Hi Im making a new boat I have a small 2 foot kyosho jet arrow now the problem I have is when i give it full power just get tons of spray at the back the boat not go any faster so tried weighing down the back keep the prop under the water still the same thing should be going like a bat out of hell too lol got a 3.5 in it with a tuned pipe

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What prop are you running?

Get pics of the transom...

If you're running the stock prop, that could be most of the problem.
That's a lot of engine for a little hull as I wouldn't have gone over a mild .18 in there.

Like Ron said.You shouldve ran a.18.+ a right prop does help. That.21 will be an over kill on your boat plus that small plastic hull isnt going to handle that big motor to well=self distructed, If that boat was bigger like 28-30 inc would work. The motor could go back about 1/2-1" to for weight factor.

a 3.5 in that small boat?,,, thats like in the old days ( ron will remember lol" putting a hemi in a vega. remember those ron? lol i do.its like the old saying.. " if big is good,,,,, bigger is better" lol not always tru...for a boat that sized, ron and joesy are right a .18. or maybe a .15 or a good running .12 with a good prop..

I've got some decent .12's in some 24" hulls and they can be a handful at times.
Like JW said, it will be a matter of time before the .21 will shake the plastic boat apart.

Hi I like big engines lol I have got a 3 foot jet stream im fitting an Irvine 61 on it at the moment its just a tad tight but i will get it right go like a bat out of hell i hope lol or i crash it and sink it lol

before it doe's that, get some video......,currently,I'm working on a 26"bby ovalmaster with a os.18,might be OVERKILL, but I like the idea of overkill........

I'd try a 42mm prop using that engine and give the hull a decent toss forward when you are launching it.

Ryan

Whats the make of .21?Misshydro has the stock.18 vegas motor in her 1/12 blueangel hydro and its flys. That boat is 28" by 14"wide. Put that motor in your boat and it will screem and realy fly. Oh we done a built 340 in a vega and it was a killer car.Had to renforce the frame and roll cage it to.

I believe the CG for a deep vee should be 29% of length. As measured from the back.

just using the standard prop think its a 34mm going to try it this weekend will post a film as soon as i do the launch and the sinking lol i hope not lol

A 34mm prop is way too small for a .21 Use a bigger prop.

Ryan

hi Ryan it is a 3.5cc thought a 34 be perfect !

3.5cc (.21) size engines run at least a 41mm prop. I run a 44mm on a mono with a .21

Ryan

37mm minimum but usually you'll find something in the 40mm will do the job.

Post a video!! I want to see it crash!! It looks like my old plastic hulled boat, except the engine looks bigger than the hull can ahndle!