mstine06

Ihave a prather lap cat (35" hull)slightly modified hull with a k&b 11cc outboard on it. I have several questions to ask. I have an Octura 3 blade and Prather 2 blade prop for the boat. The 3 blade seems to handle a lot better, but which prop would be the ultimate you would recommend for the boat? Also, when I start to get on the boat it wants to sometimes loose bite and spin out quick. I know you are supposed to have SLIGHT negative trim, but the motor was set pretty negative. Will that cause the spinning? Height wise, where do you recommend for speed, but still be able to handle the boat? The cavitation plate on the motor is level with the bottom of the sponsons now.

I am also very very interested in a gas powered tunnel hull. Would this 35-36" hull handle a zenoah outboard? What would you guys recommend to get into the gas powered tunnels?

Any other setup tricks or anything anyone knows of would be really appreciated. Thanks, Matt

ob nut

My Feedback: (1)

If you want handling, get rid of the LC III.. Sorry, but this is a 30+ year old design. Does the boat have a turn fin mounted on the inside tunnel? Lap Cats required this to stop the majority of spin outs. Never having a Lap Cat (that I actually ran), these are what I've picked up over the years of running mainly tunnels. Sounds like you have the motor to deep. The prop shaft should be even with the spoon bottoms, not the cav plate. Start at this point and make one adjustment at a time. Give a little neg / pos trim.. raise / lower the motor.. CG should be around 30% from the aft point of the spoon bottom.

Gas tunnels need to be in the 44" + range. Zipp Kits has a great tunnel for a low price. There are many others out there also that can be picked up. Try the gas section as they have a tunnel only thread.

Hope this helps.

mstine06

Thanks for the response. I do have the straight tab for the inside of the tunnel but it is not mounted. I am fairly new to the hobby, can you define the spoon bottom? I am not racing the boat, just pleasure use but would like it to run well. If the boat is setup properly will it not spin out? Right now it just seems like the boat is glued to the water and doesn't want to air out. The nose seems to low. So I need to go up with the motor and a little more positive trim? What other hull could I put the 11cc outboard on and run real well?

ob nut

My Feedback: (1)

The motor is to low per your comment that the boat is glued to the water. Tunnels like to be aired out to run. I would leave the prop shaft with just a little neg trim on it with the shaft about 1/8" above the spoon bottom. Spoon is short for sponson. Other boats to consider would be HTB360, Woodstuff and Leecraft xt-460 are a few that come to mind. If you are just starting and don't plan on racing, stick with the LC III and learn how to set it up. You might want to step up to a full racer and head out to race!

Ron Olson

My Feedback: (1)

Mark is probably typing pu something now.
Prather had a turn fin that mounted under the center of gravity to help with turning issues, a band-aid fix of sorts. Without it on it could be giving you the spinning out problem. Like Mark said, it's an antiquated hull
Here would be my pick for your OB, http://www.htbboats.com/htb_360.htm . The price might look steep but your Prather went for close to that many years ago and it didn't come a radio box, that was optional.

mstine06

Thank you for the responses. If the motor is set to the right height and trim angle will I still have the spin out problems? That is what I want to know. If the boat is setup properly andit still spins out all the time I don't want it. Iwould also like to have the outboard run as well as possible. It is stock right now, but what would you guys recommend to do to the K&B to get the most amount of power? And where can I get the parts you suggest? Thanks

Ron Olson

My Feedback: (1)

www.htbboats.com like in the link above for tuned pipes or try 707 Specialties, http://home.earthlink.net/~namba707spec/ .
The design of your tunnel ws done back in the infancy of RC OB tunnels, they've come a long way since that time. Some of the earliest ones were real dandies!

mstine06

I just got the boat the other day. I bought the lapcat and outboard together. I would just like to have a decent setup that runs well. I hope it is possible with the boat and motor combo. What prop should I balance and sharpen to run the best speeds? Any other secrets I should know with the boat? And what kind of speed should I see out of this setup when it is dialed in correctly? Thanks for all of the help? Do you know where I could get any of the above hulls mentioned used??

Ron Olson

My Feedback: (1)

My experience is only with 3.5 and 7.5cc OB tunnels so I can't advise you on a good prop, hopefully someone with experience can answer that for you. Stock, I'd guesstimate the high 40's to low 50 MPH range, a little more modded.

mstine06

Thanks for all of your help. Anyone that can give me some setup help and advice, I would greatly appreciate it. Thanks!

rcguy1411

i have the same setup as you k&b11cc on a lapcat III you can get it to run ok start with the prop shaft level with the bottom of the sponson s to start and run a little negitive trim how much will depend on setup and prop choice this hull is way over powered with this engine you will never be able to run 100% the 7.5 ob is a far butter choice for this hull but with a little work it is a fun boat mine is apart for painting so i dont have any pic s of it together and a little lead in the cockpit never hurt on windy days 1 -2 oz its a fun boat to start out with and if you get hooked on tunnels you can upgrade the hull

mstine06

Ok I will adjust the motor to that setting. What prop are you running that you like? I still need to get my motor totally tuned in correctly. I am finding it hard to do. When the low end and high end are set right it seems like the whole boat will jump out of the water. Thanks for all of your help, I appreciate it.

rcguy1411

one thing you CAN T do with your setup is jump on the go pedal as the hull is way over powered not shure what prop i have for it it is a fun little boat easy on the power or it will do a backflip also dont just cut the power and turn it will hook ease off the power turn and easy back on and you will keep it on track its fun to let it fly and with a little practice only the prop will touch the water

mstine06

I have a Prather 235 2 blade and an Octura x447 3 blade. Not sure which one will be better?

mstine06

I did have one more question for you guys... what is the best way to lube the flex shaft in the 11cc outboard? After I ran it I put afterrun in the carb and in the glowplug hole and spun the motor so it got coated. What do I need to do for the flex shaft and is there anything else I need to do?

Bellzview

Use the prather prop, it has less lift than the octura- more blades equals more lift. Rather than lead, two part epoxy foam provides nose weight for stability, floatation for flips, and strength if you do hit something. I run a tuned pipe on mine which really helps on the top end- think 60mph+. Sharpen the leading edges of your lower unit skeg and the turn fin. All trailing edges should be square and crisp. Make sure your prop is balanced perfectly, the k&b lower units are sloppy in the prop shaft, any imbalance will be amplified, resulting in power loss. All hull edges should be crisp, specifically, the inside of the sponsons, and the transom. I found that all the tweaks make for a very easy to handle boat that can keep pace with newer boats. You have to take apart the lower unit to grease the flex shaft, and while you are at it, the exposed bearing on the engine case.

Ron Olson

My Feedback: (1)

The 2- part foam can blow a hull apart or warp it.
Prather props have a constant pitch whereas Octura's have a progressive pitch.
If you're getting slop on the propshaft then the thrust bushings need to be replaced so keep some handy. Octura makes them so you don't have to deal with K&B.
You don't have to separate the lower unit to grease or oil the flex cable; never had to. Some do remove the engine from the lower unit to fill the open area in there.
It's best to lube the cable after a day's running. This way you're displacing water and it's also ready to go for your next outing.