25' Hull Strakes
 

Yeah, I'm still porpoiseing, in realatively calm water at any speed above 60 mph all the way up to a top speed of 77mph. I had BBlades lab and cup my 26 B1 twice with no success. The next option is to try a five blade. But then I did a search and found a post where a guy said that after he put an extension box on it changed his center of gravity so much that he had to extend his lower lifting strakes to stop the porpoise. He credited testing at Lake X for the solution. I will try and find the post.

My boat is the old Chaos Racing F1-16. It has an extension box that puts the Propshaft 3 inches below the keel and drive nose 20 inches behind the boat. My lower lifting strakes stop 55 inches before the transom. The bottom is straight. no hook, no rocker.

do all 25' stakes have that measurement? ( incase something was done to the bottom of my boat by the racer)

Is there any way to know if extended my strakes would correct the porpoise?

I have a picture of my boat at WOT, porpoising and you can clearly see that strake out of the water.

Any help?

Have you tried any drive height adjustments ?

I've never seen a 25AT porpoise. There would be no reason for the stock boat to do so, compared to other boats with notched transoms which are prone to such.

The 25AT was designed and built to have the drive on the transom. With the extension box, the CoG obviously changed. It sounds to me like the bottom needs to be addressed by a blueprinting professional. It was tuned to run fast while being extremely light. All it had on it was fuel, driver, and navigator. I venture to say you run the boat much heavier now as a pleasure boater.

Yeah It has a cabin, could the weght of the cushions, porta-pot and jackets weigh enough for it to drop the bow? thats all thats up front. I keep most stuff under the back seat. or would that still affect it?
Did he use a five blade?
Who do you recomend in our area for blueprinting?

Back then, I doubt they had any worthwhile 5 blades. But it could be an option today.

You might try looking up MGD Performance and/or Art Lilly in the Annapolis area.

I don't know them personally, but you can get more info on them from the guys on CBPBA.com

I have not but the drive does have a 1.5 " spacer that the previous owner installed to help get on plane.

What is the stock drive depth for the 25 AT?

Gordo's 25 One Vision also porpoised quite a bit on calm water. He didn't have an extension box when he raced, but he did experiment with one a little bit. He said he took the box off because the boat got out of shape real easy with it.

Around 80mph mine starts to chine walk like a mother but no porpoising .. if you need me to take some measurements let me know

Ok. I tried a 25" P5X today that had been indreased .6" in pitch. It didnt carry the bow any better. The rpms were way off though, I would probly need to go up 1-2" in pitch. Would the pitch being off effect how it carries the bow?

I would pull the spacer.