frank haydu

hi all . i was hoping some one here can help me , with a picture or what to use on a prather boat { lapcat 2 7.5outboard } a turning fin i had this cheesy piece of aluminum , that didnt grab the water at all and i spun out smacking the wall at sunset park in las vegas, nevada , it was so loud it echoed everywheremaking everyone tolookat their boat

SteveM

My Feedback: (1)

Outboard tunnels do not normally require or use a turn fin. I do recall one on an older Dumas 3.5cc outboard tunnel though and it wasn't much more than a straight piece of aluminum.

Ron Olson

My Feedback: (1)

The Prather tunnel boats used the turn fin as a band-aid fix for an ill-handling hull but way back when RC OB tunnel boats were in their infancy. Today's hulls can make turns at full speed without the need for the fin.

niteshadow

so your saying i dont need to hasve the turning fin on my dumas atlas van lines u-1 kit #1314 [1976] boat??
[email protected]

Dan S

niteshadow,
no that's not what they are saying, your kit is an Hydro and you need the turn fin (all hydro's).
Tunnel hulls don't use turn fins, however the Lapcat 3.5 and 7.5 had a problem and needed a turn fin placed under the boat on the inside of the tunnel so they would not spin out all the time.

Dan.

frank haydu

thank you for your help but the turning fin is not my biggest problem now , i finished the boat and had it out on the water , i must have the only yellow dolphin in the world , LOL . i cant seem to stop it porposing , i have lowered the motor gave it all the neg. pitch it could go added weights . the only weight that worked was a powerade bottle tied to the front and that k&b motor almost shook it free as it took off , any ideas ? oh what should it weight? with the motor attached or with out ? and the instructions was faguie about center of gravity thanks everyone

Ron Olson

My Feedback: (1)

On the older boats the CG was set at around 27% forward of the transom, you might want to aim for 30%.

Dan S

Frank,

sorry for asking but are we talking about a Lapcat 2 or a Dolphin? and if it is the dolphin, which one is it?
was it the one that comes with the cheap engine using a belt drive system?

Dan.

Ron Olson

My Feedback: (1)

Dan, read it again as the boat is yellow and he says that it's porpoising like a dolphin.
One other thing that causes porpoising with OB tunnels is that there is a midway point where they go from riding more like a normal boat to riding on a cushion of air. During that transition time they can slap the water. Dumas boats were imfamous for doing that, but yours just seems to be a CG problem.

Dan S

Thanks Ron for bringing me back on the straight and narrow path.

Frank, never mind my last post.

Dan

fuma

i ran my newly rigged old lapcat last weekend, the C of G is at 30%  she ran great. I have a homemade turn fin on it and she truns like it"s on rails

frank haydu

thank you for your help , what did you use ( specs please ) ,i a a little lost on the center of gravity , i understand what your saying but just dont know how to find where my center of gravity is, is that with the motor attached or offand what you do when you find it . does anyone know what the boat should weight , without the motor ? or with ? thank you all for your help so far

frank haydu

hi i finally got a video of my boat and what it is doing , i have tried evrything that was suggested i am at the point where i gonna crack it open and rip every thing out and start all over including the expanding foam that was put in there before i got it and put in a couple ofpool noodles, i just wondering what you think of the video and what steps ishould try , well it did one thing different this time it flipped over at the end . how do you add a video to the post ? i have it uploaded at you tube under "the yellow dolphin "

Ron Olson

My Feedback: (1)

I tried doing a search on You Tube on the yellow dolphin and nothing to do with an RC boat came up.
OK, two ways to post a video in here. Way #1 is to just throw a link in here in your reply. The second and much better way is to click on the You Tube button above the reply box then paste your link in between the ] and the [/You Tube. I didn't want ot complete the whole thing otherwise it might trick this site trying to find something.

frank haydu

ok sorry about that my first time uploading anything to you tube , got the title and description backwards[http://www.youtube.com/watch?v=cAN5oaHPwqw ][/youtube] ok this should work

Ron Olson

My Feedback: (1)

Here's the way to post it here so that the video shows:
[youtube]http://www.youtube.com/watch?v=cAN5oaHPwqw[/youtube]
It sounded very rich or the outboard is sitting too deep in the water.

frank haydu

the run you seen , i just got done lowering the motor a 1/4 " inch, i started the day 1/8 " above instruction specs for motor ht. and was dropping it at 1/8 " increments, when it flipped over, i was like yeah it did something different , i took it as a sign and called it a day. yes it was a little rich butt i could never get it to plane right to warm it up and fine tune the carb. oh yeah i even triedadjusting the neg. & post. tilt on the motor, a guy suggested while i was there. i want to thank you for your help ,

Dan S

I would definitely get rid of the expanding foam.
Just this alone could be the cause of your problem, too much weight, uneven throughout the whole boat.

Dan