbers or not)

Sorry you are having problems. I do have a few questions?

Looking at your pictures I would think that your attachment points are not correct for the stroke length of your struts. Also the force of the struts looks like it is too high.

What is the stroke length of your struts? What is the distance of the attachment points from your hinge point? Also is the length of your hatch a straight line from your hinge point to the bottom of your hatch or is it the length along the curved surface?

Dan Lott

[Tom&Shelly]

The discussion was in a post a long time ago, and I can't find it now, but the poster brought up that the traditional orientation of the gas struts causes upward pressure on the hinge, particularly with the hatch in the closed position. If I recall correctly, it was in response to hinge failures/detachments similar to your situation or perhaps it was the hatch lifting up near the hinge when the hatch was closed.

The poster suggested a reverse strut orientation where the mounting point of the strut closest to the bulkhead was on the sidewall instead of the hatch, and the mounting point of the strut farthest from the bulkhead was on the hatch instead of the sidewall. With the hatch closed, this reverse orientation pushes down on the hatch rather than pushing up on the hinge. This seemed to make sense, so it is how I did my struts.

Here's a picture of my galley showing the strut locations/orientation:



As always, there are some trade-offs with design changes. The downsides of the reverse orientation are: (1) when first lifting the hatch, the struts don't "engage" or assist lift until the hatch is partially open, and (2) the longer struts cause more interference with galley cabinets. It's hard to see in the picture, but I had to inset my the upper portion of my upper cabinets to provide clearance for the struts in a closed position.

Think this may be what you are remembering, Tom (starting 2 or 3 down the thread on that page): viewtopic.php?f=21&t=58263&start=15

Did you use Dan's calculator to find the attachment points and spring force?

Not to highjack the thread from Wayne, but this may work well for me, in my highly questionable "start building, then design as I go" approach.

Tom

[DWT77]

The discussion was in a post a long time ago, and I can't find it now, but the poster brought up that the traditional orientation of the gas struts causes upward pressure on the hinge, particularly with the hatch in the closed position. If I recall correctly, it was in response to hinge failures/detachments similar to your situation or perhaps it was the hatch lifting up near the hinge when the hatch was closed.

The poster suggested a reverse strut orientation where the mounting point of the strut closest to the bulkhead was on the sidewall instead of the hatch, and the mounting point of the strut farthest from the bulkhead was on the hatch instead of the sidewall. With the hatch closed, this reverse orientation pushes down on the hatch rather than pushing up on the hinge. This seemed to make sense, so it is how I did my struts.

Here's a picture of my galley showing the strut locations/orientation:



As always, there are some trade-offs with design changes. The downsides of the reverse orientation are: (1) when first lifting the hatch, the struts don't "engage" or assist lift until the hatch is partially open, and (2) the longer struts cause more interference with galley cabinets. It's hard to see in the picture, but I had to inset my the upper portion of my upper cabinets to provide clearance for the struts in a closed position.

Tom I do see how that design makes sense. I think that is how they do hard tonneau covers? I think my cabinets would get in the way though

[DWT77]

Since my teardrop is 5' tall my hatch came out to be 65" and 100 lbs for the dead weight. Spreadsheet said I needed 39" springs at 162 lbs of force each (Total 324 lbs). I was able to find 36" springs at 160 lbs so I gave them a shot. (I may have used the mounting locations from the 39" the spreadsheet recommended I don't remember if I converted the numbers or not)

Sorry you are having problems. I do have a few questions?

Looking at your pictures I would think that your attachment points are not correct for the stroke length of your struts. Also the force of the struts looks like it is too high.

What is the stroke length of your struts? What is the distance of the attachment points from your hinge point? Also is the length of your hatch a straight line from your hinge point to the bottom of your hatch or is it the length along the curved surface?

Dan Lott

Dan I took some pictures and will try to be detailed so hopefully we can find out where I went wrong.

You mentioned stroke length that got me to thinking about the spreadsheet. I'll get back to that in a minute but first here are my measurements for the hatch

Also is the length of your hatch a straight line from your hinge point to the bottom of your hatch or is it the length along the curved surface?
I took the measurement in a straight line.



