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[poddy]

Hi All

I was reading Debssnal's excellent post about his new tug(s). He mentions needing prop speed of 950 rpm for max hull speed.

This begged the question. How did he work that out then?

I found these two links. They may be of interest to someone.
[url]http://www.psychosnail.com/BoatSpeedCalculator.aspx/url]

[url]http://books.google.co.uk/books?id=8w09O4hooWUC&pg=PA48&lpg=PA48&dq=propeller+water+slippage+formula&source=bl&ots=AdoHVlmEDY&sig=gE3R-2yfdLNNcK6g_b57f6uMZ5c&hl=en&ei=j2nmS6SNDIvwmwPUiekh&sa=X&oi=book_result&ct=result&resnum=2&ved=0CB4Q6AEwAQ#v=onepage&q&f=false/url]

I typed my boat's data into the hull calculator (semi-displacement type) The results seemed pretty accurate. It told me I needed 212 watts of power, which is about what I have.

What methods do others use? Any mathematicians out there?

Mmm, now how can I squeeze in a kilowatt???

Pete

[DickyD]

Your links Pete

http://www.psychosnail.com/BoatSpeedCalculator.aspx

http://books.google.co.uk/books?id=8w09O4hooWUC&pg=PA48&lpg=PA48&dq=propeller+water+slippage+formula&source=bl&ots=AdoHVlmEDY&sig=gE3R-2yfdLNNcK6g_b57f6uMZ5c&hl=en&ei=j2nmS6SNDIvwmwPUiekh&sa=X&oi=book_result&ct=result&resnum=2&ved=0CB4Q6AEwAQ#v=onepage&q&f=false

[poddy]

Thanks Dick, I did it wrong again 

[Shipmate60]

Pete,
A lot of it is done using experience.
This model works well on these motors/props/voltage so a similar hull should behave in a similar manner.
Also models are usually overpowered as the wind/waves are not scale, but if you scaled up the environment we wouldnt be able to put to sea!!!!

Bob