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.

Ok, I will try that, its supposed to be high 60's here on Tuesday. I love all this boating into late November.

Ok, pulled the spacer. Well, put a standard drive on, same thing right. The boat still porpoised at speeds above 60, prop slip was high and had a mini rooster going, never trimmed past neutral.

Any Ideas? What is the standard drive depth on the 25's? Also what is the measurement from the end of the lower strake to the transom on the 25'? anybody.

Are you playing on flat water?
My 28 did the same thing, hated flat stuff.

Yes, usually. I understand, the boat loves a good chop. But when its calm, it looks like I don't know how to drive a boat.... Its bad.

Porpoise the same, worse or better?

Tabs aren't the answer but what happens if you drop them a little?

Throw the P5s back on for grins as well.

Porpoise was not noticeably worse or better, the same I guess.

The tabs don't change much until I lower them enough to plow the bow, which slows the speed dramatically: porpoise at 62mph at 4200 rpms. plows 62 mph around 4800rpm; thats with the spacer and labbed 28 B1.

Its getting cold up here in MD, but I'll try and make it out again. I'm usually winterized by now.

You have to run the spacer. With out it X dimension is to high, you will burn out the prop. I was always able to stop the porpoising with very little trim and dropping the tabs just a click. I do remember that that boat does not like to cruise in flat water in the 48-52 MPH range. If you try cruiseing at 45 or 55 ish the porpoise goes away. I never had porpoise at WOT. EVER. You may want to try a 1.75 or even a 2" spacer you would be able to give it a little more trim without the cavatation. Also wieght never changed much with that hull. Congrats on the radar run! Hope this info helps.

Thanks Rob,
I do remember you telling me that about the calm water, and thats why I left it alone for so long, but now its time to figure something out.
Didn't you put the spacer on? Did the boat have a spacer when you got it?

You had a lot more power, that propably help hold the bow up at WOT? I think I will try an locate a bigger spacer over the winter. Winterized yesterday. Done

Nick

I have a labbed 28 Bravo One that came on my 25Active Thunder with a HP500 you can buy

Thanks, but I have a labbed 28, thats my high speed prop. It works very well for me, other than the porpoise.

Still curious about the measurements previously listed, if any of you 25 guys want to help me out.:drink:

porpoise active thunder
 

I have mid 90's AT with twin 200 outboards on it. It a fun boat but it porpoise like crazy at about all speed. I have theboat up to about 68-70 if I could keep I under control. The boat runs great with the K-plane flat. But, as son as they come up it starts to porpoise. Then it will Chine walk so bad it will toss you off. It only runs fine with the K-planes.

The Outboards are about 18in off the transom. The lower units are the short shafts. The only thing I can think of is there is just to mush weight ouside the transom. And the props may be to high. If you look down under the hull twards the transom,, the lower unit nose cones tips are about a inch below the botom of the transom.
Some one help, I need this thing to stable out.

You must have the former U2 in Falls Church right?

Can you help me!!!

I am fairly certain that boat was built before current ownership. I'm not even sure Pat (current owner) has even laid eyes on that boat. I also think it's the only one ever with that configuration. IIRC, that boat was raced by Mike Livorsi of http://www.livorsi.com/

I'd suggest a couple things.
1) I think a lot of the items mentioned above here, and also in this thread can help you:
http://www.offshoreonly.com/forums/m...op-repair.html

2) You might give a shout down to Brett at http://www.bblades.com/
He's VERY good at tweaking props and setup recommendations.

I tend to run any boat with the tabs neutral; or at the same plane of the running surface of the hull. This really should not scrub any speed. This could help the hull balance the COG better.

Realize that both of the boats in question here, were purpose built race boats at their time of build. That means they ran with very small amounts of fuel, and 2 people aboard. THAT'S IT.

Now that they are pleasure boats and have changed hands and purpose; things are way different. These boats might have even had ballast tanks in them at one time. And now they are being run with more passengers, tools, parts, anchors, lines, beer, coolers, as well as all the other stuff we take with us when pleasure boating. This really does change EVERYTHING.

