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New to RC with a 63” bare hull - help!

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New to RC with a 63” bare hull - help!

Old 08-27-2019, 03:42 PM
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WhiteH2O
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Default New to RC with a 63” bare hull - help!

I found a 63” deep vee hull in my dad’s garage that I want to make into an rc boat since I got some lake property. I had an electric rc boat when I was a teen, and have been out of the hobby since, and with the size of this hull, I think gas is the way to build this one to avoid having to buy hundreds of dollars of batteries for 5 minute runs.

I’m not sure what realistic expectations are for a build like this, but I’d love to get speeds in the mid 40s or faster without taking out a second mortgage.

I started looking at power options and quickly found lots of options from $200 to over $500. How big is the difference between the G300PUM for $220 and a J&G 36mm for $513 (looking at Gizmo)? This hull is big and wide, I could fairly easily put in two G300PUMs for a similar price as the J&G, but would maintenance and complexity be made up with that much better performance? There seem to be lots of other options as well between those two options, and I’m not sure what the performance vs cost trade offs are.

As for driveline and rudder setup- what should I be thinking about here? Are different setups based on desired performance? Such as extending the rudder far back from the transom, or is that more for prop clearance? Advantages or disadvantages of one piece rudder strut combinations vs separate prop strut and rudders? Stinger type drives vs struts that seem like they effect prop depth (surface drive vs submerged)? Dual rudder vs single?

Any input and recommendations are appreciated!




Old 08-27-2019, 06:42 PM
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Okay, first thing's first:
1) Since you haven't been in the R/C world in years, stick with a single drive. Going with twin drives complicates things since you will:
  • double your cost in parts
  • double your maintenance
  • double your fuel requirements
  • double your aggravation when issues pop up
2) I'd go with a known reliable engine manufacturer. J&G, Gizmo and B H Hansen are all known to be reputable and for full service. The first two are more expensive as they sell engines set up more toward performance than a Hansen set up
3) You're looking at getting a specific speed. That means you need to have as little in the water as possible. Forget the double rudders and struts as they both add more drag and reduce the speed your boat can attain. A surface drive "stinger" with a flex cable would be your best bet for reaching your desired speed. As far as the rudder bracket, you only need one long enough to get the rudder past the prop though some will tell you the rudder doesn't even need to be as far back as the prop to be effective.
Old 08-29-2019, 09:55 AM
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Lots of good info, thanks for that! I had a feeling that dual engines wasn't a great idea for me. I think the biggest part for me is double the aggravation because I don't have the experience to know how to fix issues yet. Cost is another one too of course. I figured that a dual rudder was overkill as well. Looks like a basic build for this first time boat is the way to go.

Could anyone give a little input as to what size and level of modification of engine would be ideal for this build? I'm currently looking at a G300PUM BZ1 from Bonzi. It seems like a good combination of price and power. For just a few bucks over stock, it has a few minor upgrades that seem like it could help push a big hull around. Any better options that I should be looking at?

As I'm looking for running gear, I came up with another question- what determines length of shaft? I'm somewhat assuming that determines where the engine gets mounted (distance from prop to engine), so should I plan on the engine being 1/3 of the way from the end of the transom to try to get the balance point around 1/3 of the way down the boat? I'm guessing the electronics in the rear will somewhat offset the weight of the gas tank in front of the engine. Am I close to being right here? Does 500mm sound like I'm in the right ballpark? Can they be trimmed at all, or am I stuck with the length I buy?

So, as I understand this, I need to mount two stringers (plywood) 5" apart for motor mounting, and a convenient place to put a radio box? Like I said before, this is a completely empty hull. I'm working on a deck and a hatch right now as I try to figure out power, running gear, and electronics.

Once I get enough posts to be allowed to post pictures, I'll start documenting what I'm doing with visual aids...
Old 08-29-2019, 06:57 PM
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Okay, let's cover a few things that I know, not what I don't:
1) The engine isn't what needs to be at the 1/3rd up from the transom, that's where the boat needs to balance. Moving the engine forward or back is a way of achieving that balance point.
2) The shaft can be cut, but there is something you need to be aware of if you do so:
If you go with a square drive, the shaft can be cut but to do so means you will have to solder/weld on a stub shaft which can be very difficult for someone that's new to boating as length must be within a specific tolerance and welds must be almost flawless
If you decide to go with a round collet drive, cutting the shaft won't be as big of issue, but you need to be sure to cut the shaft long so you can adjust the length.
3) The most common location used for a radio box is just forward of the transom. The reasons for this is that it cuts down the length needed for the rudder pushrod(helps prevent bending) as well as keeping the weight as far to the rear of the boat as possible
Old 08-29-2019, 07:34 PM
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1. I guess I'll get all the parts and pieces and before I get out the epoxy, I'll play with fore and aft balance to see what works best. I'd assume balancing with a half tank of gas would get the average balance the best.
2. Sounds like a round drive is the way to go. I can make metal stick to metal, (TIG or solder) but sounds like round is just easier in general. Easy choice there- long round drive line in the cart.
3. Easy enough. Radio gear in back.

