Prop size?

[Deleted User]

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Scubacat

Duetta and I have emailed and his current prop was a 14x7.5 but he has ordered two new 14x9 props.
There is also some data on outboard props in the on line archive, technical data section.

Scubacat

I thought I would update on my original prop test data 

After using the 10 inch  5.75 inch 4 blade prop for a year or so, I found that whilst it had great acceleration and stopping power, it was less usable for motor sailing than I had hoped. In practice, the outboard needed to really go fast to help on those motor sailing occasions. This meant that fuel consumption was up in the 4 l / hr region.

This year we swapped to a new 9.25 by 10 pitch 4 blade prop that I did not have for my original trials. This is "over matched" to the engine, which now cannot exceed about 3800 - 4000 rpm when static. (my Yamaha is supposed to give 20 hp at 5500) However, in practical terms, the results are very good. We get about 3l/hr consumption, and achieve 5+ kts easily, and this is with 6 months of weed, in comparison to the original tests when the hull had just been cleaned. Reversing is now only adequate, in contrast to the 10*5.75 which could throw unwary bow crew overboard!.  Motor sailing is generally much improved, with perhaps a bit of a loss of the ability to punch into really strong headwinds and waves - but then that was always very uncomfortable and the crew objects to that!.     

If I get really into this I may try and get the prop modified with perhaps an inch less pitch, but for now its working really well.