porposing tunnel

[WOODY]

Does anyone out there know how to stop a tunnel from porposing at mid speed

[Reaper1]

Put the hammer down braa.........or buy a tunnel that don't porpoise!?!?

[WOODY]

Originally posted by Reaper1:
Put the hammer down braa.........or buy a tunnel that don't porpoise!?!?
Good answer braa,ever had or even sat in one?

[tahoe22]

Woody - Jet or OutDrive? If jet, do you have a place diverter?

[WOODY]

Originally posted by tahoe22:
Woody - Jet or OutDrive? If jet, do you have a place diverter?
Hey tahoe22 it's a mod 2.6 gt with nose cone and elect. jack, any trim causes it to porpose like crazy until it hits 80mph

[Reaper1]

Sorry, I mean ehhhh........

[tahoe22]

Woody - If your gonna keep the boat for an extended length of time you might wanna take a look at arneson trim tabs to keep the nose down.

[HavasuBarney]

Trim tabs will just slow you down.
Porpoise can be eliminated by shifting weight back, prop selection, engine height and trim.
For mid range, try some negative trim, bow down.
A larger diameter prop, or round eared prop will carry your bow better.
Dropping your engine height will give you prop and trim more bite.
If you have more info on your boat, we can get more specific.

[WOODY]

Originally posted by HavasuBarney:
Trim tabs will just slow you down.
Porpoise can be eliminated by shifting weight back, prop selection, engine height and trim.
For mid range, try some negative trim, bow down.
A larger diameter prop, or round eared prop will carry your bow better.
Dropping your engine height will give you prop and trim more bite.
If you have more info on your boat, we can get more specific.
Thanks for the reply HavasuBarney.
I have a 20'Starcraft tunnel,2.6 gt with nosecone & Panther elect.jack.
I've tried several props 24 4b 26 Raker 24 Cleaver 30 Chopper.
Jack has 10" lift 7" setback ,sponsons extend 15" back from transom. Any speed below 80 mph stains my shorts!
If I make 80 mph, slowing back down also can cause massive staining of my shorts.
The porposing is so violant that I cracked the transom, the gearcase goes in & out but the prop never breaks loose.
Need some help.
woody.

[HavasuBarney]

I think I know the boat, true tunnel, no center sponson.
How heavy is the boat?
What kind of top end do you have and at what RPM?
Full interior, if so, can you move your back seat back?
You want all the weight in the rear, move everything you can to the back or get rid on any extra weight up front.
Motor needs to be around 3 inches above the sponsons, start there but you want to raise it until the boat starts getting loose. Raise it in 1/2 inch increments until it gets real loose on the top end, then drop it 1/2 inch.
I would think a 26 chopper for a heavier boat,
cleaver if it's light.
Next I would increase the amount of setback, go to 12 inches or so, that will leverage your bow up better. It is a matter of finding balance.
I have a 21ft Daytona copy, running 18 inches with a 3.0 300hp Mariner. Have a very good friend with your same boat, he is running 12inches back, 3 inches above sponsons.

[WOODY]

Originally posted by HavasuBarney:
I think I know the boat, true tunnel, no center sponson.
How heavy is the boat?
What kind of top end do you have and at what RPM?
Full interior, if so, can you move your back seat back?
You want all the weight in the rear, move everything you can to the back or get rid on any extra weight up front.
Motor needs to be around 3 inches above the sponsons, start there but you want to raise it until the boat starts getting loose. Raise it in 1/2 inch increments until it gets real loose on the top end, then drop it 1/2 inch.
I would think a 26 chopper for a heavier boat,
cleaver if it's light.
Next I would increase the amount of setback, go to 12 inches or so, that will leverage your bow up better. It is a matter of finding balance.
I have a 21ft Daytona copy, running 18 inches with a 3.0 300hp Mariner. Have a very good friend with your same boat, he is running 12inches back, 3 inches above sponsons.
Thanks HavasuBarney for the info.
It does have a steped center sponson though.
12" setback and the 7" jack will put the prop in the middle of the sponsons.
Why would starcraft place the outboard so forward of the outer sponsons?
The will run 90ish 30 chopper 6500 k, but what a chore to get it there. It's a starcraft cps by ART CARLSON very small cockpit long nose and can't move things around.

[HavasuBarney]

If you have a center sponson, keep your prop shaft level with or just below the bottom of the center sponson.
Why don't you email me a picture, I was thinking of a different boat all together.
havasubarney@hotmail.com

[WOODY]

Originally posted by HavasuBarney:
I think I know the boat, true tunnel, no center sponson.
How heavy is the boat?
What kind of top end do you have and at what RPM?
Full interior, if so, can you move your back seat back?
You want all the weight in the rear, move everything you can to the back or get rid on any extra weight up front.
Motor needs to be around 3 inches above the sponsons, start there but you want to raise it until the boat starts getting loose. Raise it in 1/2 inch increments until it gets real loose on the top end, then drop it 1/2 inch.
I would think a 26 chopper for a heavier boat,
cleaver if it's light.
Next I would increase the amount of setback, go to 12 inches or so, that will leverage your bow up better. It is a matter of finding balance.
I have a 21ft Daytona copy, running 18 inches with a 3.0 300hp Mariner. Have a very good friend with your same boat, he is running 12inches back, 3 inches above sponsons.
Great advice HavasuBarney.
I tried raising the Outboard little at a time
till it felt loose,then pick up speed & raise it again. This worked great, no more porpoise.Thanks.
woody

[froggystyle]

Damn. Eggbeater knowledge is good for something Barney! I'm impressed. I think this event means you have hereby earned your diploma, and have accumulated enough "cool points" to now own a jet boat!
Just remember, Chicks dig hot tubs!