Hydroplaning Rowboat

[Horton HCCI]

Thanks for your well thought out and detailed posting HCCl! Good info on stepped hulls!

Another alternate possibility hull which has previously been discussed on this list is using air bubble lubrication. But I don't know if a boat hull or air pump could be designed to provide compressed Ram Air bubbles @ 20mph without sacrificing to significant losses to forward speed. Air bubbles have produced incredible speed results when incorporated into Super cavitating torpedoes.

I think it's has to be an air propeller (maybe variable pitch) for propulsion, there's a reason that it was chosen after extensive research by Drella, to create the original record. Also, RC test flight tested submerged versus Air props and air appeared to be considerably superior, at small scale- within the range of one man boats.

Just in case you haven't seen it already, See post 74 @ 1st video starting at 9 minutes to the end, for graphs and measured experiment testing of submerged vs. Air (90% efficient!) Propulsion..

PS. Don't all boats start in displacement mode? For a sustainable 19 knots, a one-man displacement boat would have to be very long (1.34 X wet hull length- for zero hull speed energy losses) but then- the significantly increased hydraulic skin friction can't be too high? I haven't seen any calculations that give estimation for the number of instantaneous Watts ( maximum athletic instantaneous human output = around 500 watts?) required to get a proper (not longish) planing Hull over the large energy hump required to get to planing mode. But your stepped hull concept might just work for just a few seconds, and long enough to run a speed trap measurement! It might be just a matter of building, and tweaking to get the record you want!

Hope this helps!

Hi, @portacruise --

Hooo boy--air lubrication will definitely bring up some strong opinions on this forum. I have my own thoughts about why air bubbles work on supercavitating torpedoes--I think it's not so much lubrication as it is making an envelope of compressible fluid in front of and around the torpedo's hull. Without it, you're deforming an incompressible fluid--water--at a rate such that, at a certain point, generally around 50 knots of hull speed, the water won't give way fast enough to the hull to allow it to pass through. The torpedo basically hits a brick wall. Torpedoes do. Subs do. Sailboats do, with their submerged appendages. All at about 50 knots. The air bubbles provide a yielding envelope that gets around this, and lets the supercavitating torpedoes exceed that speed barrier.

But that's not really the same thing as air lubrication at lower speeds. I think pumping "ram air bubbles" is probably not a great solution for human power--as you suggest, probably too much energy lost to creating the lube/cushion/whatever and not enough left for forward propulsion. But who knows? Entraining air through vent tunnels behind steps, into air cavities on the underside of the hull, also.....might work. Benneteau Air Step claims it does. Doesn't take any active pressurizing, anyway.

I have to side with @montero on not being a fan of air props. I did look at the video again, though, and it's hard to take issue with Daniel's method or findings. I think there's consensus that air props, possibly even variable pitch air props, are not good on "torque," i.e., getting the boat moving from a stop. Decavitator was towed to speed in tests. Not sure on the record run, but I have my doubts. They may be at 90% efficiency at design speed, but can they get there without, um, cheating?

Daniel talks about (actuator) disc area at about 12:00 in that vid on post #74. Could that be the difference? It's pretty widely accepted that if you want propeller efficiency, use as much disc area as you can, and accept whatever reduction in rotation speed results from that. I.e., move a lot of water, less quickly. Like large diameter turbofans vs. older turbojets--move way more air, way more efficient.

Efficient water props like those used by Super Phoenix were about 9" in diameter, huge for that size of boat. But that's still about 64 square inches of disc area. @Victor R and I are talking about two foils of around 18"x7.5." I'm not sure what the proper way to compare a rotary to a linear scheme is. They are certainly big, whopping "blades" (foils). If we took an 18" long foil and swung it around in a circle, we'd get a disc 36" in diameter. That'd give pi*18squared, or 1017 sq in, of swept area. Around 16 times that of the 9-inch diameter prop.

I think I'd agree all boats start at displacement. I don't believe planing boats stay that way. I'm not sure yet about hydrofoils. I claim hydrofoils create more wave energy (drag) than planing boats for the same speed, and they might even have wave-making drag equivalent to displacement boats. I haven't read any comparison studies or seen data, though. I think it'd be hard to separate wave-making drag from skin drag if you were to try to make measurements.

I've seen things that put maximum instantaneous human output closer to 1500 or even 2000 watts, for a few seconds, for track cyclists and sprinters. Champion road cyclists can now put out around 400 watts for an hour. Well, Pogacar can. Elite rowers, looks like max is over maybe 1300 watts for 10 strokes. That's probably around 10 sec, so around 100 meters. Rough figures. In the study Wilson quotes, I think rowers are roughly equivalent, in fact a bit better, than a cyclist over distance, so ~400 watts sustained.

