Dumas SK Daddle-cable through the transom or under hull?

[dannyual767]

Okay, I've asked this before and I never really got a good answer and its time to start drilling holes :biglaugh: . This thread is also posted on JRCBD as well.

Here is my Dumas SK Daddle that is 36" long. I'm going to power it with a K&B .67 nitro engine or an OPS .67. I've got both so I'll just have fun with either or both.

The hull is similar to a crackerbox in that it has a very flat bottom. I just don't know if having the flex cable exit the transom will work with this flat hull bottom :confused4: . I can picture massive amounts of propwalk ! Here are some pictures:

Here is the transom of the boat. It is only 3" tall from top to bottom! Its 11 1/4 wide.

I've got a skegged strut that I'd like to use to help keep this hull tracking straight.

Should I have the brass stuffing tube exit the transom or should I have it exit under the hull? If its under the hull, I think that I'll have the tube pretty much touching the bottom of the hull. In other words, the prop won't be full submerged but it'll be deeper than if the cable exited the transom.

What are your thoughts?

 

[jetpack]

I am glad you posted this question. I am curious also. I have a Dumas SK-Daddle Too (it is the same as yours, only it is the 20 size version) that I have ordered and is still in the box.

The instructions have it set up as having the prop completely under the boat, but I was going to go with an outdrive setup like a deep V would have it.

With this being an almost flat-bottom hull, running a surface drive would be risky on the motor. Any type of chop and it will be hopping out of the water quite a bit I would imagine and make thrust changes limited. It might want to run too wet.

Having the prop set completely under the boat would limit the thrust changes also I feel, but make chances of it cavitaing less. I don't know. It does have a nice look with it under the hull which keeps the transom clean, but I wouldn't do it if it limits my running options or it's speed.

I do not like how they specify the rudder being mounted through the bottom of the hull. If I were to go with a hidden prop I would still run a rudder bracket off of the transom. I do however like the idea of running an in-line rudder with the prop just for low speed handling's sake.

I have purchased an Octura In-Line brass strut and rudder for my Dumas Drag N' Fly 20 project, and might just buy another for this. It is a skeg strut also, and will allow me to change my prop height to being almost a surface drive, so that might be the right approach.

I am still kind of lost on the best way to do this also at this point, but those are my thoughts...

 

[dannyual767]

posted by jet,

The instructions have it set up as having the prop completely under the boat, but I was going to go with an outdrive setup like a deep V would have it............I do not like how they specify the rudder being mounted through the bottom of the hull. If I were to go with a hidden prop I would still run a rudder bracket off of the transom. I do however like the idea of running an in-line rudder with the prop just for low speed handling's sake.

These instructions are reeeeeaaaaaal old school. Like from back in the 60's ! You ought to see the picture of the radio that they show on my instructions.

There is no reason to not hang a rudder off the transom for these boats. As far as the prop being submerged, yes, I think thats what we need to do. A member on Jim's RC Boat Dock has responded to my thread there. He said that he ran a 36" SK Daddle with a Webra 60 engine. He said that it was way more power than the hull could handle. He said my motors are even more overkill. He ran his flex cable under the hull about 1/2". That sounds like what I'm going to do as well.

He highly suggested using a skegged strut as well. He also mentioned that a decent .21 size engine would work good for my hull. It would probably be plenty of engine for your smaller hull; perhaps too much .

 

[Lar'Dog]

Danny,I see You have cut out the bulkhead under the dash!!! :blink: Later

 

[jetpack]

The motor I have planned for mine is a little Webra Speed 20 with a Dynamix carb. I love the guts out of that motor, it is the first marine engine I had bought and reworked from new, and have a Rossi marine quiet-pipe to try and tune up to its chrome plated steel header.

It is not a high nitro engine but rather a high compression alky design. I have not run it yet, and saving it specifically for this boat. It tends to fit into the picture of this hull being old school. And yes, what you mentioned about the age of that radio system in the Dumas instructions is a gas! It is an old "Citizen-Ship" system - a reed type I believe! Gobbles up every square inch that radio box has to offer.

 

[dannyual767]

Danny,I see You have cut out the bulkhead under the dash!!! :blink: Later

Hi, Lary! Yes, I did. I actually cut that out about 5 or 6 months ago. I wanted to move my K&B .67 further forward and the carb ended up hitting the bulkhead so I said, "what the heck? Time to remove it :lol: !" Besides, it gives more room in front and I might even be able to mount my two tanks up there. I probably won't though since the CG will change as the tanks drain.

