Kiwiprops propellers

Although it does not seem obvious from an external observation, the propeller includes two stops and a stainless steel torsion spring allowing an angle of rotation between the molded part that carries the blades and the hub mounted on the propeller shaft and equipped with three reversing rollers.

When reversing is engaged, the water pressure against the blades causes the blades to rotate on the hub by compressing the spring which causes the inversion rollers to engage against the emplanture of each of the blades, forcing them to return to the FORWARD forward position.

The stops prevent any further rotation of the blades that now rotate with the hub. The propeller then works as a classic model with three fixed blades in reverse with the maximum pitch. The pitch of the propeller is not adjustable in reverse and automatically adjusts to the maximum angle, i.e. about 23.5°. Thus the trailing edge of each blade becomes the leading edge in reverse as is the case of a propeller with fixed blades. This device is different from the mechanism of all gear-feathered propellers whose blades rotate 180° as soon as the reverse gear is engaged.

The spring returns the propeller to its normal forward-moving configuration allowing the blades to be feathered as soon as the inverter returns to neutral.

All it takes is an Allen key to easily and quickly adjust the propeller pitch. The emplanture of each blade includes a stainless steel adjustment screw implanted on the back side for easier access. Turn this screw a third of turns to increase the pitch by 1°.
This setting is easily done underwater with diving equipment.
The pitch adjustment screws are self-locking in the blades in which they machine the footprint of the last turns as in a Nylstop type brake nut.
The blade emplanture coincides with the hub joint line to provide a reference angle of 20° if no protractor is available, for example when a blade needs to be replaced. [This heading corresponds to an angle of 18° for blades shipped after 1 April 2004 – serial number greater than 446 from the new moulds].
Attach the Allen key to a small piece of foam or cork to ensure its buoyancy if you need to intervene underwater.

No. Unless otherwise stated, the propeller comes with a pitch setting to allow the engine to reach the maximum engine speed at full power determined for each new engine for warranty reasons.
This setting is based on the information contained in our extensive database of engines currently in service. A larger pitch setting increases the cruising speed at a given engine speed but no longer allows the maximum engine speed and power to be achieved.

However, each installation is different. The angle of the propeller shaft, the back pressure of the exhaust due to the architecture of the boat or the internal corrosion of the exhaust line, the operation in seawater or fresh water, the altitude of the body of water, the cleanliness of the propeller, the age and compression ratio of the engine, auxiliary accessories such as compressors and alternators have a significant impact on the speed that the engine can reach. On small auxiliary engines installed originally by construction sites, these accessories may have a disproportionate effect on the possible engine speed.
Generally speaking, 80% of users never change the original propeller pitch setting.

The answer is no in any case.

The pitch is not adjustable in reverse but automatically stalls to the maximum. This feature corresponds to real-world situations in navigation where it is unusual to require the maximum power in reverse for normal maneuvers. And when this power is needed, a larger step is always preferable to an insufficient step. Many modern inverters, for example that of Yanmar engines, offer a reduction ratio of 3.2:1 in reverse, regardless of the forward ratio, which is usually 2.2, 2.3 or 2.6:1. This discrepancy explains the very poor performance in reverse, many propellers with folding blades whose shaft rotates more slowly in reverse than in forward.

The Kiwiprop concept solves this problem and offers exceptional performance in reverse.

All feathered propellers have flat blades to reduce drag under sail without rotating force. The pitch of conventional propellers is progressive and increases as one approaches the emplanture to take into account the decrease in peripheral velocity correlative to the reduction in diameter. To determine an equivalence with the pitch in inches it is therefore necessary to take into account the change in the pitch over the entire diameter.

Empirically, the experiment makes it possible to say that on a 17″ propeller a pitch angle of 21° is equivalent to a pitch of 12 inches.

Of course, with a larger diameter, the same angle produces a larger step in inches. It is therefore preferable to express the pitch in degrees of angle for feathered propellers.

Unlike other folding or feathered propellers, Kiwiprop propellers can be laid as is, without any disassembly. After the appropriate checks described in the user manual, the propeller can be mounted on the cone, or the grooves in the case of a Saildrive base. Then simply tighten the nut with a standard 1/2″ square for socket wrench. Then lock the nut with the 2 stainless steel adjustment screws on the back of the hub by locking them with Loctite and the propeller is ready to use.

