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  1. #1
    1QwkSport2.5r's Avatar
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    Build 6: SI3 Hydro .60/.90 size

    Building this out of 3/16" Birch 5-ply, 1/8" Carmelized Maple 3-ply, a little balsa and liteply for bulkheads & skin support. Engine mount is still on the drawing board, but will allow for 2-3 inches of engine movement fore/aft. Planning around 12" diameter props, 3" rudder, and hopefully it won't weigh a ton.



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  2. #2
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    RE: Build 6: SI3 Hydro .60/.90 size

    Brushless Electric?
    After all is said and done, more is said than done.
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  3. #3
    1QwkSport2.5r's Avatar
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    RE: Build 6: SI3 Hydro .60/.90 size


    ORIGINAL: crispyspa

    Brushless Electric?
    Oh god no. It will start life with a .90 glow, but a high revving .60 or .90 isn't out of the question.

    It would cost too much to get into electrics, and I can't stand them either.
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  4. #4

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    RE: Build 6: SI3 Hydro .60/.90 size

    lol !

  5. #5

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    RE: Build 6: SI3 Hydro .60/.90 size

    Now you got the taste
    What brand of motor you will use?OS,ASP,TT??
    Be happy is to stop being a victim and becoming an author of the history itself.

  6. #6
    1QwkSport2.5r's Avatar
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    RE: Build 6: SI3 Hydro .60/.90 size


    ORIGINAL: carlosam

    Now you got the taste
    What brand of motor you will use?OS,ASP,TT??
    I have three engines that share the same mount and thus get tested with. Main powerplant is a SuperTigre S90 on steroids, the "experiments" are a K&B Sportster .65 or Enya 60-4C. I haven't seen a 4-stroke SI3 yet... I'll try almost anything once.

    I have a few parts left to cut out and pre-fit, and get the engine mount sorted out. Then I can start doing the finish sanding and start assembling. I think I may use a radial engine mount and braze together an aluminum "saw horse" mount of sorts. I did some experiments with "Alumaweld" and I was very impressed; the aluminum brazing rods from Tractor Supply sucked. Did not bond hardly at all.

    The steroids I'm putting the engine on is a bigger carb and a Jett muffler. Hoping to get 15k on a 12x6, stock carb/muffler it turns 13,600rpm. I do not own OS, and haven't gotten a decent revving .61 yet.

    I'm stuck working all weekend, and putting my full size boat in storage. Next year I'm going to drag race my SI's against my fishing boat.
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  7. #7
    1QwkSport2.5r's Avatar
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    RE: Build 6: SI3 Hydro .60/.90 size

    Not pictured but cut out is the radio box. Just testing the engine mount I cut out. I have a little more to do to get the engine mount mounted and mocked up.




    More to come later...
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  8. #8
    1QwkSport2.5r's Avatar
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    RE: Build 6: SI3 Hydro .60/.90 size

    Engine mount is near finished. I have about 2-2 1/4" of overall movement of the entire engine mount as it is right now. I can add in another 1/2-3/4" if needed.




    Now all thats left before I start epoxying the hull together is route the control cables, put a finished edge on the outside of the hull, and sand it. I have a pretty rad idea with this one.. More progress to come...
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  9. #9
    1QwkSport2.5r's Avatar
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    RE: Build 6: SI3 Hydro .60/.90 size

    I finally took a little time yesterday to get my epoxy hands fired up. Sponsons are roughly assembled, need to be sanded flat and add in a bulkhead or two. Top deck needs to be sanded and have the tub stringers glued in. To avoid any delamination of the plywood, I ripped down some white oak and made some thin trim pieces to border the outside edge of the top deck. I carefully curved the two front pieces using boiling water, a cookie jar, and some giant zipties. Worked awesome. Originally, I was going to use some apple wood or pear wood I recently cut down from my parents yard, but being wet/green still, I didnt want it to shrink too much and I really dont want to wait 6 months for it to dry. I had some kiln dried oak and cherry, but the cherry doesnt curve as nicely as the oak did. Drying wood too fast usually causes more checks (cracks/splits) so using the oven to dry the wood was out of the question.

    Progress so far:


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  10. #10
    1QwkSport2.5r's Avatar
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    RE: Build 6: SI3 Hydro .60/.90 size

    Spent a little time getting some work done on the curled SI3. So far, the assembly is straightening the deck out. I'm almost ready to skin the bottom, and there's a little work left in the radio box. The hull already balances really nicely, so I think I'll have another custom home run. More good photos to follow the fiberglass curing in the tub.

    Radio box:

    Rudder (breakaway screw will be replaced with a nylon screw):
    Center tub 'glass down:

    I have some turn fins to make yet as well. I'm going to use two fins on the big one and one fin on the little one.
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  11. #11
    1QwkSport2.5r's Avatar
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    RE: Build 6: SI3 Hydro .60/.90 size

    Bottom is ready for skin. Ruler is 18" long as reference. I think overall length ended up being about 30.5".

    Better picture of my rudder assembly. It's not totally done yet, it still needs an epoxy bath.

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  12. #12
    1QwkSport2.5r's Avatar
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    RE: Build 6: SI3 Hydro .60/.90 size

    Some progress has been made on this thing..
    Skin is on, Radio gear is almost done, and getting some resin down is coming soon. Hope to have this ready by the end of the month (and before the baby comes!).





    The little tail on the trailing edge of the sponson is an experiment, hoping to reduce the wetted surface on the sponsons a little more maybe. If they prove pointless or negate performance, I'll cut them off.

