Hering Propellers is a Race Propeller high performance propeller manufacturer, recognized by racers and boat enthusiasts throughout the world.
Top boat manufacturers such as Cigarette, Donzi, Fountain, Nor-Tech, Outerlimits, MTI, Skater and others choose Race Propeller to equip their boats with Hering propellers over any other propeller manufacturer. For over 40 years, Hering's Race Propeller position at the forefront of performance propeller manufacturing has been a result of continuous Race Propeller research and development of unique Race Propeller materials, Race Propeller propeller designs and Race Propeller technologies. To serve our Race Propeller customers better, we have recently added additional Race Propeller machines to our manufacturing facility, allowing us to increase Race Propeller production and decrease Race Propeller delivery time. We look forward to working with you to create the most efficient Race Propeller propeller for your performance Race Propeller boat application. Is it possible to design a surface propeller with an high diameter and very low propeller turning in order to fit a 3 kw high efficiency solar boat? Which is the parameters to consider in order to define if there is any convenience to use a surface propeller instead a traditional one.
Alberto Attached photo shows a surface prop I experimented with to understand operating conditions. You will need a very special boat to achieve 20kts with 3kW with on-board solar collectors. Location: italy Efficient low speed semi submerged props In 2005 I experimented, with Genoa and Naples universities, three different designs for five-bladed large diameter semi submerged propellers.
The research was a comparative one, aimed at finding out if an already optimised conventional fully submerged twin screw installation, on a displacement vessel, could be beaten. We choose twin vs twin, counter rotating, in order to avoid the drawbacks normally associated with single partially submerged props. All trials were conducted on the scale model of a 73 mts lwl fully displacement ship, with a bulbous bow and dry transom stern. We asked Renato Sonny Levi, an undisputed master, to design the three 'challenger' surface props and the Naples university tank to modify the ship model to take the new drive system. During the entire work, we were continuously recommended by many experts (famous propeller designers and builders, lecturers from the university, ship designers etc.) to drop such a stupid research and to avoid an useless loss of money and time. Sonny designed radical props, even if there is no knowledge at all into this area of surface prop design. The ship model was towed naked (no appendages) and then all final trial were run in self propulsion mode with each set of props, at different speeds, different displacements and all the like. Regardless of the not perfect prop to hull match, a consistent certified increase in performance was achieved, reaching a +13% compared to the ?traditional? optimised screw propulsion.
The project led in fact to a worldwide patent, hold by Flexitab (my own company) which has recently been entered in an European funded research program. So I feel that your project should be fully feasible and I am convinced that you can beat, with a properly designed slow turning large diameter partially submerged (surface) multi bladed propeller, in a twin counter rotating set up, any submerged prop, at any speed. Conversely, I am not surprised that a single, large diameter, twin blade prop, with not optimised blade design, in ?surface? mode, should not work properly and produce poor performance. The two bladed prop had such low efficiency that I did not bother even trying to measure it. Originally Posted by brunello We asked Renato Sonny Levi, an undisputed master, to design the three 'challenger' surface props and the Naples university tank to modify the ship model to take the new drive system. Originally Posted by Rick Willoughby I can get 85 to 87% efficiency for lightly loaded boat props. In Rick's case the loading is very low due to limited human power and very large diameter of the propeller.
The significant point is that the upper limit of efficiency for a submerged prop is over 90% while the upper limit for a partially submerged prop is about 70%.
The overall design of hull and prop to achieve the efficiency potential wrests with sound engineering knowing what contributes to losses. Far better efficiencies are possible with lighter loadings of planning boats or very low drag boats like yours.

