Re: Bought boat, owner changed out props....
You are wayyyy over propped for your application. I assume your optimax 90 is geared 2.333 as my '02 2 stroke 90 hp is. I run a 24P SS Ballistic on a 17' boat at 5600-5800 rpm and 48ish GPS to give you some reference with 2 people and gear. Coming out of a tight turn with trim fully out, I will run up around 6000-6200 till my engine quits ventilating and gets a good bite of water. My avatar is a pic of the wake from the boat. The boat is light and fast. This is just for you to see what that engine can do for you. The boat, hull shape and load are the rest of the story.
I have seen pictures of the 17' Bass Tracker and especially with 4 people it will be riding in the water meaning you will have a lot of hull drag/water contact so you will have to unload your engine to account for that.
2 strokes love the upper end so you want 5500, not 4500 and reducing your pitch to achieve that will surely help your hole shot, as will ports in the prop. Way to prop out is to shoot for the upper end with your normal load and then adjust accordingly for variances...like if you prop for 5500 with 4 folks, then when alone you might have to cut the throttle back some to stay in the recommended rpm range, but I don't, like I stated above.
HP is torque x rpm, and a constant of proportionality. So you have a 90 hp rated engine, but you are not getting 90 out of it due to the lower rpm's. As you back off your pitch, your rpm's will go up, and it things work out your increased HP will allow your boat to move on up above your current 33 mph. An example of what I am talking about it to take your boat for example and trim the nose down, without changing the throttle setting (WOT preferred) and into the water watching the speedometer and tach. If you get the results I expect, the more you trim down the faster the engine loads up and things drop off. Conversely start out with it trimmed down at a fixed throttle setting and trim out. The faster the engine runs the faster it accelerates and the faster the boat goes....this is the unloading of a 2 stroke I was talking about.....you did nothing but change the load on the engine.
OK. So much for the bla bla. If you can borrow a prop of lower pitch it would be best because if you try several props you can get the one that best suits your needs. Don't know what any prop will do for you till you run it. All one can do is to speculate. Soooo if you want to to get up to 5500 that's 1000/200rpm/inch reduction means you need to be down to 21-5 = 16P. 17 is a more standard size and I'm betting that the increased HP you will get out of your engine will use the 17 better and get you some more top speed. No doubt at all you hole shot will be dramatically improved. Other thing to consider is the prop being apples and apples, not apples and oranges. If you change prop material types or styles, you are adding other variables that will affect your outcome.
I didn't have much to do this morning so you got this dissertation. I know I will get smacked by at least one person about shooting off my mouth.....but so be it.
Good Luck,
Mark
