AUTOPROP

The Autoprop is the only fully automatic self-pitching propeller on the market and has been available now for over 21+ years. It’s concept was developed during WWll to improve the performance of landing craft in both forward and reverse and give maximum thrust efficiency at all rpm and engine loading. The propeller is the performance leader throughout Europe and the USA as the total propulsion solution for cruising yachts.

The Autoprop is an automatically self-pitching feathering propeller which varies its pitch depending on the operating conditions, thus maintaining maximum efficiency at all times. It has a higher efficiency over a wider range of rpm settings than any other type of propeller, therefore producing higher speeds throughout your engine’s speed range, allowing lower engine rpm’s, giving greater cruising ranges and fuel economy and quieter cruising. The blades automatically adjust their pitch to match the engine torque to the varying load conditions.

The Autoprop has the Identical blade shape in forward or reverse and therefore gives more control for backing or maneuvering due to it’s superior reverse thrust and optimum pitch setting … resulting in no ‘prop walk’. The pitch setting is determined by two factors … Shaft RPM & Torque and the hydrodynamic force flowing over the blades (i.e. boat speed). RPM decreases pitch. Water flow increases pitch. The propeller will optimize the pitch setting to these two forces. Anytime you change one of the “forces” you will change the pitch setting until the “new pitch” is established based on the two new Input forces. For example, if you were going down the bay at 2200 RPM and 5.0 kts and you then increased RPM initially the pitch setting will be reduced. However boat speed / water speed will increase and so then the pitch will Increase to match the two new forces of say 2800 RPM and 7.5 kts

Autoprop is the cruising yachtsman’s propeller ‘par excellence’. Autoprops blades can rotate through 180 degrees and the subtlety of their design allows them to produce the same amount of thrust whether the yacht is in ahead or astern. It is a unique propeller which, unlike its competitors, excels in all aspects of a cruising yachts use and does not compromise any of them.

Autoprop’s unique design and superb build quality make it the first choice feathering propeller among cruising yachtsmen the world over, with drag reduction when sailing by at least 85%, and a unique ability to change pitch automatically to suit prevailing wind and sea conditions when motoring or motor sailing.

Sailing. The feathered image on the right shows how, when sailing, Autoprop reduces drag by up to 85% compared with a three blade fixed propeller; with the two blade propeller the reduction can be even greater. This drag reduction can equate to as much as one additional knot in sailing speed.

Motor Sailing. Autoprop automatically varies its pitch depending on the conditions. Put simply, as the wind or sea conditions vary so does the blade pitch of your Autoprop. The less pressure the Autoprop feels on its blades the more pitch is applied and vice versa. The result is maximum efficiency whatever the conditions, with increased speeds at lower engine revs and lower fuel consumption and emissions.

Motoring. With other feathering and fixed pitch propellers performance under engine is a compromise. No such compromise exists with Autoprop, her blades admittedly rather an odd shape, are the result of a huge investment in design time and testing. The Autoprop blades, unlike those of conventional propellers, maximise the thrust delivered whatever rpm the yachts engine is running at. Conventional propellers are designed to provide maximum thrust at the engines maximum output; at any other point up to maximum revs the propeller will be operating at less than its potential. Autoprop however, subtly varies its pitch to optimise thrust whatever the engine’s revolutions.

Manoeuvrability. In reverse the Autoprop blades swing through 180 degrees and present exactly the same blade shape as they do ahead. The result, the same excellent thrust, with greater stopping power and less prop walk.

Adverse weather conditions. Likewise in adverse weather conditions, the vessel’s speed will be reduced because of the adverse weather such as high winds and choppy sea conditions. The Autoprop senses the load acting upon it and reduces the pitch angle allowing the engine to to run to a higher maximum rpm. Much like travelling up a hill in your car, you need a lower gear ratio to allow the engine to run faster and produce more power.

Towing.This unique feature of the Autoprop, enables the full power of the engine to be used in situations such as towing, or in emergencies. With conventional propellers because the pitch is too coarse at very low speeds, the engine cannot achieve its full revolutions and therefore full thrust is not achievable.

Why Choose Autoprop?

To answer this question it is important to understand the fundamentals of propellers. All other propellers, whether fixed , folding or feathering, operate under power at one single fixed pitch setting. Yes, there are some propellers that can have their pitch settings mechanically changed such as controllable pitch propellers (CPP). However once the pitch of the blades has been changed, the propeller again operates as a fixed pitch propeller (with a new setting) until the operator changes the pitch again.

All fixed pitch propellers are set to run at their best efficiency at only one engine rpm (often called the mission profile). At their best efficiency. they are maybe 50-65% efficient. Whenever the engine is run at less then this rpm (say at cruising rpm), the propeller efficiency is greatly reduced. Less efficiency means less power and thrust and a lower boat speed. Choosing the pitch setting for a fixed propeller is like choosing one gear for your car. Once you have selected that gear, say third, then you operate the car in that gear all the time regardless of road conditions, hills, speed or towing a trailer to the dump. It is not efficient and definitely not good for the life of the engine. Having an automatic in your car is preferred.

A second way to look at the fixed pitch propeller blade is to understand that the blade is operating just the same as an airplane wing. It has both a pressure side and a lift side. This shape is optimized for maximum lift at a given air speed. Below that speed the wing looses efficiency (lift) and if there were not enough power the plane would stall and fall. At lower air speeds the pilot may increase lift by adjusting the flaps on the wings to Increase lift. You cannot do this with a marine propeller and so it is the thrust (lift) that suffers along with the boat speed. The Autoprop would change its angle of attack automatically thereby increasing thrust (lift), similar to flaps. Increased efficiency is increased thrust and boat speed.

