New scratch build 24" mono

[jfrabat]

I was going to post this in the "Show Off Your FE Boat - Pictures" section, but then I read the sticky note here titled "Use this area for people that are willing to take pictures and document their build" that says:

We are going to use this area for people that are willing to take pictures and document the building of their boats.

Questions you have about your build you are not documenting, do not need to have a thread here

Just because your topic has the word "Build" in it, doesn't qualify it to be here.

Thanks!!

So I figure this is the correct place to put this post (maybe!).

Anyway, here is the backstory:

Some time ago, I decided to do a build with my 10 year old son (9 at the time) as a father-son project. I was in to RC planes, but I figured something closer to the ground would be better suited for him to start developing his RC skills, and we figured we would scratch build a 30" cat (you can read about that boat's construction progress here). Progress was slow, but then the Pandemic hit, and suddenly we both had more time for this project. Long story short, that boat is done (well, 99%; I ran out of water hose, so I am waiting for my shipment from OSE to arrive). Here is that boat:

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Now with the boat finished, my boy, God bless him, asked me how we are going to race if we only have one boat! I love it when they ask the right questions... don't you?

OF COURSE, I now HAVE to build another boat for us to race... So this time, we decided to take things one step further. This time, we would not get the plans from the internet but rather make a design ourselves. I started looking at pictures, and decided to use a Cigarette boat as a base, then fired up AutoCAD, and got to work.

Obviously, from the base boat, this was going to be a mono hull (I figured it would also be easier to build than the cat, and it has been so far). We also decided on 24" size, and knowing that, we decided to power it using a Leopard 3650 motor with a OSE Raider 150A ESC. I also got a Chinese waterproof servo with metal gears for steering, and will use either the Tactic radio that came with my son's Minimono or added as a second model to my radio (I think the Tactic will be the way to go so that we can race!). Batteries will be 5000 MAh 4S 50C pack.

From there, the frame was made out of balsa plywood.

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Then the sheeting started...

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And added some flotation foam for safety

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[jfrabat]

Finished sheeting the hull; still have not shaped the top part, though...

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Reinforced the hatch area (I know, I went a bit overboard, but it is what I had in hand)

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Added the top shape

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Shape starts to come out!

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I probably in retrospect should have made the transom at 90*, but I can always make a flat area for mounting the hardware.

Then is now up to glassing.

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I finished the first layer of 2oz fiberglass (will do 2 layers) using epoxic resin (diluted with alcohol). After glassing, I will make the cockpit area and the stringers in the hull to make the glassing process easier (it took me a month or so to glass the cat; this one I did the first layer in a single day, so difficulty level is completely different!).

[Jesse J]

Nice to see scratch builds with wood!
That feels like a lot of weight and excess power to me. I tend to go smaller motor, lower voltage, but higher kv motor, spinning a smaller prop.
If it were me, I’d start with a 3000-3500 kv motor on 2 or 3s 2000-3000 mah pack with a 40mm prop.
Just me though.

[NativePaul]

My sentiments exactly, it is GREAT to see a real build amongst the myriad of RTR mods and off the shelf glass hull fit outs, that are often labeled builds.

I have strayed away from wood builds myself, and every time I see one it gives me some motivation to get my fingers dirty again.

I too worry about the weight of that motor, and the torque it may put to the prop. Judging against the size of the hand it looks like the beam at the chines is only about 3" or so which will make it very susceptible to torque roll. I would personally use a 2845 or 2850 motor with a KV between 3500 and 4000 on 3s 3000mAh with 432 prop to keep the weight and prop size down, in order to minimise the torque effects.

[jfrabat]

Following up on the build...

Glassed the hull. The entire boat now has 2 layers of 2oz fiberglass. I added an additional strip on the keel (about 2" wide) just for the heck of it.

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Then I sanded down the excess resin and gave it another coat (this time I did not dilute the epoxy, to make it a thicker layer) to the entire boat to fill in the low spots. I will need to sand this to smooth the resin out. Will probably need to do this at least once more due to my rush job with the second layer (lots of drips and high spots).

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Oh, and I was a bit concerned about the stability of the hull (with no weight) in the water, but I put the hull in the pool (prior to the additional coat of resin), and she floats just fine and stable.

[jfrabat]

That feels like a lot of weight and excess power to me. I tend to go smaller motor, lower voltage, but higher kv motor, spinning a smaller prop.
If it were me, I?d start with a 3000-3500 kv motor on 2 or 3s 2000-3000 mah pack with a 40mm prop.
Just me though.

I too worry about the weight of that motor, and the torque it may put to the prop. Judging against the size of the hand it looks like the beam at the chines is only about 3" or so which will make it very susceptible to torque roll. I would personally use a 2845 or 2850 motor with a KV between 3500 and 4000 on 3s 3000mAh with 432 prop to keep the weight and prop size down, in order to minimise the torque effects.

Seems you both agree the motor may be too much... I was originally actually thinking of using a 2845 with a 30A ESC (which I have) and 3S pack, but I ask Steven and he recommended I go to 3650 motor with a 150A ESC and 4S (he did tell me the 60A ESC would work, but that if the 150A would fit, it was a better choice). I know nothing of boating in general, so I just went with what the expert told me to do.