 

[dannyual767]

jetpak, this is my OS .21RG-M that I may use:

I've got an Irwin quiet pipe for it as well. The engine is rated at 1.7hp. Probably at least 3 times what Dumas designed the boat for !

 

[jetpack]

Those are beautiful engines, Danny! I always admired the OS castings...I don't think there is any better looking cases as what OS can produce. You can expect a good amount of power, especially with the Irwin.

I looked into buying the pull-start version of yours when I first started looking around at motors for my 20 SKDaddle, but looked at the numbers (power as well as price) and realized THAT one was best left up to putting in a sanctioned racer :lol: You should have a great time with it! You really lucked out on that Aeromarine collet fitting, I bet you were happy it did! It's the only decent one out there to choose from, and stainless steel also which I really like.

Here's the Webra 20 I have planned for mine I bought it "new" but 25 years old in the box...it was stuck tighter than you could believe from the factory oils that had dried out and took two days of a crock pot bath in anti-freeze to get it to even move.

 

[crrcboatz]

Good Afternoon,

I have a webra 20 exactly like that one plus one that goes further back than that. It too is a speed version but is a steel sleeve and no ring piston. Probably early 70s nib never seen fuel. I found the other webras I have. 2- speed webra 40s ringed never seen fuel, the 2 - 21s I spoke of earlier, and 1 front intake 61 speed. All are marines and except for one of the 40s all have the original box too. I like the HB PDP marine engines for this application because parts are easier to get. They run quite well and will last for ever. I have 12 of all sizes of these engines.

Curt

 

[moparbarn]

you will need to mount the prop under the hull, not through the transom.a surface drive will not work well with a flat bottom boat. will make handling a lot like an airboat. tuck the prop up as tight to the bottom as you can-back of prop even or just ahead of the transom. the inline rudder will help low speed turns, just not too far back. the extra length will change the pivot point in turns-too for back-it will spin out. it needs to pivot near the middle, just a little back from there, and use the little vee near the bow to help turn. also, a turn fin just ahead of the prop shaft/stuffing box is needed. one one the side will just cause it to barrel roll. these boats slide a lot, and need to bank a little in turns. hard to visualize on a flat bottom, but the key is to use the middle of the hull, and not catch edges or swing the stern too much, the rudder too far back will hurt handling in turns. yes, these boats do run very wet-they're a FLAT BOTTOM-you don't 'fly' a jon boat. i had a dumas skidaddle back in the 70's, i set it up pretty much like the full scale sk's, after trying other rc style set ups. ran MUCH better that way. maybe a little faster with a surface type drive, but almost unmanageable in anything other than a straight line. you could get really trick and find a scale "v" drive-engine in the back, gearbox foward, just like the full size sk's. there was one one ebay last week. find some pics online of SK or SS class boats-drag or roundy round type, and copy what you see under the hull-except the through hull rudder. good luck. i grew up around boat racing in miami in the 60's and 70's, and most of what worked then still works on my rc boats.

 

[jetpack]

Thanks Moparbarn!

Sounds by the looks of it, the best bet is to just settle on the idea that Dumas pretty much has it right with the way they have their setup suggested on the drawings.

I can get a good picture of what's going on now the way you described it and it makes sense.

A strut through the bottom of the hull sounds like the only way to go, and forget the outdrive setup then, except for mounting a close rudder setup on the transom.

 

[moparbarn]

Thanks Moparbarn!
Sounds by the looks of it, the best bet is to just settle on the idea that Dumas pretty much has it right with the way they have their setup suggested on the drawings.

I can get a good picture of what's going on now the way you described it and it makes sense.

A strut through the bottom of the hull sounds like the only way to go, and forget the outdrive setup then, except for mounting a close rudder setup on the transom.

to be true to a 'sk' through hull is it. an outdrive will work, you need to find info on 'kr' boats. basically a sk with an outdrive. mercury developed and raced them in the early/middle 70's. check out screamand fly. com, a lot of good pics and info there. it's a site for full size boats, but look at the inboard/v-drive section. racing history should be helpful, also. do a search there for 'kr' boats. they also have a forum for rc-a LOT of fast boat guys have rc boats. i've seen some of us over there..... me too, i was a member there first.

