OS FS30 marine conversion

Looking for a big rigger for windy days perhaps something like this with
the front end like a mono ship with for big waves sponsons the same
way to slice through rather than be pitched hard. Anti spray rails to keep
the engine bay from being splashed. Too windy this weekend to do test runs
we had white caps on the water.  

Saito .72 powered quarter scale driver would make it a 18ft. rigger.

So you could design the front of the hull something like the Ski Daddle bow and keep the sponsons the same more or less. Years ago, I built a 40" deep V with retractable hydrofoils the idea being that this combination would work well in either calm or rough seas.
For a number of reasons it never worked but I haven't been able to admit defeat and throw it away.

No the water is too rough for that on bad days. Think scale to the conditions
like being on the high seas. The rigger must displace / cut through the oncoming
heavy large chop like a battle ship otherwise I will be flying through the air too much.
Not good can cause diving, flipping into tumbling out of control sponson ripping wreck.


old school method


New method allows for faster speeds the water does not climb up the front as much just flat out cuts water!

For a time around 1976, I was chasing more speed and ran a Dumas CF40 fiberglass Deep V hull powered by a K&B 6.5 marine and later an OS 60FSR. The OS worked WAY better with far more torque, throttle that worked and a Perry fuel pump allowing me two run two 12oz tanks in series for decent engine run times. That boat at times would fly straight up off a wave then bury itself stern first and come back out of the water like a Polaris missile!
There were also times when it submarined killing the engine. I used a Perry air filter to minimize hydraulic locking when this sort of event occurred.
For the record, I was running a totally submerged prop around 50-55mm diameter from what I remember and was able to get a top speed of about 33mph chasing it with my full scale boat.

Hey Jim any updates on prop selection?

I have installed a OS .56 Alpha in the rigger with a OS 45 size aluminum flywheel.
78g with coupler. Hope to have a good vid this weekend. The engine does not have a
crank case oil breather nipple rather it transfers the oil up through the cam and rod tubes
into the rocker arm case and then out a small connecting port through the exhaust. I like
the extra cooling fins in lieu of no water jacket. The nominal rating is 1k more than the previous
version. Went with a different muffler, no baffle just one big open chamber. Static tests completed
during break while still rich made 14.3k no load. Will do a few rich water runs with it set at 15k ish.
I removed the blue paint off the sides of the rocker cover for a bit more direct air contact. 87 mm
total pitch for the first run nominal pitch is 2.3" and 26 deg rake. Low end NV was left at the factory
setting. This upgrade makes a bit more than double the HP of the Saito .30 should be able to launch
it at idle then punch it.










This is after 2.5 tanks just lean enough to steady out after some top end:

I received an Octura prop that I may try soon. Don't have the specs handy but it looks like 1.8 diameter and X 1.9 that in pitch. I'm at my place on Lake Superior and should get some calm weather in the next few days. I'm interested to see if the OS 56 cools well enough with just air cooling. If not, it could be a candidate for a water jacket retrofit.........(I know somebody with a lathe)

Thank you Eric, bit rich still but getting there worth a quick vid for posterity
There are only 3 vids with 4 stroke riggers on You tube at the moment perhaps a
good running vid will inspire others to try and enjoy the benefits of torque and sound.

Jim the total pitch at 3.42" should give the hull a solid amount of thrust with some speed.
46mm dia seems quite reasonable given the use with a 4 stroke. Big lake hope you can find
some good smooth water to enjoy. Wind is always the deal breaker on warm weather days for me.

I didn't like the painted Saito the heat transfer seemed to be restricted no bare aluminum to air
contact the 40 size rigger needed more HP so the OS seemed like a good choice given the attributes.
Here is a pic showing the serious effort by OS to keep the engine cool in comparison to the Saito.
I think it could accept a water cooling jacket, I plan to run 50% nitro 18% synthetic may add some
castor to bring the oil package up to 21%

Hi Jim, I've been enjoying this thread. I built the Dumas Short-Stuff (DV-10) about 25 years ago and still have it. Like yours; it's the "built-up" wood version. Mine is electric-powered though. I went with a Graupner "Multi-Speed Mono" drive from Hobby-Lobby. Watching the vids in this thread makes me want to run it!!!

I haven't run this boat in a VERY long time.. (15+ years) I built it in the early 1990's.




I just discovered that the SK-Daddle was also offered as the SK-Daddle Jr.; an 18" version for Cox .049/.09 engine power.



