Prop and shaft

[Knotical]

Hi everyone, I searched the forums but didn't find an answer to my specific questions.

1. I may have to change my prop shaft (bronze) because of corrosion, how do I evaluate whether it's time to change it or can it be "repaired"? Is there a gauge that tells how much corrosion is bad? The shaft has small pittings but I don't see a significant loss of thickness and there are no cracks.

2. If I change it, should I replace it with a similar-sized bronze shaft or go with stainless steel? Pros and cons of each?

3. Is replacement easy as in remove the old one and install the new one? Do I need to do anything else before/afterward? I will replace the Cutless bearing too while I am at it. Btw, my prop is offset to port and I won't need to drop the rudder.

4. The prop seems to be in good shape and I will keep it, how do I get that serviced to get the shine back?

Thanks,
Darshan

[Wotname]

Originally Posted by navdi

Hi everyone, I searched the forums but didn't find an answer to my specific questions.

1. I may have to change my prop shaft (bronze) because of corrosion, how do I evaluate whether it's time to change it or can it be "repaired"? Is there a gauge that tells how much corrosion is bad? The shaft has small pittings but I don't see a significant loss of thickness and there are no cracks.

Has the colour of the bronze changed near the pitting? Usually the corrosion associated with bronze is de-zincing and that causes the colour to change to a more pink (or coppery) hue. Just like brass but much much much slower.

If no colour change, then there is no significant problem (AFAIK).

The pits (if extensive in area but not deep) can be machined out assuming there is still sufficient material remaining for the torque of the engine/prop size and the colour remains as bronze.

2. If I change it, should I replace it with a similar-sized bronze shaft or go with stainless steel? Pros and cons of each?

IF bronze stock is available for the size you need, it will certainly be very very expensive. Stainless steel (in the lower grades like 316 etc) will be readily available in most parts of the world however it is poor choice for longevity. More exotic (and better) SS grades exist but the availability and price varies with location.

3. Is replacement easy as in remove the old one and install the new one? Do I need to do anything else before/afterward? I will replace the Cutless bearing too while I am at it. Btw, my prop is offset to port and I won't need to drop the rudder.

Unless you know the exact measurements of the old one, you will not be able to get a new one machined to the correct size until the old one is removed.

You will need (or should need) a puller to remove the prop. Be sure to lap the old prop to the new shaft or have the guys making the new shaft to do that when they machine the new shaft. They will of course, need to have the old prop in the shop at the time.

4. The prop seems to be in good shape and I will keep it, how do I get that serviced to get the shine back?

Sand / wire bush and then polish like any other metal.

Thanks,
Darshan

How hard is it? That depends on your skill level and previous experience. For some of us, it is easy - for others, not so much .

If you are asking then I assume you haven't done it before but that doesn't mean you can't.

If you have say, changed out a boom or a headsail furler, then you probably have sufficient skills to change a prop shaft. If such jobs have you searching for a professional rigger, then maybe you need someone to do the shaft.

By the way, how old is the existing shaft?

[Jim Cate]

FWIW: Our shaft is made from 2205 grade stainless, somewhat but not too much pricier than 316. It is stronger, stiffer and much more corrosion resistant than 316. After 30 years and ~140,000 cruising miles, I had the shaft out last September and there was zero observable wear and zero pitting. I was impressed.

Jim

[Knotical]

Wotname and Jim - thanks for your responses.

The shaft does have some "pinkish" hue but it's not extensive, I will sand it and see how bad it is - I don't want to replace it if it's not necessary. I think I should be able to change the shaft if required, I have done some work that you mention and more.

The shaft may very well be original, I have the work that the PO did but not what other 2 owners did before him.