Boat suspension

O.......K.........

Not sure what you mean. I watched this and got smarter:

And the discussion about rake on a bicycle fork adding stability makes sense. I know (I've felt) how that works.

But what are you proposing in this context? Add a swivel above the top bracket of the U joint? Just incorporate a pre-made caster into the design?

Or are you talking about a fixed caster? I don't see what advantage that would offer. That's sort of the current design.

So if you had a caster joint above and a U-joint below--OK, so now you have free pitch, roll, and yaw (and yet the thing somehow holds together). The point of all this being to unload any temporary forces imparted by impacting waves at various funny angles.

I think I see, maybe. But if you do that I think you definitely want stops of some sort.

I mean, you have to offer some resistance and fixedness somewhere. We already have free pitch and roll, and sprung and damped heave. We could allow some free sway, too. I suppose. Not suggesting this, as I don't see it as an issue. Yes, you'll face some yaw and sway forces, but nothing like pitch and roll. Heave is I think the main one, in terms of its magnitude and amplitude (this is intuition, I haven't seen data). So that's the one you want to focus on--not eliminating, but constraining.

You don't care if a float pitches way up or down, or rolls through big angles. Doesn't impede forward progress. You DO care if it yaws or sways, because you want it to track straight. You have a larger vessel to attach it to. It's easy to lock in so it ain't going anywhere. I think I still favor that.

 

My proposal is only to move your swivel brackets forward .At least further than half of the float longitudinally to achieve pulling of the float rather than pushing float. To eliminate yaw twisting.

 

Ah, but that would put my CG out in front of my step. Instant nose down. CG is already pretty far forward as it is. I could move the step even further forward, ahead of midships, but that would seem to want a deeper, longer concave bottom "cutaway" to maintain unwetted length on the aft bottom, which is one of the main purposes of the step. Plus, moving the step forward wouldn't set up the kind of "trailing behind," caster, yaw-reducing action you seek. You'd have to move the attachment points even further forward, to keep in front of the step. Not good. Can't be done, that I see.

Many people (OK, two) think I am nuts for allowing free pitch. They want me to lock it. One CAN, of course. What the current model does, hypothetically, is put a guy (load) in a boat (float) with no attachment to anything. To get the boat to float and travel level or at whatever trim angle I want, I have to arrange the load correctly both longitudinally and transversely. I have to account for the fact that at speed, the boat's riding ideally on a line a bit in front of midships, with enough weight aft that I have some transom loading right in front of the transom. Two stagnation lines, as Barry pointed out in the "50 knots" thread. Maybe 3/4 of the weight and lift on the step.

I don't have to do this. I can lock in pitch and trim angle. But I want to unlock it both to avoid spearing waves and to allow the float to tilt back and give higher trim (and lift, and drag) at startup, to get over the hump. This is what planing boats do. Drop the stern into the bow wave trough. Nose way up. Then, on plane, flatten back down.

It is very hard to get a human-powered boat up on plane. I have maybe three times the power and torque of cruise available at startup, but only for about five seconds, from my human. I'd better be up on plane by then. Shallow pitch, so variable pitch, prop, should help. Check, but this is another thread.

Weight (CG) should shift aft on acceleration regardless of where the attachment is. Acceleration goes away once cruise is reached, so CG moves forward again.

Free pitch means you sort of let the float find its own lowest-drag trim, rather than forcing it. If you don't like it, move the attachment, and try again.

 

And this probably cause need of spring for always positive pitch

O.K. Maybe my concerns about yaw twisting are incorrect .Its possible to make durable and stiff joint. I must watch more Anime for inspiration.

Two axis joint placing is critical . Models .You need many models. Waves incoming at 45 deg will create twisting moment , so you need good joint bearings to not jam .

Maybe you don't need floats steps. Maybe Aquabike arrangment is better. One hull is thousands of options , you have four of them connected and affected each other.

 

I can just see you wading into a pool or lake, taking a big kickboard and trying to swamp the thing. "There! I TOLD you it was gonna twist!" And if that doesn't do it, just take your hand and smack it.

We shouldn't forget that the whole foray into suspension is sorta tangential to the goal of the HPV record. That will be in flat water. The only excuse for putting suspension on a specialized record-attempt race boat is that notion of letting the floats, especially the rear ones, "squat" on takeoff. The fuselage should dive stern down from the foil moment, splaying the rear float back, and the rear float should drop down into its own bow wave trough and nose up. Depending on how low you sling the fuselage, it might even drop the fuselage itself into the water, which would add another temporary planing surface in the form of the fuselage bottom. Shallower angle than the float, but we'll take all we can get. At cruise, the suspension extends back down and the float moves forward and the fuselage rises back up.

Or not. But that's really the only excuse for suspension on a flat-water record attempt boat.

I still like suspension when thinking about other applications (rough water with motor power and lots of speed). That's really where the HPV is leading to, or how its lessons might be applied and broadened.

And when we reach that point, we may well have to deal with you and your case of the Twisties. But a model is so strong relative to a full-sized, heavy motorboat that I think it would be hard to get a joint to fail, and I don't want to try measuring twist forces. Somebody else's problem when they buy our boat after we win the Nobel Peace prize. Wasn't that the goal? I think I will bet you a Euro that it won't break on the HPV or model either one. Not due to TWIST, anyway. .

"Aquabike"--your mean pumpafoil? Some sort of dam HYDROFOIL? Such a dirty word. No flying if you have foils. If you want to leave the water and have your boat turn into a ground-effect airplane --and that WAS your plan, right?--then, no hydrofoils for you. GEVs and hydrofoils do not mix. The transitions are killers.