Just Another Feathering Propeller?

Propellers with flat blades are like a paddle. The flat shape is not efficient at producing thrust. At anything less than maximum rpm, the thrust produced will be greatly reduced. Independent tests have shown that at a cruising rpm flat blade propellers produce very low thrust & therefore the boat speed produced is very low; lower than a standard fixed propeller. The Autoprop blade has true camber and profiled shape (airfoil) to each blade. Therefore the thrust developed will be greater than a flat blade. This is especially true at the cruising rpm or in adverse condition such as motoring into a head sea. The efficiency is higher than that of a fixed propeller by over 10%. The Autoprop produced lower noise due to the twist and camber of the blades.

Feathering Propeller Drag

All of the feathering propellers on the market have flat symmetric blades, apart from Autoprop. They will have a greater blade area exposed to the water flow, which increases drag. This drag is even greater when the shaft is angled downwards. At higher sailing speeds the feathering propeller will begin to auto-rotate. If the engine is in gear, the propeller can cause the engine to turn over and this would create water problems within the engine. The feathering propellers are prone to catching lines and debris, like bags, weeds, lobster/crab pots etc.

The Autoprop is a feathering propeller. As the blades align themselves to the water flow when under sail they feather to the water flow, not the shaft angle. Tests have shown that the Autoprop has the lowest drag of all three bladed feathering propellers and 85% less than a fixed propeller.

Feathering Propeller in Reverse

Again flat blades cannot produce the same thrust in reverse as blades with profiled blades. True, their performance in reverse will be better than a fixed propeller in reverse, and will have pop-walk. The Autoprop blade has the same leading edge in reverse as in forward and true profile blade with the same camber and curve shape of blade so therefore increased thrust over the flat blade propellers, and no prop-walk.

Performance

Other feathering propellers have only one pitch setting under power. Autoprop has countless pitch settings, its fully automatic. Motor-sailing is vastly improved and greater thrust at lower rpm and in creased speed. Less engine rpm results in lower wear and tear, less noise and vibration, increased fuel economy and a greater cruising range. To meet the many combinations of boat and engine combinations the Autoprop propellers are available in a combination of 2 and 3 blade propellers suitable for shaft and sail drive in a wide range of diameters.

Installation

All flat blade propellers are delivered disassembled. The hub is installed first and then the gears, blades and pitch setting are reassembled onto the hub. If the incorrect pitch setting is made it will require another haul-out to make that change.

Autoprop comes completely assembled, pitched, dynamically balanced and water tested at the factory. There is some very simple assembly required to install (shaft nut and zinc), but there is no re-assembly of blades, gears and pitch settmgs to choose. No chance of making a mistake. No pitch adjustment to make after a sea trial.

Service

Autoprop propellers are well supported through numerous dealers and agents in the USA.  Parts, propellers and re-building is all available for the propeller, often with short turn around time. To enquire about servicing your Autoprop propeller please use the following link: Autoprop repair service request

Design

The Autoprop does have optimum size limitations. With conventional propellers you can reduce diameter and increase pitch to compensate for the loss in diameter. You get a far less efficient propeller, but it will work. The Autoprop cannot always be made to match a fixed propeller’s diameter & pitch and still qtve a superior performance. The blade design is important and needs to be reproduced to a high degree of accuracy. It is for this reason that CNC machines are used in the production process. It is essential that the finished blades have the correct orientation to the blade pivot axis. The blades all begin as castings that are cast of Superston (manganese aluminum bronze). The hubs are made form Nibral (nickel aluminum bronze). Superston is a harder, stronger & durable material than the more common manganese bronze & NiBrAl. Hubs and nuts are manufactured to fit all shaft sizes and tapers. USA SAE tapers (usually 16: 1) and metric also, (10:1). The Autoprop’s sealed bearings are made of high quality materials sourced from compa nies like SKF, Timken and Thomson. The Auto prop is available for standard shafts and sail drive units.

All sets of blades are dynamically balanced and matched on the propeller at manufacture. They are then assembled to a hub and put through additional tests in our purpose built water tank. These tests give information as to power absorption for a particular propeller over a range of simulated shaft rpm settings. This data will then stay with the serial numbered propeller for future reference and to assure consistency to performance for like propellers, engine specifications and installations.

Size

The Autoprop is currently available in diameters from 13″ to 39″ and engine ratings from 10HP to 350 HP covering 2 and 3 blade shaft together with sail drive installations.

Next Steps

Find out how Varifold folding sailboat propellers can benefit your sailboat by requesting a hassle free no obligation Varifold Propeller Quote. Simply enter the details of your sailboat such as boat type , engine, gearbox ratio and so on in our online web form and we will conduct a power prediction for your vessel to size the right Varifold propeller for you.  This takes a day to perform and we will provide you with the propeller details and a competitive quote. We have currently installed nearly 7000 Varifold folding propellers and counting, to happy customers the world over.  Once you have your quote you will receive a couple of technical articles on the design of the propeller which should answer any questions you have. You can also call us on (757) 962-9219 or e-mail info@kingpropulsion.com to find out more information about the Varifold folding sailboat propeller range. We are always adding feedback of from our customers in the testimonial section, giving real world insight into the performance of these amazing propellers.