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View Full Version : 10th Scale Miss Thriftway finished now what?



rat350r
11-01-2016, 09:39 AM
I am just returning to RC boat building after about 25 years. I just completed a 10th scale Miss Thriftway and have had it out doing some testing on my own. The hull is built from a kit from Classic Hydro’s. It is the Ted Jones 1955 Unlimited Hydroplane drawn by Gary Finlay. This hull comes out at 35.63” long and 15” wide. For running gear I have a leopard 4082 1250 KV motor and a Seaking 180 V3 ESC spinning an Octura X447 prop. When I built the boat I did deviate from the plans and used a .187 flex shaft that exits out of the bottom of the hull “not in a straight line”.

I have been testing the boat setup with 6S with the running gear listed above. I am a little rusty at trimming out a boat, but I think the boat is a little over powered for the hull design. I hope to link up with one of the local clubs in the area this spring to try and get the boat sorted out handling wise.

Now here is my question, what do I do with this boat? I live in the IMPBA district 12 in Southern Maryland. According to my interpretation of the IMPBA rules, the fact that my boat is over 34” long, it is too long for P hydro. Does this mean I will need to run the boat in Q hydro? The fact that my prop shaft has a curve in it under the hull means that it can’t be run as a classic thunder boat.

JimClark
11-01-2016, 04:56 PM
Got any pictures of the build?

Sent from my SM-G900T using Tapatalk

rat350r
11-02-2016, 07:10 AM
Here are a couple pictures of the finished boat.

rat350r
11-02-2016, 07:49 AM
Here are a couple of videos one 4S and one 6S. The boat at 6S weighs 9 lbs 15 oz and the CG is at 3/4" aft of the sponsors.


https://youtu.be/9P7CAFpPJJc
https://youtu.be/uQKyjLSJgbs

JimClark
11-02-2016, 05:35 PM
So how did you do the mahogany? Did you lay balsa down first then the mahogany over it?

Fluid
11-02-2016, 06:49 PM
You could run your beautiful hydro in Q Hydro class against the riggers, or in Q Sport Hydro class. For the latter you will need a name, competition number and/or your NAMBA/IMPBA number. Our club runs QSH and it is a fun class, better suited for rougher conditions than PSH is. Your motor setup is okay for the class considering the hull design. What packs are you running? One member raced a shovel nose about that size and was competive as long as he finished each heat.

You will likely find that the strut should be deeper and nearly flat on the table, especially with the CG so close to the sponson transom. The turn fin is too small and will slow the boat in the turns. A higher-efficiency prop like an ABC 2014/10* or 2016/10* will hold the tail up and give more speed too. As always, check temps at first to be sure the setup is safe.



.

CatBoi
11-02-2016, 09:01 PM
Now that is quite beautiful!

rat350r
11-03-2016, 10:16 AM
Mr. Clark

I put 1/2" strips of Mahogany over the 1/64th layer of birch plywood that came in the Classic Hydro's kit. I sealed the birch with West Systems epoxy, then used contact cement to glue the Mahogany strips.

Fluid,

I am using 3 Giant Power 2S 7.4V 2 CELL 6000MAH MAX PERF 65/130C packs. They just fit up in the bow in front of the ESC.

As for the strut setup I have been trying to get the boat to stay on the water at full speed. I started out with the strut with 0 prop angle and the center of the shaft level with the bottom of the sponsons. I also had the CG about 2" aft of the sponsons. With this setup the boat would dance on the prop down wind and go airborne upwind. I then moved the CG as far as I could by moving the battery packs as far forward as I could. The result of that change was the boat was still way light in the bow.

Next I lowered the strut and put some angle in the prop attempting to keep the bow down. This helped some, that was the run in the 6S video above.

My last change was to lower the strut and angle the prop to what you see in the pictures above, that result was the boat became a submarine at full speed.

After doing some research on this forum I think my next move is to try an air dam under the bow. I made an air dam out of pine strip, ripped down to 1/4" on a 45* angle. I used double stick tape to fasten it about 2" from the bow up in the tunnel. I also think I will set the strut back to 0 angle and back even with the sponsons. I may also move the CG back to around 1 1/2" and give this a try.

As for the turn fin, the one in the picture needs to be replaced. The aluminum is way to thin and it actually bent under the strain. I have cut out a new turn fin out of a stronger alloy of aluminum and it is thicker. The one I made is about the same size and shape of the one in the picture which is a copy of the turn fin drawn on the plans. If you could recommend an approximate size and shape of turn fin I will cut one out and give that a try.

Thanks to all for your interest in my project and for the advice given.

Bruce

leonard feeback
11-04-2016, 04:09 PM
Hi Bruce, really great Mahogany job. I have found about blow over problems. It looks like your air traps go all the way down to the running surfaces of your sponsons. I have found that removing part of the airtraps towards the bottom of the hull helps the boat from blowing over as easily. I would go up about half way to the bottom. If you find a club that runs 1/10th scale class you will probably only be able to run 4s pack. Not sure what IMPBA runs but good chance it's 4s total.

rat350r
11-08-2016, 09:08 AM
From what I have seen in my area, they do run Classic Thunderboat, but I think this is the 1/8th scale 26CC gas motor class. I suspect I will shoot for the combined Sport 40/Q sport Hydro class.

As for trimming the air traps down, I think this is a valid idea. I suspect that the plans the boat was built from were intended to be setup as a vintage Hydroplane running 4S. With the added speed of the 6S battery and motor the hull aerodynamics are overwhelmed and too much air is being trapped under the hull, and too much lift over the hull making it hard to keep on the water.

If anyone has had any experience trying to trim out a 10th scale vintage shovelnose hydroplane on 6S power I would welcome their impute.

Thanks

rat350r
11-14-2016, 01:12 PM
Went out Sunday afternoon, the weather was great, sunny with very light winds. First test was with the air dam installed, strut even with bottom of the sponsons, zero prop angle and the CG ¾” aft of the sponsons. The boat was very flighty, with the bow very light and the left sponson lifting high and dancing on the prop. This was with less than full throttle and I was able to catch it before it blew over.

Second test I lowered the strut with just a little angle in the prop to try and hold the bow down. The result was about the same.

Third test I removed the air dam and didn't see any change, still dancing on the prop with less than full throttle.
My next test was going to be adding some weight to the bow to move the CG forward, but one of the ESC connectors had a bad solder joint and came loose.

I think I am going to cut out half of the air traps and give that a try. Any other trimming tips or advice would be greatly appreciated.

JimClark
11-14-2016, 04:08 PM
What did you use for the air dam?
Still running the 6S?
What kind of speed are you looking for?
Can you post pictures of the bottom?