Do you remember the Ske-Vee 10? It was another model in that same class.




Brad (1/2ANut) has mentioned that the Dumas flywheels furnished in their 1/2A running-hardware kits need to be "bushed" for running on a Cox .049/.051 engine. I have a theory about this. Dumas wasn't in the engine-business.. and likely sized the hole in their flywheel to fit the Cox .09 engine. The .09 engine has a 6-32 threaded crank.. whereas the .049/.051 engines have a 5-40 thread. Running their flywheel on the latter engines without properly bushing the hole, can cause it to run "out-of-balance" quickly wearing-out the crank-journal in the engine's case. You'd think that Dumas would have acknowledged that issue at some point. I'm glad that Brad mentioned that issue to me in another thread.. because I have a couple of those flywheels.. and a 5-40 screw "does-indeed" float-around if not bushed.

I have a Dumas AVL hydro kit for Cox .049/.051 power.. and this is good info for when I get around to finishing it..

Do either you (Jim) or Brad have any experience with running the Dumas cooling-clamp designed for the Cox .049/.051? It's a heavy piece.. actually twice as heavy as a Cox heat-sink designed for the same engines.







I realize we're not talking "airplanes"... but that's quite a difference in weight.. plus the complexity/plumbing/drag of a water pick-up fitting in the case of the Dumas water-cooling jacket when compared to the simplicity of the Cox air-cooling heat-sink.

Dumas actually shows the Cox heat-sink being utilized on the box-décor of their Ske-Vee 10.

I never ran an 049 inboard so have no experience with the Cox cooling clamp. I would just use the heat sink instead to minimize plumbing complications. I own a Sea Fury 0.060 outboard and the only cooling I can see would be the air fins and heat transferred away through the lower unit. It seemed to run fine without overheating and I suspect the small displacement Cox engines would be ok with just air cooling. The Ski Daddle Jr is adorable. I'd build one but have been spoiled by my marine 4 strokes. There is something neat about the way these flat bottom hulls turn.

And handle rough water!

I have used both the best method for cooling is using aluminum tube rapped around the cylinder.
The trick for good fit (which is a must) is to use something smaller in dia. to form the coil then
walk down the coils on to the engine expanding the coil just enough to fit rush this and you loose
the spring action. The tight fit will create less black goo when the engine is vibrating against the
aluminum mixed with exhaust oil.

Out of the two cooling versions you have the Car version cooled the best, both are clunky extra
weight but the Dumas version is the worst.

Notice thrust washer / bearings the least amount of load on the engine and stops wear on
the aluminum crank case which creates black goo. Nice clean running with the muffler.






This is an old rigger from the late 80's too heavy made with left over ply from a 25 size rigger.
It worked though with a TD .049 and QB the QB seem to launch better less flame outs due to
the extra mass of the piston / crank.

Thanks for the info fella's. I'm looking forward to more discussion and videos. I like Brad's cap-visor-cam! I've wanted to shoot video many times lately. My camcorder is ok.. but it can't compare to what's available now.

Ok gents the weather was getting bad but was able to do a break in run of the new engine with a 25 size 2 stroke
prop was not enough load to change the rpm of the engine from bench to water but least it was easy on the
internal parts as everything got a good seating. Now I know what the engine loading is like I ordered 3 new props
to try. Set the NV rich when it was hot out by the time I ran it the cool air from the storm made for a very rich NV.   

Went from sunny 95F to around 76F cloudy / was very nice cool weather. Even in hard turns at the end just before it
ran out of fuel the rpm did not change least in relation to prop loading. I need a good amount of prop to phase the torque
output of the engine. In the mail a 58mm and 55mm high pitch props on the way. I ran a Prather 220 for the break in run. By the time I was ready for another test run the lightening was just getting too close for comfort. I was going to lean it up 5 clicks for another round.

That moved along really well considering the load on the engine. What rpm/speed would you be getting there? I took my Ski Daddle around our island yesterday on its 6 oz tank (about two miles). Could have gone a lot further if my chase boat was faster than 6mph!

Best pass came from legging out the straight away it managed to hit 31 mph
Started around 15,400 rpm stayed up in that range most of the run but was
slowly dropping as the cool wind from the  storm came in to 14,780 by the time
it was doing tight circles it hit 14,473 twice a few bit higher. I should have brought
it in before running it out of gas the rich setting cut the tank time short at 5.24 mins.
Should be able to do about 9 minutes once the NV is in the sweet spot.

