Is this shaft anode fitted properly?

[MattS]

Sorry to revive an old thread.

I sent an email to MG Duff asking for their opinion on my anode installation which is the opposite orientation to what MattS has just done. They asked to see my set-up (see pic below) before commenting.

View attachment 115765

The reply was -

So there you go. Maybe it's because mine is slightly further away from the bearing than MattS.

Thanks @Tradewinds - very useful!

I ended up launching with the anode tapered end pointing backwards, but I did actually move it a bit further away from the P bracket so hoping my setup won't do me any harm for a season!

 

[greeny]

For me, there are two things at play here. Water flow into the bearing and probably more turbulence/drag if you fit it square end to the bow.
If I was fitting it close- ish to the bearing I would probably fit it with the taper end to the rear to allow water to flow into the bearing easier. Otherwise if fitted a good way forward of the bearing, I would probably fit it with the tapered end to the bow to reduce drag maybe. The only thing that would bother me really though would be not to restrict water to the bearing. Everything else is small fry in the grand scheme of things.
Although no doubt someone will come along and give me a lesson in hydro-dynamics or whatever it's called and tell me I'm wrong.

 

[Hoist]

I would disagree with a lot of the advice here

Do not put it too close to your P bracket.

This will hamper water flow to your cutlass and also if you have to move your shaft back like I did to remove my gearbox then the pesky anode ill be in the way.

I would also say you put flat side first. classic teardrop shape. if you think otherwise then look at your keel



this year I counted 8 boats in the marina with the big pear anode round the wrong way

 

[Tradewinds]

this year I counted 8 boats in the marina with the big pear anode round the wrong way

I'm sure they're going a lot slower. ( ).

 

[greeny]

I would disagree with a lot of the advice here

Do not put it too close to your P bracket.

This will hamper water flow to your cutlass and also if you have to move your shaft back like I did to remove my gearbox then the pesky anode ill be in the way.

I would also say you put flat side first. classic teardrop shape. if you think otherwise then look at your keel

View attachment 115818

this year I counted 8 boats in the marina with the big pear anode round the wrong way

I would disagree with a lot of the advice here
The anode in question is not the shape of a keel chord or the shape of the photo you post. It has a flat end and is not teardrop shaped. Look at the photo in the original post. Either way round won't make even a gnat's cock of a measurable difference on your boat speed. But yes, I agree it needs to be clear of the bearing for water flow purposes.

 

[vyv_cox]

Disregarding the water flow for a moment, I know from my own experience, as well as rotordynamics theory, that putting a heavy anode in the central between bearings position is likely to affect vibrations due to resonance. The natural frequency of the prop shaft on my boat is just below 2000 engine rpm. Putting the anode forward from its usual position about 15 mm ahead of the P-bracket definitely increases vibrations at this rpm.

 

[Bouba]

Disregarding the water flow for a moment, I know from my own experience, as well as rotordynamics theory, that putting a heavy anode in the central between bearings position is likely to affect vibrations due to resonance. The natural frequency of the prop shaft on my boat is just below 2000 engine rpm. Putting the anode forward from its usual position about 15 mm ahead of the P-bracket definitely increases vibrations at this rpm.

Thank you, this is the information that I’ve been looking for. I don’t have a shaft anode but am thinking about it

 

[MattS]

The anode in question is not the shape of a keel chord or the shape of the photo you post. It has a flat end and is not teardrop shaped. Look at the photo in the original post.

@greeny The anode in my original post is teardrop shaped - see this photo from a different angle (from before I switched the orientation around).

 

[MattS]

Disregarding the water flow for a moment, I know from my own experience, as well as rotordynamics theory, that putting a heavy anode in the central between bearings position is likely to affect vibrations due to resonance. The natural frequency of the prop shaft on my boat is just below 2000 engine rpm. Putting the anode forward from its usual position about 15 mm ahead of the P-bracket definitely increases vibrations at this rpm.

Interesting - thanks @vyv_cox - I ended up putting mine about 40mm from the P bracket - will be interesting to see if it causes vibration at different revs, which I will keep an eye on over this season!

 

[dragoon]

Dragoon has knurled sections on the shafts for the mounting of the shaft anodes. I would say they are 1/3 of the way from the P-bracket and 2/3 from the entry point into the hull. There is a balance between being too close to the P-bracket and restricting water flow to the cutlass, and being too far up the shaft where their unbalanced mass will have an effect on vibration.

 

[vyv_cox]

Interesting - thanks @vyv_cox - I ended up putting mine about 40mm from the P bracket - will be interesting to see if it causes vibration at different revs, which I will keep an eye on over this season!

I don't think 40 mm will make a lot of difference. It's anodes more like 40 cm away that cause problems.

 

[greeny]

@greeny The anode in my original post is teardrop shaped - see this photo from a different angle (from before I switched the orientation around).

View attachment 115832

You cry strange shaped tears then. It doesn't matter to me anyway, as I said it makes no difference in my mind to boat speed or anything else for that matter unless it's close to the bearing.