Re: yamaha tach
To rise the rpm you have to drop the pitch. To gain about 800rpm, you would have to drop the pitch by 4 inches, so probably with the pitch 21 you would be close. However, the performance will depend on the setup you are running and all this is assuming that you are trimming the engine properly and that everything else is ok, the tach, the height of the engine on the transom, etc. From your other post I understand you have just got the boat, so the height of the engine may be worth checking - as a general guide the anti-cavitation plate (the biggest plate on lower unit) should be in the range of one inch below to one inch above the keel, the latter being the good point to start the transom height tuning. The lower the engine on the transom, the higher the drag.<br /><br />About the top speed, it is difficult to anticipate the result after putting the different pitch, the best thing is just to try. Anyhow, even with less top end, with 800rpm more this would be much healthier for your engine.<br /><br />If you want more info on propping, check out the bulletin the UU has on his web site search for any post from UU and click on his homepage icon. Good luck.
