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Discussion Starter · #1 ·
I have an Islander Freeport 38, also known as an Islander 38C. The original engine was a 42hp Pathfinder 50. Not sure what transmission it had or the gear ratio. The prop was a Sailor 2 blade 17 RH 8. I repowered it with Yanmar 4JH2-TE rated at 63hp at 3600rpm with a KBW 20 transmission.

The people who installed it also changed the prop to a three blade 17X14. The prop size (they said) required a 1.25" bore size while the shaft is a 1" which I had to keep because of the size of the shaft passage through the keel. Since the shaft had a smaller keyway then the prop they used a bore reducer and a stepped key to fit both the prop and shaft. After about 200 hours the key broke allowing the prop to spin on the shaft. I had it hauled and the mechanic fitted another key to it. This broke after 40 hours. My question is in two parts.

1. Does anyone know of a prop that is compatible with my engine and transmission that has a 1" bore that will fit my shaft, either 2 or 3 bladed?

2. Can my original 2 bladed prop be adapted to this engine and transmission by changing the pitch. I realize that it will be under proped but right now at 3200 rpm (80% of rated capacity) I max out my hull speed anyway. It seems that I can foresake high end speed and still be ok, but not sure how that will affect the wear on the engine.

Since my prop comes out of the keel there is very little restriction on diameter of the prop. Any response will be greatly appreciated.
 

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Discussion Starter · #4 ·
I agree with what you are saying. The shaft is a tapered shaft and and they used a bore reducer to make the prop fit the shaft. It is a tapered nylon sleeve that fits over the shaft and makes the prop fit the shaft, however there is no way to lap it with this type of fitting. That is why I would like to go back to a prop with a 1" bore. The problem is that I was told that they could not get a prop with a 1" bore that had the diameter and pitch needed for this transmission and engine specifications. I'm not sure if that is true and I will be consulting with some prop experts next week. I was also told that this bore reducer and stepped key is quite common and rarely causes problems. Not sure if I believe that now.
 

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Discussion Starter · #7 ·
RichH, the shaft comes through the trailing edge of the keel and only extends out about 6", just enough to get the prop on and a donut style zink on it. I'm not sure how that is reinforced within the keel, whether it is just fiberglass or if there is some metal incasing the shaft passage and the cutlass bearing. I will take a look at it when I haul the boat in a couple of weeks. That is certainly an option although I'm not an accomplished enough fiberglass tech to attempt it on my own so I will have to factor the cost in of having someone do it for me. A new shaft is cheaper than a new prop so that will be a factor also.
 

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Discussion Starter · #12 ·
I admit I don't know a lot about props, pitch and engine/gearbox reduction. I find it quite confusing but my understanding after reading lots of stuff over the weekend is that a 3 bladed prop is less effecient than a 2 bladed and if it were possible to use a one blade (oar) that would be the most efficient. So going from a 2 blade to a three blade you would increase the pitch by a couple of inches, say from a 12 to a 14. So a two blade 17X12 would be the right prop for my boat with the current engine/gearbox. If I can increase the pitch from 8 to 10, it may not be optimal but with the increased HP of this engine I may be able to do hull speed at 3200rpm. Right now if I crank it up to 3200rpm I am stern down and creating a wake like a power boat. Too much for normal operation so I have tended to run at about 24 to 2500rpm, not optimal for this engine. So if I go to a two blade 17X10 I would sacrifice high end speed which I don't need anyway. I will definitely consult with a prop shop or two on this but like the last poster said, $70 to be ok is better than a major redesign of the shaft passage, or a new prop or changing the transmission. Had I known all this I would have never gone with this engine in the first place. Better yet the company that sold me this repower option should have never sold it to me in the first place. I won't mention their name here (yet) as I am still discussing it with them and this is not the only problem I have with the engine.
 
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