name that prop..

[BravoVita]

My prop needs replacing and I have a few questions. The prop is starting to chip apart and it looks like rust on the inside. I am wondering if this is typical of 20-30 year old props or if it's a possible indication of the PO not being on top of sacrificial zincs. My main reason for asking this is because I am not familiar with prop issues and I want to avoid having to buy another prop soon. The million dollar question is what is supposed to go back on there and where should I buy it from? The old one has some obscure looking marks/numbers and I have not been able to wrap my head around all the numbers involved in online prop calculators. As always, all of your help is appreciated.

84' SOVEREIGN 28 (LWL 23', Beam 8.3', Displacement: 6800 lbs)
Yanmar 2gm (Freshwater cooled) 3,600 rpm, 16 HP, Gear Ratio 2.62:1

The prop I pulled off is about 14" in diameter with a 1" tapered shaft (I believe it is a Clockwise rotation.)

[BravoVita]

Originally Posted by BravoVita

84' SOVEREIGN 28 (LWL 23', Beam 8.3', Displacement: 6800 lbs)
Yanmar 2gm (Freshwater cooled) 3,600 rpm, 16 HP, Gear Ratio 2.62:1

I now believe this is actually a 2GMF with 15HP.

[DougR]

Using the info that you have given, my prop program says:

Top speed - 6.2 kts
Theoretical best 3 blade prop:
15.6 X 8.8 X 3

Next best in descending order:
15 X 9.4 X 3
14 X 10.5 X 3
13 X 11.5 X 3 but this prop will suffer from cavitation at high loads due to inadequate blade area.

Theoretical best two blade prop:
16.3 X 9 X 2

Next best in descending order:
16 X 9.25 X 2
15 X 10.2 X 2
14 X 11 X 2 with cavitation problems as mentioned above

Things to remember when buying props in the US:
- Normally sold in whole inch sizes on both diameter and pitch, but a prop shop will adjust pitch for you.
- Although larger diameter props are more efficient at displacement speeds, you should maintain blade tip clearance of 15% of the diameter between the blade tip and the hull. Anything less may be noisy and give some vibration.

Your existing prop is indeed a RH turning prop. It was made by Radichi (?) an Italian builder, and because of that you should check carefully and make sure it is a 1 " shaft and not a 25mm shaft. Metric shafts normally have a different taper angle than SAE and they are not interchangeable.

Hope this helps....
DougR