Coursekeeper vs. ring propeller: How effective are steering aids in practice?

Long canal trips are often a horror, especially for skippers of smaller gliders. The reason: older boats in particular often still have hull shapes that are perfect for fast gliding, but have significant deficits when it comes to directional stability at slow speeds. Snaking lines, or yawing, are the result. In practice, the helmsman has to constantly correct the course, which is more than annoying. The same applies to mooring and casting off manoeuvres in confined spaces. Here, the slightest breeze can shift the boat and turn the mooring manoeuvre into a show for the entire harbour crowd. The reasons for this lie in the underwater hull of the boat: In some cases, the rear hull sections are designed so flat that the lateral plan, i.e. the area that counteracts lateral drift, is so small that the boat has hardly any longitudinal guidance.

Coursekeeper vs. ring propeller

Steering aids such as the Coursekeeper, also known as Ruddersafe by other manufacturers, or so-called ring propellers, which are designed to better concentrate the propeller thrust and thus increase manoeuvrability, promise to help. Regardless of which solution is chosen, it is clear that additional drag surfaces are introduced into the water. But what effect do these drags have on speed and consumption when gliding? And how effective are they really at slow speeds? To get to the bottom of these questions, we had both a Coursekeeper and a Ringprop delivered to us and tried out both steering aids on an almost 40-year-old Variant wooden cabin cruiser (6 x 2.2 m). The Variant is characterised by the fact that it achieves planing speed even with a small engine, in our case a Yamaha F 40. This advantage comes at the cost of an extremely flat underwater hull, which is difficult to keep on course at slow speeds.

How do mooring manoeuvres work with the respective propeller?

In addition, it virtually "slides" over the water during tight mooring manoeuvres. For this reason, the shipyard has given the modern Variant plastic version a small keel that reliably solves this problem. The test programme initially included measurements without a steering aid using the standard aluminium propeller (11¾ x 10 x 3). The Variant exhibited the handling behaviour described above and reached its top speed of 35.6 km/h at 5500 rpm. The maximum fuel consumption was 0.39 l/km, which was reduced to 0.34 l/km at the most economical gliding speed of around 5000 rpm (30 km/h). The boat acknowledges fast turns with a powerslide in which the propeller ventilates (draws air) early. The resulting lateral forces are low.

Practical test of the Coursekeeper

Next came the measurements with the Coursekeeper. For our 6 metre boat, we chose size 2, which according to the manufacturer is suitable for boats up to 6.5 metres in length. Installation is simple and can be completed in around an hour, even by non-experts. The Coursekeeper is attached to the anti-cavitation surface of the outboard motor using the enclosed clamping device. No holes need to be drilled for this. Thanks to its folding mechanism, the Coursekeeper is designed to fold up automatically at high speeds to prevent the boat from oversteering. After just the first few metres at slow speed, we noticed a significant improvement in course keeping. The boat stayed on the chosen course, eliminating the need for constant corrections. The increase in comfort during longer straight-ahead journeys and mooring manoeuvres is enormous.

As intended by the manufacturer, the coursekeeper folds up as the boat exceeds the planing limit. However, this causes water spray to form, which increases at higher speeds. However, our assumption that this water spray would have a measurable effect on top speed and fuel consumption was only partially confirmed. With the Coursekeeper, the Variant achieved almost the same top speed and fuel consumption increased by just 0.04 litres/km - which is acceptable. In fast bends, the rudder forces increased noticeably, the turning circles became slightly smaller, but the propeller ventilated as usual when the steering wheel was fully turned.

To summarise, it can be said that the Coursekeeper does a great job and delivers the promised effect without negatively affecting consumption or speed.

Practical test of the ring propeller

Let's move on to the next candidate, the ring propeller. This steering aid is also easy to install and is used instead of the conventional propeller. It is important to keep to the same propeller dimensions. For our test, we chose the 11.8 x 10 x 3 version. The circumferential (eponymous) ring is intended to concentrate the thrust generated and thus improve the manoeuvring characteristics. In addition, the sensitive blade tips are protected, which should prevent damage in the event of grounding or hitting the beach. The ring propeller also protects any floats in the water. Before we come to the test results, we would like to point out that the ring propeller we tested is currently not available. Nevertheless, we are publishing the test results because they are also representative of similar products.

As with the Coursekeeper, the ring prop also makes the boat easier to control at slow speeds. The bundled propeller downforce increases manoeuvrability. Whilst the Ringprop cannot completely prevent yawing when travelling in the canal, it does reduce it to a tolerable level. Course corrections are rarely necessary. During the transition to planing between 3500 rpm and 4000 rpm, the measured speed - compared to the standard propeller - is reduced by around 1 to 2 km/h, which seems acceptable to us. However, the speed reduction at full speed is not acceptable. Here, the Ringprop slows down the engine by almost 500 revolutions (with the same propeller dimensions), which has a negative effect on both the speed and the kilometre consumption. At a maximum speed of 28.7 km/h, the boat is around 7 km/h slower with the Ringprop and consumes 0.05 l/km more in this situation.

The manoeuvres performed at top speed show that the ventilation limit of the ring propeller is higher and that the boat can be steered well in tight turns with low steering forces.

Conclusion: Propeller in comparison

If we summarise the individual results, we come to the conclusion that both steering aids, the Coursekeeper and the Ringprop, do their job well. Nevertheless, we favour the Coursekeeper as it has less influence on speed and consumption. In addition, it increases the lateral surface area of the boat, which counteracts drift in windy conditions.

Measurement results