New CAT Build - Please comment

[teamvictory]

Hello all,

I'm planning out a new nitro-powered semi-scale offshore catamaran and want to hear what everyone thinks about it. The Hull is a fiberglass 32" Hydro & Marine Agitator that will be reinforced with carbonfiber. Here is what I'm thinking:

Power: fully mod'd (ported, turbo crank, etc.) GO Engine "GO Tech" .25 motor - stock claimed HP 2.8@31000rpm

Collet: Aeromarine .187 cable collet for 7mm SG crank (may use OS .21 collet with spacer - Remy @ Aeromarine is hooking me up so we'll see!]

Flex Cable: .187 with 3/16 stub shaft

Flywheel: suggestions? Need one wide enough for a collet to fit inside and deep enough to allow the collet to grab enough crank threads.

Mounts: .21/.25 Alum.

Fuel System: twin 250cc tanks, one in each side of the hull.

Pipe: .21 pipe (approx. 8.75" long)

Hardware: OCTURA Aluminum Strudder Package 92 C with offset rudder

Prop(s): I have an idea but open to suggestions

I think that's about everything but if I missed something please let me know and any recommendations on parts or setup would be appreciated. I'm aiming for 50+mph

teamvictory

 

[tampa1330]

Sounds like a good setup to me. The only thing that throws up a red flag to me is the .25 Go Tech. I've heard only a little about the Go engines and that they're good for the price. I've found that a lot of the .21's are more powerful than the .25's. And keep in mind that you're using a car motor. There's alot factors that go into a true marine motor such as port timing, compression operation temp. Just puting a water cooling head on a car motor doesn't always work as easy as it seems. The car motors are designed to be air cooled and run at a slighly higher temp. Water cooling is much more effective than air cooling. water is much more dense than air and therfore can absorb much more heat at a much faster rate. Think about if you took two red hot pieces of aluminum and set one on the table and dropped the other in room temp water, which one would cool faster? If you can't get the engine up to operating temp then you can't get that full 2.8hp. Also the power band might be at the top end only. Marine motors need a full power band. cars and trucks have transmissions and sometimes with mutiple gears so the engine is at top end most of the time. The other parts seem like high end components so I would try to match them up with a high end motor. The motor is the basis of the entire set up so your limitationis would be created the motor. I am new to this hobby myself, so I don't preach the gospel, but I am an engineer and design is my profession. Through civil & structural engineering I've learned that detailed research is a critical element of design. That Hydro & Marine hull is a nice boat. If you keep it high end and I think you'd be much more satified in the end. I know some sport 20's are 60+mph. On my last project I went the other way. I started with a RTR hydro and replaced the engine with a high end .21 and i'm hitting the 50mph line and I have plenty room to go. What I learned is the chain is only as strong as it's weakest link. In my last build the weak link is the hull. At 50 mph I can't keep it on the water. It was designed to hit 30-40 not 50-60 so the airfoil creates too much lift at 50mph and it blows over too easily. Again this is my opinion, not gospel.

 

[moparbarn]

you might try contacting jerry wyss - on here under that name. he has done a few car/buggy engine conversions. mostly thunder tiger, but he may have some useful info on tricks to make a car motor more suitable to a boat's power requirements . hope it helps.

 

[teamvictory]

Thanks for your input. You definitely made some good points. In terms of possibly over-cooling the motor with a water-cooled head, I'm not too concerned as there are ways of limiting how much water flows thru the head. I made a water-cooled copper coil for the exhaust header; In very cold running conditions (or if the motor just won't come up to temp) the outlet tube off this coil can be re-routed to the inlet of the head so that water warmed by the header enters the head, and then exits the boat. This gets temps up a bit and keeps the motor within operating range. I had this system on another boat.

The port timing is something else that can easily be changed, if need be. This can be done by simply shiming up the sleeve a little (from the crankcase) and then taking a little material off between the head button and sleeve - this maintains the motor's factory compression ratio, which is changed when you only shim up the sleeve without further correction.

These modifications can be done quickly and inexpensively. I purchased the motor brand new for $100 with a nice water-cooled head and aluminum flywheel. I checked out all the reviews I could find on these GO Tech motors and read nothing but great things about them. For $100, why not give it a shot?!

teamvictory

 

[moparbarn]

hell yeah, try it. not trying to be negative at all...... you sound like you know what you're doing fairly well, already. keep us posted.

 

[tampa1330]

I have used the header to warm the water prior to cooling the head. I also have some valves that can be spliced in line to regulate the flow. Just a simple fuel on off valve works great. I have never run a cat before although I just bought one last week. should have it by the end of the week or the following week. Be sure to post some pictures and vids. I like those Hydro & marine hulls. very high quality.