D-27 TUNNEL STILL PORPOISING !

[riggerman]

Hi all i tried all the suggestions that Kris Mike and Robert had mentioned the boat still porpoising down the straights i checked the hull on my setup board no twists in hull a put a metal straight edge on both sponson bottoms 120% STRAIGHT no rockers or hooks but the 1 thing i noticed between the K&B AND OS lower units is the difference in length from the transom to the prop hub .Would this contribute to my problem ! I put in a 3/4 inch pine spacer to give me a distance of 6 inches from transom to prop hub to = the os dimensions if this does not help im at my wits end . Any other suggestions ! Regards Andris Golts .

 

[Kris Flynn]

Please post some photos of your boat and setup.

What Prop are you running? Have your tried multiple props and got the same result?

Did the boat used to run without a porpoise and now it has one?

 

[Brandon Atwell]

What kind of porpoise? Is it straight up and down or does it seem to do a side to side lift?
What prop did you run prior to the switch to electric power?
Post a photo of your lower unit, side profile and from the back.
Your skeg may be bent or the engine could be slightly crooked. Is it an old KB or newer style from their recent runs?
You may also just need more prop. If it is running out of prop it will also porpoise. You can try to drop the motor to load it more or move up a 445

 

[riggerman]

Hi Kris &Brandon thanks for the suggestions for props i tried x473 +x440 3 blade for 2 blade x637 x440 m440 1640 215 x442. For prop height from 1/8 bellow sponson bottom to 9/16 above sponson bottom adjusted in 1/16 incriments prop angle o degree . Boat still porpoises up and down at the bow . When the boat was set up with os .21 ran perfectly flat. I will have to borrow a digital camera for pictures . Brandon when running .21 stock used x440 /3 prop K&B LOWER long skeg post 1983. Regards Andris Golts.

 

[Wasted wages]

deleted

 

[Brandon Atwell]

I personally would test the extended distance and if that doesn’t fix it, prop up.

Like I said, a porpoise is also a symptom of running out of prop. Believe other are running M545’s on their P-Limited setups.
Mike was also on point with raising the motor but if that didn’t work then these would be my avenues to follow next.

 

[Mike Hughes]

DId you try a different prop? I have had props that the blades are not the same. It does bad things and the blades are fighting each other. Shape and pitch can effect it. How much did you raise the motor? Did you see any improvement? Sometimes you need to go way beyond what you think it needs and your learn new things.

 

[Mike Hughes]

I see you change to electric. Did you cut out the tank well so that you can get your batteries as far back as you can? CG is important. I would try and set CG to the same as nitro. Sorry about the double questions above.

 

[Mike Hughes]

Take some pics like guys said before. That would help a ton to skip to the fix.

 

[Wasted wages]

Guess I missed that part....about going to electric.

 

[RobertDoak]

So...has there been any closure to this..or is there still issues...

 

[jaxracer]

Hi Kris &Brandon thanks for the suggestions for props i tried x473 +x440 3 blade for 2 blade x637 x440 m440 1640 215 x442. For prop height from 1/8 bellow sponson bottom to 9/16 above sponson bottom adjusted in 1/16 incriments prop angle o degree . Boat still porpoises up and down at the bow . When the boat was set up with os .21 ran perfectly flat. I will have to borrow a digital camera for pictures . Brandon when running .21 stock used x440 /3 prop K&B LOWER long skeg post 1983. Regards Andris Golts.

Sounds like the issue is the lower. If it ran fine with an OS and then hopped with the K&B, must be the K&B. The different units have different lift characteristics based on shape. In addition, K&B wasn't the greatest at providing a consistent product so I've seen several warped units that caused the boat to do odd stuff.