Any advice before I buy the same one?

[halfor]

Need advice on prop selection for a 78 merc 70hp (700) it has a 48-73136A40 13P on it now. the previous owner (my father) got the used boat 78 Crestliner 16? tri hull (Muskie) it had a 48-61824A1 16P this apeared to be for a older 65hp. Someone along the line told him it was wrong and got him straitened out with the current 48-73136A40 13P. I would like a second prop and was wondering if there is a better selection? I do not have a tach or speedo, sorry I believe that is required to correctly size. I?m thinking it goes prety good now just running WOT but if I were to pull a tube or a skier could I make a better prop selection? maybe a different pitch, size or material type? Knowing nothing about boating and getting into it has been a adventure to say the least.
here is a pic of current prop is it in ok condition? it is not sharp, mostly flat on the edges?

1) Performance issue you are trying to correct.-- All seems good as is but don?t know enough to try to correct. Maybe just make better if I were to pull something.
2) Current prop manufacturer, model, aluminum or stainless as a minimum.?Think it may be aluminum can?t tell, it is black with # 48-73136A40 13P on it.
3) Current prop diameter and pitch (required). From p/n description = dia.10.38, pitch 13deg, 3 blades, std rotation (cw).
4) Wide open throttle RPM and speed with an average load (very helpful)?No clue will gps after this weekend for speed.
5) Engine/drive make, model, year, and HP?Outboard Mecury, 700, 1978, 70hp
6) Boat make model, year, length and weight?Crestliner Muskie, 1978, 16ft, ? lbs.



Thanks in advace.

 

[SparkieBoat]

Re: Any advice before I buy the same one?

must have WOT RPMs..or we cannot do anything but guess. a used tach is about $10-20..well worth it. hard to tell..but just at a glance of your picture the motor could probably go up a hole or 2.

 

[halfor]

Re: Any advice before I buy the same one?

Thanks for the reply, I?ve been kicking around the tach idea more and more, need more research on hookup and type then where to put it, there is not a good spot without moving something. Unless it is a small gauge (more research in a different topic, but 10-20$ I need one). I know zero about boats so I need to ask, u mention ?moving it up a hole or 2? is there a optimum depth the propeller should be when motor is all the way down or up when running WOT? Also I was thinking about taking a file to the propeller, then thought it would be a bad idea because it would be removing material, even if it is a flattened edge (not sharp) at least the metal is still there keeping balance? am I even close with this thought?

 

[SparkieBoat]

Re: Any advice before I buy the same one?

you could file it some if you want...but if it is really nicked up, you need to replace it. the optimum motor height is "as high as you can get it without cavitation". On my boats I rasie my motor as high as I can, on my bass boat I have it in the bottom holes, and it will cavitate just a little if I start out with motor turned and floor it, I can only trim up a little while running, but I jump out of the hole way faster now, stay on a plane at lower RPMs, and gained 4 MPH, so get your motor as high as you can, you will notice a big difference. they also make a digital timing light that has a built in tach. you could even hook up a temporary tach and not permanently install. but I use my tach everytime I run my boat, I have found a sweet spot at about 4200 RPMs where I get best MPG, so that is where I run most of the time.
went back and looked at pic..your prop does not look too bad to me.