twin outboard cat?

[scorpien boats]

well... i went to the local rc boat club yesterday and i decided to sell the rc cars and make a cool boat.. :)

i want the boat to look cool and be different, it dosn't have to be a big preformer.

question #1 is it possible?

#2 do they make a counter rotating outboard or could i just start the engine back ward and get a counter rotating prop?

#3 will two k&b 3.5 (water cooled) obs be enough power?

#4 what hulll would be good? (i like the idea of a cat)


thanks for the help

[BoatDoc]

the k&b motors are meant only to run one way. sure, you can start them backwards...but as soon as they hit the water the engine will die. plus it will damage the drive cable. there was a thread a while back about a quad-outboard. i think it had 11cc motors, but i don't remember.

[scorpien boats]

i remember the quad thread but it didn't say anything about how or if he had them counter rotating...

do i have to have them counter rotating?

[RCGUY76]

the engine will run backwards.....I know a guy who had a prob with his KB outboard starting one way and kicking backwards....and YES..it hit the watter and pulled the boat backwards....It did not kill the engine!!!! I dont know exactly how good it is for the engine....the instructs to my 7.5 say not to start it backwards..I'm not sure if your gonna really need it to counter rotate....I have seen a couple twin inboard set ups and from what I have seem...they dont. Might have to dial In a little more rudder to keep it straight, but unless your racing...the speed your gonna scrub off with alittle more rudder is gonna be limited...I know the advanec rc boat modeler book has some info on running twin or more engine setups....might want to check out that book if you can get your hand on it principles should be the same. Center of Gravity will just be majorly difffernt with both engine that far back

[BoatDoc]

running an engine backwards would require a different crankshaft. remember...it's the crank that controls the intake timing. on an outboard, the drive cable is wound to turn one way, it will try to come apart if you run it backwards. i've had my K&B start on the kickback, or i've forgotten to switch my starter leads and started it backwards on accident. it will idle, it will rev, you will throw it in the water and then you will realize it was a bad idea! if you want twin outboards, i think it's a great idea. you'll just have to live with a little bit of prop walk. i agree with rcguy...just trim it with a bit of rudder and you'll be fine, and you'll have to play with the CG too.

[Ron Olson]

Scorp, not to burst your bubble but you're not ready for twins yet, believe me. I'm not ready for twins nor do I want the hassle of them.
I've seen pix of the 4 engined Cat, too cool but the hassle, no thank you.
I know a guy that is working on a twin 3.5 OB Cat, I've seen him try to get both engines dialed in without much luck so far.
The weirdest one that I've seen that maybe some of you older guys might remember, it was in RCBM back around '97 or '98 was a triple engined Dumas Quickee 40 'rigger. A K&B 3.5 on the transom and one on each front sponson. I got it on video, talk about roostertail and propwalk!

[BoatDoc]

ron...i've heard about that triple boat before. was that a guy from the illinois area?? it seems the guy who got me into boating in the first place, saw that boat run up at lamm's farm. it's a place a little north of chicago. just trying to imagine that boat seems like a pain in the neck.

[Ron Olson]

He is from here in Michigan, Potterville, it's just SW of Lansing off I-69. The guys name was Leslie (first or last name I can't remember). He built off-the-wall boats, nothing normal. The front engines has the skegs removed and he had home-made heat sink heads long before K&B did it with the SS engines.
It's possible that he ran it at Lamb's Farm. Too bad that they're not racing there anymore.

[scorpien boats]

is his name Steve Colby?

[scorpien boats]

that boat looks so cool... i just cant get over it

[Ron Olson]

Yup! :D

[BoatDoc]

no more racing at Lamm's Farm??? that sucks!!!! that's the first place i ever turned bouys at. my high school shop teacher, a guy by the name of mark dauer, used to race there. he built some FAST boats. i bought my first boat from him, my prather vee. i still run that boat all the time too. i better stop before i start getting teary eyed about my early days of R/C madness.

[scorpien boats]

just wondering... whats so hard about twins?

i could see twin inboards being a hassel......

[Ron Olson]

Exactly matching 2 carbs, two throttle linkages and getting the alignment right between the two engines.

[RCGUY76]

ok....you know when you start a nitro engine....listening to how the engine is running is a normal tunning tip besides temp....so you start one engine....its running ok....you start the second....do you think you gonna be able to hear how it sounds.....next is the entire running temp issue....you really hypothetically need to get both enegine to be running the same speed...getting them tuned in to match each other is a huge pain the a$$....the engine you start first is always gonna be warmer unless you richen that engine up and lean the second engine you start so it heats up faster..but then eventually the leaner engine is gonna get hotter than the richer engine....do you see where this is going?? Dont get me wrong, it would be a cool looking boat to see run, but I personally like to go out and run my boats and not have to sit and fiddle with the needles the entire time
good luck

[scorpien boats]

well see the reason i don't see it as a big problem is because the k&b 3.5 outboard that im running right now on my tunnel hull runs so cool that i can hold my hand on it after its done running...

wouldn't the water cooling even out the the temp...

as far as hearing it start, couldn't you just look at the prop?

[RCGUY76]

what I mean by listening to it start is how the engine its self is running after it starts....not just running...you throttle up a engine and hear ifs it too rich, ect with both engines running its dificult to hear and hard to turn....but if you up for the hassle....go for it...by all means.....it'd be cool as hell

[Chris LaPanse]

what you do is you start one, tune it, and kill it. Then, you start the other, tune it, restart the first one, and you're boating!