70" CRC Outerlimits Electric Build

[WheelMan]

Hi all,

Being a long time RC hobbyist/enthusiast, I've built many custom vehicles over the years. However, I have yet to do a boat build. And I've decided it's time to do so.

So, after a couple months of research, lots of reading, and searching around, I decided on the basic goals I wanted for this project, and started gathering some of it up. My basic goals include: large scale build, electric (utilizing electronics I already have), single prop setup, built for fun/entertainment (not for racing), and roughly 50-60mph speed goal.

I started with what seemed to be the most obvious component to me, the hull. Being located in IL, I found Central RC Marine, only about an hour and a half from where I live. Since I already have most of the electronics I decided I wanted to use for this build, I had something to base my hull decision off of. After meeting the man behind Central RC Marine, choosing my hull, and speaking with him for a while, I placed an order through OSE for many of the smaller components needed for the build: stinger strut, flex shaft, rudder assembly, trim tabs, turn fins, motor coupler, etc. He suggested SpeedMaster for many of these products, and I have to say I believe his recommendation was quite good, as their products seem to be of great quality, and very popular. Also, through browsing of the forums here, I found several mentions of DrProps. I looked him up and after speaking with him in depth about my build, he suggested a prop, which I have purchased and is currently in transit. I loved the idea of a stainless prop that comes ready to go, sharpened, balanced and polished. So that is what I went with, a 62mm dia 3-blade 1.4 pitch propeller.

Being a first time boat builder, there was a lot for me to learn, just to make it this far. And there is definitely a lot left for me to learn as I get further into the build. I've learned just enough to be dangerous in the ways of purchasing what I need to get started. I'm sure I have made some choices already that some might have done differently, but I'm here to learn and take constructive criticism. I am hoping some of you more seasoned builders can offer some advice/suggestions along the way as I build this thing.

I will update here as I make progress. Hoping to have some fun on the water with this thing before the summer season has passed

IMG_20190728_194150.jpgIMG_20190728_194043.jpg

[sammyha]

Good for you, WheelMan. Sounds like you did your research, you have modeling experience and you're not afraid to try and/ or learn. I've found this to be true here on the OSE forum, the guys know their stuff and are a great help. Good luck with the build and that's a sweet looking boat...

Sent from my SM-G950U1 using Tapatalk

[fweasel]

Great looking hull. My friend just finished his gas build this spring.

https://forums.offshoreelectrics.com...ain&highlight=

[WheelMan]

Good for you, WheelMan. Sounds like you did your research, you have modeling experience and you're not afraid to try and/ or learn. I've found this to be true here on the OSE forum, the guys know their stuff and are a great help. Good luck with the build and that's a sweet looking boat...

Sent from my SM-G950U1 using Tapatalk

Thank you, much appreciated!

Great looking hull. My friend just finished his gas build this spring.

https://forums.offshoreelectrics.com...ain&highlight=

That's a sharp looking build, thank you for sharing!

One thing I would like to ask for suggestions/pointers on, is in regards to attaching mounts to the inside of the hull. Obviously it seems most are using epoxies of some sort, but there appear to be dozens of different kinds out there. I plan to make my mounting plates from either Carbon Fiber (as it seems most do) or 1/8" 7075 Aluminum plate (which I have a lot of experience working with), or a combination of the two. My hull is fiberglass, with a carbon fiber inlay.

So, is there a certain brand, or exact epoxy that is regarded as the best solution for this application? I must admit, I'm very much a fan of building things that actually fasten together with hardware, and not much into "gluing" things. But with boats, there's not much choice it seems, haha. Which means I need to get used to it, and just find the best materials and process for doing so. I have found a mention or two of certain types of epoxy, however those posts were rather old and I realize there may be better versions available now. So what should I be planning to use in this department?

Thanks in advance for any help/suggestions!

[fweasel]

I use JB Weld and West System G Flex to mount stuff in hulls. You can glue T nuts to the hull and use stand offs and bolts to attach mounts to those. Sand/scuff up the mating surface first.

[Fluid]

Can you share the Lehner 3080 Kv and the voltage you plan to use? To achieve 60 mph you will need around 25,000 rpm under load.

[WheelMan]

I use JB Weld and West System G Flex to mount stuff in hulls. You can glue T nuts to the hull and use stand offs and bolts to attach mounts to those. Sand/scuff up the mating surface first.

Got it, thanks!

I have seen a few builds done that way with the nuts and standoffs, good idea.

Can you share the Lehner 3080 Kv and the voltage you plan to use? To achieve 60 mph you will need around 25,000 rpm under load.

The 3080 is 875kv and I plan to run 15S lipo, so about 61v I believe it is.