I tried to do the dead weight again because now I want to re-check everything but with the hinge not secure now I was having an issue with it and not sure if the weight I was getting was correct.
So for now lets stay with the 100 lb dead weight (I will double check when I get the hinge back on)

So on to the spreadsheet. When I filled out the spread sheet I used the above numbers. It came back with this


I couldn't find 39" but I did find 36"
I ordered these gas springs
https://www.amazon.com/gp/product/B007M ... UTF8&psc=1
Extended Length: 35.43" (900mm) (center to center of ball socket ends)
Compressed Length: 19.29" (490mm)
Stroke Length: 35.43 - 19.29 = 16.14"
Force: 80 lbs (356 N) (Total = 160 lbs)
End Fittings: 10mm nylon ball sockets

I made the distance of the bracket attachment point to the hinge point as close to 13.72" as possible

I had the hinge secured and screwed in. Then I measured on the outside of the hatch rib 13.72" Then I marked it with a pencil (this was before I had everything painted) Then I transcribed that on the inside of the gusset using a square. I took some pictures just now for reference.


Then transcribed it to the interior side of the gusstet


I got the gas struts from above installed and the hatch would not stay up. As soon as I let go it fell.

So I was like well maybe I am just off a little bit either on measurements or something so I tried these struts. Which are 90 lbs instead of 80 lbs
https://www.liftsupportsdepot.com/lift- ... t-support/
Extended Length: 36.00
Stroke C [in]: 15.20
Compressed Length B [in]: 20.75
Force (Lbs): 90

The same thing happened. The hatch just fell when I let go of it.
Now I am thinking ok I did something wrong.
I went back to the spreadsheet read it again and looked it over.
I changed the number of springs to be used to 1
The required force in gas springs changed to 312 lbs of force
I was like oh ok the spreadsheet is for each gas spring needs to be the 162 lbs not a total. Which this made sense because even at 2 springs @ 90 lbs each (Total 180 lbs) my hatch still wouldn't stay open

So then I bought these gas springs (Which were the ones installed when the hinge failed)
https://www.liftsupportsdepot.com/lift- ... t-support/
Extended Length: 36.00
Stroke C [in]: 15.20
Compressed Length B [in]: 20.00
Force (Lbs): 150

Which is a total of 300 lbs and is not as much as the 324 lbs the spreadsheet said I needed. (So I think anyways if I did everything correctly)


With all of that said it brings me back to the stroke length you asked about.
The original stroke length on the first set of gas springs was 16.14"
The ones for the last gas springs that failed were 15.20"
I never entered the 15.20" back into the spreadsheet to change the bracket attachment points. (I did change the bracket position a little after they broke loose the first time so not to use the same screw holes)

That is right at 1" bracket mounting difference.

Did I input all of the numbers correctly?

Did I interpret the spreadsheet correctly?

I hope all of that made sense. Please let me know if I need to clear anything up.

Thanks for the reply and the help!!

[Tom&Shelly]

Since my teardrop is 5' tall my hatch came out to be 65" and 100 lbs for the dead weight. Spreadsheet said I needed 39" springs at 162 lbs of force each (Total 324 lbs). I was able to find 36" springs at 160 lbs so I gave them a shot. (I may have used the mounting locations from the 39" the spreadsheet recommended I don't remember if I converted the numbers or not)

Sorry you are having problems. I do have a few questions?

Looking at your pictures I would think that your attachment points are not correct for the stroke length of your struts. Also the force of the struts looks like it is too high.

What is the stroke length of your struts? What is the distance of the attachment points from your hinge point? Also is the length of your hatch a straight line from your hinge point to the bottom of your hatch or is it the length along the curved surface?

Dan Lott

Dan I took some pictures and will try to be detailed so hopefully we can find out where I went wrong.

You mentioned stroke length that got me to thinking about the spreadsheet. I'll get back to that in a minute but first here are my measurements for the hatch

Also is the length of your hatch a straight line from your hinge point to the bottom of your hatch or is it the length along the curved surface?
I took the measurement in a straight line.



