Insane idea for catamaran suspension system

I would use numerous epdm rubber straps (one for each 7 or 8 lbs of suspended weight, individual breaking strength >50lbs) to suspend the crossbeams from the posts coming up from the hulls. The bridgedeck or bridgedeck cabin would be suspended from the crossbeams using a similar method. Hopefully these sketches will portray the concept. Just quick sketches to get the idea across so no need to tear the idea apart based on the sketches. The hull and crossbeams would be allowed very little lateral/rotational movement relative to each other in that plane, but the crossbeams would be allowed fairly free rotation relative to the hulls in side view, thus allowing the hulls to ride up and down waves independently. There is an assumption that there will be little force in the longitudinal direction for the hulls relative to the crossbeams so little accommodation need be made for this motion, but more straps on the front and back can be added for controlling this if necessary.
I've looked at other suspension ideas but none of them allow flexibility in every plane.

I understand that the weight suspended will stretch the top straps and slacken the bottom straps, so more straps would be added to the top than bottom. Assuming 700lbs suspended that would be about 100 top straps dived between the 4 hull posts.

The whole idea is to increase comfort, reduce structural loads, and increase efficiency moving across waves.

Epdm is known for having good UV resistance.

Stupid or genius? Has anyone experimented with anything like this?

 

Hi dustman, it seems workable to me, unqualified to say anything, but I wonder about rubberised connections setting up harmonic issues, and to a lesser degree, variability in overall hull geometry causing handling issues when flexing, making quirky reactions. Keeping an eye on strap deterioration would have to be be continuous. It could be genius. Try it on a model with weak rubber bands, to see what happens.

 

Power cat or sailing cat?

 

Looks like 4 independent suspension, with quite a bunch of resonnant mode to handle. Jet-ski or speed boats addicts really like being rocked in every direction, and it's maybe ok for them like this.

Otherwise, why don't you consider coupling the suspension by pair, either by hydro-pneumatic pumps, or by rigid links, coupled with the platform by only two longitudinal cylinders ?

Anyway, i think your Idea IS excellent to have some more fun on the water. Here is another concept that I like. Simplicity... Crazyness.... Sexyness...

 

Sailing cat.

 

Rubber is fairly self damping, almost like a spring and shock absorber in one. But that is definitely something to consider and test. By hull geometry you are meaning the geometrical relationship between the two hulls, or put more simply, their alignment with each other? I had considered this as well, and came to the conclusion that the hulls would stay aligned longitudinally unless subjected to large non-symmetrical loading like a breaking wave impact on the front quarter. In a condition like that I'm thinking a temporary misalignment would be a small price to pay for the shock absorbing qualities in such a situation. Just to clarify, there would be only two hulls, not four.

Yes, I'm thinking they would need to be replaced once a year, at a cost of $200-300. Would most certainly be keeping an eye on them. The advantage of multiple small elements would be that the failure of one or even a few would not be catastrophic and would be an indicator of the need for replacement, and they could be replaced underway due to the small loads in each element and the way they would be mounted.

I plan on incorporating this design into my smaller hobie 16 sized test boat.

 

You think that would be an issue at the lower speeds of a sailing vessel? Rubber is somewhat self damping so I wasn't really concerned about resonant oscillations, like on a car with bad shocks. I'm envisioning more of gently flowing over the waves, the hulls moving up and down, but the suspended bridgedeck moving gently.

I'm having trouble envisioning exactly what you mean. The suspension pair on each side would be coupled by the rigid hull. Each hull would be able to move independently but would be held in longitudinal alignment with each other. Here is my original concept drawing, but the layout of the straps has been significantly altered, eliminating unnecessary straps and changing they way they are mounted and aligned, but it may give you better idea of the concept.

What a crazy contraption! Looks like fun for a bit but I prefer gentle cruising and taking the time to appreciate the wonders of nature and water rather than doing battle with it. I guess that's the basis of my concept, to work with the water rather than against it.

 

Seems like several degrees of complication to achieve a boat that won't perform.If the boat is of sufficient size just install truck seats with inbuilt damping.A sailing boat need stiffness to perform well and responsively.Wharram disciples may argue if they wish.

 

Not sure why it wouldn't perform? As long as the hulls stay aligned I would think it would perform better by conforming to the waves rather digging or bashing through them. I understand the responsiveness thing, but isn't it a good thing to dampen sudden accelerations, like from a wind gusts or whatever else?

I think James Wharram and Hanneke Boon are geniuses with an excellent understanding of what makes a good and safe sailing boat, but perhaps a little too mired in tradition. I know I have learned a great deal from them.

 

Full suspension catamaran video
Already been built

 

The one in the video is only suspended in the vertical plane, and requires strong and rigid mounting to handle loads in the other planes.

 

The suspension covers pitch and roll.
Doubtful Heave, Sway, Surge and and Yaw are significant in a planing hull

Heave, up and

1. Pitch describes the up and down motion of a vessel. This is characterized by the rising and falling of the bow and stern in much the same way as a teeter-totter moves up and down.
2. Roll is how we describe the tilting motion of the ship from side to side. Wind and waves push against the ship and cause it to rock back and forth.
3. Yaw spins the ship on an invisible middle line similar to swiveling on a chair. This can be caused by waves moving in perpendicular to the motion of the ship and can change its heading, or direction.
4. Heave defines the up and down motion of a ship in large swells. (their system accommodates this)
5. Sway this sliding motion occurs when the hull of a ship is pushed by the wind or current.
6. Surge occurs with following large swells, which can push the vessel forward and impact the front to back motion of the ship. (similar to pitch- not significant in a higher speed boat)

 

Think again!


You should read the article "Essentials of Catamaran Structure Designs" Proboat Magazine, Dec/Jan 2020, issue 182.

 

James Wharram designed a good system in the 60's. Those boats are still being sailed and built.

 

By that you mean the way the the crossmembers are lashed to the hulls?