wow had no idea.. i just looked up mr 3000 rx and it sounded good... i just always wrapped my old school rx's in a balloon and never had a problem like i'm having now with these two gas boats...thanks once again guys.. very helpful !

You absolutely need it for the Spektrum transmitters! Don't run a boat without them unless you like chasing them across the lake. I've seen 2 of them lose radio contact within 100 feet. I've driven my buddies boat with the Marine RX in it and it's solid as a rock.
For the Futaba, it has to be FM or better for gas boats.
NEVER ever add or shorten the antenna as you can easily throw it out of tune unless you really know what you're doing. Radios of any kind work on wavelengths and they are actually measureable in inches, feet, etc. Most of the 2.4 Gig systems are what's called top-loaded antenna's, a tiny coil of wire at the end. You don't want to bend them over as you can break the coil.
I learned a lot of this stuff way back in my CB radio days. A 1/4 wavelength on CB's is 108". Short antenna's used a coil at the base or half-way up. On a 27 Mhz RC you'd be using something like a 1/16 wavelength. RX's are pre-tuned at the factory.

ok... thanks. like i said i have had a few boats, back in the day ,but i have been doing planes for quite a few years and just recently got back into boats...i will most def pick up a mr 200 or mr 3000 for my 1/5 scale! as far as the other boat ill have to do some tinkering and see whats up.. i still think its metal on metal noise making it twitch. because it does not do it until i start the engine gonna start with the prop shaft in the tube...

Do you run a battery at the max of the receiver's voltage?
How much is your antenna is out side the hull?
Have you tried any shielding / filtering?
In the past I had to wrap the radio gear with tin foil, ground stuffing tube to engine / motor

I use spektrum for my Truggy's and has been flawless. I have seen 1st hand boats take off and hit trees on the shore , fly into the parking lot at our pond with guys using spektrum on the water. Some guys swear up and down it works great and other guys not so much. I use Futaba Fasst 2.4 and never had a problem. 3PM-X is a great Radio

well i decided to stop at hobby shop today and picked up an mr200 rx.. the thing is i have never had either of these two gas boats in the water yet.. but the owners before me have ...so they say lol... so when i go to put this new rx in my 1/5 do i need to put it in foam like the other one? ..also tootalltechie.. the original antenna was about 2 inches out of the tube.so about 10 inches of antenna... . and the battery was a 4.9 volt 4 cell.. standard issue really.. ni cad ....

I went to mounting my 2.4 Gig RX's on the radio box lid as close as possible to the antenna tube. Call me paranoid but I prefer to have as much antenna in the air as possible.
I only use 5-cell Ni-Cad or NiMH battery packs. I haven't moved up to the fancy packs yet as these hve done me fine for years.

WEL F*&^%%$!!!!! i give up ???? brand new mr 200 rx and the boat is still effing doing the same thing !!!!!!!!! and then when i shut it off, the rudder servo sits and twitches untill i shut the power off !!!!!!!!!!!!!!!!!!!!!!!!!!WTF !!!!!!!!!!!!!!!!!!!!! this is why i fly planes ....

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Is your receiver pack fully charged, and what do you charge it with? I'm pretty sure the receiver your using is rated at around 3.5-9.6V, and the minimum discharge voltage for NiCd's is around 0.85V per cell (you wouldn't run it that low anyway). I'm wondering if your getting some low voltage spiking. Just thinking out loud.