Yes, That make perfect sence. There two gas gauges on the port side,,,,,, for ballast tanks,,, I guess?
I only run the K-planes flat with the hull. The boat run like a dream then. It can really handle some ruff water smoothly. I had some 4 blade bravo 26" on it and the problem almost went away. It was about 80% better. I don't think those props had as much rake angle and the MAzco's I also had a big cooler in the front. Thanks for the help.

No porpoise with my 25 at any speed, I run a hydro QIV, think its a 25. It does tend to chine walk at speeds over 60, but it settles with a little tab. Hope to invest in a bravo next summer if I can use it more than 3 times :angry-smiley-038:

No Chine walk at all, here.
How would you know if you have too much bow lift?

Sorry I didn`t get back to you sooner, had to erase your PM`s I can only keep like 3 at a time.
ok so my strakes end 53" before the transom.

What other measurements do you need?

p.s. I have wondered about the fill in piece between the couches.. what holds that up above the floor, I think I`m missing something

Sorry I'm late. I got lost on the way here...

The One Vision Active Thunder really has no porpoise issues unless you are running 30 to 35 mph in perfectly GLASS water. We have played with standoff boxes, "shortie" drives, various props, and probably lots of other stuff that my damaged brain can't remember.
Some of the facts we learned;
My 25 Thunder did not respond well to the standoff box.
We gained maybe 1-1.5 mph, but the boat did not handle well and wanted to launch the nose to the moon in any .kind of rough water. We could slide the box up & down so we played with various drive heights, using various props (Hydromotives & Bravos). We studied a lot of video of our boat as well as the Neville Moberly "Chaos" boat, that aslo had a box. After a LOT of testing, we removed the box and never looked back.

So Gordo, what drive depth do you run for the most efficiant speed without the extension box? In the ruff, the way the boat is set up now, it allways flies pretty level.

Drive depth. From bottom of boat, to center line of prop shaft.
I don't have any fill in piece in my cabin.
Are you trying to upgrade to one of those 28's or 37's?

Thanks

The drive isn`t level right now and batteries are sitting in the basement nice and warm so I can`t level it out for ya. I imagine you`re looking for the drive to be level to take the measurement?
I can guesstimate..


I wouldn`t mind something larger/ more storage .. I have a waiting list of free loaders lol that always want to come with and it gets cramped when we take the kids.

Looking at longer boats why is it that only the cuddy gets bigger but the seating pretty much stays the same I don`t get that.
Baja does quad seating that makes sense and 32' Sunsation midcabin is another great set up for a family sport boat.

I want more seating space who cares about the cuddy I never use it except for storage.
AND I want anchor storage at the bow dammit!
I`m tired of handing it up thru the cuddy window or dragging it thru the boat!
Wow I just went of on a tangent:lolhit:
If it sells fine if not no biggie

Not sure, pretty stock 502 mag only goes 68~69 at 4900~5000. think the chinewalk comes from the hydro(sternlifting) From the pics I had at WOT was flyin pretty level,bow out of water, on a flat calm day.Not sure how too post pics anymore.

I'll try to get over to the storage barn and see if I can get you a measurement, pretty sure I left the drive down.
May take a couple weeks.

Is it snowing there, yet? :evilb:

APBA measured ours at the transom from the centerline(crankshaft/pivot pin centerline) down to the lowest point of the keel. The max allowed by rules was 19.5" which is where mine should be.

Huh? so then you could still change your drive depth by installing a shorty and/or drive spacers. If I'm understanding that correctly.

Nick, put some antifreeze in that thing already.:lolhit:

I did, I did. Sad day. One of the last times out, Dave M was out in his new 30' Superboat, and Randy had the Fountain out, running good. There were a couple other performance boats out around Gilligan's, it was probably high 50's. Are you going to have a new boat next year?

NO. Had to be factory/stock Bravo drive top-to-bottom with no aftermarket lowers

But you could install an aftermarket ext. box?
Thanks for the info.