Re: Does raising the motor up higher on the transom help the boat plain better.
There is room on my motor brackets to raise the motor up about 2 inches. Will this help me plain out better on my boat. What is happening is when 2 of us are in the boat and want to take off if we both sit in the back the motor just seems to run low until I move up closer to the front and then the rpms start raising and the boat picks up speed and then it will plain out. Ive tried the tilt and trim but that isnt working. my prop is a 10 3/8 x 13-G. If I need another prop to plain out can you guys tell me what I need or can I just raise the motor up and see what that will do. Thanks
You are describing a 2 stroke engine that is overloaded. That's what they do. Like I said, you have to unload the engine and let it develop some RPM's. The equation for HP and that is what "turns" the prop includes rpm, torque, and a constant of proportionality. When your engine is overloaded, which yours definitely is, you just said so, it cannot develop it's hp. So, rather than having a 90 hp back there you have more like a 40 and that ainta-gonna-getcha-outta-da-hole.
Less pitch would surely help but pitch is determined at usual load, WOT, trimmed for best performance. There is where you measure engine rpm's and for a 2 stroke the upper limit of the recommended range is where you want it and that is what you set your prop pitch (primarily) for.
The big guns on here always preach "get your setup fixed then play with the prop". Well to me your setup is ok for what you have. You don't have a setback transom or a jackplate so that you have to get all that adjusted. Raising the engine 1 notch (3/4" wouldn't hurt (looking at your last set of pictures shows that it has plenty of room for lifting in the mounting bracket) but I wouldn't raise the engine with that alum prop. Like Jimmbo said, you would surely have blow out problems especially in rough water. You need a cupped prop to stop that, like you will have with your new SS bow lifting, high performance, PORTED prop.
So let's walk through it:
Take what I said above out and max out your mph. At that point read your rpms. Compare that number to the Yammie recommended max rpm for that engine....5500 to 6000 most likely. Figuring 200 rpm per inch of pitch change, figure how much pitch you would have to lower (I'd bet in your case) your pitch to move your current rpms up to the limit as specified. Say you are running 5100 and the limit is 5500. That's 400/200 means you need to drop your pitch 2".
Now get on here and find you a super whizbang bow lifting SS prop with the other amenities I mentioned. If your numbers are what I have for an example (you adjust accordingly) get 2" less pitch than you currently have in the same approximate diameter and spline count to fit your engine. (The actual diameter will vary slightly as a function of the prop design so don't nitpick fractions of an inch.) The cupping at WOT will pretty much make up for the extra 2" you lost and the better efficiency of the thin blade SS will allow the rpm's to come on up since it isn't working so hard with the streamlined prop.
The 2" drop will surely help your hole shot without the ports but you want them too.
Now the punch line. The ports, and like I said, we had to get to 3/8" diameter to fix the problem with the other boat I mentioned, (course he was rolling a 13" diameter prop and you may not need but 1/4 to 5/16 to work for you) allow exhaust gas to blow out across the blades when in the hole. The gas is compressible, unlike water, and unloads the engine....... it's like the engine is now trying to get a 14' alum fishing boat up on plane. Walla, with the load relieved, the engine is happy, rpms come up rapidly, HP is developed, the prop spins and before you know it you are outta-da-hole. After things clear out and you get going, the pressure of the water flowing by the hub offers more resistance than the hub exhaust port so all the gas goes out there....course you are up and running 30 or so mph and there is a vacuum pulling the gasses out anyway.....
With the holes effectively sealed, the prop sees solid water, more load, engine feels the load, hunkers down to push it and your rpm's drop, just like a car does when going from 3 gear into overdrive. In the process the engine propels the boat faster and you move on up to your WOT max mph.....tweaking trim along the way.
With a ported prop, you may or may not get your best hole shot with the engine tucked all the way in. You will have to see what works best. On mine, I get a faster hole with it vertical, like you had it in your last set of pictures, 2nd picture.
Once you see how all that works, then you might want to raise your engine, but probably won't have to.
Ok my man. You have the ammo, balls in your court.
My 2c,
Mark
sorry you put so much into helping me but thank you anyway:redface: I going to sell it and get me a bigger HP outboard motor this fall.That should fix my problem.