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Thread: Prop KV and amp draw help

  1. #31
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    i'm not sure i even know which hull you're talking running those electronics in.
    Vac-U-Tug Jr (13mph)

  2. #32
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    That makes 2 of us. I don't know what the hull is other than looking at it.the pictures are up in the thread.

  3. #33
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    Quote Originally Posted by fweasel View Post
    i'm not sure i even know which hull you're talking running those electronics in.
    We are talking the 48” cat hull Ryan.
    Jimmy, I think I’d be more in the 50mm range on props, perhaps 47mm. I don’t think id worry about the amp draw with 6s on 1250kv. You should be good there. I think 75 amps is where I’m at with 447’s and 1700kv Motors. Might even be less.

    A few things to add to Ryan’s comments,
    #1: I think the silicone would work fine in this situation. I did it on my little boat WITH flood tube when I started having sealing issues. Two years and no issues.
    #4: I haven’t done the ‘annaeling’ process as I find the bends usually gentle and can be gently worked into shape. One size over and under tubing helps to get leverage.

    And I was looking at the pics you posted and you’ll have to glass up that hatch but then I think that lid should seal pretty well. Bit of foam tape perhaps.

  4. #34
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    Jimmy, do you have a pic of the stinger you speak of? Perhaps a strut would be better.

  5. #35
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    Thanks for the prop size recommendation. Given your setup with higher kv, you're probably right I need something like x450. I think I'll try that first.

    I'm definitely glassing the hatch. It likely won't look pretty for now since I don't have a ton of time, but I'll get her sealed up.

    I don't have pictures of the stingers since they are in the mail. But these are what I ordered. I don't want to do a strut simple because I've done that before and wanted to try stingers.

    https://www.ebay.com/itm/3-16-left-r...-/142314976890

  6. #36
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    Ok yeah Promise hobby is good to deal with. The tubes I usually run the tube just inside the stinger. Enough to go inside but allow the stinger to move up and down a little. Should only need a few degrees of travel positive/negative.

    You shouldn’t really need to move the brass tube up and down within the hull.

    CNC for 50mm props. I just got some from RCboat bitz I believe.

  7. #37
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    Those are fairly expensive compared to Octura for $12. Is it just because they are already balanced? Since I'm still not sure on the size I might go with cheaper props until I know what size I'm going to stick with. I'll still balance and sharpen though.

  8. #38
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    Quote Originally Posted by Jimmypooh View Post
    Those are fairly expensive compared to Octura for $12. Is it just because they are already balanced? Since I'm still not sure on the size I might go with cheaper props until I know what size I'm going to stick with. I'll still balance and sharpen though.
    Oh I guess you are looking at plastic ones. Yeah they would be fine too as your not spinning 40k

  9. #39
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    Sorry looks like that correct size is $15 from here on OSE site: https://www.offshoreelectrics.com/pr...?prod=oct-x450

    I don't mean to be too cheap, but in the next couple months I'll be buying at least 4, maybe more.

  10. #40
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    IMG_20190720_142054.jpg

    First boat is complete. This is a fiberglass 32 inch Dumas Deep V 40 that someone made from a plug of my Grandfather's wood version. It's far too heavy because the fiberglass was laid too thick which is why it was given to me for free years ago. I call it the tank.

    It weighs 4.3kg (10lb) all up and uses a 4074 2000kv Goolrc motor with a Seal 130a esc and Banggood special 40 x 1.9 prop with 2p 5000mah batteries. It draws 55amps peak jumping in and out of waves. My guess is that it does about 30mph, but I will clock it later using my 1:1 boat. The speed is about perfect for the rough conditions I plan on running it in. I may go up in prop diameter while going down in pitch, but this prop did fine.

    For my test run I taped some plastic to waterproof it, but now that I know the boat works I need something more permanent. I'm open to suggestions for simple cowl materials. The tough part will be dealing with that weird front and back lip.

  11. #41
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    I'm getting close to finishing the 48 inch Cat. I just ordered x447 props (right and left handed). Here are the specs. Can anyone see any glaring issues?

    All Up Weight: 18.5 lbs
    Dual 4092 1250kv SSS motors
    Seal 130a 6S ESCs
    x447 Props
    10,000mah 6S battery
    CG at 30% from the transom

  12. #42
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    All looks good to start. Just watch the startups with that heavy of a boat and only 130amp ESC’s. It’s gonna takes bit to get it up and moving. Hopefully 447’s are up to the task

  13. #43
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    Thanks. It's getting cold here now, so I might not get a chance to run this boat until next year.

  14. #44
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    Quick update and a couple questions in case anyone is still watching this thread.

    The black mono has been doing great. With 10Ah 3S battery, it has a long run time. I made a cowl for it out of plexi, but it's cracking where the thumbs screws hold it down. I'm going to have to come up with a better design.

    The big twin cat is complete and I've put 4 sets of batteries through it. It's a riot in rough water and pretty fast. The question I'm having is that I can't seem to get the nose up high enough. I have the stinger trimmed all the way up, and the weight as far back as I can make it. Should I put some washers on the bottom bolts of the stinger to get some more angle out of it? I think there is a lot more I can get out of it if I can pull the nose up some more. Below is a video of it running.


  15. #45
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    It definitely sounds like it is working at it a little hard. If you balance the boat (Loaded ready time run with hatch on) on a dowel or something Where is the balance point in relation to the back of the transom? It should be about 30% of the length.

  16. #46
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    Yes, that's about where the balance point is. I took another look at the transom; it's angled down, so therefore doesn't give the stinger as much room to angle up as if it was flat. I'll try adding some washers to the bottom bolts and see if the extra angle I get out of it helps. Thanks!

  17. #47
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    Quote Originally Posted by Jimmypooh View Post
    Yes, that's about where the balance point is. I took another look at the transom; it's angled down, so therefore doesn't give the stinger as much room to angle up as if it was flat. I'll try adding some washers to the bottom bolts and see if the extra angle I get out of it helps. Thanks!
    Oh I see, yes you want the stingers to run straight with the desired ride attitude. If that makes sense put in those words

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