Wow that was still a good bit of distance Jim, the water buoys at the club are set for
6 laps around gets you 1 mile, 3 buoys per 50' turn radius gives 281ft. on the straights.
Will figure out what prop gets the rigger dancing and post another vid hope to see around
50 mph should be running pretty loose at that pace.

706jim wrote:That moved along really well considering the load on the engine. What rpm/speed would you be getting there? I took my Ski Daddle around our island yesterday on its 6 oz tank (about two miles). Could have gone a lot further if my chase boat was faster than 6mph!

That's sOoOo cool Jim! I wish I had a chase-boat. It's one of the things that deters me from IC-engine boat-modeling. There's a reservoir within walking distance from our house. We've lived here for 6 years.. and I've yet to run even my EP boats there.

I sourced some tiny surface-props that I've been wanting to try on a small (18") self-designed outrigger for Cox .049 power.




Lots to figure-out with a surface-drive though. I'll have to make my own. Brad has given me some very helpful advice.. but my self-designed hull needs to be proved-out. The best I can do right now is to study Brad's methods for a drive set-up and follow his advice in a number of areas.

Those props are replacement-parts for the little Aqua-Craft "Reef-Racer" boat.. which is a "mono"..



When I bought the props.. I also bought the Reef-Racer 3mm solid-shaft drive-kit.. in hopes that I could adapt it to the Cox .049 engine.




Here's what my hull looks like..




I'd like to try to make this design work.. but there's a LOT of variables involved in getting a rigger "up on step". I'm a "tinkerer".. and enjoy designing my own models. Anybody can go out and buy a RTR boat.. or a build a proven hull-design. I guess I just prefer models that are unique one-off creations. I certainly enjoy reading about a self-designed model.. and looking at the photos; knowing that it's the only one that exists. That's really cool to me!

Well, in the process of getting your project going, you run into a dead end with some sort of adapter, I have a beautiful lathe in my garage just waiting for some custom project to come up.......

706jim wrote:Well, in the process of getting your project going, you run into a dead end with some sort of adapter, I have a beautiful lathe in my garage just waiting for some custom project to come up.......

That's VERY kind of you Jim. I wish I'd gotten into metal-working/machining younger in life. I ran CNC routers for years working in sign shops. A few years ago I got my "feet wet" working in a small machining "job-shop".. as a set-up/operator. I ran a Fadal CNC vertical milling-machine.



I was supposed to learn programming (MasterCam) and Proto-Trac.. but business got slow and I was laid-off. Subsequent job-searches in that field led nowhere. Employers wanted prospects who could program/set-up and operate. It's really just as well.. because I'm also a professional musician (piano/keyboard player) and metal-working can be hazardous to the "digits"... I can always make extra $ playing gigs to supplement any other income.. as long as I have that ability.

Are/were you a machinist by trade? It still fascinates me to see machining being done.

Ironically, I attended a high school that promised shop options to arts and sciences students. Except that after grade 9 we were told we had to take Latin or music, so machine shop went by the wayside. (Turns out the principals wife taught Latin......)
So ended up being a self taught machinist doing CNC programming of punch presses, plasma cutters and later machining centers and lathes. Then got a job teaching this stuff at a community college. (Also was a semi pro guitar player for a rock band for many years, so I know about fingers and machines). I am one of those lucky individuals who had the opportunity to program and then RUN the actual machine tools. Most places you do one or the other.
While I hoped to get a VMC home after retirement, I did get a lovely Graziano engine lathe for my garage, and I still have access to the machines where I used to work. And during my time teaching learned Anvil 5000 software and later Catia. The school presently uses Catia for modelling and Mastercam for CNC students.

It's interesting that you have similar interests and background.

Very interesting indeed! There's quite a few CEF members who are also musicians. The "My other hobby" thread exposes some of us.. I'd like to see a photo of your Graziano engine-lathe if you have one handy. I did run a lathe at that machine-shop when I first started there. It was a simple job that involved removing material from the underside of the head of "thousands" of 3/8" "Allen-head" bolts (cap-screws) that were too "high" when installed for their application. Talk about a boring/monotonous job-run.. I did that for weeks.

I have a few new props to try big enough to load the .56 will be posting a run vid soon.

Will test a ABC S-20 first it's a 1.6 x 55 prop took about 1.5hrs to prep it for use.