prop swap results: 14x15 to 13.38x17

[zj-jeepster]

Ok finally had a chance to do this prop swap this morning.<br /><br />1974 Evinrude 85HP V4 model 85493, pin in second hole, new power pack, new coils, new plugs, carbs rebuilt unknown, stator replaced '96, new aftermarket starter.<br /><br />compression: 120, 115, 117.5, 120 psi.<br /><br />1976 Starcraft 16 ft. American open bow V bottom, been in slip since may, may have approx. 5 gallons of water in bilge (?), bottom fairly dirty, hydrofoil installed, just myself and full 15 gallons of fuel.<br /><br />with 14x15 aluminum OMC prop (in like new condition) I'm able to pull WOT 5000 rpm at 32 mph clocked using Etrex handheld GPS.<br /><br />with 13.38x17 stainless steel OMC prop (in used condition, some minor dings) WOT is now 5200 rpm at 35.3 mph clocked using same handheld GPS.<br /><br />lake condition at Hopatcong NJ (9:30am) was windy and a slight chop.<br /><br />hope this is interesting to anyone. thanks for your bandwidth <br /><br />.

 

[Spidybot]

Re: prop swap results: 14x15 to 13.38x17

Thanks for sharing!<br /><br />A little surprising that going 2" up in pitch (yet a little down in dia) raises your rpm <br /><br />Rule of thumb suggests it should be opposite....

 

[SeaMasterZ@aol.com]

Re: prop swap results: 14x15 to 13.38x17

stainless props tend to do better, I guess cause they are thinner - give better speed<br /><br />I thought ol lake hoppie was a 9.9 lake, not a 99 lake, lol<br /><br />of course, when Ranger Smith chugs up in his 15 horse 9.9 catcher, is he in for a surprise!!!<br /><br />I am surprised tho, I thought an aluminum boat with that sorta power would go faster, the guy that sold me Hydrophobia, 18 Starcraft with 125 Johnson on the back, said he went almost 60 ... then again, Ive been known to buy magic beans<br /><br />still waiting on the beanstalk, lol<br /><br />the 14 footer did keep up with a 15 knot party boat with her 7.5 McCulloch, course, that was practically a sea going canoe, lol

 

[zj-jeepster]

Re: prop swap results: 14x15 to 13.38x17

guys,<br />the 3 mph increase is noticeable. this old boat is fiberglass and the bottom is pretty dirtied up. maybe with t&t it could go a little better. holeshot seems unchanged. i did the swap from the cat walk with motor locked in the up position.<br /><br />one lesson learned. i did the swap from the starboard side and cut up my fingers real good. next time i'll do it from port side

 

[sharkcat]

Re: prop swap results: 14x15 to 13.38x17

You will probably find that the aluminium prop has more cupping.Also the dings in the SS prop may be causing a loss in efficiency hence the higher WOT rpms.Get it fixed & you may gain even more You could also get some beans off Ray .When i change a prop I use a block of wood to stop the prop from turning saves your fingers...

 

[zj-jeepster]

Re: prop swap results: 14x15 to 13.38x17

i just read something even wierder. in my OMC service manual as well as the owner's manual this engine makes its maximum 85 horsepower at 5000 rpm. the upper service range is 4500-5500 rpm. why would it or any engine spin past its maximum power rpm (5000 in my case)?