Porpoising Nitro

[Mike Nelson]

Hi all.



I have a 2005 640Lx/90Hp Optimax, 20p Laser 2. I have cranking motor mounted in the back and he trollin motor batter mounted as far up under the front deck as it would go. My boat has bad porpoising when making left turns with only two people in the boat and live well empty. I can trim down a fair way but it will still do it untill i straiten out.



What can i do to reduce this ? I thought by puttin a bit more weight up front it may sove the issue a bit.?



Thanks



Mike

 

[fatrap]

My only suggestion would be that before you make and sharp turn throttle way down and trim the motor under quite a bit. I don't know if your trying to make a high speed turn while trimmed up all the way but it isn't a good idea as you can easily lose control.

 

[Dan J.]

I don't believe it's a weight displacement issue since you're up on pad when this happens. If you have a jackplate on this hull, it could very well be a "short boat" issue. (No offense intended, but there's probably not enough pad and hull in the water on turns.) I've seen this before and the best (cheapest) fix is throttling AND trimming down in turns. Good luck and let us know how it goes!

 

[TOMMY RICH]

Prop can make a difference..what kind of RPM @ WOT are you running?

I'm running a 21P on my 90/185 combo and it did make a diff between the stock prop and this one as far as porpoising.

 

[Mike Nelson]

Currently i am running a 20p laser2 at 5750rpm. Prop probably needs a little more cup revs out easy. now these turns i am talking about ar tighter turns long drawn out turns dont seem to bother it. However i am only running at around 4800-5000rpm. if i turn right it will be happy but if i turn left it will porpoise. i have been trimming down a bit but it does not seem to help.



Any other 640 guys have issues?