After all these years, suddenly I have questions!

[wrvond]

Hi, I have a 2002 Tracker Tahoe Q3 18 foot I/O bow rider with Mercruiser 3.0 and Alpha I out drive I bought new. It had some initial problems back then, such as inop fuel gauge, inop bilge pump, some kind of broken/missing line through the transom - this allowed the water to enter the engine compartment so fast the bilge pump wouldn't have been able to keep up even it it was working - and an engine that blew it's crankshaft through the oil pan. The dealer made everything right though, and it has been a great boat for us over the years. This past week end the battery gave up the ghost, but I can't complain, it is original to the boat, so I've gotten my money's worth out of it!
Anyway, one of the things the dealer did (without talking to me) was change the prop; I don't know what he changed it to, but upon launch it struck the out drive's trim tab resulting in mutual destruction. He replaced the tab and the prop, and it's been on there ever since. But I got curious and dug out my "spare" prop to try to figure out what prop I "should" have been using, what I've actually been using, and any pros and cons to using one over the other.
I've been able to determine they are both 19 pitch props but the factory prop is 15 inches (3X15.3X19R) on the side, while the prop that has been on there is 14X19 pitch. Both props are aluminum with three blades.
Would I benefit by installing the factory prop? There is only my wife and me on the boat and we tend to tool down the river (or up) just fast enough to maintain steerage way so hole shots and high top speeds are not important. Maximum recommended WOT is 4400-4800 RPM.
An explanation of the performance difference between these two props is most appreciated!

 

[Chris1956]

MerCruiser outdrives use 1 of 3 different trim tabs. The standard one will work with standard performance props. Higher performance props have more rake, and will usually hit the standard trim tabs. For those props, a trim tab with the fin set behind the center is used. Mercruiser also makes a trim tab without a fin. These can be used on any motor with power steering.

The real question is why the dealer changed your prop.

 

[wrvond]

He never gave an explanation for changing the prop on a brand new boat, and at the time I was more concerned with getting it running right. Considering he installed a prop and didn't even try to give it a spin by hand to check for interference, I'm not sure he particularly had a reason to change it.
Weather permitting, we will be on the river this weekend, so I guess I'll change to the larger diameter prop and see what, if any, difference it makes.
Probably not a good photo but this is what it looks like right now with the 14 inch prop in place:

 

[Sea Rider]

You have to dial a prop for engine to rev around it's full wot rpm range as factory stated and as currently loaded, it's not a will be using this, that prop, you could be lugging the engine at wot/load and not knowing a thing about it which is bad for the engine.

With chosen prop go for a wot spin as usually loaded on flat calm no wind water cond and report back wot rpm tached with that prop. If having more than one prop, keep the one which revs towards the max wot rpm range, from there could go for a prop maximization to be at the sweet max rpm range.

Happy Boating