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        Build Log 1/2 Scale 72" Mono

#1 TGKconnectors Sep 26, 2011 02:18 PM

1/2 Scale 72" Mono
1 Attachment(s)
I found a set of plans for a 72" Mono hull which everyone said noone had built yet, so I decided to have the plans scaled down to 50%. I am going to build this boat leading up to building the bigger one.

I started cutting out the frame today.

#2 scorpion1 Sep 26, 2011 07:24 PM


#3 TGKconnectors Sep 27, 2011 09:57 AM

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Yes the over all length is going to be about 36" I hope. Unless fedex messed up during the scaling down.

Last night I traced out a few more frame members.

#4 TGKconnectors Oct 03, 2011 12:40 AM

4 Attachment(s)
I worked on the frame pieces a little bit more today.

#5 TGKconnectors Oct 03, 2011 12:41 AM

I ordered a bunch more wood, as well as a bunch of pieces from Hobbyking.

#6 TGKconnectors Oct 07, 2011 01:50 AM

I glued the frame together tonight and was missing one piece so sheeting the bottom will be the next step.

Anyone have any comments?

#7 scorpion1 Oct 07, 2011 07:40 AM


#8 cyberhoops Oct 07, 2011 11:49 AM

Looks very good to me. Are those 1/8" thick bulkheads? You did a nice job with the cut outs. Those are always a challenge for me. It looks like you drilled a set of holes and linked them together. The last time I tried a Dremel tool with a spiral cutter bit. It was pretty effective but hard to control accurately. (Where is that laser cutter when you need it.)

I guess I have two questions: Are you going to use the "wood over foam" method and what thickness of wood are you planning for the sheeting?

#9 TGKconnectors Oct 07, 2011 12:49 PM

The bulk heads are actually 1/4" and so are the runners. I think the runners were supposed to be 1/8" because I had to recut everything.

I tried drilling the holes and linking them together but it didnt work to well. So I went to harbor freight and bought a $25.00 mini router and cut them out with that.

I saw a picture where they used foam blocks between the bulk heads and sanded them down to match, I think I am going to have to follow suit because I can not get a noodle down each side.

As for the sheeting, I was thinking about using 3/32" balsa and then fiberglassing it and getting it painted.

#10 cyberhoops Oct 07, 2011 03:16 PM

Personal opinion: I dislike balsa for boats even when the outside is fiberglassed. Any water getting to the wood will soften the balsa and that caused catastrophic failures in my first two hydros.

I now use 1/32nd plywood for sheeting which also works very nicely over foam. I seal it with 20min epoxy for those cases where I don't use lightweight fiberglass cloth over the plywood.

When possible I always use the a foam block, usually the pink foam insulation, between bulkheads and cut/sanded/carved to shape. It helps make a rigid structure and gives more surface area to attach the sheeting.

I know there are builders who use balsa effectively - but I won't use it anymore.

#11 TGKconnectors Oct 07, 2011 07:50 PM

Where do you purchase 1/32 plywood cost effectively. I also do not know where to purchase the pink foam blocks of insulation.

#12 coriolan Oct 07, 2011 08:23 PM


Originally Posted by Mtrchs (Post 19532877)
Where do you purchase 1/32 plywood cost effectively. I also do not know where to purchase the pink foam blocks of insulation.

Depending were you live, you can get pink foam insulation 4'X8'X2" at the "Home depot" for a few $. If you need more tickness you can tack glue several together. For thin plywood you can get some at the LHS, 1/32" or 1/16" doesn't cost much in 48"X24" sheet(would be cheaper and lighter than balsa+Fiberglass/epoxy). I use 1/32" ply for small fast electric but for a 36" hull 1/16" might be better.

#13 cyberhoops Oct 08, 2011 12:42 AM

I order all of my wood for sheeting from National Balsa off the web - it is about $9 or $10 for a 2'x4' sheet of 1/32 or 1/16th plywood. They do have a minimum $25 order, but it is far cheaper than picking up sheets from the LHS. As for pink foam, as Coriolan mentioned I get mine in a 4x8 sheet from Home Depot.

I use 1/32nd sheeting on 1/10th scale electric boats, which are in the 34 to 36 inch range. Where it is backed by foam it is very solid. In open areas on the bottom of the hull I used to use 1/16th, but now I just use 1/32 and glue in some carbon fiber strips for stiffness. It is probably right on the border line of how far you can take 1/32nd plywood, but I am trying to keep the weight down on the hydros.

#14 TGKconnectors Oct 08, 2011 02:52 AM

I dont think my Home Depot carries it, I'll check tomorrow. I also will make a stop at the hobby shop.

#15 cyberhoops Oct 08, 2011 10:36 AM

Blue foam works as well, but since I am building a Miss Renault, I went with pink. :)

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