[WheelMan]

Fluid got me curious to learn, so I did some research. Found the following calculator (which I'm sure you guys are probably very familiar with), and according to that, DrProps seems to have met my mark. Unless I am mistaken somehow?

RC Boat Calculator

Octura Props List

DrProps 6214/3 prop

The calculator does not have propeller data entry fields, but instead has specific model Octura propellers to choose from. So I went out and found a list of Octura props and started searching for one with the same dia and pitch as the one DrProps sold me, and bang, found one. Octura X462 seems to be the one. And my photos below say the rest I believe.

Seems if I wanted, I could run 10S, to meet my 50-60 mph goal?

DrProps.jpgOctura.jpgSpeedCalculator1.jpgSpeedCalculator2.jpg

[Fluid]

Very few in this hemisphere run more than 10S to 12S. The real issue is that your boat is very very big and would benefit from 15S.....but not with that motor configuration. The 875 Kv is way too high, with an unloaded rpm of almost 50,000 rpmon 15S. But, it appears from the photo that you can configure the motor for a lower rpm (how you connect the ESC wires to the motor). I’d guess that Kv would be around 600, more reasonable for 15S - if you want to run that much. The advantage to higher voltage is a lower amp draw for the same performance, assuming the correct motor Kv and prop size.

The question to me is, will the small prop provide enough thrust for that big hull with that huge wetted surface? Hulls that size were designed to use props in the 70mm to 75mm range with gas motors, which provide up to 50% more thrust than the little 62mm does. Just because the pitch spec provides a calculated speed does not mean the boat will run that fast....prop efficiency is very important and a prop which has an inadequate thrust cone won’t achieve the calculated speed.

Finding the right voltage for the larger, more efficient props for the motor you have may be the big challenge. But the 62mm prop is worth a try first.

.

[WheelMan]

Thanks Fluid, I appreciate the detailed response, very helpful indeed.

I do understand the calculator is theoretical, and by no means fact or proof that the outcome will be exactly as it says. But it is a good way to get in the ballpark at least, or so I understand.

I am familiar with the benefit of running higher voltage equating to lower amperage draw. This is one of the main reasons I have this motor/esc combo in the first place, as it was capable of very high voltage (I previously used it in a 1/5 scale 4x4 rc vehicle, which was very heavy, making it an amp hog). This is also why I decided to use it for a large scale boat build. I figured it could handle a boat that's lighter than the truck it seemed to do very well in. But I understand these are two very different applications too.

Anyways, I had completely forgotten that my 3080 was capable of being connected in two different configurations. I learned this back when I originally purchased it. However, I had long forgotten about it until you mentioned it here.

So, I went in search of this, and found the info you can see in my photo below. Does the star configuration get me closer to where you suggest I need to be?

Regardless, it sounds like I may need to go up in prop size a bit.

3080.jpgCalculator3.jpg

[bogieboy]

there are some great easy to use calculators on this site :)

https://www.offshoreelectrics.com/conversion.php

if my numbers are right, with the 15s, and the star config, you appear to be looking at 22460 rpm, and a 1.4p 72mm prop will push you to 63mph, with a 25% slip for a mono hull in the calc.


also FYI, i just got a 1.4p 72mm bronze three blade for my 46" Dumas powered by a weed eater... had a 1.6p 78 that was way too much prop for it initiallly... should rev higher than it did here...LOL

https://www.youtube.com/watch?v=DVeP1oCYAuU

[Mike W]

Oh yes go with the star config 500KV. And may as well make it 16S. Looking forward to this!

[WheelMan]

there are some great easy to use calculators on this site :)

https://www.offshoreelectrics.com/conversion.php

if my numbers are right, with the 15s, and the star config, you appear to be looking at 22460 rpm, and a 1.4p 72mm prop will push you to 63mph, with a 25% slip for a mono hull in the calc.


also FYI, i just got a 1.4p 72mm bronze three blade for my 46" Dumas powered by a weed eater... had a 1.6p 78 that was way too much prop for it initiallly... should rev higher than it did here...LOL

https://www.youtube.com/watch?v=DVeP1oCYAuU

Thanks for the info! I completely missed that OSE had a calculator,

Oh yes go with the star config 500KV. And may as well make it 16S. Looking forward to this!

Will do! And the 15S vs 16S is because I already have three 5S packs to use. I am looking forward to getting this thing on the water, for sure!

[WheelMan]

Got some pieces in the mail today

IMG_20190803_135534.jpg

[WheelMan]

Got the Dr Props propeller in, and a motor mount from none other than Punisher himself (Thank you Peter!)

drive_prop_motormount.jpg