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 Installing gas hatch supports
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norman

Canada
362 Posts

Posted - May 01 2007 :  09:50:58  Show Profile  Reply with Quote
It's time for me to install those gas supports to my engine hatch (lifting this thing is killing my back). Is there some kind of 'formula' on what size support to use? Where do you install them in relation to the hatch itself? i.e. the middle of the hatch or closer to the front or somewhere in between?

It's difficult to tell how much weight I'm lifting but I can tell you it's one of those hatches that also lifts the stern bench and the whole thing is heavy.

The hatch lifts from front to rear and is the entire width of the cockpit.

The boat is a '92 Doral Prestancia.

Anybody ever done anything like this?

Thanks,

Norm

PJS

USA
156 Posts

Posted - May 01 2007 :  12:47:41  Show Profile  Reply with Quote
I just finished a project with the gas springs but on a much smaller scale. I put them in some overhead cabinets to help lift and hold them open. They were fairly heavy doors and I used 35# springs so you are probably looking at something much more substantial. I went through a trial and error method starting with the known maximum closed spring length I had to work with (based on the size of the door) and how much stroke I needed to get them to an acceptable open position. Then I bought a gas spring based on my estimates and tried it. I had to return the first one I tried (stroke wasn't quite long enough and the door wouldn't close). That gave me a much better understanding of the size I needed. Unfortunately for me it was very hard to find the right size, I ended up ordering them from an engineering firm in California. It took awhile but was well worth it, my wife no longer complains about having to lift and hold those doors open.
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rommer

13309 Posts

Posted - May 01 2007 :  13:15:37  Show Profile  Reply with Quote
I've tried to get this information in the past and it seems to be a closely guarded secret! Couldn't find anything that made sense but still willing to learn how.



Boats, yup, 5 of em...
WLC - We love Champlin's!
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LouC

1628 Posts

Posted - May 01 2007 :  16:24:09  Show Profile  Reply with Quote
Try e-mailing the manufacturer of the boat, they may be able to tell you what they used originally. I did this with my 88 Four Winns when I got tired of lifting up the sunpad. I used 2-60 lbs units.

1988 Four Winns 200 Horizon 4.3 OMC Cobra
1998 Jeep Grand Cherokee 4.0 Selectrac
2007 Jeep Grand Cherokee 5.7 Hemi Quadradrive II
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jav1

USA
492 Posts

Posted - May 01 2007 :  16:53:33  Show Profile  Reply with Quote
Norman,

sorry man but there is no simple formula, you have to engineer each application. If you care to understand why it's because the gas springs will usually travel in a straight line while the object being lifted is pivoting. The force the gas spring actually exerts on the object is related to the hinge point of the hatch, base mounting point for the gas spring and moving point that the gas spring pushes against. The gas spring force is essentially constant but the resulting force applied to "lifting" is related to the angles of the 3 mounting points... and to complicate matters, one of those points is moving which causes all the angles (and resulting force) to change as the hatch opens. Also, the hatches orientation to gravity opened and closed effects how you mount the spring, as does the hatches length and the springs working travel. It's actually a fairly involved process.

If you tell me your hatches size and weight, I can try to run some calcs and let you know what options you might have. I deal mostly with smaller gas springs (under 120# of force and 12" of working travel). I'm sure there are larger units which may work but lifting a large horizontal hatch will reguire a fairly low mounting point... which can be problem depending on where the engines are.

J Viveiros

Edited by - jav1 on May 01 2007 17:01:18
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abalmuth

USA
5551 Posts

Posted - May 01 2007 :  17:06:32  Show Profile  Reply with Quote
jav1
sounds like you know this stuff - quick question
I had 3- 40lb(120lb total) gas spring lifting/holding the hatch to my bridge
One is now missing and the other two are bent from being forced
If I replace the 2 outbound with 70lb each is that too much?

_
Cruisers 5000 Sedan Sport/CAT 12LTR's -
Light travels faster than sound. This is why some people appear bright
until you hear them speak.........
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norman

Canada
362 Posts

Posted - May 01 2007 :  19:11:05  Show Profile  Reply with Quote
Thanks for the info. This is going to be trickier than I thought.

Jav1 I understand what you're saying (sort of). The tricky part, it seems to me, is installing the supports where a) they will close properly when the hatch is closed and b) provide the lift necessary to open the hatch easily. Obviously, the length of the supports and where the two ends of each support are mounted is critical. Finding those points doesn't sound easy, especially since you're working with the support in the fully extended postion and can't retract it.

I'll be at the boat in the next day or two and grab as many measurments as I can.

Thanks again,

Norm
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jav1

USA
492 Posts

Posted - May 02 2007 :  11:19:06  Show Profile  Reply with Quote
abalmuth-
without seeing the arrangemet, the best I can say is- as long as the mounting points for the 70# springs will support the load in shear, it should work. Keep in mind that both the hardware and the material supporting the hardware will be subject to this force continuously and, the forces will spike at the end of the spring's travel due the hatches inertia decelerating to a stop. If your existing springs are bending, there is something else wrong. A pic would be helful.