I tried to do the dead weight again because now I want to re-check everything but with the hinge not secure now I was having an issue with it and not sure if the weight I was getting was correct.
So for now lets stay with the 100 lb dead weight (I will double check when I get the hinge back on)

So on to the spreadsheet. When I filled out the spread sheet I used the above numbers. It came back with this


I couldn't find 39" but I did find 36"
I ordered these gas springs
https://www.amazon.com/gp/product/B007M ... UTF8&psc=1
Extended Length: 35.43" (900mm) (center to center of ball socket ends)
Compressed Length: 19.29" (490mm)
Stroke Length: 35.43 - 19.29 = 16.14"
Force: 80 lbs (356 N) (Total = 160 lbs)
End Fittings: 10mm nylon ball sockets

I made the distance of the bracket attachment point to the hinge point as close to 13.72" as possible

I had the hinge secured and screwed in. Then I measured on the outside of the hatch rib 13.72" Then I marked it with a pencil (this was before I had everything painted) Then I transcribed that on the inside of the gusset using a square. I took some pictures just now for reference.


Then transcribed it to the interior side of the gusstet


I got the gas struts from above installed and the hatch would not stay up. As soon as I let go it fell.

So I was like well maybe I am just off a little bit either on measurements or something so I tried these struts. Which are 90 lbs instead of 80 lbs
https://www.liftsupportsdepot.com/lift- ... t-support/
Extended Length: 36.00
Stroke C [in]: 15.20
Compressed Length B [in]: 20.75
Force (Lbs): 90

The same thing happened. The hatch just fell when I let go of it.
Now I am thinking ok I did something wrong.
I went back to the spreadsheet read it again and looked it over.
I changed the number of springs to be used to 1
The required force in gas springs changed to 312 lbs of force
I was like oh ok the spreadsheet is for each gas spring needs to be the 162 lbs not a total. Which this made sense because even at 2 springs @ 90 lbs each (Total 180 lbs) my hatch still wouldn't stay open

So then I bought these gas springs (Which were the ones installed when the hinge failed)
https://www.liftsupportsdepot.com/lift- ... t-support/
Extended Length: 36.00
Stroke C [in]: 15.20
Compressed Length B [in]: 20.00
Force (Lbs): 150

Which is a total of 300 lbs and is not as much as the 324 lbs the spreadsheet said I needed. (So I think anyways if I did everything correctly)


With all of that said it brings me back to the stroke length you asked about.
The original stroke length on the first set of gas springs was 16.14"
The ones for the last gas springs that failed were 15.20"
I never entered the 15.20" back into the spreadsheet to change the bracket attachment points. (I did change the bracket position a little after they broke loose the first time so not to use the same screw holes)

That is right at 1" bracket mounting difference.

Did I input all of the numbers correctly?

Did I interpret the spreadsheet correctly?

I hope all of that made sense. Please let me know if I need to clear anything up.

Thanks for the reply and the help!!

Hi Wayne,

I wonder if you need to take the entry at C32 in Dan's calculator and set it to the actual distance of the hatch mounting point from the hinge? Since you are using the answer from G26, it should be set to that value (I think). That yields 130 lbs per strut, vs the 162 lbs you are getting. Might make the difference...?

Dan, please tell us if I'm wrong!

Tom

[DWT77]

Hi Wayne,

I wonder if you need to take the entry at C32 in Dan's calculator and set it to the actual distance of the hatch mounting point from the hinge? Since you are using the answer from G26, it should be set to that value (I think). That yields 130 lbs per strut, vs the 162 lbs you are getting. Might make the difference...?

Dan, please tell us if I'm wrong!

Tom

Tom that may very well be a big part of the equation/problem I made

[danlott]

I wonder if you need to take the entry at C32 in Dan's calculator and set it to the actual distance of the hatch mounting point from the hinge? Since you are using the answer from G26, it should be set to that value (I think). That yields 130 lbs per strut, vs the 162 lbs you are getting. Might make the difference...?

Yes you should have entered the "Ideal Spring Attachment to Hinge Center Point in Inches" that is in G26 into the C32 cell as shown below.



Since your attachment point is already at 13.72" that is the value I entered into C32 instead of 12.92 which is the ideal attachment point for the stroke length that you have.

This gives you a value of 130 lbs per strut as Tom noted in his post. As a side note if your attachment point was at 12.92" the value would be 137 lbs per strut.

