I have mounted the 'old' prop now as a reminder of a number of things:
- Spending eight days on the 'hard' while waiting for a replacement
- That sometimes what appears to be the right thing just doesn't work as intended
- It is still a beautifully sculpted work of art!
A two-bladed folding prop is at once a simple and at the same time complex piece of equipment and I have learned a considerable amount in the interim of waiting and discerning the right replacement. I'm reliably informed that the two key variables are diameter and pitch, and changing one will impact the other.
Other factors involved are the displacement of the hull, the angle of the shaft and its proximity to the hull, the ratio of the gearbox (forward and reverse), and the horsepower of the engine. Factoring all these together you can make an educated guess as to what prop is required.
So, bearing all this in mind, the previous owners chose the above. However, it does now appear that they hadn't factored in the gearbox ratio and the ability of the prop shaft to turn quickly enough to fully open the blades, especially in reverse. This provided some issues in approaching docks and stopping in time!
They also consistently ran the engine at lower revs than recommended (1900 rpm as opposed to 2500-2700) as a working range for the engine to run efficiently. This was partly due, as it turned out, because of the loose prop strut that was never detected/repaired and which contributed to severe vibration at higher revs.
This old prop would appear to be the right diameter but had too much pitch or 'bite'. Consequently the engine would bog down and we could not get it to rev high enough.
I did some reflecting with the EDBC congregation about the nature of a 'propelling' spirituality and the lessons learned from our old prop:
- Of the need to have a capacity for both forward and reverse (we find value in looking look back and ahead!)
- Of the need to be fully open to be functional and effective (not closed minded or lop-sided)
- Of the need for the right power to turn and function (to be connected to the right source)
- Knowing that the two blades complement and balance each other (we profit from a both/and approach to spirituality)
