hi guys. new to the forum and i was wondering if i could get some constructive critizism. a couple of years ago i bought a custom shark marine 70' offshore nitro boat. i bought it off ebay and it has a cmb 90 nitro engine in it.(the guy i bought it off of said it has 6 hp) i recieved the boat and everything looked great. except the servos and remote arnt the best. it has a 2 blade prop (not sure what pitch or brand) and it has quad exhaust. there is no tuning pipe on it. its just right of the motor to the quad pipes. i started the boat in my garage just to see if it ran and its INSANE!!!. excellent throttle response and seem to idle very well. but when i put it in water it dosent rev out. like the boat only revs out about have way when at full throttle. i really dont know much about it at all and i really dont know what to do to fix it. is the motor big enough. any help would be greatly appriciated.

If the boat has good throttle response on land, it is probably too lean.

Warning: Do not rev up the motor out of the water. This could destroy the motor. Only do little "blips" to see what the throttle response is like.

I have no idea what motor is good for the boat. So if it is over propped, you might get the same results as running too lean...

Sean

Is there anyway to post pictures? The exhaust could be an issue, prop could be an issue also. There are alot of things that could be whats holding it back, it does sound like the boat is really big ( so I wouldn't consider it to be a race boat, but the engine you have should push it nicely). Pictures of the engine compartment and engine and pictures of the transom or back of the boat would be great. If you remove the prop most of them say what they are on the end under the nut.


Paul

if the boats been sitting for a coupla years you might want to clean out the fuel system,and carb,reset needles to factory specs and go from there, you might want to consider a tuned pipe which you can also plumb into that quad exhaust........

thanks guys. in a couple of days ill get some pics and post them on here. (not quite sure how to post pics on forums) and ill let you guys check them out.

to post pics you can put them on photobucket.com.......then copy and paste the image code on your forum post.....they will be kinda big..but thats how i do it

heres some pics. the prop i have is a prather 280 and its 70 inches bow to stern
sorry guys it needs a good cleaning. its been sittin in the basement for awhile

Ok I would bet if you put a tuned pipe on the boat it would run much better (the length of the tuned pipe is very important, someone with knowledge of CMB 90's would know how long it should be) , based on the pic the prop doesn't look real sharp either. I would bet you could go with a bigger prop also, thats the same prop thats on the shockwave 36 which has a .32 engine and is 36" long. One problem looks like it might be hard to offset the tuned pipe around the radio box, so you could still use one of your existing exhaust outlets on the back of the boat. You might also consider putting some extra flotation in the boat, pool noodles work good for that. Do your push-rods attached to the servos have good water proof seals so no water gets in the radio box, and the wire nut on the antenna wire should be soldered and shrink tubed if you are going to keep it like that. These are just some ideas what you do is all up to you, I would guess this boat will easily out run your big boat behind it.


Paul

Are you SURE that is a 230? If that is a 70 inch boat, and that prop looks like it is pretty scale with the hull, I would guess it is atleast a 270, if not a 280. Also, if you are running 1/4 inch flex cable and stub, the 230 wouldn't even fit because it is a 3/16" prop.

Like gooy said though, sharpen and balance the prop, and get a tuned pipe and it will move much better!

Another thing I noticed (need another opinion on this) I wouldnt think that you should need to have that bend on the outside corners of your turn fins because I think that will be more drag than it is worth.

Yes the trim tabs are a little questionable with them bent down the way they are on the outer edge, and I just noticed your rudder is really short I am pretty sure it should be about 1" longer than it is ( Yes I could be wrong, but I would think when the boat gets up out of the water on the prop/plane the rudder wont be in the water anymore?)


Paul

the angle of that pic does make the rudder look short, but maybe it is just an illusion. I bet a tuned pipe would be the ticket for this thing.

BIG engines like these need to run rich also..........FEED IT WHAT IT NEEDS !!!......good thing about that big boat,you can run twin 20 oz.saddle tanks for a total of maybe 10-15min.LOL...........

heres some more pics that you guys were wondering about
the fins on the back
the rudder its about 2.5-2.75 inches below the bottom of the boat


so what do you guys think of this boat. does it have potential? did you ever see one like this one. i was told i was one of a kind. also the prop is a prather 280. sorry about that. it was a little dirty and i thought it said 230

i am going to build another box for the servos and probably get better servos. these ones are horrible. if i get a tune pipe for this boat what should i do with the holes from the quad exhaust. any advice is greatly appriciated. thanks alot guys. you have been really helpful.

Well for the holes on the back of the boat , this is an idea there are probably alot of ways to do it but this is one. You could use something like this http://www.grainger.com/Grainger/items/3LN64 and silicon around or epoxy in so they will be water proof. They start at 1/2" and go upto like 2". I was thinking easy fix without having to do painting or more complicated patching, and they don't look that bad.


Paul

A much better choice is to use RCU's built-in attachment facility. This way, the pictures initially load thumbnail sized instead of forcing everyone to download them full sized. Additionally, they stay around essentially forever, instead of becoming dead links at whatever point photobucket, or wherever else, decides to delete them. You can find instructions in [link=http://www.rcuniverse.com/forum/m_5218588/tm.htm]this thread[/link].

If you like the look, you could just leave the 4 pipes sticking out the back to fill the holes...

Or three, and see if you can get the tuned pipe to exit through one of them...

Sean

I know xxxboatworks has some awesome chrome tips that you could put back there for looks. I think that the prather 280 is probably a bit large, maybe a smaller prop would get you some more rpms. I always thought the 280 was nice for weedie boats because they could get decent speeds at lower rpms since the prop was so big, but I could be way off there! I think you have a pretty cool boat there and with a little elbow grease and a couple new parts you will be having a ton of fun with it!

if i were to get a different prop to try what size and brand should i get. also does any one know what kind of power a cmb .90 engine has. hp? and if i were to get this boat running perfect what kind of speeds am i looking to get out of this boat.

you can try an x460/3 blade,this gets the back end to lift a bit and not seem so sluggish,plus it will allow the engine to "wind out" as nitro engines love to do,,,I believe the person you bought the engine from is right that it's output is around 6hp. I'm not sure but it looks like your engine was slightly modded from the external views you provided...(lightened flywheel,and head tapped for water exit) looks like he had that engine in a rigger before,I started a thread awhile ago asking the power losses involved in plumbing a tuned pipe into a quad exhaust and most of the replies agreed that power loss would be minimal.....if any.......[:-]

Maybe the trim tabs are bent like they are because the original owner was having handling issue's and that would slow the boat down a little and bring the nose down also. You can always adjust them after you get the engine running at full speed, ya know a tweak here a tweak there (to figure out what works best).


Paul