Why we upgraded to a feathering prop?

Upgrade of our propeller:

Why I chose a feathering prop!

Ein Propeller mit festen Flügeln kann unter Segeln zum Beispiel einfach mitlaufen. Er belastet damit aber sämtliche Lager und man hört vor allem im Schiffsinneren wie sich die Welle mitdreht. Alternativ dazu legt man einen Gang ein und hat damit Ruhe. Doch dann wirken die Propellerflügel wie eine Bremsfläche im Wasser. Und je nach Geschwindigkeit übt der Wasserwiderstand teils gewaltige Kräfte aus. Also keine der beiden Optionen ist wirklich ohne Nachteil. Daher wurden die sogenannten Faltpropeller, oder als weitere Möglichkeit, Drehflügelpropeller entwickelt. Hier erkläre ich die generellen Unterschiede und für welchen Typ ich mich letztendlich für unser Boot entschieden habe.

Folding propellers are generally used in sailing yachts and auxiliary propulsion gliders. When the engine is running, they unfold in rotation mode due to the centrifugal force, the blades come under thrust against a stop and act like a normal propeller. This works when driving forwards and backwards. When the motor is at a standstill or the shaft is at a standstill, the wings fold under the flow of water and often also supported by spring force along their axis backwards. This reduces resistance almost to zero. The principle of the feathering propeller is very similar. In the case of such propellers, the centrifugal force does not act, but an integrated gear actively moves the blades into the respective position. So the wings turn for either a forward position, a backward position or neutral. If the machine stops, the blades turn into a horizontal "sail position" due to the inertia of the propeller and the shaft on the one hand and the flow of water on the other. There are different models, each with different characteristics. You can find plenty of explentation videos on YouTube or in sailing magazines.

Two considerable issue of some models:

1) In theory it sounds wonderful that a folding propeller unfolds due to centrifugal force, but in practice this doesn't seem to be that easy and is not entirely true. At least there are some very impressive examples on YouTube that problems can occur especially when reversing. I have given two examples below. There is also a nice propeller test published in the German language  magazine "Segeln". However, the tables are very telling in every language: reverse is not the strength of every product. I am pretty certain the same evidence exists in English.

2) Some types of propellers have exposed moving parts, e.g. gear wheels. And even if you want to protect your prop with the appropriate paint, it may be that sea creatures or just sand or stones get stuck here. This blocks the mechanism and disrupts proper operation.

So, despite the somewhat more larger structure, I decided on a Variprop feathering propeller with 4 blades. It comes from the manufacturer SPW, which specializes in the manufacturing of such propulsion systems. To date, the prop has never let me down, so I'm completely satisfied. In the course of the refit, the stuffing box, which was pretty worn out already, was replaced and the shaft rebalanced. The only downside: again an expensive investment that you can't see ;-)

A special feature of the feathering propeller is that the incline can be set separately for forward and reverse speed. This is a big advantage over other designs. To find the correct settings for your boat, you need to be able to determine certain parameters with certainty: length at waterline, displacement, payload, engine power at certain RPMs, gear ratio and much more. This is where a science begins that has so far remained hidden to me and I personally can only advise working with experts. Have fun exploring this part of your boat!

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