Prop information. 13 x 19p vs 13 3/8 x 16p what to expect.

[Dirtyshawn]

Ok new to how props work . I have a 85 stratos 375v bass boat with a force 120.
It came with 2 props one is what I think is a stock #13r19mwc the other is a Mercury vengeance 48-16976 A5 16p the alum one has been damaged​ from rocks and the SS is new. What can I expect for swaping them ? My GPS said I was running at 48mph on the old prop with 3 on the boat and half tank of gas at work. I'm not looking to haul ass every were but I do want a good speed and a fast on plane with my family on the boat.

 

[ThomW]

What were your RPM's at WOT with the old prop--the 19 pitch? Although it is not a science, generally you tend to gain about 200 rpm's per inch of pitch that you drop. However, stainless props flex much less than aluminum so you usual need to drop the pitch by 2 inches to remain at the same RPM's as the aluminum. So by going from a 19 aluminum to a 16 stainless, you will probably gain maybe 200 RPM's at WOT and a few MPH. Stainless lasts longer than Aluminum, as it is more durable.

Just be careful. When you hit something with the lower unit/prop, failure occurs at the weakest point. With an aluminum prop, the prop is that weakest point and the prop bends and chips, as you experienced with your own aluminum. A stainless wont give that easy and hitting something with decent force while running a stainless prop can cause failure in the gears of the lower unit instead of just dinging up your prop, as the prop is no longer the weakest point.

 

[Dirtyshawn]

No clue on the rpms that's the next thing I'm fixing the tach don't work nore the trim guage . And the pee hole likes to cloge up.

 

[Sea Rider]

Test all props with a tach on a wot run as usually loaded, stay with the prop that makes OB to run middle to max wot rpm range. If the closest does not dial say wot rpm range, have it re pitched at a prop shop.

Happy Boarting

 

[Maclin]

I can't tell from the posts which pitch is old and new.

 

[Texasmark]

You need the gear ratio and rpms for any technical answer. With that you can go to www.go-fast.com and look at their prop slip calculator and get your answers. Prop slip depends primarily on hull type, speed, and setup. 15% is a good general number. Higher for tubs and lower for speedsters.