Gripenland

KAP, your argument doesn't apply on Viperfitness1 seats. Since they are belt-in-seat. You will not compress the spring when putting tension on the shoulder straps. All the belt fixations are "above" the spring.

Not sure if I make any sense?

With the correct spring and damper settings the above design will reduce forces on the spine.

Catmando

How would that design translate to a pleasureboat?

kap328

Comment:

Your spine is not static it will move....how do you control the g force on rebound exerted by the spring.

Where is the data on the seat? Using a ATV shock absorber on a metal frame with a rigid tub fiberglass/carbon fiber seat needs further analysis.

If your going to simply conclude that my prior post doesn't apply back it up with data and facts. I could build you one rather quickly out of square tube and use a Elka shock with preload and rebound compression adjustments. It doesn't mean it will be good for you to use!

In addition, anytime you have movement in the seat in rough environments you are moving the person in and out of the restraints. If you add another variable... holding on to the steering wheel in rough seas going up and down in a seat... it seems like a chore in and of itself and that is being diplomatic.

I would rather have someone take me through the data/analysis than conclude straight from A to Z that it works. If thats the case every Trophy truck team in town would adopt such seating arrangements. Lest you forget the Baja 1000 is a extremely long race with lots of unpredictable g forces upon the driver and co-driver. Far more than anything in a boat and for a longer distance...hours of WOT.

KAP

P.S. I don't think you can adjust a spring to absorb the compression and rebound effect on the big stuff....not without causing injury. I could be wrong but I wouldnt bet my back on it.

onesickpantera

iTrader: (1)

You guys are talking WAY over my head here but I can comment on what controls the rebound of the spring. The shock does that. The rate the shock compresses AND rebounds is controlled by valving and spring pre-load, rate, etc. It's not like the spring violently rebounds. It would be similar to the swingarm shock on a dirt bike or a rear track shock on a sled.

I can kind of put my head around what kap328 is saying. But my simple mind thinks of how my sled's rear suspension works. It compresses over bumps and obviously rebounds, both of these rates are based on spring and shock settings. I then try and picture riding with no suspension at all and it seems like the violent hits of no suspension would compress the spine far more than the rebound of the suspension.

Maybe I am way off? Like I said I have a simple mind!

Gripenland

KAP, obviously my post didn't make any sense so I'll try again.

Your argument is valid if you have a suspension seat with belt fixations in the walls and/or floor i.e fixations that doesn't move with the occupant. With that type of arrangement it is possible to pre load the spine when tensioning the shoulder belts.

But with the set up above it is not possible to pre load the spine with the spring no matter how hard you pull the shoulder belts. That is a fact.

I agree that the spring and damper needs correct performance to minimise forces on the spine.

Most of the current biomechanical data regarding spinal compression comes from the US military. More specificity from helicopter seats designed to prevent spinal injury in case of a crash. Some of this data is public. But it is also based on data from young men in excellent physical condition so it is natural to assume that that average Joe will have a lower g-force threshold.

I need to check the the actual limits since I don't trust my my memory...

But for the sake of argument let's say that the limit is 10G.
The use of Newtons second law give us a force that needs to be matched by the spring damper system.

The mass of the seat and occupant= M

Mx10G= F
F is the maximum force the spring and damper should generate in an compression.
Some additional math will give recommended values for the spring and damper.
I'll check some data and we can do the math in this thread if that is ok?

What type of spinal fractures are common in off-road racing? Burst, wedge or flexion and distraction?

Viperfitness1

Kap, Thank you for taking time to offer a valid concern. However i believe you are comparing apples to oranges with suspension seats previously used in off road truck racing. Maybe you should send those guys a link to this thread so they can see how i have solved the issues you are describing with shock absorbing seats.

IMO gripenland is on the right track on how to make the upper half more rigid in the event of a sudden stop in any direction. i like the idea of cold rolled steel tubing for the framing and is the direction we are headed...

In my short career as a boat racer i have figured out one thing. You CAN NOT strap yourself to a rigid seat in a vee bottom boat @130 mph and hit a set of 6-8 footers and expect your back to absorb the impact. It is physically impossible. Trust me!

Safety is and will remain the top priority in our program. But absorbing the shock of waves the boat impacts under high speeds is a MUST for powerboating safety! and thats the bottom line.

Gripenland

I have crash tested a few belt-in-seats in my career. Both with and without shock absorbing.

All of them has failed the first test due to strength issues. Failed hinges, failed seat belt fixations, failed floor fixations and so on.
And they have been seats made by large seat manufacturers...

The forces are a lot higher then you might think so a shock absorbing seat will be heavy.

If the seat and frame are not strong enough the seat belt will only create a false sense of security.


If it was me who were building a shock absorbing seat I would:

• Use a metal frame. Robust, cheap, easy to change and strong.
• Test the strength by pulling the seat fixation points.
• When the frame is strong enough to pass the pulling test I would bring out the drill and drill a few holes to reduce weight.
• Test it again, drill some more holes, test, drill, test, drill and so on

But that is just me. There are many ways to build and test a seat. Just sharing some thoughts on the subject.

bwd

iTrader: (1)

I love a post with good knowledgable points made about interesting subjects. Hey Vipe, update this thread when you start running, especially in the rough stuff. Hope it all makes for a better ride while you're whaling the tar out of the whole package.

kap328

Hello Viperfitness:

In automotive racing you have about 5.5g of lateral force constantly on a driver in oval tracks. In off road racing you have various loads on the driver and co-driver in excess of 6g's both in flexion and compression type situations.

This brief video demonstrates what types of forces I was talking about. The vehicle has tub style seating with minimal padding...typically Sparco or same or similar seating.

Baja 1000 is 1000miles in about 18 hours....brutal IMO.

Let me know when you get one of those seats into a Trophy truck.

[YOUTUBE]http://www.youtube.com/watch?v=88rkNR_n9_0[/YOUTUBE]

This video demonstrates the rebound and compression forces they contend with in one race. Try that with your suspension seat you really would not make it past the first jump.....and or be in control of the truck.

Good luck on your endeavor.

KAP

P.S. I really considered suspension seats for my boat but everything I researched indicated I would be far better with a kevlar/carbonfiber tub style seat.

As for the best suspension seats for a v-bottom.. they are your legs...take a look at some of the Mc Manus Apache videos. The crew in the boat is standing up.

prostock85

As a complete outsider, I don't know how you can compare the two. The trucks have a suspensions, boats don't. If those trucks has both a truck and seat suspension, many times they would be out of sync making it nearly impossible to drive, but in a boat, the only minor give you would get is through the viscosity of the water. I think the idea of a suspension seat in a boat is a great idea....in a Baja truck, not so much.

I see how a trophy with seat suspension could be at opposite ends on both their available travel but not in a boat. In layman's terms, I think you are describing what its like to jump on a trampoline that someone else is jumping on. Sometimes it can launch you higher, and other times it can buckle your knees, or even stop you dead.