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Thread: 70" CRC Outerlimits Electric Build

  1. #1
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    Default 70" CRC Outerlimits Electric Build

    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
    Last edited by WheelMan; 08-02-2019 at 09:25 AM.
    WheelMan Designz - Custom RC Creations

  2. #2
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    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

  3. #3
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    Great looking hull. My friend just finished his gas build this spring.

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

  4. #4
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    Quote Originally Posted by sammyha View Post
    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!

    Quote Originally Posted by fweasel View Post
    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!
    WheelMan Designz - Custom RC Creations

  5. #5
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    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.

  6. #6
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    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.
    ERROR 403 - This is not the page you are looking for


  7. #7
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    Quote Originally Posted by fweasel View Post
    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.

    Quote Originally Posted by Fluid View Post
    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 Designz - Custom RC Creations

  8. #8
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    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
    WheelMan Designz - Custom RC Creations

  9. #9
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    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.

    .
    ERROR 403 - This is not the page you are looking for


  10. #10
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    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
    Last edited by WheelMan; 08-02-2019 at 01:47 PM.
    WheelMan Designz - Custom RC Creations

  11. #11
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    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

  12. #12
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    Oh yes go with the star config 500KV. And may as well make it 16S. Looking forward to this!

  13. #13
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    Quote Originally Posted by bogieboy View Post
    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,

    Quote Originally Posted by Mike W View Post
    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 Designz - Custom RC Creations

  14. #14
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    Got some pieces in the mail today

    IMG_20190803_135534.jpg
    WheelMan Designz - Custom RC Creations

  15. #15
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    Got the Dr Props propeller in, and a motor mount from none other than Punisher himself (Thank you Peter!)

    drive_prop_motormount.jpg
    WheelMan Designz - Custom RC Creations

  16. #16
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    That mount is really nice looking!
    Vac-U-Tug Jr (13mph)

  17. #17
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    Been working on this build, trying to make some progress.

    Transom plate is almost complete. Still needs a couple holes yet (water cooling inlets & steering link hole).

    I'm learning the real challenge in this build is getting a stuffing tube made. Getting the proper amount of bend in the tube, so it lines up with both the strut and the coupler on the motor, is proving quite tricky, and time consuming. Not to mention ss tube is hard to bend, haha. This is no surprise to you guys I'm sure, but this is my first time doing this, so I'm learning.

    My first attempt (pictured below) has too sharp of a bend in it I believe, as the flex shaft does not spin as freely as I'm sure it needs to, when I install it in the tube and spin it by hand.

    However, I've grabbed some fresh tubing, and will attempt again (and again if necessary) until I get it right.

    IMG_20190924_223703.jpg
    WheelMan Designz - Custom RC Creations

  18. #18
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    Looking good! My technique is to install the flex cable into the collet, allow it to take its natural curve, then trace that on a piece of cardstock and use it for a tube bend template.

  19. #19
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    Everyone has their preferred method for bending a stuffing tube. I prefer to anneal mine. Heat the area that needs to be bent so it just starts to glow, then immediately quench it in water. I agree with Mike, I like to put something in the tube while bending. An annealed brass tube will bend quite easily with finger pressure. Once you have the shape you want, heat it up again and then allow to air cool and it will hold its shape. polish it up with some steel wool or fine grit sand paper to get rid of the carbon char and tarnish.
    Vac-U-Tug Jr (13mph)

  20. #20
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    Quote Originally Posted by fweasel View Post
    Everyone has their preferred method for bending a stuffing tube. I prefer to anneal mine. Heat the area that needs to be bent so it just starts to glow, then immediately quench it in water. I agree with Mike, I like to put something in the tube while bending. An annealed brass tube will bend quite easily with finger pressure. Once you have the shape you want, heat it up again and then allow to air cool and it will hold its shape. polish it up with some steel wool or fine grit sand paper to get rid of the carbon char and tarnish.
    Doing that to S/S will harden it. Brass tube absolutely.
    NZMPBA 2013, 2016 Open Electric Champion. NZMPBA 2016 P Offshore Champion.
    2016 SUHA Q Sport Hydro Hi Points Champion.
    BOPMPBC Open Mono, Open Electric Champion.

  21. #21
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    Made some more progress this weekend.

