Wrong Prop

[HermannLenz]

My boat ( 34 ft. / 10 tons ) is driven by a Mercedes OM 352 engine , 95 hp at 2600rpm , gearbox 3:1 and has a 20" x29" 3-blade prop . I think , this prop is´nt the right . She runs 6 knots at 1700rpm , 7 knots at 2300 rpm with a 3 - feet wave behind her .
Who can tell me the right prop or can give any tipps ?

Greetings
Hermann

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[boatone]

Give Steel Developments a call 020 8874 7059.
Theyre usually very helpful mand props is their business.

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[Baltimore_Bill]

A very quick hack through the Surfbaud spreadsheet and it turns up:

22" dia x 21" pitch for a hull speed of 8.5 knots. (If you have room for a 22" diameter prop.) So 29" pitch is probably a bit OTT

Do you get lots of black smoke out the back????

I would suggest that the 3 foot wave will probably be there regardless at that speed unless you retrim the boat.

But talk to Steel Developments, they'll be able to suggest alternatives and fine tune the numbers.




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[stamfordian]

my prop calculator says your prop should be 26inches by 21 inch pitch to give max speed of 8.4 and says that increasing DAR will not be enough,can you get a larger diameter prop on, this might help.

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[brianrunyard]

Running your figures through PropCalc gives:-
22" Pitch x 26" Dia; max speed 8.16 knots.
If you want to try PropCalc or Propking they are both downloadable from the net, there are links on my site.
Regards,
Brian
http://homepage.ntlworld.com/brunyard

<hr width=100% size=1>Brian
http://homepage.ntlworld.com/brunyard

 

[HermannLenz]

Thank You for answering.
I thought , that the prop isn´t the right. But the place is for only 22" dia.
Perhaps I´ll fit some 22" prop in the next year , ´cause the actuall prop is quite demaged by a big stone on the ELBE river .

MfG
Hermann Lenz

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[HermannLenz]

Hy, Brian ,
thanks for information. Have loaded down propcalc and will try to use it.
But I knew , that 29" pitch and 20" dia is "the worst case" for the boat and your result is the much better.
But I can use only 21 - 22" dia , as the area is restricted .
In the next year....I´ll try.
Thanks
Hermann


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