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  13. #13
    1QwkSport2.5r's Avatar
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    RE: Build 6: SI3 Hydro .60/.90 size

    Its finally done. It looks pretty good, IMO. Everything is buttoned up and ready to run. Hoping to get it out on a thawed lake or pond very soon!

    Everything is adjusted, mounted, tightened, locktited, waterproofed, etc. It should run well.


    Big honkin' Jettstream muffler!

    Turn fin:

    Without fuel (16oz tank), its a little nose heavy. I set it up this way intentionally; It should balance level with a full tank of fuel. If not, I can shift the engine forward more if needed.

    Both of my SI3's side by side... the little one is tiny compared to the big one...

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  14. #14
    1QwkSport2.5r's Avatar
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    RE: Build 6: SI3 Hydro .60/.90 size

    I made the engine mount a little too light-weight... When I ran the engine for the first time, the engine and fuel tank vibrated pretty bad. So bad the fuel tank looked like green cool whip. So I toughened it up. It's super tight now, just need to test run it again. Hoping to get it on the water for a maiden this weekend.


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  15. #15
    1QwkSport2.5r's Avatar
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    RE: Build 6: SI3 Hydro .60/.90 size

    Maiden run! It ran pretty well, despite hitting a turtle and taking out the turn fin bracket. Overall I'm happy with it.

    http://youtu.be/Nv3cABdj9xg
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  16. #16
    1QwkSport2.5r's Avatar
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    Bringing this old girl back out for a few modifications. First trouble I need to fix is sponson/deck flexing. I haven't had it moving fast enough to have a problem with it, but with one of the other modifications I have planned.... There's gonna be a LOT of flexing all over! So in the first group of photos, I'm proposing to use aluminum arrow shafts to make a strut on either side of the radio box to one of two locations on the deck to stiffen the deck/sponson area.

    Next modification is a complete engine mount overhaul. A nice welded aluminum mount with firewall type engine mount is my ideal choice which I will make at some point, but for now a wood/aluminum hybrid will be my choice for now. I made the mount longer than I originally planned due to having a larger than normal fuel tank (14oz bubbleless). The next time I place an order at Jett Engineering, I'll order one of his 8oz BubbleJett fuel tanks. Second group of photos is my current engine mount idea. The engine and tank will be mounted to the 3/4"X3/4"X1/8" aluminum angle stock. I did this on my SI3 .20 series with Jett .35 engine so the mount wouldn't crack from vibration. I will remove material to save weight and mill slots into it so the engine can be moved to adjust CG.

    Last major modification will be the addition of what I call my "Eleanor" engine... Or in Dub Jett's words; "The animal engine". Jett BSE .56LX (AAC) high performance. Rated to turn a 10x6 APC at 18,000rpm, but likely will do a little better than that once broke in all the way.

    This boat needs a new turn fin bracket too, will show pictures of it when I get the parts made.
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  17. #17
    1QwkSport2.5r's Avatar
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    Getting the engine mount close to completed. Next up will be adding some stiffeners for the sponsons so they don't flex as much. I used some thinner plywood than the SI3 kits come with so deck flex is a problem for me. My SI3 20 series doesn't exhibit this problem but likely due to its smaller size. Some photos of the progress albeit not showing a lot.
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  18. #18
    1QwkSport2.5r's Avatar
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    Starting to assemble the finished engine mount. I went a bit overboard (no pun intended) on building strong (heavy!) so I'll have to sacrifice a little strength to save weight. The 1/8"x3/4"x3/4" aluminum angle is heavy so I'll add some holes o lighten the load while keeping it strong. As pictured its weighing 8 pounds 9 ounces. A fair bit heavier than the 7 pound 14 ounces it weighed with the ST .90 and old engine mount.
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  19. #19
    Mine ended up at 9lb 7oz :/

  20. #20
    1QwkSport2.5r's Avatar
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    I can trim some fat off of mine to get it closer to 8 pounds. I'd be okay with 8 pounds 6 ounces RTR minus fuel. I think 8 lb 15oz is around the norm with a .61 engine and standard muffler minus fuel. This Jett .56 is in a .40/.46 sized case and turns a 10x6 at around 17-18k. I have to work to keep the weight down as I'm using essentially a .46 on steroids. Mine was built using 3/16" plywood instead of 1/4" so my hull weight should be a fair bit lighter than the kit versions albeit with more deck flex that I have to stabilize more. So we'll see how it goes. I'll be test running this pig over the July 4th holiday coming up.
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  21. #21
    1QwkSport2.5r's Avatar
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    Well, I added some holes to the aluminum bracketry to save some weight - got 2oz knocked off without sacrificing much. I'll save close to 3oz by omitting some hardware where unnecessary (flat washers). I think I can further simplify the engine mount and omit the flat plate below the engine pylons and use a spacer between the mount tabs on the hull and the engine pylons. I'll have to look at what liver I have that will work and not counteract my weight cutting measures. I'd like to get as close to my previous RTR weight of 7#14oz as I can, though I'm not sure that'll happen. I could swap out the HS645MG servos for some HS82MG servos and save a ton of weight and gain some speed too.
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  22. #22
    1QwkSport2.5r's Avatar
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    Here's my Swiss cheesed mount brackets. Hope they don't crack.
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  23. #23
    Still plenty of meat left on those!

  24. #24
    1QwkSport2.5r's Avatar
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    Yeah, it should work good. I bolted most of it back together earlier tonight.
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  25. #25
    1QwkSport2.5r's Avatar
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    Pictures of the tuned pipe mounting, servo mounting, and the proposed location for the sponson struts. Those sponsons are gonna flop around like mad at speed. A lot of the work is done now, but still need to tie up loose ends. Sponson struts and turn fin needs to be done.
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