Which shaft zinc do you like?

[John Stone]

The engine/shaft redesign provides zinc options. For the uninformed, please enjoy the 24 page engine installation thread for the Far Reach. Might help you get to sleep. Or maybe give you nightmares.

Anyway, I have two zincs options that support the flex o fold two blade folding prop. One is the bullet. The other a standard donut. The donut has a little more diameter—about 5/16”. The grey PVC pipe represents the shaft log. I can fair it to match the diameter of either zinc for good hydrodynamics. No problem.

The bullet is longer. Twice as long as the donut. Means the unsupported shaft is longer.

Obviously there needs to be a gap between the shaft log and the zinc due to the bearing being proud of shaft log 1/4” and room for water access to same.

What do you think—hydrodynamically, practically, economically, common sensically....

Convince me. One way or the other. Lay it out there. No Jim. This is not agonizing.... Perhaps obsessing??

[Jim Walsh]

I’d go with the donut since spares could be stored compactly, are commonly used, and available. I use one of the streamlined shaft zincs purely to enhance my performance under sail.

[Keith]

The donuts are also available in different width to fit what ever gap you have.

Keith

[wikakaru]

You should consider the tip clearance available for the prop in the two different positions. If you have plenty of tip clearance, I'd give a slight nod to the shorter donut to keep vibrations down when the prop becomes unbalanced from marine growth; if you are a little short of tip clearance, push that prop farther back and go with the bullet. Also, keep in mind that the decisions you make here may keep you from ever changing the prop to something different. You might see what size prop you would be using if you changed to, for example, 2- and 3-bladed Max Props and other brands of folding props.

Experts vary on recommend tip clearance--anywhere from 10% to 25% of the diameter of the prop. I'd err on the large side and have plenty of clearance for less turbulence around the prop when motoring.

Smooth sailing,

--Jim

[John Stone]

You should consider the tip clearance available for the prop in the two different positions. If you have plenty of tip clearance, I'd give a slight nod to the shorter donut to keep vibrations down when the prop becomes unbalanced from marine growth; if you are a little short of tip clearance, push that prop farther back and go with the bullet. Also, keep in mind that the decisions you make here may keep you from ever changing the prop to something different. You might see what size prop you would be using if you changed to, for example, 2- and 3-bladed Max Props and other brands of folding props.

Experts vary on recommend tip clearance--anywhere from 10% to 25% of the diameter of the prop. I'd err on the large side and have plenty of clearance for less turbulence around the prop when motoring.

Smooth sailing,

--Jim

Jim,
All good points. Have taken all into account. Tip clearance was the big one and played a big role in chopping four inches off the top of the rudder. My design estimates indicate plenty of clearance with either zinc. Once the engine is in and the bearing too I’ll have a more precise way to measure. I agree on prop vibration. But don’t know how much difference 1” will make. The bullet zincs were not easy to find. The donuts seem to be common. I’m leaning towards the donuts.

I don’t see much value in compromising design considerations for the flex o fold for the possibility of installing a different prop. Worse case it would require a new shaft. I want to do all I can do to maximize the design for this prop to work as well as possible. I admit that the whole thing is a bit of an experiment. I “think” it’s going to work fine. I’ll “know” soon enough. I accept the compromises required are not insignificant. The nod has always been towards sailing performance and away from motoring. It’s the right approach for me though I appreciate most anyone else would go the other direction. Just the way I am wired. I’m looking forward to seeing how this turn out. I have never installed an engine in a sailboat. It’s been fun and I have learned a ton....