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Thread: Later-Model Dumas Scarab 38KV > AVS Build

  1. #1
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    Default Later-Model Dumas Scarab 38KV > AVS Build

    This was an RCG find unbuilt hull with the white gelcoat inside and the molded stringer insert. I like this newer version hull so much better! I decided to step the hull and make it the '98+ AVS version.

    Power will be Rocket 5692s 730KV on 10S with a Flier 300 Twin ESC.
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  2. #2
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    A set of Stinger drives was modified with RC car parts to create a scale-ish offshore adjustable-height stinger look. The rams are shocks gutted and fitted with an aluminum plug left-threaded and the shock shafts are now Ti turnbuckles. Rudder will be the largest Speedmaster unit.

    I may notch the upper brackets to fit the shock in the center of each.
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    Last edited by Mike W; 04-12-2019 at 05:17 PM.

  3. #3
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    The hull bottom was cut out for the steps and the necessary trimming and fitting performed to match the side of a full scale AVS. The vent boxes are being constructed from 2mm Cf plate, and will be laminated with 6 oz. cloth top and bottom when completed.

    The drive gearboxes will be recessed necessarily so the props clear the rudder, but this will also massively strengthen the large flat transom for the long rudder.
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  4. #4
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    Multiple days of epoxy cure times later the vent boxes are complete and prefilled for the layup which will probably continue to the transom and end just forward of the first step. A final inlay of 6 oz. glass and then another of carbon will finish the inside. The outside should only need some filler work to get it all true. The camera makes it all look crooked. A couple strakes were removed also.

    I'll probably move on to building the drive recess next.
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    Last edited by Mike W; 04-12-2019 at 05:30 PM.

  5. #5
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    WOW this is going to be AWESOME!! I can believe you cut it and added the steps in the hull!! I'm a fan of the 1:1 38AVS also such a great looking boat!!

  6. #6
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    For a 20-year-old (?) hull I was surprised how much it all moved once cut apart. I had to span the sides with threaded rods and brace all the running surfaces with wood pieces hot-glued and screwed until everything set up. It’s solid as a rock now can’t wait till all the glasswork is done so I can start with filler.

  7. #7
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    Dang bro, you is no coward with yo saw! Nicely nicely!
    Would you be able to replicate those drives for me? Or at least list the parts one would need to make another?
    And where will the rudder be, center?
    "Look good doin' it"
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  8. #8
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    Yes of course! They are all HOTRC parts I believe. Center rudder. 2" billet scale tabs.

    Made a bit more progress on glasswork. Vent boxes glassed outside and entire hull CF'ed inside. Struggled a bit with the 21x40 piece and messed up the weave some trying to get the lay over the vents and alignment at the transom.
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    Last edited by Mike W; 04-18-2019 at 07:55 AM.

  9. #9
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    Formers are made up and tacked with a small bead on the downhill side. Will complete in several stages probably adding glass to the drive box and motor mount plate. Might add a rear support and/or doubler across the top of the mount plate.

    Servo mounts and a shaft support still need to go in along with hull pickups. Rudders pickups will cool the motors and the 3-cooling-circuit twin ESC will use 3 hull pickups.
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  10. #10
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    Finalizing positioning before the final glasswork of reinforcing all this structure completes. This looks like my best option for nearly the shortest potential cable lengths I’ve ever set up. The single battery forward low will go on a long tray and provide plenty of CG adjustment by itself.
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  11. #11
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    Very nice work Mike. Very nice indeed.

  12. #12
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    Putting in a full day today! Back to the garage for a final sand of the glasswork in the vent boxes and a full coat of filler on the entire area. That will sit now until I’m ready to invest another full day into completing that filler/blueprinting work and priming the entire bottom.

  13. #13
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    Moving back inside. The outside of the rails are glasstaped, and now the insides are prepped and ready for glasstaping. Small forward battery is also going in.

    Transom is about 3/32” concave at the center and was fairly well spidercracked through the gelcoat so will get a lamination or two of cloth in the center to straighten it before a final coat of filler.
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  14. #14
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    Some beautiful work there Mike.
    This will be a sight to see on the water.

  15. #15
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    Dang bro... super bummed we didn’t meet.. you got some mad skills and I’d have liked to have learned from a master!!

    Your “messed up” cf inlay is so nice, the wobble in the weave is a “thumb print” in a masterpiece!

    Hope to meet you soon. You going to nats?? It’ll be my first time.
    J
    "Look good doin' it"
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  16. #16
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    Yes, funny how I fell into HOTMBC right after you left. What a club! And definitely the largest reason I'm hooked on boats again. Thanks so much Jim!

    No nats for me and still bummed I missed Dallas. Maybe next year. LOTO is the big event planned for this year!

