Boat Porpoises At Any Trim Angle

[o/b tech]

I have a 1976 17' J Craft with a 150 Ficht motor on it. It also has a hydrlaulic transom jack with a six inch setback.
The excelleration is amazing but any trim angle and the boat porpoises. However it still gets to 54 mph with the boat running flat and little bow angle. This boat is a flat bottomed hull with two fins underneath for stearing. Have trim tabs on boat with sixty pound shocks and has helped, in that It used to porpoise until it got to full throttle. The boat performs amazing but would like to get more bow angle and faster speed at top end. Any ideas would be greatly appreciated.

 

[mr 88]

Re: Boat Porpoises At Any Trim Angle

www.screamandfly.com will probably get you the answers you seek.

 

[DJ]

Re: Boat Porpoises At Any Trim Angle

Too much weight aft is usually the culprit or a hooked bottom.

 

[Shabah 182]

Re: Boat Porpoises At Any Trim Angle

Get a pair of Smart Tabs and for a little over 100 bucks and your problem will be solved forever.

 

[Bifflefan]

Re: Boat Porpoises At Any Trim Angle

While I tend not to like smart tabs, moving weight forward will help tremendously and bennett or other simular tabs are better investment.

Do the weight first.

 

[o/b tech]

Re: Boat Porpoises At Any Trim Angle

Have smart tabs on the boat and they have improved the handling. Most of the weight is forward in the boat. Can the hydraulic jack be creating more problems than adding performance gains and would putting a wedge kit on the transom help.

Thanks for the replies to date!!!!!

 

[sschefer]

Re: Boat Porpoises At Any Trim Angle

Pourpsing happens when the hp at the prop lifts the bow but can't hold it up. A hook in the bottom will force the bow back down just like trim tabs do or trimming the motor down does. The trick is to find the point where the motor can hold the bow up untile the boat gets up and over the bow wave then allow it to fall and stay as flat as possible.

I think you can solve your problem with a prop change. Go over to www.screamandfly.com and see what prop will be best for your setup. I'm almost willing to bet a cleaver would cure it.