    Got the stuffing tube right, once and for all. Ended up needing to adjust the strut down a little, to get it pointing straight back, 90 deg to the transom (is that what it should be? Someone please help me here if that should be different?). Adjusting that down called for less bend in the stuffing tube, so that helped. Also, I just put a more gradual and larger radius bend in it, which made for far less drag on the flex shaft when installed. I'm happy with the final result. And I cut it a little shorter to leave about an inch of flex shaft showing between the end of the stuffing tube and the coupler on the motor. Seems to be about right based on what I've seen in pictures of so many other builds, so I hope I got that right.

    Steering servo is mounted. Steering link is fabricated (aluminum rod with stainless rod ends). Boot installed in the transom to seal water out. Steering is pretty well set up.

    ESC is mounted. Need to do some solder work, make leads to the motor and for lipo connection.

    Getting close to epoxy time for the center rails and transom plate here once I get the final holes in everything.

    Battery mounting is after that.

    IMG_20190929_214859.jpg IMG_20190929_214918.jpg IMG_20190929_215211.jpg
    WheelMan Designz - Custom RC Creations

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    The strut position, height from the keel, looks a little too low to me. Usually the center point of the stuffing tube as it exits the transom is a little higher. As far as angle, you can start with the stinger set parallel to the keel and adjust as necessary after the maiden depending on how the boat runs.
    Vac-U-Tug Jr (13mph)

  23. #23
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    Quote Originally Posted by fweasel View Post
    The strut position, height from the keel, looks a little too low to me. Usually the center point of the stuffing tube as it exits the transom is a little higher. As far as angle, you can start with the stinger set parallel to the keel and adjust as necessary after the maiden depending on how the boat runs.
    Well shoot, how much am I too low by on the strut, roughly? How will this change the boat's abilities, the way I have it?

    I do have the strut set parallel to the bottom of the hull though.
    WheelMan Designz - Custom RC Creations

  24. #24
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    Hopefully someone with more v-bottom build experience will chime in with a more detailed height measurement for you. I've based my past build off a survey of other boats. I've also corrected boats that were setup with the strut too close to the keel. It can put the prop too low in the water if the boat is heavy, like yours. On smaller, lighter boats, where the prop can still get up to where it likes to run, it forces the hull to far out of the water, causing instability and chinewalk.

    The best I can find are some rough photos of my friends 70" CRC build showing the approximate position of his stuffing tube from the keel.

    IMG950413 (Medium).jpg IMG950440 (Medium).jpg
    Vac-U-Tug Jr (13mph)

  25. #25
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    Thanks for the help man, much appreciated. Seems I've made for a lot of rework if I am going to move it. I thought I had done my research on this, but I guess I should have posted in here and asked before popping holes.

    Did your friend have a build thread for that 70" CRC build of his? If so, I'd love to check it out.
    WheelMan Designz - Custom RC Creations

  26. #26
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    He doesn't post on the forums, but I did put up a few other pictures as well as a video of it running here: https://forums.offshoreelectrics.com...ain&highlight=

    Let me know if there are other pictures you need and I can get them.
    Vac-U-Tug Jr (13mph)

  27. #27
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    oh yeah, doh! That is the one you linked me to earlier in this thread. Sorry about that.

    Thanks again for the info.
    WheelMan Designz - Custom RC Creations

  28. #28
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    Just sharing some photos. Not a ton of progress has been made, but a little. Motor & Battery leads soldered up. Water inlets & outlets installed. Need to make a stuffing tube support, and make a few more final tweaks to the main cf rails.

    Almost ready to start epoxying things in, and get started on the lipo mounting. Have some MBP adjustable lipo sleds I plan to use.

    Once fabrication is done, and I have the maiden voyage in, it will be time for paint

    IMG_20191008_172620.jpg IMG_20191008_173013.jpg IMG_20191008_171828.jpg IMG_20191008_172759.jpg IMG_20191008_173303.jpg
    WheelMan Designz - Custom RC Creations

  29. #29
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    I would suggest you raise your trim tabs up higher on the transom so that the leading edge is not flush with the bottom of the hull. Most recommend about a 1/16" to reduce drag. You might be able to just slot the mounting holes in the hull and fill the gap later with epoxy prior to body work and paint. The rest of the layout looks so clean, it makes me want to push my outerlimits build up onto the workbench.
    Vac-U-Tug Jr (13mph)

  30. #30
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    Thanks for the suggestion man. I did not realize flush was not the goal.

    I appreciate all the insight you've given me here on this build.

    I really have very little clue what to expect out of this thing once I get it on the water. I'm sure I will learn what I've done right & wrong. But that's part of the fun!
    WheelMan Designz - Custom RC Creations

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