Obviously, blades are not as strong or stiff as bronze blades, but the real question is whether they are strong enough for the purpose for which they were designed. Almost all modern aircraft are equipped with propellers made of composite material.

In terms of weight ratio, Zytel contains about 35% glass, making it a very strong and rigid material. The black color is not due to the presence of carbon which eliminates a corrosion factor. DuPont’s website contains comprehensive technical information about the physical characteristics of the many Zytel variants that the company produces.

With the choice of a propeller with 3 blades rather than 2, the forces applied to each blade immediately increase from 50% to 33% of the total mechanical stresses applied to the propeller. Another aspect that comes into play in the design is the cost reductions inherent in the choice of a composite material that allows in a catastrophic situation, to sacrifice a blade without significant financial consequences. After a large impact at its end (surface that always receives shocks first), the blades invariably tear beyond the outer end of the fixing cavity, leaving all other parts intact.

We are convinced that it is better to lose a blade that is easily replaceable and whose price does not exceed 100 €, rather than the entire propeller or transmission after a stranding or impact with a tree trunk or wetting chain. The cost can still be much higher with a saildrive engine where the entire base can be damaged.

The ropes caught in the propeller simply cause the engine to stall and so far the reports we have received on this type of incident indicate that the Kiwiprop propellers have always come out intact. The shape of the blades with the leading edges well rounded at the emplanture was designed to deal with these problems.

Until today we have never had to repair a blade and we are convinced that their resistance corresponds well to the intended application. Keep in mind that composite propellers are now available for outboard engines up to 250 hp.

In other words, they are largely quite solid !

If you own a catamaran without a keel on which the propellers touch the bottom first in case of stranding, we advise you to embark a set of blades.

If you are embarking on a long cruise with the prospect of sometimes finding yourself in very isolated areas or if you have to sail in regions paved with coral blocks or characterized by a significant risk of encountering floating debris, do not hesitate to embark a blade, or even a set of spare blades.

In many cases, the most economical and safest insurance is to carry a spare propeller with three fixed blades that will always allow you to reach a port.

We believe, however, that for the vast majority of boaters, there is no need for replacement blades than for any other type of propeller. Apart from the situations indicated above, we receive very few orders for spare blades.

This topic is developed in the user manual but in summary, the propeller as delivered, contains enough lubricants to require no intervention until the next fairing. It is necessary to grease each blade via the lubrication hole by removing the small pozidrive stainless steel screw on the face of each blade. The propeller also includes two additional small lubrication holes, one very close to the Delrin™ front cone in the cast bronze part that holds the thrust of the pitch screws and one near the outer perimeter of the bronze domed part in the rear part of the propeller. The holes are chamfered so as to allow the use of a fine-tipped greaser. The external protection of the lubricator must be removed.

Each of these five lubrication points must be filled with high-quality marine grease, e.g. Shell™ Nautilus Marine Grease – NLGI No. 2.

Check that the reversing rollers rotate freely and facilitate rotation with a light lubricant – such as CRC, use clamps if necessary. These rollers can in the long run, be braked by marine deposits when the propeller has not been used for a while.

To achieve a laminar flow of water guided by the hull and which influences the performance of the propeller, all propellers need a minimum gap between the blades and the hull. Too narrow a space can also cause vibrations to pass through the hull. Indeed when in their rotation, the blades pass close to the hull, the turbulence caused by the displacement of the incompressible water, can generate these vibrations.

Some empirical methods recommend a free space equal to at least 10% of the diameter of the propeller – but a larger space often requires a greater inclination of the shaft which impairs the performance of the propeller.

Due to the low speed characteristic of low-motorized moving sailboats, this space is not as critical a factor as in many other configurations.

With thin ends, unlike folding blade propellers that use the mass of the ends to create the thrust in reverse using the centrifugal force generated, our empirical experience shows that a decrease in this space has virtually no effect on performance or vibration.

We recommend a minimum deviation of 12 mm (1/2″), but obviously more space is better.