 

[Marty Davis]

Okay, I've asked this before and I never really got a good answer and its time to start drilling holes :biglaugh: . This thread is also posted on JRCBD as well.
Here is my Dumas SK Daddle that is 36" long. I'm going to power it with a K&B .67 nitro engine or an OPS .67. I've got both so I'll just have fun with either or both.

The hull is similar to a crackerbox in that it has a very flat bottom. I just don't know if having the flex cable exit the transom will work with this flat hull bottom :confused4: . I can picture massive amounts of propwalk ! Here are some pictures:

Here is the transom of the boat. It is only 3" tall from top to bottom! Its 11 1/4 wide.

I've got a skegged strut that I'd like to use to help keep this hull tracking straight.

Should I have the brass stuffing tube exit the transom or should I have it exit under the hull? If its under the hull, I think that I'll have the tube pretty much touching the bottom of the hull. In other words, the prop won't be full submerged but it'll be deeper than if the cable exited the transom.

What are your thoughts?

If I were building this boat, I would put the strut out the back of the transom and get it has high as possible. That will eliminate most of the probalem with prop torque. Since there are several of a similar boat running with gas engines (very well), I would put a fin up forward in the middle of the boat. The place for the fin, I have no idea. Most of the gas boats have MANY holes where they have tried the fin until they got it correct.

You might even be able to run a 1400 series prop, which should make the boat go...

Interesting project, let us know how it works out.

Marty Davis

 

[dannyual767]

Whew! A lot to try to respond to but I'm going to try to write some of my thoughts.

Obviously I've never run one of these Dumas SK boats but I have run a real Sanger V-drive runnerbottom with a BBC that belongs to none other than me . I've owned the Sanger since 1986, less than a year after I came in the Air Force. Of course the real boat has a strut under the hull and the rudder is also under the hull.

Dumas' 1960's plans call for the same type of thing. Back then they didn't have anything else for models. Today we've got much better drive systems for monohulls. If I'm not mistaken, some crackerbox guys run their cables out of the transom. However, I agree with moparbarn. I don't think that this will work too well with the SK boat so I'm going to run the shaft out of the bottom of the hull.

posted by moparbarn,

tuck the prop up as tight to the bottom as you can-back of prop even or just ahead of the transom. the inline rudder will help low speed turns, just not too far back. the extra length will change the pivot point in turns-too for back-it will spin out. it needs to pivot near the middle, just a little back from there, and use the little vee near the bow to help turn. also, a turn fin just ahead of the prop shaft/stuffing box is needed. one one the side will just cause it to barrel roll.

moparbarn, it sounds like you suggest going with the original Dumas setup with an underhull strut. It seems to me that this angled driveline will cause all kinds of headaches. I'm planning on bending my stuffing tube and make the driveline parallel to the hull. As far as the strut goes, I still like the idea of the transom mounted strut. I think that it has more potential. Its way more adjustable than a through-hull strut. My prop will be about 2" behind the transom. In the end, if it doesn't work, all I've got to do is plug 4 small mounting holes and cut a slot in the bottom to use a through-hull strut setup.

I'm most definitely going to mount a skeg under the CG point. My Sanger has a skeg under there as well.

Looking at the 1960's pictures in the Dumas instructions, one can see that Dumas never intended this hull and driveline setup to go any faster than maybe 8-10 mph. Maybe that was exciting back then but today...............

 

[dannyual767]

posted by Marty,

If I were building this boat, I would put the strut out the back of the transom and get it has high as possible. That will eliminate most of the probalem with prop torque. Since there are several of a similar boat running with gas engines (very well), I would put a fin up forward in the middle of the boat. The place for the fin, I have no idea. Most of the gas boats have MANY holes where they have tried the fin until they got it correct.

I like the idea of the transom mounted strut as well. Are you saying to get the prop as high as possible out of the water :unsure: ? I think that higher the prop gets, the more likely I'll experience propwalk. Over on Jim's RC Boat Dock, crrcboatz said to run the stuffing tube about 1/2" from the bottom of the hull. I'll start with that and adjust deeper or more shallow from there. If the transom mounted strut doesn't work out, it won't be hard to plug the 4 holes and then cut a slot in the bottom of the hull to mount a through-hull strut.

