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Thread: Aquarama
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11th September 2019, 07:51 PM #16
I have only played around with model powerboats with smallish glow engines and 540/550 series electrics (buggy motors basically) and quite light hulls. I am anticipating that your hull might be developing a bit of weight if it is double planked with Tas Oak and Pine and will then be epoxied. The ones that I mucked about with were either ABS plastic or scratch built balsa.
Power will be a function of what will fit, how heavy the hull is, and what you want the boat to be, a scale type model, a win at all cost racer, or something to while away the hours. Some people I know find pleasure in building their model, but get bored using it, others can't be bothered building, and just need something to run at the pond asap, others enjoy spending winters and nights building and getting to run them every week or so.
Generally when building, it is easiest to have a target weight, and have the power system planned in advance so that you have a good idea of where everything will go, and can trim bulkheads etc to provide clearance before things get glued in place. There are two primary issues for prop shaft angle, the closer it is to parallel with the hull, the higher the proportion of energy supplied to the prop that is directed to inline thrust to propel the boat, and the lower the proportion that is lost as a vertical vector trying to lift the hull out of the water. To counter this the closer the shaft is to being parallel with the hull, the less room is available between the shaft and hull to situate a prop, so smaller props are used, but they don't produce as much thrust.
It appears that you are working from an established design, so following their suggestions for prop sizing and shaft angles should get you into the ball park, except that you are looking at two separate motors rather than a single motor using gearing to split between two shafts. I guess that the original gearing system would have been a Graupner item matched to the motor. Without knowing the gear system, it is hard to estimate the shaft speed and torque available, and thus match up with a modern system. The Kv rating system for the motors effectively relates motor speed to voltage available, and hence current that can flow through the motor. It does not however address the issue of how much heat the motor can dissipate safely, or the amount of power it can handle without overheating.
I haven't had anything to do with brushless motors in this context, but one of the significant issues with brushed motors at higher power levels used to be the brush contact area, so I suspect that at a given power level a brushless should outperform an equivalently rated brushed motor.I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.
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11th September 2019, 08:53 PM #17Senior Member
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These days I suspect an electronic solution utilising two motors will be easier and simpler to set up and get rid of the gearbox entirely.
Either a dedicated 2 output ESC or with the modern transmitters an ESC for each motor and use the transmitter to mix them to get the results you want.
I suspect a lot of reading/design and thinking is in your future.
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14th September 2019, 08:58 AM #18Senior Member
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52.jpg
Second layer of cedar
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Final plank
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All sanded.
I will build the convex curved transom and swim entry board next.
I have sprayed all inside with lac to stop moisture - now I really need those prop tubes in so I can paint the bottom. With resin paint. I will clear lac the red cedar. A crime to paint red cedar according to my Pa. I am not fiber-glassing anything.
Thanks for the suggestions.
I am at the stage I need to cut in the tubes to progress so I will have to settle on a setup soon.
The original plan (very old) suggested 18 deg and 40mm props. There was no specs on the batteries.
I will have to get a progress weight so far maybe that will help. All of the wood above the chine is red cedar so that is a bit lighter.
I really don't care that much for outright performance as this was primarily a woodwork project and seems that powering it would be some fun. As long as it runs respectively and gets onto the plane that would do.
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17th September 2019, 04:30 PM #19Senior Member
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Been a bit quiet, the cedar is playing hell with my sinus. Makes them pain a lot. Trying to control such light dust is very hard, price we pay for lovely wood I suppose.
Fabrication of transom. Very difficult to get my head around from sketches and photos from the 60's
Attachment 461555
Cutting in exhaust ports. Very difficult, the pilot holes were already in the back bulkheads and had to be brought out through the newly planked under transom. I worked a 6mm auger drill through the pilot holes with a pair of vices grips, turning the auger a small amount while using a block to advance the bit. Once the sharp point of the auger was just poked trough the back I removed the bit and gut a neat hole back into the boat using the little hole as a guide. It worked! Real neat, there will be 6mm brass tubes put in there later.
Attachment 461556
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28th September 2019, 04:15 PM #20Senior Member
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30th September 2019, 05:45 PM #21Senior Member
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5th October 2019, 08:24 AM #22Senior Member
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Riva Aquarama
Swimmers entry way complete. This is also a removable hatch to provide access to the rudders, servo and exhausts.
The hatch pivots on the upper edge of the transom and is wedged in tight when down by a upper dummy bulkhead having a tight fit with station 12. I hope this is tight enough in use. Might fly out when the boat is going? Maybe two tiny ss screws strategically placed? Yet another problem for another day.
This is a great project to learn new skills and soak up heaps of time.
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I added some expanda foam to the two front bulkhead voids to provide some buoyancy in case of a disaster at sea. That would mean I would have to possibly swim to get it? Read some horror stories about old guys swimming out to get their RC boats and drowning oooooh, better take me old surfboard.
There was some online chat about the foam expanding and breaking the structure but it never did and I let it ooze out the top and back for relief. I trimmed it easily with a hacksaw blade and sandpaper. The oozed out the back foam is yet to be trimmed.
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Onto planking the forward deck. Difficult to clamp in the area due to all of the curves, hard to get downward pressure on the pieces.
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Prop tube holes.
I read up as much as I could on how to do this job. How to drill a hole at an angle to a curved surface and parallel to the keel and make it come out on the other side within mms? There seems to be many ideas out there but no set procedure that everyone agrees on including the proffessionals. Many ways to skin a cat right?
