Prop Selection ????

[DansBlown73Nordic]

Im looking to replace the prop on my Nordic. The one I ran this year looks like something that came from the bottom of the ocean. :crossx: It is rusted and pitted very badly. I mean so bad that it looks kinda scary.
My problem is that it is so rusty I have no clue what it is. It has these huge big ears. Its two blade steel.
I bought two props on E-Bay. One is a 11 1/4 X15 and the other is a 11 1/8 X 15. I tried one of them last year and it vibrated like HELL..... :220v:
Gears are 18% motor should be around 650 H.P. With the BIG ear prop it will turn 6,500 RPM,s
Im sure you guys will say put a set of 25s in the box and buy a 10 1/2 X 14 I really don't want to change gears. Should I get one of these props repaired? :hammerhea

[mickeyfinn]

First thing I would ask is how many rpms do you want to turn? Are you loooking to get down around 5k or want to stay up around 6k? Without knowing what engine you have and where it makes horsepower it will be difficult to recommend what size prop you need to try. As for the vibration, a 2 blade will vibrate some. You said your old prop was a 2 blade so I am assuming that the new prop vibrates a LOT more than it did. If the boat runs smooth with it then your prop probably needs some balance work. Bottom line what prop you need depends on what you want the boat to do. If you want more more speed you need more pitch. If you go up in pitch and the rpms go down further than you want then you need to look at a similar pitch in a smaller diameter. Tell us how many rpms are running, how many rpms you want to run, what pitch you have and then I'm sure someone can give you a better idea of what prop to try next.

[Moneypitt]

Take/sent your prop to a prop shop and ask them to tell you what you have now. This will allow you to go in the right direction from there, or to replace the scary one with a better shape/quality..........MP
PS: The vibration with the different prop could be an indication that the prop was riding on the key, not fully seated on the tapered shaft.

[DansBlown73Nordic]

I never gave that a thought MoneyPitt....I could use some tool makers blue and see if it contacts the shaft.
I would like to stay around 6,000 rpm,s. The motor is a 454 4 bolt with dimple rods. Forged pistons. B&M Blower.

[Moneypitt]

Simple, just install the prop without the key. Measure the gap to the strut with a feeler gauge, then use the key and measure the same gap. It should be the same or less..........if the prop is truely seated on the taper..........MP

[DansBlown73Nordic]

I have about a 1/2 inch from the strut to the prop. I don,t think they make feeler gauges that thick.... :rollside:

[mickeyfinn]

Check the one that vibrates like was said and get it to spin without vibration. May need to have it balanced. Run it and see how many RPMS you are spinning with it and go from there. How many RPMS's did you get out of the one that vibrates when you tried it? I guess you probably shut it down before WOT so you may not know yet. Once you get a known prop to work with you will have something to give you a baseline to work up from.

[DansBlown73Nordic]

Exactly I never really got on it. It didn't shake real bad just made my face go Numb!!!! :messedup: lol

[VD CRUISER]

I have seen very few 2 blades that didn't vibrate some at take off and lower speeds. Usually not noticeable at top speed though.

[jockorace]

First thing you should do is spend the $20 bucks or so and have the prop magnafuxed. If you ever spit an ear off a 2-blade (I have) , it's ugly and dangerous. I spit one accelerating at approx 80-85 (110mph blown flat) and luckily I didn't get wet, but it literally broke EVERYTHING. Ripped the strut right off the boat , damaged the hull, actually cracked the v-drive cases in half horizontally! ($4K in damage). All because I was too cheap at the time to have the prop checked out. Not preaching, just concerned about the safety aspect.
Dave