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Old 25-06-2015, 20:58   #1
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3 blade props on SD20?

My 12,000 lb cat came with 3 blade props on the SD20 powered by 2GM20FC engines. The spare prop is a 15 x 12 so I expect the ones on there are the same. While motorsailing, no problem but when motoring only, one engine is working too hard and when sailing, the 3 blades seems to be slowing me down. I noticed that originally the SD20 came with 16 x 11 or 18 x 12 2 blades. We will be hauling out later this summer, should I consider switching back to 2 blades in preparation for full time cruising?
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Old 26-06-2015, 03:27   #2
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Re: 3 blade props on SD20?

Not sure why or what you mean about one engine is working too hard? We have same eng and drives w the two bladed props.
What is your performance and consumption like motoring? And any comparative data to other cats like yours w 2 bladed set ups?
Our 38 Athena motors in calm conditions 6 knots at 2500 we avg 2/3 gal per hour at this cruise . 4.8 on 1 eng. Going to 3000 rpm we gain maybe a knot but consumption doubles.
Not sure where you are but it seems we tend to motor more then sail. If motoring perf is great. Id keep the 3 blades unless they are killing your sailing.
Another fyi we gain half a knot when sailing w drives in neutral. They do hum a bit more and if it's lobster or crab season we keep them locked in gear to prevent snags. Folders may be your best bet.

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