Thanks again Hydro Junkie. I see you are just about an hour and a half north of where I am (Gig Harbor, WA). I hope to get the chance to see you and some of your boats some day!

Build update: Got a deck put on the hull today. Started fairing in the rough areas on the hull to start sanding tomorrow to make it pretty. I need to come up with a plan for a superstructure and build it. Finally clicked "order" on my ebay cart with assorted drive gear and other random parts and pieces. Also found a 19" hull my 10 year old son is starting to build (that one will be electric). Got a deck put on that one also. Pictures to come when I get my post count high enough.
Old 08-30-2019, 01:00 AM
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At the moment, I've only got one that's running and it's a 1/8 scale hydroplane.
Click image for larger version

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Eventually, I should have 8 or 10 boats ready to go. Just a matter of time and money, when I have one, I don't have the other
Old 08-31-2019, 11:20 PM
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A little progress today with getting a superstructure built. I thought I started this project with a lot of epoxy and micro balloons, but they are quickly dwindling into nothing. Still changing my mind on a powerplant a few times a day, not sure about a paint scheme, and trying to keep myself occupied while waiting for hardware to come. I should have enough sanding and fairing to keep myself busy for a while. Tomorrow I'm off on a work trip, so no progress for a few days.

I think I might be able to add pictures now; let's see...

Empty hull in rough shape, but the price was right. Just have to be careful sanding the outside- only one layer of glass then kevlar. Don't want to sand into the kevlar, because it likes to fuzz.


Deck on and working on getting rid of the wavy edges on the hull.


Working on a superstructure. This is going to use up a lot of micro spheres and sandpaper to make this a usable part.


Not 100% happy, but it will do. Lots of sanding left to do, but its almost starting to look like a boat. Really couldnt stand the primer grey, so a quick coat of black applied. Oh man, it looks so much better in black.
Old 09-07-2019, 12:26 PM
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You're better off running it without a hatch. Gas engines generate a LOT of heat so it needs to go somewhere.
Compare prices. Great buys on Zenoah's from www.gimzomotors.com and running hardware from Welcome to Zippkits! , both great places to deal with offering 2-3 day shipping to you.
Old 09-21-2019, 06:19 PM
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Well, I think I have figured a lot of this out by reading up on a lot of different forums and dealer websites.

Since I last posted, I've ordered running hardware and have installed it. I added a few pounds of paint and clear coat- I decided that red with black racing stripes is going to be acceptable. The transom isn't vertical, and has about a 15 degree rake, so I had to bend the trim tabs and make a bracket out of HDPE to make the rudder sit vertical. I have a radio, steering servo, throttle servo, and some other odds and ends. After much research, I have decided on a Zenoah G320PUM from BH Hanson, and I'm just finishing discussing the details and will be ordering in the next day or two. I'll bolt on a ZippKits exhaust once I get the engine mounted and see what header would work best. I still need to order odds and ends like pushrods, water hose, gas tank, gas hose, and figure out a radio box (tempted to use tupperware or similar). A Prather S280 prop is in my shopping cart, but I haven't clicked order yet. I've also been tempted to go three blade Octura Y572/3, but the extra cost is pushing me toward the S280. It would be super easy to change over if/when I want to try something else. I haven't bent the drive line yet since I don't have the engine, and don't know where it will be mounted due to balance, so that gets to wait. I have a clutch and a water pump waiting to be mounted as well. The fuselage has a big vent in the back, but I agree with the previous post that the engine needs more air flow, and I'd rather use the top instead of running it open, so I have some air intakes in progress that will be added soon. Hopefully, it will be enough along with water cooling of the motor and exhaust.

Question- when I start placing everything in the boat to figure out balance- do I do this with a half tank of gas to get an average balance point? With an electric boat, it seems easy to move batteries to change the balance point to find the "sweet spot", but how is this done with a gas boat?

I'll also add some updated pictures. If anyone sees any glaring issues with the build so far, let me know! This is all based on other people's posts on forums, discussions with others via email, and what dealers recommend on their websites.



Old 10-23-2019, 10:14 AM
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Alright, I'm in the middle of all the fun stuff- figuring out the interior layout and balance. I've come up with a few questions due to my inexperience.