In short – if the rotational speed of the shaft is greater than 1500 rpm [Divide the maximum engine speed by the reduction ratio of the inverter], if the angle of inclination of the propeller shaft is large, if the blade surface is very small or if the propeller rotates in a still turbulent flow of water, no propeller, including a Kiwiprop, cannot achieve its optimal level of efficiency.

The possible performance improvement depends mainly on the level of performance optimization of your current propeller that the existing configuration allows to achieve.

We consider that a Kiwiprop propeller achieves very roughly the performance of a fixed three-blade propeller with perhaps a loss of speed of about 0.1 to 0.2 knots at cruising engine speed.

From experience we know, however, that in many cases the original propeller is not perfectly adapted. In this situation, the Kiwiprop propeller makes it possible to achieve superior performance to the engine.

Very often the Kiwiprop propeller is mounted as a replacement for a fixed two-blade propeller with insufficient blade surface or a fixed three-blade propeller that was originally incorrectly sized. The variable pitch allows an optimal economic adjustment, unlike the costs related to the need to increase the stock of fixed-pitch propeller models.

Refer to the user testimonials on our website for specific examples of the most common engines and transmissions.

It is always very difficult to provide accurate data because of the number of variables to be taken into account. According to the results of laboratory studies published by MIT, a 16″ fixed three-blade propeller creates a drag greater than 30 kg at 8 knots. This figure was published by the journal “Practical Sailor” in the October 1993 and January 1995 issues. [See our Inernet website].

This value has a significant influence on performance under sail. Our empirical knowledge allows us to affirm that on a standard hull of 30 to 40 feet sailing close to 15 knots of wind, the speed increases by about 0.75 knots while the angle of ascent is improved by 10 degrees, which translates into a significant improvement of the VMG compared to the same boat equipped with a fixed three-blade propeller.

At the bearing the speed gain can reach 1.5 knots – again depending on the specific characteristics of the ship and the situation encountered.

In short, the improvement in performance under sail is spectacular and this is an important reason to adopt this propeller as a replacement for a fixed blade propeller.

Compared to a folding propeller, the sailing performance remains unchanged, but the improvement in reverse efficiency is spectacular.

The ends of the Kiwiprop propeller blades are strongly beveled for two reasons.

First of all, the profile of the blade section must pass through a flow and activate the feathering even when the propeller is mounted on a shaft that forms an angle not only with the waterline and even more so with the orientation of the water nets parallel to the rear slender lines of the hull that invariably rise in the stern area near the propeller.

The beveled ends make it possible to maintain the stability of the angle of attack of each blade according to their respective position in relation to the water nets whose flow is disturbed by the angle of the propeller shaft and the inclination of the rear slenderness. In addition, since the ratio between the diameter of a propeller and the power required is about 1/5, it is clear that most of the thrust is produced by the ends.

This principle has long been known to aeronautical engineers – it is enough to observe the shape of the most recent helicopter blades or propellers of the new turboprops of short-haul aircraft, which gives a good indication of the current trend.

It is therefore particularly important to give the importance it deserves to the profile of the section of the blades at their end. In propulsion unlike the flag position, the shape of the tip of the blades corresponds to what is usually seen on the best propellers currently available on the market. According to defined criteria, the shape of the profile is comparable for aeronautical and marine applications.

The effect of these design constraints is that a diameter at the ends of the blades must be greater than that of comparable propellers.

By taking the measurement in the middle of the distance between the shorter leading edge and the longer trailing edge, a “medium” diameter is obtained that is roughly equivalent to that of competing propellers.

Our recommendations are therefore based on what we call the “nominal diameter” which is about 13 mm less than the maximum outer diameter measured according to the available space and generally about 13 mm higher than the recommendations applying to competing models.

An appropriate warning is clearly indicated in the quote form. If a simpler system existed, we would use it without hesitation, but when it comes to taking into account the beveled end, these measurement problems are unfortunately inevitable.

The propeller bearing the No. 17 was installed in November 1997 on “REWARD” – a Lidgard 44 equipped with a Bukh 48 engine with saildrive base that has sailed extensively since then.