Looking at building the Oh boy oberto Nov 93 RCBM .Going over the drawing i noticed the sponson sides and the sides to the center section are 3/32'' balsa from past experience i know nomatter how you seal balsa there is almost no resitance to anykind contact with any object on the water surface that balsa will disinigrate into kindling i was thinking of using 3/32'' birch ply for sponson and center sides but on the weight test the 3/32'' ply weights 4 times what the balsa weights i was may be also considering 1/32'' or 1/16'' birch ply for sponson and center section sides and ca 1/8''x1/8'' spruce square stock around the edges for extra gluing surface for decking i was still considering using 3/32'' balsa for the frames as these parts will be sheeted over with birch ply this hull will be run on 12 cells with anything from a Cordite 700 to a brushless system a while back i posted about this hull and a gentlemen replied who had built several different versions of this hull but i forgot his name .Any suggestions would be great.
Building the Oh boy oberto Nov 1993 RCBM
- Thread starter riggerman
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Garry Finlay
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- Feb 23, 2005
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I use 3/32” balsa on all my little 1/16th scale boats. Top, sides and bottom. The sponson runners are 1/32” over the balsa. But that’s it.
Krylon sanding sealer, then Krylon top coat. Has held up for years.
Garry
Krylon sanding sealer, then Krylon top coat. Has held up for years.
Garry
jayt
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One of our club members has built two (well, really three) of the Obertos from the plans, and he discovered to his chagrin that the balsa made this large hull too weak for today's 12 cell power. The boat was designed in a day when 40 mph was fast for a 12-cell sport hydro, while today we are running them in the 50s. He replaced most of the balsa with liteply of various thicknesses. The boat is slightly heavier, but it is far stronger.
The less-porous ply takes less finish to give a smooth surface, meaning less weight over balsa sheeting. I don't know what he used, but I have had good success with LustreKote from Top Flight. It is more expensive than Krylon, but it covers better so you use less. Most of my boats are yellow, so I have to lay down a base filler coat of white first - the yellow is pretty translucent. No primer, just the LK covered by LK clear. This means less chance of the tape pulling up the paint.
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The less-porous ply takes less finish to give a smooth surface, meaning less weight over balsa sheeting. I don't know what he used, but I have had good success with LustreKote from Top Flight. It is more expensive than Krylon, but it covers better so you use less. Most of my boats are yellow, so I have to lay down a base filler coat of white first - the yellow is pretty translucent. No primer, just the LK covered by LK clear. This means less chance of the tape pulling up the paint.
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Garry Finlay
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- Feb 23, 2005
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This is quite true. Smaller hulls can get away with the lighter wood. On my 12th scale hulls now-days I still use 3/32 balsa throughout but, the outside sheeting is laminated with 1/64" birch ply "wing-skin". Best of both worlds. The Oberto would benifit from this also.
Garry
Garry
Steve-O
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- May 2, 2006
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Hey Riggerman,
I am the guy who jayt referres to in his post and I think may be the guy that responsed to you earlier.
If you are going to build the RCMB "Oh Boy Oberto" from plans. Please do youself a favor and use 3/32" birch plywood for the formers. I built one of those boats from a kit that had the balsa and it was very difficult to avoid twisting the sponsons when putting the skin on the sponsons. The assembly process for this boat (build the center pan, then two separate sponsons, then glue them all together) is difficult to correctly achieve, especially if you use balsa, because of the potential to have twist in the sponsons and center pan.
I have now built two of these boats using 3/32" ply for the formers and 1/32" ply for the skin. I used some basswood for stiffeners and some spruce to frame the canopy opening. Both boats have been easier to build, the hulls came out flatter and seem to be holding up well in club racing. One of the newer boats was built as an LSH (12 cells and a 700 brushed motor) and it runs fast and smooth. If you want to see some construction shots and the finished LSH go to our club website "www.HOTMBC.com" and check out the photo Gallery You will see Mike Brannans "Oh Boy Oberto" photo's there.
Regards,
Steve-O (HOTMBC.com)
I am the guy who jayt referres to in his post and I think may be the guy that responsed to you earlier.
If you are going to build the RCMB "Oh Boy Oberto" from plans. Please do youself a favor and use 3/32" birch plywood for the formers. I built one of those boats from a kit that had the balsa and it was very difficult to avoid twisting the sponsons when putting the skin on the sponsons. The assembly process for this boat (build the center pan, then two separate sponsons, then glue them all together) is difficult to correctly achieve, especially if you use balsa, because of the potential to have twist in the sponsons and center pan.
I have now built two of these boats using 3/32" ply for the formers and 1/32" ply for the skin. I used some basswood for stiffeners and some spruce to frame the canopy opening. Both boats have been easier to build, the hulls came out flatter and seem to be holding up well in club racing. One of the newer boats was built as an LSH (12 cells and a 700 brushed motor) and it runs fast and smooth. If you want to see some construction shots and the finished LSH go to our club website "www.HOTMBC.com" and check out the photo Gallery You will see Mike Brannans "Oh Boy Oberto" photo's there.
Regards,
Steve-O (HOTMBC.com)