    Underside filler work and blueprinting is complete, and the top is all blocked and filled 80-150. Just a few filler touchups remain before a final sanding with 320 including the edges then it gets primed.
    Last edited by Mike W; 05-13-2019 at 08:25 PM.

  17. #17
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    Wasn't happy with the step alignment. Almost lost my mind trying to make sense of the step angle-of-attack, offset, etc. and the two steps being different lengths didn't help much. The hull bottom also reduced deadrise as it approached the transom. Lots of straightedge checks, measuring, and eyeballing! I try not to think about how much time I have into this hull mod but it is finally ready for primer and the decals are ordered. Definitely cannot recommend this mod.
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  18. #18
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    Hey Mike,
    Thats gonna be cool!!
    What does the empty hull weigh?
    South Jersey Vice

  19. #19
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    This DUMAS Cigarette is very nice, I like how you modified the powertrim drives.
    The steps are not scaled but this is not a problem. I hope those mods won' t affect the efficiency of this boat on the water.

    Who will reissue a 1m or 1,20m Cigarette hull?

    What do you think about the inexpensive Rocket Motors?
    Last edited by Alfa Spirit; 05-24-2019 at 05:02 AM.

  20. #20
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    I’ll weigh it when I get a chance. The bodyworked areas were primed with Featherfill and blocked out to 320. The entire hull will be primed in 2K next then off to a body shop for paint.

    The steps are larger and deeper, as well as set back a little farther on the hull but these changes seemed suitable for the model boat at model speeds. Less of the boat is in the water?

    The Rockets look good we’ll see how they run in a few weeks! I decided to make the drives steerable and a few parts are being machined now to make that happen. Hopefully the turn radius will be tight enough.
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  21. #21
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    I am super interested in these drives! Do you have a list of parts and how you modified them?
    Can’t wait to see/ hear how the boat runs.
    "Look good doin' it"
    See the fleet

  22. #22
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    Quote Originally Posted by Jesse J View Post
    I am super interested in these drives! Do you have a list of parts and how you modified them?
    Can’t wait to see/ hear how the boat runs.
    Well it started with a HOTRC servo mount I found for another build. The name fit so well with HOTMBC I decided to see what else they offered.

    Any cat drives with rear pedestal mounts will work. Discard the rear pedestals and replace them with some modified car shocks mounted to the transom and they work on a V hull with an offshore racing look. I used some similar to these, removed the shaft and replaced it with a Ti turnbuckle, and left-threaded an aluminum dowel plug inside the shock body. The location of this plug will be fixed with epoxy once the drives are finally mounted and the desired adjustment range is determined.

    https://www.ebay.com/itm/Hot-Racing-...oAAOSw5qdb5Olh

    For upper mounts my original plan was to notch these in the center to mount the shocks.

    https://www.ebay.com/itm/Hot-Racing-...ss!78641!US!-1

    These ball links mount to the bottom of the Ti turnbuckles and couple them to the drives at the pedestal mount location.

    https://www.ebay.com/itm/Hot-Racing-...0AAOSwo3BbykiD

    Before I decided to try to make them steerable they needed to be locked together parallel so this spacer was the right length.

    https://www.ebay.com/itm/Hot-Racing-...72.m2749.l2649

  23. #23
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    Finished up two LOTO cat bottoms and got all the boats primed today. 👏🏻
    Jeremy Moore is cutting some steering ram mounts and drive angle brackets to allow the rams to mount and the drives to be coupled with ball joint tie rods now instead of solid standoffs.

    Nice to have the hull sealed up in its last coat of primer so all the remaing assembly can be completed inside!
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  24. #24
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    I thought I had lost the engine cover. It was in the pantry under a large jar of marinara because it was so concave. Some improvement but still not flat. I beadblasted the bottom to clean it up for adhesion, ground quite a bit away on the backside to smooth it for a layer of CF. And glassed in a chunk of foam for more strength and flotation.

  25. #25
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    When this cures I’ll flatten the top and bond on a pair of Sniper 45 supercharger scoops.
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  26. #26
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    Scoops and decals came in. I need to finish this hatch so I can get this painted next week but it pains me some to destroy the nicely done louvers. 🥴
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  27. #27
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    Coming along. I think the finished scoops will make you forget all about the louvers!
    Vac-U-Tug Jr (13mph)

  28. #28
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    Quote Originally Posted by stac1627 View Post
    Hey Mike,
    Thats gonna be cool!!
    What does the empty hull weigh?
    I weighed it today. With engine cover and all my formers inside it weighs just under 8.5 lbs. I'm using a flat cockpit cover initially that will add more weight, and if the boat proves itself I'll build a scale cockpit this winter.

  29. #29
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    You won' t glue those scoops, right ?
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  30. #30
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    Quote Originally Posted by Alfa Spirit View Post
    You won' t glue those scoops, right ?
    Oh yes. They'll be blended right in. Why not? They might be ripped off in a flip?

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