How fast does my prop spin?

[PabloPicasso]

I have a 9 hp Volvo engine, single cylinder type, through a 110 saildrive. So how fast does my prop spin at max revs?

 

[sailorman]

depends on the gear reduction
engine what 3600 RPM 2 > 1 reduction

 

[Avocet]

I'd guess at slower than that. Avocet's got a single cylinder 1 horse BMW engine and a Hurth gearbox which has a 2.7 : 1 reduction going ahead. Probably doesn't rev much higher than about 3000 most of the time either.

 

[sailorman]

I'd guess at slower than that. Avocet's got a single cylinder 1 horse BMW engine and a Hurth gearbox which has a 2.7 : 1 reduction going ahead. Probably doesn't rev much higher than about 3000 most of the time either.

the OP stated WOT

 

[alahol2]

3200RPM at 1.66:1 => 1925RPM ???

 

[Tranona]

I have a 9 hp Volvo engine, single cylinder type, through a 110 saildrive. So how fast does my prop spin at max revs?

Your gearbox reduction ratio is 2.19:1. If your engine is a 2001 then max revs is 3200. So shaft speed is 3200/2.19 = 1461 rpm. Most Volvo saildrive combinations aim to get a shaft speed of around 1500 - for example the later 2010 has a reduction of 2.48 and a maximum revs of 3600 giving a shaft speed of 1451 - virtually the same as yours.

 

[PabloPicasso]

I'm just trying to assess how much oversized anodes on the hub of my folding prop might cause an imbalance problem. Current anodes can be done in 3 months. I'm looking for a solution and bigger anodes seems to be the most obvious one

 

[nimbusgb]

I'm just trying to assess how much oversized anodes on the hub of my folding prop might cause an imbalance problem. Current anodes can be done in 3 months. I'm looking for a solution and bigger anodes seems to be the most obvious one

3 Months! Find the electrical fault instead! Sounds like you have a serious leakage current! Is the boat connected to shore power a lot of the time?

 

[macd]

+1 with Nimbus.
Prop anodes are concentric so won't cause imbalance. But that's not the way to go: fixing the leccy issue is what's needed. If on shore power, do you have a galvanic isolator?

 

[PabloPicasso]

+1 with Nimbus.
Prop anodes are concentric so won't cause imbalance. But that's not the way to go: fixing the leccy issue is what's needed. If on shore power, do you have a galvanic isolator?

No not never connected to shore power. On a swinging mooring. Battery disconnected by keys every time I leave the boat. This type of hub often seems to be reported as having anode problems like this. I believe, now, it is the quality of the hub itself and poor anode design. Hence the need to fit bigger anodes

 

[macd]

No not never connected to shore power. On a swinging mooring. Battery disconnected by keys every time I leave the boat. This type of hub often seems to be reported as having anode problems like this. I believe, now, it is the quality of the hub itself and poor anode design. Hence the need to fit bigger anodes

I'm aware of your earlier thread, although I can't recall all the details. Before going to the bother of one-off anodes I'd be inclined to investigate the practicality of a hanging anode bonded to the whirly bits when the boat is on its mooring. However, I'm not particularly familiar with saildrives, so suggest you take further advice on precisely how this might best be accomplished.

 

[Tranona]

I'm aware of your earlier thread, although I can't recall all the details. Before going to the bother of one-off anodes I'd be inclined to investigate the practicality of a hanging anode bonded to the whirly bits when the boat is on its mooring. However, I'm not particularly familiar with saildrives, so suggest you take further advice on precisely how this might best be accomplished.

See my reply to one of the many similar posts by Pablo. The prop is electrically isolated from the drive and the anodes are wasting because of the materials used in the construction of the prop. There is no way of connecting it to an additional anode. The anodes are screwed around the boss so any larger anode would have to be specially cast to fit. However, at the rate his anodes seem to be going, even doubling the size would not solve the problem.

If it were my boat and I could not afford a Flexofold (which I have on my own boat), I would fit a standard Volvo 2 blade aluminium prop and tolerate the small loss in light airs sailing speed. Motoring performance would be better and no worries about galvanic corrosion.

 

[bigwow]

Volvo's previous folding prop did not have the anodes fitted and the spline used to corrode along with de zincifying of the prop itself which used to lead to problems with the meshing teeth. My anodes last about 8 months, but I am connected to marina mains and being a cat we change them on the beach while my granddaughter plays on the sand.

 

[vyv_cox]

Would it help to paint the prop? Reducing the area of blade forming the galvanic couple might help. Any experience?

 

[PabloPicasso]

Would it help to paint the prop? Reducing the area of blade forming the galvanic couple might help. Any experience?

Yes this seems to be a good approach. I'm thinking of painting with a zinc (cold dip) type paint or zinc phosphate like the big ships. I'm not sure what paint to use?