Prop Size

carlywolf · Post by **carlywolf** » Sat Aug 11, 2012 8:24 pm

Ok so, after i refit with new chevy 350 i kept my 14-9 cupped prop on and when my mech and me went on sea trial smooth as silk till 3400 rpm then prop spinning with no top end which would have been 5200. Not that ill go that speed in this F26 anyway but, sooo had prop brought to 14-11 cupped now i throttle up in spins pretty quick no bite. Foofer has a 14-12 cupped and i was going to get for spare but that might not work at all if i need to go 14-14 cupped , the lower the pitch the quick out of the hole yes? On Monday im going to go back to mech , marine shop and ask what they think . Also once you have your prop done at prop shops does one have to pay again if the one they did isnt working for the boat? I believe torque on engine now is 280 and the Hp is 330. With props you can only go up or down 2 prop pitches from its original size right? Any suggestions would be greatly appreciated ... Thx

kevin babineau · Post by **kevin babineau** » Sat Aug 11, 2012 9:34 pm

I thought 330hp was a 454 merc?

kevin babineau · Post by **kevin babineau** » Sat Aug 11, 2012 9:34 pm

I thought 330hp was a 454 merc?

prowlersfish · Post by **prowlersfish** » Sat Aug 11, 2012 10:10 pm

kevin babineau wrote:I thought 330hp was a 454 merc?

It can be ,many 454s were rated at 330 hp . But you can also have a 350 rated at 330 hp . The 350 will have to turn much higher rpm to get 330 hp.

prowlersfish · Post by **prowlersfish** » Sat Aug 11, 2012 10:28 pm

Carl what ratio gear are you running ? 1.256 to 1 ? your running a ZF 45 right ?

MattSC · Post by **MattSC** » Sun Aug 12, 2012 12:52 am

Carl,
I went through this awhile back when I repowered with a 350 MPI rated at 330hp. Not sure which transmission you are set up with, but I have a borg warner velvet drive 1:1. The recommended rpm band for my engine is 4800-5200. Below are some of the props I've tested on it..

14 x 14 was the first prop (according to the yards software program) couldn't get anything over 3400rpm at WOT. The yard doing the repower did not charge me for this prop, they supplied the 14x11.

14 x 11 no cup. 5000 rpm at WOT, but was a dog had to run at 4000rpm to get 17kts. Prop seemed to be ventilating.

14 x 10 cupped Dynajet 5100 rpm at WOT. 17-18kts at 3000 rpm, 31kts at WOT

I currently have a new Michigan DJX prop 14x10 with a cup. This has less slip than a dynajet. .056 to .061EAR. I am going to test it for the first time tomorrow, I've been laid up most of this year and haven't been able to go out. I'm looking forward to it, been way too long. I will let you know how it works out.

Matt

prowlersfish · Post by **prowlersfish** » Sun Aug 12, 2012 11:37 am

Got rember thats a 5000 rpm engine and you want it to turn full rpm . It won't take as much prop as a 454 that gets its hp at a lower rpm

carlywolf · Post by **carlywolf** » Sun Aug 12, 2012 3:23 pm

Yes it is a zf hurth 450 1 -1 ratio . at 14=9 cupped it was like a bat of hades out of hole then ventilating at about 3400 =3600. 14-11 cupped started ventilating when i put the hammer down. You should have seen me coming back in from 20 miles out fishing. Following sea about 2-3 footers, a couple of guys behind me were on the radio singing : rolling rolling rolling. I couldnt stay ahead of the waves , wont do that again till im reproped correctly. So im thinling......... 14-10 cupped ? Feels great to be back in the saddle again though

And yes this is an Indmar 350 mpfi vortec chevy engine . Specs on it say 330 HP. And thx Matt let me know how it goes with prop trial, im thinking 14-10 cupped too.

DOUBLE R · Post by **DOUBLE R** » Sun Aug 12, 2012 5:51 pm

I believe the boat originally came with a 14x10. Would cupping ,help that much?

MattSC · Post by **MattSC** » Sun Aug 12, 2012 9:42 pm

Hi Carl,
Out of curiosity what was your max rpm with both props? Prowlerfish is right, you want to make sure that you are within the recommended rpm band for your engine, otherwise its going to put too much of a load on it.

I'm really happy with what the new prop did today, unfortunately I couldn't get my new chart plotter to cooperate and display my speed, but it was noticeably much better than the Dynajet. It held plane at 2500rpm and maxed out at 5000 on the nose with full fuel/water 2 passengers. I had to be running 2800 or above to maintain plane with the old prop. Much quieter as well. Going to try and figure out this new plotter this week, Raymarine e7D and will post some speeds for you. Once you get the prop straightened out you shouldn't have a problem in a following sea. The new engine once propped right made it a different boat for me. The two photos are for your reference, you can see the DJX has a sharp edge, while the Dynajet is more curved. Both are Michigan Wheels. A long time ago I spoke with John at Marine Tech and was told that my model was shipped with a "supercupped Dynajet 14 x 10.
Matt
would like to see some photos of your new setup. Best of luck with it

Michigan Wheel DJX 14x10 with full cup

Michigan Wheel Dynajet 14x10 with full cup

MattSC · Post by **MattSC** » Sat Aug 18, 2012 10:24 pm

Sorry it took me so long to get some results for you. Went out this afternoon, 5 adults full of fuel and a cooler full of ice and beverages at the back of the cockpit. I was pleasantly surprised. 2800rpm achieved 18kts, this was with a 1.5kt current pushing me along so a good 16.5 kts. 3200rpm saw 21.6kts, realistically it was 20 when you subtract the current. I didn't take it over 3200 rpm today as I know it hits 5000rpm at WOT. 2800 rpm seems to be the sweet spot as the boat rides the best for me around 16-17kts. This was around 3000 rpm with the old prop. 14x10 Dynajet. Much quieter at 2800rpm vs 3000rpm. It also seems to have more bite in docking maneuvers. Look forward to seeing how you make out.
Matt