Electric Launch Design optimized for semi-displacement speeds

WILD ROOSTER, a recently built copy of the Uffa Fox-designed Ankle Deep, on sea trials in Lunenburg, Nova Scotia. Ankle Deep http://www.uffafox.com/ankledp.htm

Do you consider this Uffa Fox design simple or complex, Jurgen? Paul Scott - am I correct you would regard it as complex because it's not hard chine & developable?

 

What I wonder is whether the very deep forefoot of Ankle Deep and the Clara 8m is specifically so the bow will NOT lift. If so, perhaps the bow could be more cut-away (and therefore lower wetted surface) if lift could be generated at the stern so lift is generated at both ends, stabilizing the trim. That may be the thinking of Walt Shultz at Shannon Yachts, whose designs feature a radical hook at the stern: SRD is a better hull shape, fast, fuel efficient, stable https://shannonyachts.com/shannon_srd_technology.html

This is my thinking as well (but I think the Shultz hook goes too far).

 

Um, no, it's the other way around. The very fine entrance has a tiny waterplane and lowers the KM(l) value compared to a bow with a greater entrance angle, less draft, and the same volume. The effect is to pitch up more for a given pitching moment. The question then becomes how do the pitching moments compare? And with the bow out of the water in the high speed case, you can't answer that with bow geometry, you need to look at the rest of the boat.

I have been fiddling around with some specs. First, trying to find real batteries and chargers that you can actually buy, and for which there is published data sufficient for one to design an installation, is proving difficult. But my 1200kg weight estimate doesn't exist in today's marketplace. I'm upping that to 1500/3000kg as an onboard package, minus chargers. Torqueedo's Deep Blue system is apparently still vapor ware. Absolutely none of the necessary engineering data on the design and install is currently available. Batteries and chargers are all listed as "while supplies last", which I guess sounds better than "don't got none yet".

I'm currently running a hull trace using Godzilla on hulls with design cruise of 4-4.25 m/s (8 knots) and various top speeds from 5.75m/s (11knots) on down. There is essentially no change to the optimal hulls or resistance curves above 9.5 knots top end. The basic constraints are a displacement of 4 tons, a waterline of 11 meters, and a transverse metacenter at 1.5m above waterline.

I will try to do a length trace and a displacement trace about the more promising hull particulars. This will get us tradeoffs from cost of weight and cost of length.

We need an income metric also. Operation should break even on 50% pax, so we need that weight trace for that as well. No one really cares about efficiency once you start making decent money. So optimization is usually done about the economic break-even point. That's where the competition ends up.

At the moment, my thought is to try and get 50% efficiency from power pole to propulsion power.

 

Do you mean when the boat hits a wave? I had in mind the change in trim that occurs as one enters the semi-displacement regime - typically trim up by the bow - assuming flat, calm water. My thought was that a boat with a fine and deep bow would trim up by the bow less because the sum of the vertical components of the velocity-induced water pressure (the lift at the bow) would be less. (Surely I have that correct, yes? I'm not understanding what's inducing a pitching moment in your scenario.)

 

I don't know what inducing it either, I just know how stuff responds. The finer bow responds with a greater pitch angle to whatever is pitching it up. It's the same as saying it will ride smoother through chop, because it doesn't try to fit itself to the wave. It takes larger immersion from a bigger wave to induce the same pitching moment, and it takes more immersion to balance a given external pitching moment.

 

But I haven't referenced chop or a wave. The only dynamic element I'm talking about is the forward velocity of the boat and its relationship to change in trim.

