4 cyl. Outrigger Hydro


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Amp Eater

Well-Known Member
Apr 23, 2006
Has anyone tried running a 4 cycle. engine in a outrigger?

Example the car guys use OS Surpass engines up in 19k - 22k range.

I have a new Saito FA .72 / 11.8cc engine 7mm shaft , can run at 15k. The sound would be cool,

but more so wanted it for windy days when the water is rough. Long lanky wide stance stable

enough to handle some air time smacking into large chop. The extra torque for it's weight will

be helpful. No idea what size prop at lower rpm the pitch will have to be up there. Run it on

20% nitro, able to get up to 50 mph on calm days.
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I put 2 twin cylinder Quickdraws in an 84 inch Apache hull.


Counter rotating

95mm props




Sent from my VS985 4G using Tapatalk
i bench tested a new Saito .30 it was able to hit near 13k without much fuss.

Looking for this sort of sound with valves and rockers.

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Long narrow big stick for pushing through rollers as high as 1ft.

Tapper front and rear only wide enough to fit the engine in.

Rigger big water.JPG
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I put 2 twin cylinder Quickdraws in an 84 inch Apache hull.


Counter rotating

95mm props




Sent from my VS985 4G using Tapatalk
I remember seeing pics of the 84" twin Quickdraws years ago in rcboat modeler magazines,,,awsome...
Top view of the big water rigger looks like 30" spacing any wider and I will need more than

1/2in OD thick walled carbon tube.

7ft. Apache hull would be a site to see.

Big Water Rigger Top.jpg

Rigger big water.JPG
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What are you going to use as a driveline?

Similar to the Japanese offshore 90-Hydros.


Mark Sholund
Hi Mark,

3/16 steel drive line with an array of roller bearings thick walled aluminum stuffing

box with thin wall tubing inside to space out the bearings and shim up for the prop.

With such a long tail reducing the spinning mass on the engine and over all weight

management with an aluminum flywheel should help keep it fast for what it is.
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Hi ,

i had running a rigger with a Webra T4-40 . This was a drumvalve 4 cycle motor with toothbelt drive of the valve drum .

http://antiquemodelenginesrunning.blogspot.de/2011/05/webra-t4-40.html. This motor was able to rev up to 20000 rpm .

I run it at about 15000 rpm with Octura competition line propeller where the pitch has 1,8 x dia . I have currently the OS Wankel turn diske motor that run very cool but have to design a rigger for it.

Happy Amps Christian
Hi Christian,

Yes I think a 4cyl engine is going to be unique, sound great at high rpm passes with more

torque to swing high pitched props. I have had many over the years and enjoyed

the speed and sound they make flying fast. So now wish to do the same with an outrigger.

I will try a Octura 2160 as a base line test to see which direction I need to go. The round

Wankel engine would be an interesting project fitting very low inside the hull and would

be a treat to run. Honda makes a belt type 25cc 4cyl engine for lawn care. There are some

conversion for aircraft use and show good promise. The goal here is for a rough water

outrigger for windy days. Must be built strong to handle the pounding it will have to take.

Will have to use a cowl on extreme days to keep the water off the engine.

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Nice would sound kick arse at full throttle zipping along at 70mph + a rigger can provide.
I have an OS 120SP saved for a future project.

Great engine. That photo brought back memories of flying pattern in the 80's. I had one in a Patterntec Miss Beatle airplane. It was the period when pattern went to flying in a set box and no longer zoomed in and out of the judging view. Speeds slowed down and engine torque and braking the 4 stroke 120sp provided were the ticket, especially competing in Colorado (high altitude ) where the supercharge really helped make up for the lack of oxygen the thin air afforded. Nice NIB engine you got there. Thanks for sharing.
I bet there are plenty of folks with sweet sounding 4 strokes collecting dust. I have

kept my eye out for a rigger application over the years no one has posted anything

on the net that can be searched. I look forward to putting a rigger together with

the Saito .72. Will use all birch ply for the endeavor, can be bought in 48" sheets.

I have procured the wood down to committing to a design. Need to start gathering

up hardware before I start.
Following up on this need for a thumper screaming along beyond it's typical aero rpm

I have started a project with a Saito FA 30SH Golden night. The flashy gold rocker covers

will be some additional eye candy as it make it's way on the water. The original idea with

the 72 went to the waist side in lieu the smaller displacement able to make more rpm

for it's given stress on the metals that created the little beast.


- Here is the original conceptual drawing, leaving room for a upgraded engine in the future.

- Engine exhaust has two knuckles to redirect the upgrade 40 size muffler for a bit more


- I hate making two of anything seems grueling to me so started on the L sponson first leaving

the R sponson to do last having the entire completed project egging me on to finish up.

- 16" long sponson came out with a reasonable weight having a balsa core and ply overlay

- The layout of the gear simple easy enough the rudder servo puts out 4.6 lbs of torque on a 6.6v

- Would be nice to make a 16ft full size outrigger with a single cylinder 750cc Harley engine..thump thump...

- Mirror image overlay of the left sponson on the right side to get a handle on the stance.

- Nearly there some pics of the rigger rounding up to being finish if not for that second sponson yet.

- Turn fin fabricated will hinge off the aluminum boom tube and have a 3mm nylon shear bolt.

Carbon tube is 7mm OD x 5mm ID

This is a fast and dirty build log showing a quick progression of the design, will drift back in this post

once the rigger is finished for a few more pics and post a vid when it goes out for testing.











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Are we talking about 4 cycle or 4 cylinder? Mike Bontoft bought 4 Sato 4 stroke (I believe) cylinders for a Dumas Typhoon scale project. As far as I know it never got built. There is no way a four stroke can develop the power of a racing two stroke of the same displacement in model sizes. The supercharged YS engines come closest, but are rpm limited. They work very well in pattern airplanes where throttle-ability is important. In a racing application where full throttle power rules, they will have around 2/3 to 3/4 (at best) the power of a tuned pipe two stroke.

Lohring Miller
Yes very true this project is not about balls out speed more so just for sport running with a pleasing

sound. The RC car guys have taken advantage of the torque output and some have reported running

up to 19k rpm. I have bench tested the engine thus far with a aero prop static load was 12.8k.

I would like to load it down on a open pass around 15k ish will be enough to enjoy with a ABC SK 1523-29-38

Perhaps around 42 mph with it. Bench testing with a 9x7 it developed .61hp / 456w on 20% nitro.

I will use 40% for the rigger to help cool the engine, will also keep it a bit rich with 20% oil. The tub

is 3" wide enough to hold a Saito .62 puts out 1.3hp with a big jump in torque, perhaps 55 mph ish.

Really have not seen any riggers out there with 4 cycle engines in them so this should be interesting

to see whats possible, just for kicks.
Thank you David,

I made the right sponson today, paint in cure mode.

Need a few parts in the mail perhaps vid next weekend or the following.

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