[Public-List] Yanmar 30GM30F prop size

[Bill Wallace]

The prop on my boat, Alberg 30 # 626 "Chewan" powered by a 2GM20F is a Dynajet 13x12 RH 3 blade.  That is the largest diameter prop which will fit - really it should max out at 12", not 13" as it is a bit too close to the edge of the aperture.  The prop is a bit too much prop for the engine - I'm not getting full RPM range (to 3000 rpm) at hull speed.  I can keep pushing it past about 3/4 throttle, but it only goes marginally faster with more horses after about 3/4 throttle.  I've run it for hours at 3/4 throttle and it seems fine.  The meter claims I'm getting 2100 rpm roughly at full throttle/full speed.  I'm going to measure that in the summer against the actual propshaft if I can figure out how so I can tell if it is really overpropped or the rpm is reading low.  With 50% more horses in the 3gm30f, I would probably go with something similar in size to the 13x12 prop, assuming you can make it fit.  The 3gm30f will need a 3 bladed prop to
 absorb enough power in the given aperture size.  

Bill.



On Monday, December 2, 2013 4:58:02 PM, John and Robin Churchill <grafpatrick at earthlink.net> wrote:
 
hello all-
I am helping a friend with an older A30, repowered with a 3GM30F.  Too much power IMHO, but she still will not make hull speed so I suspect the old underpitched Atomic 30 prop is still in place.  Anyone with practical experience with a good prop size?  Thanks.
John Churchill
Sanibel FL
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