 

The hook was fashionable on Div 1 boards for awhile, but on racing longboards the go to lately has been concave / flat / vee or IIRR, vee / flat / slight vee, although flat shows up a bit. The argument seems to center around water release. A tail has even resurfaced (pintail with horizontal flat wings, but the board needs to be vanged at Archimedean speeds), then rotatet flat when planing. Begs the question- If you think of the horizontal wings as Porsche like adjustable spoilers, retracted at displacement speed, and then brought on as speed increases, then you’d have a hull easy to get up to speed, and deploy more wetted surface when you need it. Kind of like horizontal Finn Class centerboards. One of the big rig cab builders put a spoiler on top of the cab ( they’re everywhere, you’ve seen them) and gave the driver control over its incidence, and just going by the driver’s feel, most of them got close to optimum aero quickly. So upping the prismatic when desirable. Besides, low cp hulls accelerate more quickly and with less power. Something to chew over, at any rate. I really think power requirements and hull weight need to go down to make the kind of hull you’re thinking about more agreeable. Kind of a postmodern take on Vingt et Un. My $0.02.
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The wings are called batwings- take a look
Phantom Race Windsurf Board https://windsurf.star-board.com/windsurfing-boards/windsurfing-longboards-raceboards/phantom-race-windsurf-board/

 

SD:
Do you consider this Uffa Fox design simple or complex, Jurgen?

As long as you have not presented a proper SOR, this thread will continue to go in circles backwards.
I'm not interested in participating in your speculations and guessing games.
JS

 

The deeper forefoot does several things concomitantly - added damping, maintains a longer waterline length.

As the hull moves through the water, it creates its own waves system. At the bow, the wave profile is positive i.e. above the static waterline. This in turns makes the static waterline unbalanced, therefore the bow rises, and thus, the stern sinks….slightly over generalising here…to maintain equilibrium of mass = buoyancy.

Thus the stern sinks ergo = squat….which is a result of the trim.

The GML, whilst plays a part, is minor in his context.

A deeper forefoot prevents the early onset of the bow rise above the forefoot of a more conventional hull shape – especially if it is semi-displacement or so. Since these hull forms are designed to promote the separation of flow, at the bow, to enable the wave system generated by the hull, to be “under” the hull to create the lift.

A deeper forefoot delays this and also, by definition maintains the longer waterline length = better LD ratio.

The deeper forefoot adds damping in the vertical directional and thus reduces vertical accelerations in head seas.

I could go on, but it is lost on those barking to the moon as they would rather post endlessly with no SOR, nor appreciation of their blunderbuss posting hoping that something will stick, than actually read what is going on hydrodynamically.

That sums it up nicely!!

 

2 Torqeedo 48-5000’s with 2 Cruise 10 outboards? Or three of the same for that matter. Multiple outboards are fashionable anyway…. That, and you’d have descrete systems with warrantees. Not cheap! It would help keep prop rpms down?

Power 48-5000 - Torqeedo https://www.torqeedo.com/us/en-us/products/batteries/power-48-5000/2104-00.html

 

That is certainly an option that we know exists. I'd prefer a higher voltage solution. There exist a decent number of inboard e-motors for conventional prop shaft arrangements. But so far the motor performance curves aren't published, so you have to request the engineering info from the mfgs. I'm still cranking out hull resistance traces. It will be a matter of picking two or three hulls to fit two or three propulsion options, which is hard to do if the engineering data on the motors isn't out there. The outboards wouldn't hit my completely arbitrary 50% efficiency goal, either.

 

It's been a long time since I did prop calculations as a student. At that time I was relying on Bp curves for the propellers. Are those published for props like the interesting multi-bladed one I see on the Cruise 10? Are you using your own spreadsheets, a program like HydroComp, something else, or just cranking through things by hand?

Contra-rotating twins would be especially nice, yes?

On another topic, could this drive mounted hydrofoil play the same role as a HullVane?
Mercury Racing E1-X | Boating Mag https://www.boatingmag.com/boats/mercury-racing-e1-x/
I'd like to ask Paul Bieker, who pioneered I-14 (sailboat) rudders that worked on similar principles.

 

Geoff Van Gorkom electric boat: The Caper Skiff Power Boat from Van Gorkom Yacht Design https://www.vgyd.com/project/caper/