 

[moparbarn]

posted by Marty,

If I were building this boat, I would put the strut out the back of the transom and get it has high as possible. That will eliminate most of the probalem with prop torque. Since there are several of a similar boat running with gas engines (very well), I would put a fin up forward in the middle of the boat. The place for the fin, I have no idea. Most of the gas boats have MANY holes where they have tried the fin until they got it correct.

I like the idea of the transom mounted strut as well. Are you saying to get the prop as high as possible out of the water :unsure: ? I think that higher the prop gets, the more likely I'll experience propwalk. Over on Jim's RC Boat Dock, crrcboatz said to run the stuffing tube about 1/2" from the bottom of the hull. I'll start with that and adjust deeper or more shallow from there. If the transom mounted strut doesn't work out, it won't be hard to plug the 4 holes and then cut a slot in the bottom of the hull to mount a through-hull strut.

from what i can remember from 35-40 years ago (LOL), the full size racers played with prop shaft angle a lot. the trick was to use the downward angle of the prop shaft to lift the boat, and use the trim tabs to balance this effect. these boats ran a "trim plate" that ran the full width of the hull. i would be worried about a strut on the transom, because of the extra leverage, and the pivot point. this was a HUGE problem for the outdrive sk (kr) boats for a while. never was into outdrive raceboats, so i don't know what helped. but, if you ask over on screamandfly, you will probably learn how to make it work. a lot of factory engineers and drivers from 'back in the day'. get the right info from the people who lived it, so to speak. find some of the galleries that show these boats running, you will see they need to get the bow in the water to turn. a surface drive or transom strut may be too far back to work. with the boat pivoting that far foward, the thrust that far back could cause the issue i'm cautioning about. danny, think about the way your sanger (cool boat, btw) handles. do you really want to swing the stern that hard? i'm not saying that it will never work, you can't learn much by not trying something different. just saying that the full scale racers never made it work. we didn't have surface drives or today's prop technology back then, either. like you say, it's just 4 small holes, and not a lot of work to change. keep us posted, i'm interested to hear how the setups work out. i've always been an ob guy, but sk's and hydros had HEMIS. how could a guy named moparbarn NOT like them?

 

[crrcboatz]

As I said on another site, I built and owned one of these in the mid 70s and will tell you that if you will set the strut center 1/2 inch below the hull, not over power the boat and put a lower pitch prop on it with the center skeg you can have fun with this little beauty. With regard to bringing the nose down, you have an adjustable rudder, use it to accomplish that process. Move the rudder in a little and the nose will drop. you don't want the nose down too much as it will run wet and get very little speed. The 21 engine you spoke of and sent me a pic of will be quite adequate for the hull. You can start at the 1/2 inch setting and play with it as well as props. Good luck and remember to send me some pics of your results.

Regards Curt

 

[dannyual767]

from what i can remember from 35-40 years ago (LOL), the full size racers played with prop shaft angle a lot. the trick was to use the downward angle of the prop shaft to lift the boat, and use the trim tabs to balance this effect. these boats ran a "trim plate" that ran the full width of the hull.

I've got foot operated plates on my Sanger. I use them only during part throttle running because at certain speeds the boat wants to "porpoise." My boat is set up well and when I'm at wide open throttle, the boat takes a real nice set and I don't need to touch the plates.
I would never try to turn my boat at speed because it's pretty much a "go fast in a straight line boat" plus the fact that I'd probably roll the boat and maybe kill myself ! At part throttle, it turns okay but it still makes fairly wide turns.

i've always been an ob guy, but sk's and hydros had HEMIS. how could a guy named moparbarn NOT like them?

Amen :lol: !

 

[moparbarn]

i guess that's one thing i didn't ask. are you drag racing or circiut racing? all my experience was with closed couse and endurance racing. my input was directed towards turning. for straight line running, hang it out the back and air it out! something about slowing down for turns doesn't excite me. i want to cut it sharp and have to hold myself in tight as it carves a nice, tight arc. in a straight line, length = stability. driveline can be thought of as length in this regard. i thought you wanted it to handle, also. let me know what you do, and how it works.

 

[dannyual767]

mopar, I do want the SK to handle. I was talking about my Sanger being only straight line when at full throttle. I'd like to be able to have a little more "sport fun" with the SK. I want it to handle decently and I think that it'd be real cool if it does slide some in the turns :lol: .