Prop problems

[Caddpro]

I have a 14' Mckee Craft loaded with 2-6 gal gas tanks, 2 batteries, 4 seats, about 70 lbs of fishing gear (cooler, poles, tackle box), and of course me and a buddy (~400 lbs total). The motor is a '75 70HP Johnson. I have pulled hte prop off and can find no #'s to identify the pitch. The diameter as I measured is just over 13". It had a few dings in the along the front edge of the blades so this past weekend I pulled the prop off and filed the blades to debur it. I did it equally on all blades. Afterwards I went out just to play around on the water and now it blows out like crazy. As I noticed the the tach would jump from ~5000 to 5800 a few times before it would blowout. @ blowout the motor would jump to 5900-6000 and I would immediately throttle down, but cannot figure it out. Before I did this it was ~5500-5600. I would like to get a better prop to get on plane a little faster as well as dropp the RPM a little. Any suggestions? I was told that I had a 13.25x15, but the shop said that was only a guess.

 

[mkuehnl]

Re: Prop problems

Props and prop selection is an art and needs to be taken very seriously. I have been boating and proping boats for about 20 years and I do not feel comfortable working on a prop. That is something I leave to the right person with the right tools.<br /><br />From what I can determine is that you have two choices:<br /><br />1 Go back to square 1 and get the original prop type from the manufacturer or similar scource. This will give you a starting point and can then determine your best course of action regarding pitch and such.<br /><br />2. Take the prop to a qualified prop repair shop and have them determine what pitch it is and do the necessary repairs. I do not know how long you have owed the boat or what the previous owner may have been attempting with the present prop. He may have been looking to max out the speed and pushing the upper limits of the engine rpms.<br /><br />Over-reving your engine because you may have the wrong prop on or may have modified it due to your filing the edges can cause extensive damage to your engine.

 

[Caddpro]

Re: Prop problems

New update, I have a 13x19 3 blade prop with a spun hub. Local shop guy took one look at it and said that the rubber shavings was a dead givaway. After he used a little cleaner the numbers appeared out of the grim- 384142 13x19. Now that I know this, I want to get a new prop. I was turning ~5500 RPM with this prop before, I cannot find anywhere in my manual what the max RPM's are. The guy @ the prop shop said for a '75 70HP I should be around 5000. Does that sound right? If so do I go to a 13x21? He told me that would slow the motor, but kill any hole shot I might have had. All comments are greatly appreciated.

 

[cobra 3.0]

Re: Prop problems

Alos, maybe the hub has spun?

 

[Caddpro]

Re: Prop problems

The hub has spun as Iindicated in a previous post. Now I need a little advice on my next prop. I am looking @ the Hustler props, anybody got any experience with them? Also the prop I currently have is a Stainless Steel prop, the local prop shop said it would be a little over $100 to fix the hub and another $50 or so to fix the dents and dings. Is it worth trying to keep the old one, or should I just get a new one (aluminum, cheaper)?

 

[cuzner]

Re: Prop problems

Hey caddpro, A prop will either give you better hole shot,or lower rpm,you have to decide wich one is more important. Just a suggestion (its your money),have the old one repaired and see how it performs. If your not happy you should be be able sell it for almost as much the repair was.A 17p prop will improve your hole shot,but lower your top speed + raise rpm. Hope this helps.<br /><br /><br /> Jim