Joakim If the solar boat is going to achieve 20kts with 3kW it will have a lightly loaded prop. None of the partially submerged prop data I have seen would come close to matching that efficiency.
If the solar boat can really reach 20 kn with just 3 kW, it could use a very small propeller with good efficiency.
Having 3 kW of solar power requires close to 20 m2 of surface area, which would add weight and aerodynamic drag and also probably spoil weight distribution of a planning vessel.
Location: italy Pictures of Tank testing in Naples by Flexitab The data discussed in my previous message is not available online and is part of a research program which is still very active today, I attach a few pics to show what we are working on. We think that quasi propulsive efficiency, or what you can actually achieve with a drive system physically installed onto a vessel, is what really matters. The Flexidrive H Drive, developed for heavy displacement vessels, has no appendage drag (yes, it does matter) except for rudders, and the thrust line is horizontal as the axial flow into the prop disk is. There is a lot of work to be done, I know, but note that we went straight into two very reputable universities, Naples and Genoa, regularly doing commercial work, explained our goal and challenged them to choose one of their best self powered ship models, with twin submerged counter rotating props.
Flexitab is making a huge economical effort to make these advances and patent them worldwide. We are now in a very advanced stage of CFD virtual replay of the trials, which is matching very well with all test data. I see a fundamental flaw in your work in that you are setting up the props to give the very best efficiency possible from new technology and drawing comparisons with old submerged prop technology.
Existing ships propellers are the result of evolution in a period when fuel was in great abundance and efficiency was not a significant driver. To make a realistic comparison with a submerged prop you need to start with a clean slate and target highest possible efficiency with that technology. When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. First there was the bicycle, then the pedalo boat, then the pedal-powered aircraft — and now, thanks to a team of French engineers, the world has the pedal-powered submarine. Of course, we’re sure you all want to know how long you can spend underwater in the Scubster.
Please note that gratuitous links to your site are viewed as spam and may result in removed comments. With over 40 years of Race Propeller experience in the offshore powerboat racing circuit, we've built a Race Propeller reputation that the competition can only follow.
With the latest in CNC machining technique and program design, we can build anything from standard industry specs to Race Propeller customized propeller pitch and designs. The aim was to achieve good efficiency at relatively low speed - I determined it cannot get good efficiency for a variety of reasons. A single large diameter surface prop, is normally difficult to tune and make efficient, mostly because of the high side forces it develops. The model had already been tested with a conventional submerged twin screw set up, in self propulsion mode, and all data were available.
According to the ?experts? it would never work, since surface drives are ok at high speed only. We got all the props models nc machined from billet, tested them first in the Genoa cavitation tunnel and then in isolation in the Naples tank, using a Z-drive style pod. Matching resistance vs power absorption curves, it was clear that the props needed tuning for top performance (pitch adjustment), which in fact was not done for this first set of trials.
A lot of work needs to be done, but we feel the result was spectacular ? and a lot of sceptical ?experts? became our sponsors. We have now developed an in house code for a full CFD analysis on a surface propeller, matching the available physical test data we have, with very good results. I concluded that aeration, centrifugal water particle scattering and water splashing (together with the acceleration of water added mass) during blade entrance were the enemies to fight if one wants to improve efficiency.

I just wanted to point out that 70% is not at all a bad efficiency in many real displacement boats and ships. The smallest racing boats (3.1 m) can reach 32 kn with an unmodified 15 hp outboard at total weight of 160 kg. We have definitely beaten the fully submerged twin prop set up, especially at the higher speeds (due to shortage of knowledge on the lower end, where we are still closely matching).
The cyclic loading of a conventional prop in the up and down position is a fact, as the angled flow into the prop disk is. What we get in the cavitation tunnel and in the isolated prop tests, is exactly what is delivered to the vessel, when installed.
Their wrote the final reports, they made all tests, they were the first to be totally amazed. While I was the one with the original concept, it would have been impossible to make it work without Sonny's knowledge and huge experience, which never interfere with his free thinking approach to design. Unfortunately, while the sub’s cockpit is water-sealed, the driver has to wear an oxygen tank and mask to breathe and see. Because of Hering Propeller's Race Propeller attention to detail, Race Propeller performance results, and Race Propeller personalized customer service. The actual ship had been built after the tank testing and tank data were found to be reliable when scaled up. Already some results were quite interesting, since these props, due to peculiar geometrical factors and slow turning, showed some surprising results, departing from ?conventional? surface prop behaviour. According to Savitsky method even those would need more than 3 kW of effective thrust at 20 kn, thus at least a 4 kW motor.
The craft features a pedal belt connected to a twin-propeller system that, depending on the fitness of the driver, can reach speeds of up to 8km an hour (5mph). This is neat but unless pedaling is more efficient that fin swimming, bottom time would be less.
An unconstrained open water prop for 3kW at 20kts will achieve around 90% efficiency while a surface prop will achieve a best efficiency around 70%. These propellers have normally wide blades designed to avoid cavitation and vibration and can not typically have a very high efficiency in any condition. The mini-sub can currently reach a depth of 6 meters (20 ft), making it perfect for peddling through rivers, and shallow ocean excursions. However during trials in in the Mediterranean waters off the Cote d’Azur, the submarine was submerged for a full hour. I don\'t know why it can\'t be just a fairing, pedals and drivetrain, and maybe flaps you wear on your hands. Also the transition from being part of the machine and free swimming to investigate something wasn't mentioned. In typical displacement boats and ships the thrust loading coefficient is high, since the propeller diameter has practical limits and speed is low. Just the most basic propeller theory limits the efficiency well below the figures you are giving and above that comes the restrictions caused by cavitation and actual propeller design.
The reduction in drag and the more efficient propulsion should make it superior to flippers. Are they more efficient than flippers?) On the other hand, the water will create drag on your legs, so maybe it is a wash.

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