First, I'm really surprised how far aft I'm having to mount the motor to get the balance correct. With that location, the exhaust will stick out he back pretty darn far. I know it is uncommon, but what is stopping me from mounting the exhaust tuned pipe forward, and having the exhaust leave the hull through the side of the boat about 1/3 of the way back from the front? I have the setup layed out with high temp tubing and a through-hull exhaust port. Seems strange, but I can't think of any reason it wouldn't work just as well as an aft exhaust. I've come up with a few air intakes to keep airflow through the boat, so I don't think I'm too worried about heat build up.

Hooking the fuel to the carb... I have the G320PUM with the 1107 carb. The carb has two fittings on it, and I can't figure out if they should both be hooked up to gas, or something different. I don't think one pressurizes the gas tank, because I see most gas tanks are just vented to equalize pressure. I've searched to see if I could find pictures of how they are hooked up, and it appears that both are hooked to the gas tank, but on separate lines (as opposed to the same line split with a T or a Y). Is the top one just for priming and the bottom the normal feed?

Balance with the gas tank. Do I aim for balance at 1/3 forward from the rear transom with the gas empty, full, or 1/2 tank? Should I do what I can to try to get the gas tank right on the balance line so that the fill level of the tank doesn't affect the balance as much? Also, what is the common way to secure the tank to the hull? Seems like it should be more permanent than velcro, but less permanent than epoxy.

Prop location and angle- I know a lot of this is adjusting the prop to tweak the performance, but I'm looking for a place to start. Where should the prop be in relation to the bottom of the V of the boat? Should the center of the shaft be right in line with the bottom of the V? Or should more prop be in the water than that? Should the prop be perpendicular to the water line, or do I want it slightly angled down to push the boat up just a little? I'm planning on securing the stuffing tube with silicone to start in order to allow adjustment, and when I get it set just right, I'll pull out the silicone and replace it with epoxy for a permanent install.

Any help would be appreciated!
Old 10-23-2019, 12:52 PM
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Your CG should be at about 20-7/8" forward of the transom. Keep in mind that the headers come long so you'll have to cut a good 3"-4" off it if not more. CG is done with the tank or bag empty.
The fuel system. I'm assuming that you have a carb with a primer on it. You can leave the fitting by the primer alone then hook up to the inlet under the carb.
Measure up 1/2" up from the bottom of the Vee for the centerline of your prop and shaft. Start it off level with the bottom of the boat.
It looks like you're using a hard tank in the boat. I haven't used those since my nitro days as I use the IV bag type setup for my gassers. I get mine from Zippkits and make up my own mounting bracket from 30" 4-40 threaded rod. I use part of it for the throttle or rudder linkage then the rest for the bracket. Usually the 4-40 rod is only about 10 cents more for the 30" piece over the 12" piece.
Old 10-23-2019, 01:05 PM
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Another thing real quick. You might want to get a longer stand-off for the rudder to get it at least even with or behind the prop. That one is better suited for hydroplanes or Catamarans. Joe at Zippkits has them. I chose this shot as this boat I built for someone used Zippkits hardware.
Old 10-25-2019, 03:44 PM
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Thanks Ron! Lots of great info!

I got my header pre-cut for the tuned pipe that I got it with. I'm still playing with different ideas, but I think the exhaust will end up facing forward. Either that, or it is going to be sticking out the back pretty far. That will make me able to put the gas right next to the CG, so the CG won't move much as the gas levels change.

Thanks for the clarification on the carb inputs and prop angle and location!

I'll look into a rudder that sits further aft. I'll probably use this one for a while since I've gone over budget with this build already, and put that on the upgrade list for later.
Old 10-25-2019, 08:02 PM
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If you're using a 2" offset header at 12-1/2"-13-1/2" you should have room. This is inside of a 50" Jersey Skiff. At the transom I had to use an exhaust outlet.
Old 10-25-2019, 08:06 PM
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Thunderboat
This is a 50" Thunderboat with a standard 1" offset header and there's still room.
Old 10-27-2019, 08:04 AM
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After messing around with a bunch of different ideas, I got it to work. The trick is to use the hatch/cabin on the boat. Most of the weight of the hatch is aft of the CG. That is the only way I can get the CG aft enough to be able to get the engine forward enough to have room for the exhaust. I have everything in now, and the balance is pretty much perfect with the gas tank empty. I still have quite a few little minor things that I have to do before the boat is done, but I'm very close. And now that the hatch is going to be on while running, I am going to add a few extra air scoops to try to assure adequate cooling. I'm a little nervous about how close the exhaust is to my radio box, but worst case, I can wrap the exhaust there to keep the heat away. It is looking pretty good, I'm getting excited. I hope it's going to be fast!

To do list:
Permanently mount gas tank
Balance and mount prop (Prather 275 stainless)
Waterproof stuffing tube outlet in hull
Radio box guts- mount servos, connections, mount on/off switch
Add air scoops for cooling
Few other odds and ends...

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