Norman,

the mounting points are tough to figure out... unless you have a CADD system. If you get me some pics and some dimensions, I should be able to help. Keep in mind that in your case, your looking to minimize the force it takes to open the hatch from a horizontal position, and then ot keep it in a vertical position. The force needed will be high initially, and decrease as the hatch opens. This means the spring will need be close to vertical with hatch closed so that all the spring force is pushing straight up. I'd need to see what kind of room you have available on the sides of the hatch from about the hing point to the hatch mid point. Pics are always helpful.

J Viveiros
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abalmuth

USA
5551 Posts

Posted - May 02 2007 :  11:48:12  Show Profile  Reply with Quote
quote:
Originally posted by jav1

abalmuth-
without seeing the arrangemet, the best I can say is- as long as the mounting points for the 70# springs will support the load in shear, it should work. Keep in mind that both the hardware and the material supporting the hardware will be subject to this force continuously and, the forces will spike at the end of the spring's travel due the hatches inertia decelerating to a stop. If your existing springs are bending, there is something else wrong. A pic would be helful.


John
Does this help

_
Cruisers 5000 Sedan Sport/CAT 12LTR's -
Light travels faster than sound. This is why some people appear bright
until you hear them speak.........
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jav1

USA
492 Posts

Posted - May 02 2007 :  13:54:35  Show Profile  Reply with Quote
Yes- it does. I presume the other gas springs were mounted right next to those in tandem? The ideal would be to use 4 again- as this would desperse the load and help with dampening but, 2 stronger springs should work as far as offsetting weight.

Just so you know -those springs are mounted in a common way... but it's not the recommended way. The ram (the arm that telescopes in and out of the body), should be pointing down (not up as they are). This keeps what little lubrication there is inside the spring body in contact with seals and some believe (as I do) that it extends life.

J Viveiros
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abalmuth

USA
5551 Posts

Posted - May 02 2007 :  14:03:30  Show Profile  Reply with Quote
quote:
Originally posted by jav1


Just so you know -those springs are mounted in a common way... but it's not the recommended way. The ram (the arm that telescopes in and out of the body), should be pointing down (not up as they are). This keeps what little lubrication there is inside the spring body in contact with seals and some believe (as I do) that it extends life.

John
thanks for your feedback!
I will also mount the new spring pointing down ;-)

_
Cruisers 5000 Sedan Sport/CAT 12LTR's -
Light travels faster than sound. This is why some people appear bright
until you hear them speak.........
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jtybt15

USA
24401 Posts

Posted - May 03 2007 :  01:19:07  Show Profile  Reply with Quote
It may or may not be applicable for all cases but I mounted the gas 'springs' in a way that both mounting points would pass the horizontal in the closed position so there would be a positive closing force on the hatch.




Charlie

There is much to be said, in a world like ours, for taking the world as you find it and fishing with a worm.-Bliss Perry, 1904


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sclancypb

USA
53 Posts

Posted - Feb 21 2008 :  18:31:30  Show Profile  Reply with Quote
I m trying to retrofit gas supports for fish box lid! JAV1 can you help?? Check out my fish box support thread under detailing and fabrication.
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Flutterby

USA
16143 Posts

Posted - Feb 21 2008 :  19:04:42  Show Profile  Reply with Quote
Norman, I believe Rinker did what you want on their boats. Check them out at a boat show or a dealer near you. Or check their website???? I had a boater friend with a 27 ft Rinker five years ago with that arrangement. They got out of boating when they had kids and sold the boat.......
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Ultra

USA
14 Posts

Posted - Feb 21 2008 :  22:00:03  Show Profile  Reply with Quote
There is information on calculating gas springs at the McMaster Carr web site mcmaster dot com. under the find products type gas springs. there "about gas springs" is very informative.

Edited by - Ultra on Feb 21 2008 22:00:53
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sclancypb

USA
53 Posts

Posted - Feb 22 2008 :  11:52:37  Show Profile  Reply with Quote
thanks ultra. i ll check it out.
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jtybt15

USA
24401 Posts

Posted - Feb 22 2008 :  12:15:27  Show Profile  Reply with Quote
Clancy,
For your application there is very little need for 'indepth calculations'. All you need is gas springs strong enuff to hold the lid open. Maybe 10 lbs max. Too strong a spring affects the mounting point which I suspect is plastic in your case. It also may allow the top to pop up all by itself or during rough water or flapping fish.

I replied to your other post.




Charlie

There is much to be said, in a world like ours, for taking the world as you find it and fishing with a worm.-Bliss Perry, 1904


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Flutterby

USA
16143 Posts

Posted - Feb 22 2008 :  13:42:30  Show Profile  Reply with Quote
I have a hatch similar to his and it is made of fiberglass and very heavy! I can prop it open, but not remove it. Mechanics [men] usually remove the thing when working on my engine.
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