Two props came with my 2000 Sport Nautique

1. 12.5 x 15.5

2. 13 x 16

See photos.

Which one would give me the most top speed?

Thanks

Jerry

The prop's diameter is boat specific.  Not too big so that the blades pass too close to the hull, and not too small so that the prop sacrifices efficiency.  The pitch should allow the engine to just achieve the engine manufacturer recommended maximum operating RPM at wide-open-throttle (WOT).  External impacts on WOT engine RPMs are things like altitude, people / weight in boat, etc.  The cup will also impact propeller performance.  The cup is the "bend" on the prop's trailing edge.  The idea behind the cup is to change the effective pitch by adding camber to the prop blade shape.  So, a prop with less pitch and a bigger cup may allow the engine to spin up faster at slow speeds without sacrificing too much speed at WOT.  Keep in mind that not all "cups" are created equal.  Cups will vary in effective pitch.  One rule-of-thumb for cups is: "When using a cupped propeller, the design pitch value should be reduced by 1-2 inches compared to the non- cupped propeller."

So...not an easy answer.  Also, a repaired prop often (not always) does not perform as well as an original (non-repaired) prop.  Give 'em both a try and see how the boat performs.

CCF member TRBenj often frequents the site and has a lot of good info on props.  He can likely give you more useful information.

JQ

JQ gave you the only answer you really need, due to all kinds of variables ...........try both props on the boat.

From your description and no picture, .your other prop is unknown to anybody

It could be a newer design Acme 422 as a guess, but a prop swap will tell you everything you're trying to find out

 the other prop pic is now showing.

Still the same answer...........try both

11 out of 10 people would say to put the 422 on for a try/comparison

Interestingly the speed from both props were essentially identical, 38 mph and 41 mph at the two RPM levels respectively.

The 422 prop appeared to allow RPMs to go into the 5200 range (briefly) where the other prop got to just 5000 RPMs briefly.

So I won't be using the 422 prop as I want to help insure that red line is not accidently exceeded.

It is still too cold to get in the water to test with a deepwater slalom start but there didn't seem to be any difference getting up to 32 mph between either prop.

Thanks all for the feedback and suggestions.

Jerry

Even adults when out with friends sometimes have fun racing each other.   1 or 2 MPH can let you win sometimes?   Maybe I am just a 65 year old teanager out there having fun?

Since both props ran the same speed at 4,800 I am assuming it goes faster with the 422?

Umm.............go read what he said again

4000 rpm they each went 38

4800 rpm they each went 41