Here's a snapshot of p. 93 in my edition of Bicycling Science, on rowing vs. pedaling:

"Free" rowing means no stops at the end of leg extension and arm pull. "Forced" means you push against stops. "Fixed feet" means sliding seat. "Fixed seat" means sliding rigger/footplate. Curve 5, forced sliding footplate, gives most power over all durations up to five minutes. DaggerRo uses a forced (or "constrained") sliding footplate, rowing configuration.

Wilson notes that the watts/hp figures are for "active men," not record athletes.

 

[Horton HCCI]

Here's a new video that cropped up on ground effect planing/flight:

Not human-powered, and un-personed, but about the size of DaggerRo (~4m x 3.5m). Final weight unspecified, but in excess of 20 kg. Thrust 100N total (Concept 2 forum indicates elite rowers can put out in excess of 1,500 N max, "hundreds" sustained). Actually, that model is at least 5m long, might be 6m. Wingspan may be comparable, but DaggerRo chord is about twice. Current DaggerRo model has no tail. Will post latest DaggerRo sketches shortly per @montero 's suggestion.

 

[HelmutSheina]

I have an emerging idea on transverse foils. Admittedly I didn't read the thread thoroughly, as it was getting bogged down in minutea as occurs when ideas are fomenting, so my thought may have been covered.

It seemed to me that one of the issues with running a foil along a track for propulsion was in returning it for the next power stroke.

How about if multiple foils were mounted on a continuous belt, chain or rope rather than one on a track car? With two always in the water, perhaps with a weighted fence to keep the active set vertical and some light guide rails to assist the inverted returning foils. Slight similarities to longitudinal tracked land vehicle propulsion or waterwheels.

The computer exploded and I'm on a phone, so will not attempt diagrams, but I think the concept is easy enough to follow.

 

[wet feet]

Rowing,moving foils independently of the hulls?I think you need to think a bit more deeply and perhaps polish the thought or something,Helmet.

 

[portacruise]

Consider search for "unusual human power boats" for ideas. I think "Tuhsnelda" is the one with 2 pedaled floating treads giving a spinning pontoon tracked configuration. Like combat tank treads but floating and super lightweight. Clever because it uses skin friction with water as an advantage, instead of a drag, ie. the greater the friction the faster it goes! It did not break any records though, so the losses may be considerable. Don't know if the treads could incorporate foils of some kind to improve performance. Hope this helps, if not- just discard as rubbish, ha...

 

[Victor R]

I have an emerging idea on transverse foils. Admittedly I didn't read the thread thoroughly, as it was getting bogged down in minutea as occurs when ideas are fomenting, so my thought may have been covered.

It seemed to me that one of the issues with running a foil along a track for propulsion was in returning it for the next power stroke.

How about if multiple foils were mounted on a continuous belt, chain or rope rather than one on a track car?

A new propulsion concept for high propulsive hydrodynamic efficiency:
https://cris.vtt.fi/ws/files/54275579/1_s2.0_S0029801821016036_main.pdf

 

[HelmutSheina]

Rowing,moving foils independently of the hulls?I think you need to think a bit more deeply and perhaps polish the thought or something,Helmet.

Or maybe you need to get your feet wet occasionally?

 

[Horton HCCI]

It seemed to me that one of the issues with running a foil along a track for propulsion was in returning it for the next power stroke.

How about if multiple foils were mounted on a continuous belt, chain or rope rather than one on a track car?

With two always in the water, perhaps with a weighted fence to keep the active set vertical and some light guide rails to assist the inverted returning foils. Slight similarities to longitudinal tracked land vehicle propulsion or waterwheels.

Hi, Helmut--

I think I see your idea. Does Victor's link capture it pretty well? Like a chain saw, or a belt sander.

I've considered such a setup, particularly for a model where it's easier to use a rotary motor as your power source. What I don't quite get is how to control pitch (angle of attack) once the foils round the pivots. Seems it would be a complicated mechanism, and I don't do complicated mechanisms well. But Victor sure does. He may be able to speak more to whether or not he thinks the mechanism in the link is viable.

I've recently been musing on a way to get a mechanical oscillating power source, like a hydraulic or pneumatic pump, driving a double-acting piston back and forth with valves. Some challenges in trying to magnify stroke, if that's your aim, and in handling what might start to get a pretty wide footprint. I might orient piston and cylinder longitudinally along a hull or fuselage, but then you have to move your plane of oscillation from longitudinal to transverse. I came up with lines and pulleys, but then it starts to look a lot like my human-powered boat.

