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Old Apr 20, 2014, 06:20 AM
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Help!
Weedwacker build, 43" V-hull

I need some help with finding hardware for a 110x35cm / 43x14" hull.

So far I've figured out these parts:
# Electronics
# Engine mount
# Radiobox
# Flex shaft should be minimum 6mm / 1/4"
# Rudder length 160mm / 6"

These are the questions I have so far:
1) What parts do I need? Drivline, rudder, shaft, etc.
1a) Where can I find them to a low cost? I'm located in Sweden.
2) Exhaust. The engine has two screwholes for the original exhaust but from what I've seen everything is made to be held in place with springs. Are there adapters avalible? DIY solutions?
3) Propeller size? 2, 3 or 4 blades?

The engine is a Jonsered RS38 so I'm guessing it's ~38cc and revs about 10k.

Pictures of the hull: http://imgur.com/a/tgaBd
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Old Apr 20, 2014, 12:58 PM
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Homelite trimmers are the easiest to use and work with. You will need to add some wood rails to mount the mltor and fiberglass to glass them to the hull . Some aluminum to make mounts. I use a 3 point mount system. as for the running hardware I use Prather products. But you can use any gas running hardware you want. Used is the cheapest and ebay is the best place to find parts.
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Old Apr 20, 2014, 07:48 PM
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Don't rely on the number in RS38 to be the cc size.I have a Stihl FS45 trimmer engine and it is 19.8 cc.
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Old Apr 21, 2014, 04:06 AM
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Did some quick measuring and it turned out to be around 37.4cc, give or take a little.
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Old Apr 21, 2014, 07:16 AM
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Is this a trimmer engine or from a chainsaw. If from a chainsaw the rotation on the clutch side would be clockwise.There are props available but not as many as in counterclockwise rotation.
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Old Apr 21, 2014, 07:32 AM
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I was doing a search for dealers of r/c gas boat parts in Sweden,but came up with none. Most US dealers like Warehouse Hobbies,Aeromarine and others will ship to other countries. A place with desent prices is Zippkits and you can ask Joe the questions you have and he has about everything you'll need. I think he answers emails fairly quick. http://www.zippkits.com/
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Old Apr 21, 2014, 07:39 AM
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Don't rely on the cc size. You need at least 1.5 hp to run a gas boat . 2 hp is better.
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Old Apr 21, 2014, 02:08 PM
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It's a trimmer engine so counterclockwise prop it is. Some pics of the engine with the hull: http://imgur.com/a/5PwBL By comparing Jonsereds current trimmers and subtracting some effect due to it being an older model this one should have about 1.5hp

I've found this shop located in UK (http://www.prestwich.ndirect.co.uk/) their prices seems to be good. And they got this: http://www.ebay.com/itm/360744768222...84.m1423.l2649 From what I've learned this plus a 160mm rudder it would do the trick. Comments on my choice? Can I find cheaper alternatives?

Should the COG be at 1/3 of the hull length from the rear?
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Old Apr 21, 2014, 03:27 PM
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You would be better off with a Homelite engine as you don't have much room. 30cc are 2 hp. That motor you have is taking up too much space.
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Old Apr 21, 2014, 04:59 PM
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As txt said,the motor is too big . It's simular to the old Ryobi type engines but bigger and a real pain to use in a boat, even a boat way larger than yours. You also need room in the back of the boat for the radio box and somewhere to put a fuel tank or IV bag and still keep the CG between 28 and 30 %( between 12" and 13" give or take a hair). That engine when stripped down would probably make a good engine for a very large r/c airplane.
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Old Apr 21, 2014, 05:59 PM
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It looked like a Ryobi which I wouldn't even consider for a boat motor. I wouldn't go any smaller than a Echo gt2000 motor. It is a little smaller than a 25 cc Homelite motor but way better than a Ryobi.. You can find used motors for $30-50 US. or go to a salvage yard in the spring and fall and find one for free. They will need a little work. I have found several and they all run good after a tune up and a few parts.
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Old Apr 21, 2014, 07:55 PM
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The normal engine rail spacing is 5" between,but I usually go 5 1/8" because I found some mounts are not exact and are a tight fit.You should have an engine that you can mount between the rails,even if it takes a little trimming of the engine shroud or metal.I've even had to do a small cutout so the carb would let the engine go down further between the rails.Most engines use a 4 point mounting system ,but some use a 3 point like txt uses. Below is an engine that had a 3 point but I made it into a 4 point by using a piece of flat 1/8" x 1 1/2" flat aluminum and cutting a hole for the tip of the shroud and bending it to make the mount..This engine is a 25cc Homelite.I have aluminum cups that go over the rubber isolators in the third pic to stiffen them up,but are not on in the pic.
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Old Yesterday, 06:11 AM
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So the physical size of the engine is too big and would make it hard to fit electronics and get the CG right? I see it as a challenge to make it work There's plenty of room in the back of the hull for electronics and the fuel tank will probably be in the front or possibly right above the clutch.
The hull is wide enough for the engine but it's the top half that causing problems. But, I will make mold of this hull and the top half will be modified to suite the engine and tank.

I got the hull and engine for free so it's gonna be this or nothing at all. My goal is to make it for fun and learn something new not to race or be the fastest. Of course, the more speed I can get out of it the better (speed=fun)

sleepwalker, in what way do you mean it's pain to use this in a boat?
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Old Yesterday, 06:55 AM
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I'm assuming from the engine position in the pic that the exhaust port is down towards the bottom of the hull.Not a good place for the exhaust and if you turn the engine over your pull start will be down.Also where will the carb adjustment needles be ? If in a hard to reach location ,that's not good.Also this is an air cooled engine.It needs air flow to cool properly.You said this engine is around 10,000 rpm. I read somewhere on one of the other forums that when propped and in the water ,you would loose about 25% of your rpm taking it down to 7500 rpm.Even with horsepower you still need higher rpm to move the boat with any fast speed,unless you're satisfied with about mid 30's.It should have good torque so a bigger prop is probable,which may help.If you're up to the challenge,whether it be putting this engine in the hull or using the hull to make a mold,then you should at least give it a try.Good luck and post pics of your progress.
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Old Yesterday, 07:35 AM
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Ryobi engines don't have torque. You will never see 30 mph from that motor. The opening at the back of the hull is where the radio electronics box goes for easy reach. The motor you have is taking up that space. The gas tank should be next to the motor.The motor takes up all that space too. You won't be able to mount the rails in the hull of the boat the correct way as the motor takes up all the space needed. The motor is just too big for the hull. Modifying the hull to make the motor fit is a waste of a good hull and time. Even if it was free.
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