1979 mercury 80hp

[duff]

I have a 17 1/2 challenger bass boat (almost a tri-hull type) with a 80 hp merc. one of the blades on the prop is pretty tore up on the edge. I would like to replace it and increase speed but do not know size or pitch of my prop. what props should i look at for this boat/motor combo. current prop is aluminum.

thanks in advance

duff

 

[WillyBWright]

Re: 1979 mercury 80hp

Unfortunately the 80s came with different gear ratios depending on the year, and only a factory manual has that info. So you need to find out what prop you have. There are numbers someplace on that prop, even if it's just a part number. We need to know how many RPMs you're turning at full throttle with an average load. You need a prop that allows the motor to run at max recommended RPMs (5500?).

Your prop may be repairable, and it can have the pitch adjusted by up to two inches plus or minus.

The performance props of the day were 2-bladed bronze props. They come up on eBay often. I've also heard of Laser stainless props doing well. Generally you need the next pitch steeper than the aluminum prop that gets you full RPMs at full throttle when going to a perf prop. Say if it's a 17 aluminum now, I'd be looking at a 19 stainless or bronze.

 

[duff]

Re: 1979 mercury 80hp

boat is not running right now and have no gauge to find the rpms once it is running. how should i find the rpms once running?

 

[WillyBWright]

Re: 1979 mercury 80hp

You'd need a marine tachometer. Or might you have a timing light with a digital tach? Or any tach that operates off induction.

 

[Silvertip]

Re: 1979 mercury 80hp

Please read the very first post titled "Help Us Help You Select a Prop"?

 

[rord]

Re: 1979 mercury 80hp

If your outboard is 1979 blue band 4-Cyl, the Max RPM is 5200 WOT. I have a 1979 80HP and run a Mrcury Vengeance 48-16988 18P 3-Blade Stainless at 39mph/5200 rpm on the mark trimmed. Your boat may be heavier, which must be taken into consideration. I also have operated the Mercury Trophy 17P 4-blade with good results as well and plan to try the Mercury 20P High-Five, which may end up being too much for the amount of fishing gear I carry. I have purchased and tested many to find the right combination. Good luck!