Porpoising FIX without trim tabs!

[Codylee]

Made a wedge for my xp and decided to make a pair for my 98 speedster. Only difference in design when I made a pair for my boat verse for my ski was to unincorporate the two little bilge holes in the top of the wedge. Anyways I made a pair of 3 degree wedges and flipped them upside down. This did two things for me. Made my boat plane out super quick and also kept the bow from porpoising. Works awesome! Plus trim tabs are expensive and very hard to mount on a twin engine. That and I hate the idea of drilling holes under the water line lol. Here is a link to them on eBay http://https://www.ebay.com/itm/122734490498

 

[Sportster-2001-951C-Stock]

"flipped them upside down." Did this point the pump upwards or downwards from the original position?

My sportster was pretty porpoisey on plane so I pointed the 2-position nozzle towards up I think (it's been a while so I don't really recall if up or down), using the 2nd notch of the lower pivot and this seemed to help, it's livable now.

 

[Codylee]

I flipped them upside down which forced water at a slight downward angle out of the pump nozzle which in turn helped to keep the bow down. I don't know much about the 951 sportster but my 98 speedster and 99 sportster 1800 has no type of adjustments on the pump.

 

[Sportster-2001-951C-Stock]

Yep, I believe these boats are prone to porpoising due to the aggressive rocker in the keel. Definitely helps when you trim them out, not sure why Seadoo was content with the angle.

Confirming update for my case, I positioned the nozzle from down to up. This helped a lot as mentioned but didn't eliminate the porpoising completely. And yeah, the pumps are quite different.

 

[LawnDart]

Does it have any effect on top speed? Fuel economy?

I was shocked at how such a small trim tab could make such a big difference in plane time and porpoising. Only downside is I seem to have lost some part throttle cruise fuel economy. I wonder if a wedge combined with a shallower trim tab angle could get some fuel economy back.

 

[Sportster-2001-951C-Stock]

Extending the hull (using trim tabs) is the ticket I've seen most used for hulls with too much rocker. A wedge is an acceptable way too, IMO, or relieving rocker, which isn't easy. Big $$ is spent on re profiling racing boat keels, there's an art to it.

By extending the hull, this doesn't imply having something hanging down that creates a hook although that can get the hull on plane faster, hook slows the hull.