Need more thrust.

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Hello,

I have a 9m lifeboat, 3m wide, ~3000kg displacement hull. It has a perkins 50hp@3600rpm, 2:1 gear and a 15"-13" screw.

It is reaching its maximum speed (stern digs in) in still weather, but in moderate waves or headwind the speed degenerates a lot.

I figure I need a bigger prop, and I would like to install an adjustable one. I have my eyes on a three bladed 52cm dia adjustable prop, can I use it with the same engine and tranny?
Will that improve the performance in heavy weather?

Thanks,

Sigurd

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Oddly, the Surfbaud xls sheet suggests that my pitch on my current setup should be 10, while the local propeller expert says that it should be 13, like it is now.