For reference, the beam is a tad over 5.5" (140mm). Here is a pic for reference.

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Ignore the globs of resin; I have to sand it still!

Since the motor, ESC and props are already on the way to the freight forwarder (I live in Panama, Central America!), I think I will have to make do with the big motor, and maybe limit the speed on the radio (especially since this boat is for my son, so he can race me in the cat). After all, returning it means paying for shipping back to the US! I hope it is not too overpowered or heavy and that the torque does not cause a lot of issues!

[NativePaul]

If you need to limit the torque it is more effective to do it with a smaller prop, thus not only is the torque smaller but the leverage with which it is applied to the hull is smaller. It also has the benefit of the ESC running more efficiently and cooler at full throttle.

It is a lot wider than I thought, do you have big piano playing hands or was my estimation well off (no offence meant, just curious). I revise my recommendation above to 3500kv and 35-37mm prop.

[jfrabat]

If you need to limit the torque it is more effective to do it with a smaller prop, thus not only is the torque smaller but the leverage with which it is applied to the hull is smaller. It also has the benefit of the ESC running more efficiently and cooler at full throttle.

I was thinking the same thing today. I have props coming in (40-1.4, 43-1.4, 40-1.6, 42-1.6) so I will play around with those (I will start with the 40-1.4 and take it from there). Or go to a 3S battery and reduce RPMs (and weight!) could also work.

It is a lot wider than I thought, do you have big piano playing hands or was my estimation well off (no offence meant, just curious).

Oh, I have big hands... HUGE hands!

I revise my recommendation above to 3500kv and 35-37mm prop.

As I said, since the motor is on its way, and I am overseas, that motor will go in. I will have to make do with it by adjusting the prop. If I need to reduce the prop to 37~38 1.4, I rather get a new prop than pay to return the motor and then pay to get the new one sent...

[jfrabat]

Back to the build... finished sanding the thick layer of resin (spent all morning sanding!)

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Cut out small triangles from 1/8 Balsa and used them as stringers? Chines? What is the correct term? Anyway, I glued them with CA

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Then I thinned out some more resin and covered the entire boat once again.

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Once this dries, I will sand everything again, and then it is off to primer (and bondo most likely!). The cockpit will all be in the hatch cover, so I will not mess with it at this time.

[Jesse J]

Lift strakes, and I like to test run before adding them. I have removed way more than I have ever added.

[jfrabat]

Lift strakes, and I like to test run before adding them. I have removed way more than I have ever added.

Wish I would have known that the day before yesterday... I have seen them in all the mono hulls I looked at online, so I added them. I tested the hull in the pool, and it parted the water in a nice, laminar flow kind of way, and I even told my wife I was going to miss having that once I added the strakes... Anyway, I "primed" the hull (i use quotation marks, because I did not have any primer left, so I used a high coverage silver paint I had!). There were more imperfections than I expected...

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Then I started the bondo part of the process.

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I think I used too little hardner, as it is taking forever to really dry. I guess I will just have to wait it out...

[jfrabat]

Well, I messed up. I had to sand everything off, and it was a REAL PITA!!! The bondo never hardened, and it became this gooey paste that was hard as hell to sand off because it would clog the sandpaper. I ended off using a bit of brake cleaner on paper towel (which removed the paint, but not the bondo) and then going over the entire boat with 000 steel wool (this is what got rid of the bondo!). I then decided to use light paste (which I have used in airplanes before) as filler.

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Once the paste was dry and sanded down, I painted the boat again, this time, in white.

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It still has some imperfections in the body work (you can easily see them in the pictures), but I think this time it is staying like that! I do not want to mess with Bondo again!

[jfrabat]

Decided not to leave things like that... Sanded down the white, after filling some holes with light puddy, and repainted the top in black. Looks much better, but I will still sand down the black once again, and repaint it to get a better finish.

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You can still see some imperfections, but much less noticeable than before. By the way, the color scheme is black on the top and sides and white on the bottom of the hull...

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Will have to get the name cut out from white vinyl after the lock down! The cigarette logo I can make here with white waterslide decal paper.

[jfrabat]

I sanded down (a little) he first coat, and gave it a second black coat. Then, masked the hull for the racing stripes...

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After 3 or 4 (or 5, I really do not remember) coats of red paint, WE GOT RACING STRIPES!

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Finish is A LOT better now!

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I also think the racing stripes are a bit too far apart, so I am going to ad a thin white stripe towards the center of each red stripe to make them look better. But I ran out of white, so that and the second and third coats of the bottom hull will need to wait.

[jfrabat]

I also think the racing stripes are a bit too far apart, so I am going to ad a thin white stripe towards the center of each red stripe to make them look better. But I ran out of white, so that and the second and third coats of the bottom hull will need to wait.

Well, OBVIOUSLY, I went in a different way... I had some silver, so I painted a center silver stripe. I like the final look!

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I also got started on the hatch. Idea is to use 2 dowels at the front, and 1 or 2 nylon screws on the back.

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