On returning the foils on a human-powered boat with lines and pulleys--yup, gotta have something. I favor elastic. Just exercise bands. You can pair up as many as you like. My pull length is about 80 inches for a huge 6'8"-type rower, and that starts to get pretty long, and put a lot of stretch into the elastic, if you're trying to lay that all out along the fuselage. So my current plan is to use a sort of inverse 1:2 block-and tackle. Exercise bands are 41.5 in long, typically, and can stretch to about 2.5 times their length. So add maybe 4-5 inches of pre-stretch and you're pulling the elastic out, let's see, 80-41.5 plus say 5, so 43.5 inches; total length of elastic about 85 inches.

I'm guesstimating a big rower can pull maybe 400 lbs peak, so if we put half of that to each foil, we have 200 lbs. Let's say we try to get relatively even power on the outbound and return stroke; that means we need to "rob" half of the pull force to build up potential energy in our elastic. Half of 200 lbs on each foil goes to water, half goes to elastic. 100 lbs to the elastic on each side. But we have the inverse block and tackle, which doubles force and brings us back to about 200 lbs per band. That's a lot, but bands typically come in sets, so you can double or triple up. Normal mortals not going in an all-out 10-second sprint can't push/pull 400 lbs, so that's top end for a monster. And of course may be way off.

 

[gonzo]

None of those contraptions will get close to the efficiency of a standard racing shell setup.

 

[Horton HCCI]

None of those contraptions will get close to the efficiency of a standard racing shell setup.

Would you like to make a bet on that? $1 USD. I take Venmo.

 

[portacruise]

Standard racing shell shaped k1 versus hydrofoil kayak called a "flyak" contraption, which also beat a K4 ( -4 man) racing shape. The one man flyak is slower than the world human powered boat speed record holders, AFAIK. Efficiency helps, but doesn't necessarily beat out of the box contraptions for the stated goal? The biggest Factor for World Records appears to be The Brute human power and skill of the competitor. Mark Drella used an air prop for the world record, but might just as well have set the world record with a conventional water prop hydrofoil boat- if he had trained on that instead. Decavitator air propeller was later beaten by a water prop hydrofoil boat in a side-by-side race. I like KISS, but it just hasn't worked so far this competition.

 

[wet feet]

I'd suggest that the video above shows two things,once foiling has been achieved a displacement hull can't catch the foiler for the duration of the paddler's energy reserves.Once that level of energy has been depleted the drag of the immersed foils would probably reverse the situation.A rower would have to carry the additional weight of the rowing hardware and the movement of the athlete is likely to change the incidence of the foils,which might have to be accounted for by a more aggressive forward foil angle and it's attendant drag.

 

[Skip Johnson]

I believe @gonzo is right, a well deigned and built rowing shell is a gold standard for minimalist efficiency. I've spent a lifetime optimizing marathon canoes for paddlers obsessed with winning races. None of those canoes ever won a race but have been as sharp a tool as I'm capable of designing for them to use.
It's interesting that the current MR 340 racers are going to peddle powered paddles rather than propellors to win the race.
IMO Decavitator was a unicorn but somewhere down the road some fork may lead to some improvement, my money would be on the one that was blindingly simple.

 

[portacruise]

I believe the OP was interested in decavator event SOR, fast as possible speed measured through a speed trap?

There are also other events like maximum distance record over 24 hours, where most foils designs wouldn't work at all.. Exception maybe a foil which could be quickly kicked up out of the water and periodically lowered for Speed depending on the energy of the competitor? Last I heard the record for the 24-hour event was held by a displacement mode pedal design water prop, with rowing or paddle? designs not far behind. So I can see how a well-designed efficient rowing shell powered by an exceptional athlete could hold that record for possibly years, as that has happened in the past, before leg power peddling props became a thing..

 

[Horton HCCI]

Mark Drella used an air prop for the world record, but might just as well have set the world record with a conventional water prop hydrofoil boat- if he had trained on that instead. Decavitator air propeller was later beaten by a water prop hydrofoil boat in a side-by-side race. I like KISS, but it just hasn't worked so far this competition.

I have read that some accuse Drela and Decavitator of having had a tailwind (as well as going downriver) in their record 100m run. I believe they also faced a challenge of getting enough force from a standing start to get up on foil, due to the limitations of their air prop and the fact that they didn't have the ability to vary pitch once underway. They did a lot of towing behind a motorboat in early tests, anyway.