I drove pilot holes for the propeller tubes. I first drilled two vertical 3mm pilot holes down thru the floor at what I thought would be the angled extremities of the tubes. I made a jig set at 18 degress using a digital angle gauge to the floor to get a good line on the entry holes.
Then using the guide I drove a 300/4mm drill I fabricated from some hardened steel rod I had at the required angle through the floor and the square logs from the bottom up and the top down using the 3mm vert holes as a starting point.
The holes met in the middle - just about.
I then worked the Dremel with a 6mm straight router bit in it working from each side to open up the holes. When I get the prop tubes the holes will then be opened out to the actual tube diameters - about 10mm.
I used a 300/4mm rod to check the alignment and then a chain saw tooth file to clean out and align the holes.
This makes a mess of the lovely smooth bottom but I will fill and paint all of that later after the tubes are set.
When I then used the measurements for the motors I want to get and the actual position of the tubes I found I had made a mistake in the tube sizes i have ordered. I put the actual measurements into the CAD program and found the 300mm prop tubes I ordered are too long and would foul the rudder or leave no room for the motors - duhhh. So I have reordered 250mm tubes and chalked it up to my lack of inexperience.
No wonder the wooden boat builders of old were held in high regard - this is a very difficult job.
93.jpgLast edited by duke12; 5th October 2019 at 09:39 AM. Reason: Additional info
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5th October 2019, 10:06 AM #23Senior Member
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13th October 2019, 06:31 AM #24Senior Member
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Work on rear hatch cover. I wanted a removable cover so to access the steering gear and servo for maintenance. This was not in the original plan so I had to make a neat fitting hatch by guesswork and some trolling about the net. I have it a pretty tight fit at this time but may need to keep an eye on it as I lacquer the wood.. swelling etc.
Bringing the hatch planking out to the gunnels. They are intentionally long at first as they need to be trimmed to a curve inside the rear cockpit.
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Planking and sanding done, still a bit tight, can't see where it is binding. Might try to look underneath the hatch with a bore-scope.
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Planking progressing on the fore-deck area. Busted another bandsaw blade, that is three this month, arrrrrrg. Going to try a different brand or supplier.
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20th October 2019, 03:22 PM #25Senior Member
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Work on rear cockpit
Roughed in with balsa blocks and shaped vertically. Will be then covered with red cedar.
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Cedar trim in, this will be covered with padding all around the inside eventually, shame.
Started work on the pine coaming capping, very tedious much of it went in the bin before I got it right.
Had to trace the pine from below, I got a very small young helper in there to work the pencil while I held the blank pine above.
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All of the front upper deck is planked and being sanded here.
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Put a different brand blade on the band saw, seems better, pity I was not rich enough to get some decent gear, oh well make do.
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27th October 2019, 08:54 AM #26Senior Member
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All coaming capping finished.
Rear hatch finished and trimmed.
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Dash board work, done sunshade over dash. Template for gauges wheel etc to see where it all goes.
Temp dashboard, that's number 4 tryout dash. When I get ir right the dashboard will be Huon Pine.
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Trailer full of reject and mistakes. See the complete skeleton, was made with too many errors so I chucked it.
Live and learn eh. This project is quite a learning experience.
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Prop tubes have arrived - more fun to come.
Now how do you do that?
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27th October 2019, 09:15 AM #27Senior Member
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Thanks especially for the trailer full of mistakes, too many projects only show the final result and not the hard yards to get there.
Are you asking how to install prop tubes? Brass can be epoxied in without too much problem if you key the surface, especially as there will be little to no force on them.
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27th October 2019, 10:36 AM #28Senior Member
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Yes I was wondering how to install the prop tubes.
They are 9.5mm stainless outer tubes 300mm long.
I have the holes bored through the logs on the floor and confirmed the angle is 18deg and correct.
At some stage when I am happy with the setup I guess I could epoxy them in place, was wondering how I could key the SS so the resin would adhere properly.??
It would be pretty sad if the tubes leaked water into the hull or worse yet moved and that the props crashed into the rudders which are only m away.
I think a pretty decent bump might dislodge the tubes, maybe not.
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27th October 2019, 04:11 PM #29Senior Member
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Epoxy will stick to stainless no problem if you make sure of the basics.
Clean, no oil and key it using 80-100 grit paper just before gluing.
There will be next to no longitudinal force on the tubes and if you get the epoxy in the holes you have bored you have a huge surface area to stick to so I don't see any chance of significant movement.
I'd go so far to say that silicone would also do the job fine if you wanted to use an alternative.
I'd get the glue into the length of the hole via a syringe or similar and block up your tube when you push it through to make sure the shaft is fine and you have glue anong the entire length.
Messy but will make sure there is no gap between tube and the hole you have bored.
Looking forward to seeing how you do it. This project is inspiring me to consider a similar project, I had an old mouldcraft boat my father and I restored which I would like to replicate in model form.
Something like the ones here.
Mouldcraft Vintage Timber Runabout
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27th October 2019, 05:20 PM #30Senior Member
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Aha thanks for that.
I will do as you suggested rough it up and epoxy. I will steer clear of silicone as I don't want that stuff anywhere near this job as I get towards painting etc.. I have 3 coats of spray clear lac on already. I will paint the bottom white when I can get a smooth surface ready for masking the bottom off along the waterline. White then a 5mm turquoise stripe along the water line before the clear sides and top.
I am wondering though, should I paint the bottom prior to setting the prop tubes first or insert - epoxy them and then mask off paint around the protruding parts?