I see a few issues. The first is that the struts that did the damage to you hatch have too high of a force rating. Also the attachment point of 13.72” instead of 12.92” will cause your struts to be compressed greater than the ideal. Gas struts should ideally only be compressed 85%. Assuming that your lower strut attachment point inside of the gallery wall is 36” from the hatch hinge point and your upper strut attachment point on the hatch is 13.72” from the hinge point than your struts would have been compressed to 91% which would have also placed a greater force on your attachment points and galley hinge.

It is very important to know the true dead weight of your finished hatch. The dead weight and overall length will then help you determine the ideal strut length. Once your find struts that are as close as possible to the ideal length you have to determine what the stroke length of those struts are. The stroke lengths of the struts that you are able to find will then give you the ideal upper attachment point of the strut. After you enter the ideal attachment point into cell C32 the spreadsheet will give you the required force for each gas strut. The lower gas strut attachment point should be equal to the overall length of the struts that you end up buying.

It is a little confusing since there are several variables that go into calculating the proper strut force and placement. A change in anyone of the variables affects all the other variables.

I am sorry that you have had these issues. Once you have fixed your hinge and can determine your correct dead weight of your hatch I will assist you as much as possible to located the correct rated struts and the ideal attachment points. You can PM me and we can figure this out together.

Dan

[KTM_Guy]

I just found the pictures of the problem I had. I made brackets out of 1/8" angle. And after a few weeks I could see it was bending. Then after a rain and not being in the galley for a few weeks I found this. Not to bad, the top of the cabinet is pulling up. This was the drivers side.



This is the other side. This was a pain to fix.



My solution, over build out of 3/16" flat bar. The old one is next to it, and you can see it is bent.



This is the inside of the cabinet. So far so good.



I don't have any pictures of the hatch side but I mad those out of 1/8" angle. I'm going to remake those to just to be safe. I'll try to get some pictures tomorrow.

I need to paint them or take and get powder coated.

Todd

[Tom&Shelly]

I just found the pictures of the problem I had. I made brackets out of 1/8" angle. And after a few weeks I could see it was bending. Then after a rain and not being in the galley for a few weeks I found this. Not to bad, the top of the cabinet is pulling up. This was the drivers side.



This is the other side. This was a pain to fix.



My solution, over build out of 3/16" flat bar. The old one is next to it, and you can see it is bent.



This is the inside of the cabinet. So far so good.



I don't have any pictures of the hatch side but I mad those out of 1/8" angle. I'm going to remake those to just to be safe. I'll try to get some pictures tomorrow.

I need to paint them or take and get powder coated.

Todd

That looks like a good fix that will transfer the load to the wall, so it doesn't bend the counter Todd. So, from the direction the counter bent, it looks like the attachment point on the counter is closer to the hinge than the attachment point on the hatch, so that the strut, when the hatch is closed, is pushing toward the bulkhead and up? Is your configuration similar to Aggie79's (Tom's) in that way, as he showed earlier in this thread?

With that configuration, I think an adjustment may be necessary to Dan's spread sheet (or at least in how we use it). I was going to ask him about this in a PM, as my hatch build got further along, as I too, am now thinking about building with that strut configuration. His spread sheet assumes the attachment point on the hatch is closer to the hinge than the center of mass, and it computes the strut force using that ratio. Reversing the attachment points, the attachment at the hatch will be further from the hinge than the center of mass, and so less force on the strut should be required (if I understand the mechanics correctly). Dan, once again, please correct me if I'm wrong.

If in fact, one uses the calculator for the original configuration, and then simply reverses the attachment points for the hatch and galley wall (or counter), I think the strut force the calculation yields will be too strong.

Tom

[aggie79]

Did you use Dan's calculator to find the attachment points and spring force?

Tom

Tom, I didn't use the calculator. I did the "Kentucky windage" method of lifting the hatch, guessing the weight, and dividing that weight by two (one for each side). This gave a rough starting point for the strut rating. The first set of struts were too light, the second were too strong, and the third set was just right.

The calculator may eliminate the guesswork and expense, but given my experience, I would also consider a strut length that is available in a range of strut ratings. If you have to increase or decrease the rating, you don't want to also have to move the mounting points.

[tony.latham]

The first set of struts were too light, the second were too strong...

Did you get them from McMaster? They haven't blinked on returns in the past.

T