You don't have to have steps when you plane, but you almost surely do if you want to plane and stay planing on human power. That's the diabolical nature of choosing that design space. It makes everything SO. HARD. But that's the fun! No pain, no gain. Makes going back to putting suspension on any old planing motorboat look like a cakewalk. If you have a motor, you don't need steps, but you still won't address your twist problem.

 

My mistake :
Wetbike - Wikipedia https://en.wikipedia.org/wiki/Wetbike

 

I was thinking about motorboat suspension , not very optimistic.Inland waters I dont'care of waves. Sea going motorboat ? You need scale up , lot of fuel , unsprung mass , propulsion problems , big waves handling depend of scale I doubt that any suspension will help.How long last joints with permanent work in ocean water ?
I have some ideas but I 'm not sure that they are any good .

 

What about retractable foils ? Only for take-off ? And planing landing?

Have you checked the operation of the steps at such low speeds? Maybe they will work more like a water plough .

 

It's easy , you have dimensions of the float , bottom shape , weight , you can easy check float handling at speed on not disturbed water , using some boat and rod attached to two axis bracket. It's also possible make some drag measurment.

 

Well, you're going to have SOME waves in inland waters, even if only other boat's wakes. We were always on inland waters when I was getting my teeth knocked in on our little runabout.

People have just come to expect and accept that they'll either have to slow down in chop or not go out, or they'll grit their teeth and put in their mouth guards, or stand with knees bent ready for the shocks, or use a suspension seat (they help, but your boat should not be bucking in the first place.). They've decided it's fine and makes sense to drive down the highway with no suspension. Even horse-drawn wagons had rudimentary suspension, yet people were glad to get out and walk or ride the horses because the jarring was so unpleasant.

FAST BOATS NEED SUSPENSION. All of them. Period.

 

@montero --

A ray of light for you, maybe--

Part of the challenge of twist comes from having a lot of hull in the water, length plus depth.

But, and I'll try not to offend any in the community who may be reading--what if we're doing it wrong?

The point is, things like deadrise and vee are are adopted to try to use the act of displacing water itself, plus buoyancy, as a cushioning and damping measure when the boat encounters waves. It works to some degree, but it's very draggy, and the faster you go, the harder the impacts get, and the less effective deadrise and vee are in softening the ride. Correct? Your "water suspension" is starting to fail you.

Meanwhile, if you want to plane fast on least drag on flat water, you don't use any vee or deadrise at all. You go with a flat bottom. DEAD flat, like a Jon boat or air boat. And a square, scow nose. And you go with a lot of surface area, and short L/B. We all know this by now, or should. Low bottom loading. Shallow draft. The whole goal is to go OVER the water, not through it. That's the best shape, if that is your only goal. Bolger's Skimmer. Kitchen table, basically.

At speed, once you're up on plane, you will find that, on your kitchen table on flat water, you are just SKITTERING over the water. Ask people who drive flat-bottomed planing boats in very protected waters. Drag just falls away. You can get, as one "Skimmer" operator describes it, "extreme increases in speed from very little throttle input." I think it's roughly that. I can find the quote. Like a pat of butter sizzling in a hot griddle. A puck on an air hockey table. The Skimmer guy says it's so slippery, and handling becomes so skittish, it scares the bejeebers out of him.

And if you want to take this low-drag situation up even another notch, and reduce skin friction from all your surface area you used just for rest buoyancy and to pop up on plane quickly--which flat-bottomed boats are known to do, by the way--well, then you can use steps. Reduce your wetted bottom area. Wholly HECK, are you skittering now. Inch or so of draft. It's ridiculous. You have so little friction, concentrated about midships, it's almost like you're on WHEELS. It's almost like you're driving a CAR.

Great, huh? But you've now made yourself incredibly vulnerable. You hit a wave when you're in this state, even a little one, and you're going to be in a very dicey situation, very quickly. Oops. WHAM! Ouch. Whoa! That one kicked me over into a scary, sudden roll. Whoa, you have, like, no control. You're skittering and slewing around all over the place. Whoops--I think you just "caught some air," on that last impact. Yikes!

NOW is when you need suspension. And four widely-spaced, shallow, short hulls, with free pitch and roll. Keep everything low, like a Lamborghini, to keep your weight (VCG) down. Maximize your "wheelbase," like a Citroen DS or F1 car. NOW you're ready for whatever the waves throw at you.

But what of yawing forces? Well, you do have some things in your favor. You are not IN the water, you're (mostly) on top of it. And because of your step, most of your contact, and weight, and lift, is concentrated midships, which is about where your single point of attachment--your "hub"--is. When you hit a quartering wave, not all of the length of your hull, or even much of it, is getting impacted by twisting side loads. You have very shallow draft, remember? If you did it right, your hull(s)--let's say you have four--are broad and short. Water just can't get at you to get a purchase and try to lever you around --to yaw your hulls/floats. Yes, a little, but handle-able, with a stout (U-joint) connection.

Does that bring any hope, to the picture?

 

"Retracting skis" have been tried. Dicey, lots of complexity. Best example I know of is Rob Borland's " Sea Phantom." His suspended "skis" hinge at the front, I believe, and they're actually buoyant floats at rest. Seemed to work, to some degree, but narrow stance led to vulnerability in overall vessel roll. His wings are way too small and stubby to get much aerodynamic lift at not ridiculous speeds.

 

No.

 

Sea Dart . Has already been discussed here.

 

Sea Phantom sounds good.