F-25 Prop match..Need help!!!

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dirkpitt1
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F-25 Prop match..Need help!!!

Post by dirkpitt1 » Fri Mar 31, 2006 3:25 pm

I have a 1978 F-25. I have a rebuilt 305 closed system engine installed with only a 1:1 tranny, no room for a reduction gear. I had a 14x14 on it and I could not get but 2500 RPMs wide open, I then put on a 14x12 and got 3500 to 3800 RPMs. I am looking for a LH 12x10 this should put my RPMs where I need them, but no biting as much water. I lack top end, and I can barely get up on plan. Anyone else have a 305 in their F-25 that can help me out?....Steve

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prowlersfish
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Post by prowlersfish » Sun Apr 02, 2006 8:04 am

I belive a 12x10 will be what you need I checked a prop cal. I have
based on 200-220 hp and 5500 gross weght ( I only guessed ) this should get you top end high 20s (4500 rpm) cruse at 3000 apox 20 mph
if your weght or hp is difrennt let me know and I will recheck

Paul
TROJAN F36 Conv.
6BTA Cummins diesels
Life is to short for a ugly boat :D
2009 TROJAN RENDEZVOUS
Port Kinsale 2010 & 2011. Solomons get together 2011.

dirkpitt1
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Post by dirkpitt1 » Mon Apr 03, 2006 11:59 am

Thanks Paul, I have tried to locate a 12x10 LH prop. I cannot find one!!! Does anyone have one that they would care to part with? I have a 14x14, and 14x10 that I would trade, or I will buy it outright. I need one. Also, on that same engine, at idle I am getting a hint of fuel from the exuast. Could this be by cam or a vacum problem in my carb.? I know if there is any amount of gasoline in the crankcase will displace and thin the oil causing premature wear and bearing failure. Any ideas on this? Thanks in advance guys.

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rossjo
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Prop Calculator says 12x10, but ...

Post by rossjo » Mon Apr 03, 2006 12:06 pm

204HP, 1:1 drive, inboard
23' waterline lenght
avg. planing hull

Max speed w/ 14x7 3 balde cupped prop is 29knots @ 4,500 RPM @ 12 gal/hr.
& Cruise is 13.5knots @ 2500 RPM @ 2Gal/hour (nice!)

For your 1:1, it recommends a 12x10 3 blade cupped prop.

Best case would be a 15x16 with 1.6:1 reduction.

I personally recommend a 13x12 and a 4-barrel carb so you can kick in more top end., and cruise more steadily. Otherwise, the 12x10 should work ok.

results____________________________________________________
MAX PERFORMANCE
Available Power: 203.7 SAE hp ( 151.9 kW) @ 4500 RPM
Max Speed: 29.8 kts
Fuel: 12 US Gall/Hr (typical)
CRUISING PERFORMANCE
Cruising Power: 42 SAE hp ( 31.1 kW) @ 2500 RPM
Cruising Speed: 13.5 kts
Fuel: 2 US Gall/Hr (typical)
RECOMMENDED PROPELLER
Diameter: 11.7 in. Pitch: 9.8 in.
Blades: 3 Cupped: Yes
Increasing the transmission ratio will improve prop efficiency.
PROPELLER BASED ON INPUT DIAMETER
Diameter: 14.0
Pitch: 7.0
Blades: 3
ALTERNATIVE GEAR/PROP COMBINATIONS
Gear Ratio Shaft RPM Dia. Pitch
1 4500 11 10
1.2 3750 12 12
1.4 3214 14 14
1.6 2813 15 16
1.8 2500 16 18
2 2250 17 20
2.2 2045 18 21
2.4 1875 19 23
All are acceptable - but the lighter the row color - the more efficient the prop at this boat speed.

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Captain Ross, 2009 Trojan Boater of the Year
"Viva Mahia" F32 Cummins 6BTA diesels,
"Mack Attack" Chaparral 244 Fish, SeaPro 180, McKee 14, Montauk-17
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prowlersfish
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Post by prowlersfish » Mon Apr 03, 2006 5:57 pm

dirkpitt1 have you check with bob at Becon marine or try calling near by prop shops and there is all ways ebay I belive rossjo used the same prop calc. as I did is so you fuel burn will be higher then what is posted. the fuel burn looks like its for diesel . other then that it should be real close I have have real good luck with that calc.

Paul
TROJAN F36 Conv.
6BTA Cummins diesels
Life is to short for a ugly boat :D
2009 TROJAN RENDEZVOUS
Port Kinsale 2010 & 2011. Solomons get together 2011.

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rossjo
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GOOD POINT

Post by rossjo » Tue Apr 04, 2006 12:03 pm

prowlersfish - good point on the fuel burn. Gas will be more - probably 25% more or so.

I have purchased about a dozen different props on eBay - only 1 stinker so far. The feedback is important, so check that!

LH 12x10's are hard to find though ...
Captain Ross, 2009 Trojan Boater of the Year
"Viva Mahia" F32 Cummins 6BTA diesels,
"Mack Attack" Chaparral 244 Fish, SeaPro 180, McKee 14, Montauk-17
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rossjo
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eBay 13L-12 for $250

Post by rossjo » Tue Apr 04, 2006 12:04 pm

Captain Ross, 2009 Trojan Boater of the Year
"Viva Mahia" F32 Cummins 6BTA diesels,
"Mack Attack" Chaparral 244 Fish, SeaPro 180, McKee 14, Montauk-17
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