Propped correctly or ????

This is a puzzler. I have a Yamaha 80 h.p. on my 1995 20' Bayrunner Baja. Just bought it last year. When running along at about 15 mph you pour the coals to it. when you get up to the cruise speed you want - 20 mph or so - , the boat will start to "porpoise". You can trim it just a bit, but even when the water is tabletop flat, the boat will cruise along and the bow will rise and fall almost like it was meant to do this. this is only at approx 1/2 throttle. It has a lot more to go, but I just don't feel it will get better going faster nor should it be doing this in the first place. ANY help!!??

Re: Propped correctly or ????

cubbug,<br />a lot of it depends upon hull design, weight distribution and your transom deadrise/angle. You can trim some boats more than others. Are you saying that with the engine tucked/trimmed full down it porpoises? If so, you can get "transom wedges" that bolt between your engine and transom that will give you more range of trim.<br />I'm not familiar with your boat but at 20 mph mine is just barely up on plane. If I trim hardly any at all at this speed, mine will porpoise too. Pour some more coal to it then try trimming and see what happens.<br />Except for some higher performance boats (and of course this varies) your engine cowl should be about level or a touch above at full throttle & full trim, more or less.<br />An 80 seems small for a 20' boat unless its pretty light weight.

Re: Propped correctly or ????

If you have a lot of weight in the bow, try moving it to the stern.

Re: Propped correctly or ????

At 20 mph it's gonna do this anyway in alot of cases. As JD said, that's just barely on plane, the hull is fighting itself.<br />Are you sure the tilt-pin is all the way in??? If not, it may not be letting the trim pull full fwd.

Re: Propped correctly or ????

Hey! Thanks for the ideas. The harbor is still frozen up hard here in Homer, Alaska, but Spring is coming along. Sure looking fwrd to doing a bit of tweaking with this settup. You guys may be right - I may be holding off on the power a bit too much. Just got to pour a little more coal to it to see how she responds. Many thanks, and hope you all have a good season, Dave