36" Dumas Atlas U76

[peter ostertag]

Hi All

I have an old Dumas Allas U76 I built for nitro years ago but never finished, it's just been collecting dust, so I decided to continue the build and convert it to electric just for fun. Doing some research on this site I learned a few things that would improve the design of the boat like reducing the sponson depth, cutting lightening holes in the old framing and replacing some of the wood with 1/16 aircraft ply. Thinking of using 2x3s in series so i can put them on either side of the motor. I took the bottom sheathing off to gain access to the framing, this is where I'm at with the rebuild. Let me know if guy guys have any other tips for this old hydro.

 

[Hydro Junkie]

I would make three changes before reinstalling the bottom panels:

1. add glue blocks even with the bottom of the cross frames on the inside of both sponson insides to secure the new bottom to. Epoxy alone won't hold up the the flexing and pounding the hull will take without something to secure the bottom to, other than just butting the bottom against the sponson insides
2. add a doubler, either 1/8th thick 6061 aluminum or 3/16th aircraft grade plywood, to the inside of the right sponson transom to secure the turn fin bracket to. If you use the aluminum, you will need to tap threads into the holes you drill while with the plywood, you will need to install blind nuts or threaded inserts to secure the mounting screws into. If the kit had the fin on the face of the sponson inside, it won't work. In that location, the fin will throw water up against the bottom of the hull, making it much more likely to roll in the turns
3. add glue blocks to the sponson lengthwise framing as in my first change. Again, the outer bottom panel won't hold up, especially on the inside edge secured to just epoxy.

Here's some links to pictures I took while building a redesigned 30" version of that kit several years ago. All the glue blocks and stringers are 1/8th inch spruce:
https://www.rcuniverse.com/forum/attachment.php?attachmentid=1647750&d=1375582311
https://www.rcuniverse.com/forum/attachment.php?attachmentid=1647753&d=1375582311

One last thing that you might want to consider is the widen the tunnel. I know people that have tried to race the Dumas 36" blue Atlas, without any luck. One person cut the hull in half down the middle of the engine bay and widened it an inch. That modification made the boat more stable and prevented it from rolling over due to engine torque. I made the same change on my build, as shown in this picture:
https://www.rcuniverse.com/forum/attachment.php?attachmentid=1647744&d=1375582310