Inboard Experts

[dsharp]

I don't profess to be an expert but an automotive engine turns counter-clockwise(left hand prop)You always look at a marine engine from the rear. on the 71 and 72 series borg warners the only box that reverses is the 1.9:1. They made a 2.1 to 1 and 1.9:1 to run pairs that used standard rotation engines. Most counter-rotating conversion change the timing chain for a timing gear. Cam turns same dir- crank rotates opposite direction. Some mercruisers used chains and everything ran counter. The starters are always different. Some people have tried to reverse the rotation in the borg warner but they won't hold up because the reverse clutch pack has fewer plates and discs. Physically it will do it but it will not last long. Most rudders are offset like a couple have noted to simplify shaft removal without dropping the rudder. I think Gary made the point that the most important thing about props is the engine has to be able to turn the rated rpm's at full throttle. Some rough rules of thumb are 1" diameter = 2" pitch. Reducing 1" pitch will pick up about 200-300 rpms. A cup will be about the same as 1/2" of pitch. There are really to many variables to try to compare what someone else is running. You can shift the weight in a planing hull and lose 300 rpm. Like I said these are rough guidelines. The best way is to run the boat with normal fuel load, gear etc and see where your at. You generally don't want to get to far off from square though. No expert-2nd generation boatyard rat.

[Gary Hill]

JEFF H,
What are your RPM's at wide open?

[Miles Offshore]

well, prop playing again- i went with the factory specs this time- 16x 17 5° cup- pick it up tomorrow and will put her on this saunday probably (i hope). (king fishing saturday, how about you gary?)

[GetReel]

4800 and about 29 NPH, done leave her there too long!

[Miles Offshore]

I got 24 knots at 3400 yesterday but my 4 barrel is knot working,(kicking in)lol. By myself with light fuel( 30 gallons). 13/14 gph. but what I liked though was the 21 knots at 2800 prms and 9.5 gph. this is the new 16/17 5°nibral i picked up off of ebay for 70 bucks - reconditioned for 120, and 40 for shipping= 230- sick

[GetReel]

Nice numbers for that wheel Craig, better than my 4 blade which I refuse to take off ...I have to run about 3100 to get 21 knots, does seem like that you just cant beat the original spec for overall numbers. Did you get the nibral on a hunch or did you guesstimate it would improve performance?

[Miles Offshore]

hey Jeff, still doing the 4 blade huh? mine finally sold on ebay and i recouped 20% of what i put into it,lol. Better than the yard ornamenty it had become,lol. Anyway, yea i decided to go the factory spec path and just stop playing with it. I was going to go bronze but when the nibral showed up I just figured that was an extra bonus. A little better hole shot maybe but I dont push the rpms up that much from the start for it to make much difference.

[Fr. Frank]

Finster is right about the reason for the rudder offset, it's only to facilitate maintenance, although it does make a difference in rudder effort and torque steering, but not enough to worry about.

[Miles Offshore]

Mine has an offset but the shaft isn't coming by it because the offset is at the rear of the rudder vrs the leading edge. Makes sense to me Fr Frank/ Finny, i just wish it worked on my boat without having to drop the whole rudder to pull the shaft. Its just not happening (on my boat anyway). Craig

[riprunner]

Miles, you officially have me on the market for the same prop. I checked ebay last week and couldn't find anything even close. Any suggesions on searching for our prop on ebay?