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Building a Crackerbox step by step with lots of pics!

Old 07-29-2009, 01:20 AM
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CrackerboxSydney
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Default Building a Crackerbox step by step with lots of pics!

Hi all, I'm building a crackerbox from the jerry dunlap plans and i thought I'd post my build here and get tips as i go.
I'm new here so be nice!
And PLEASE give me advice as i go - especially with the 'next step' as you see it coming. I'm a beginner here so no offence will be taken unless you're super rude about it.

Started off with the plans from http://www.mariosrcmodels.com/crackerbox.htm
The plans are alright, not much description to go with them unfortunately. In hindsight, i should have gone with the a kit from zippkits!

Here's what i've got so far. Lots of cut out bits on 3mm ply bought from bunnings:


Here's the nosepiece, with the 2 doublers on each side (4 doublers total) making it 15mm wide. Hopefully stiff enough to handle a pocket bike engine.


And here i'm holding the keel (left piece of timber) which is 5 pieces of ply glued together.



Ok now i've got some more progress:

Here you can see how i've sandwiched the 5 front keels together. To get them smooth, i had to run it carefully through the table saw. You can see a bit where i sawed a bit too much off.


Had to use the plans to line up the front and rear keels correctly:


Heres the 'scab' gluing the front and rear keels together. Note i'm using PVA glue for now. Plan to later encapsulate the whole lot in paint to avoid water ruining the glue.


And some precariously balanced weights adding pressure to the glue as it dries.



Now i'm gluing the bulkheads into position:

This is how i'm holding the keel vertically, a nice thick chunk of wood is very useful for this:

This is the back (6th) bulkhead. It is made of two pieces of ply.

First bulkhead
'
Second bulkhead:

Third bulkhead:

4th and 5th bulkhead.



Old 07-29-2009, 01:29 AM
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Default RE: Building a Crackerbox step by step with lots of pics!

looks good mate you should bring it out penrith when its done

cheers
Old 07-29-2009, 01:42 AM
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CrackerboxSydney
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Default RE: Building a Crackerbox step by step with lots of pics!

Who meets out at penrith? Is there an rc boat club? I live near blacktown so its not too far away.

My bro-in-law is building one too, but his is going to be powered by a 50cc pocketbike engine! What parts do you think we should we brace more strongly to handle the extra power for his one?
Old 07-29-2009, 01:52 AM
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Default RE: Building a Crackerbox step by step with lots of pics!

I would suggest encapsulating with epoxy or fiberglass resin, paint will crack and let water in. I don't think they will let you run a 50cc at Penrith ether, up to 35cc is ok though.
Old 07-29-2009, 02:35 AM
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Default RE: Building a Crackerbox step by step with lots of pics!

http://www.modelboatclubofnsw.com/
Old 07-29-2009, 02:58 AM
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Default RE: Building a Crackerbox step by step with lots of pics!

ORIGINAL: MrMikeG
I would suggest encapsulating with epoxy or fiberglass resin, paint will crack and let water in. I don't think they will let you run a 50cc at Penrith ether, up to 35cc is ok though.
Isnt epoxy the same as fibreglass resin? I hope to encapsulate it, but epoxy is so expensive so if anyone can suggest an alternative that'd be great!

Hmm maybe penrith isn't going to be tough enough for us then! (kidding) haha - i may be able to sweet talk it, given that a souped-up zenoah would put out more power i'm guessing.

I've glued in little cubes of pine, as reinforcement:



Cut out all the stringers! Instead of following the plan, I'm thinking of simply using 6x6mm stringers all round (instead of 5x10mm on the top&bottom). Is that OK?


Also, i un-coiled the starter when trying (unsuccessfully) to convert to a cordless drill starter. Any ideas how to re-coil it?

Old 07-29-2009, 02:59 AM
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Default RE: Building a Crackerbox step by step with lots of pics!

Not having luck with the links, i'll try again:

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Old 07-29-2009, 04:30 AM
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Default RE: Building a Crackerbox step by step with lots of pics!

Epoxy resin is stronger than polyester resin however you can use polyester if you havent used epoxy glue in the build?.If you used any epoxy in the build polyester resin wont bond to it so you would need to make sure the skin is well sanded and clean of any epoxy.Usually when sealing a hull we use epoxy resin,you need slow setting epoxy at least 3 hr stuff which gives arround 30-45 mins work time.The slow setting time allows it to soak into the grain and get a better bond.If you used wood glue to bond your boat then you can use poly resin to seal it or to glass it using a thin woven cloth on the outside.
Mart
Old 07-29-2009, 05:48 AM
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Default RE: Building a Crackerbox step by step with lots of pics!

Manly Dam also is a good spot to run boats.

You should be able to race your boat against the real boat

Good luck

JC
Old 07-29-2009, 06:50 AM
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Default RE: Building a Crackerbox step by step with lots of pics!

Thanks a ton for the tips, Martno1fan (marty?)
Ithink i'll follow your advice - use only superglue and PVA wood glue to hold it together, and polyester resin to encapsulate.

Question:Can anyone suggest a cheap supplier of polyester resin? Cheapest i've seen is at bias, and i just know that's not a budget place to shop.
Question: When do i encapsulate? Just before putting on the bottom/side sheets, and again after they're on?

Anyway, i've been busy - flipped it, and braced the bottom keel-to-bulkhead joints with some more pine blocks. Hopefully this'll compensate for not using epoxy! See the pics.
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Old 07-29-2009, 08:08 AM
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Default RE: Building a Crackerbox step by step with lots of pics!

The one thing I see that you did wrong at the start of your build was that you didn't attach your frames upside down to a building board.That's what the tabs are for sticking up from the deck area.You should have started with a building board about 2'x4' and draw a line in the center of the length and then draw lines across the width of the building board where each frame would be placed according to the plans and made sure these were at a 90 degree to the building board.You could have screwed small blocks or used L angle pieces of aluminum at each frame location and clamped the the frame tab to the block or L angle piece. You would then begin building and would leave the frames on the board until all the sheating is on to keep the boat from twisting.You would then cut the tabs off almost even with the deck. If you don't have the sheating on you still may be able to do this.The pics are when I was building a Dunlap crackerbox
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Old 07-29-2009, 08:43 AM
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martno1fan
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Default RE: Building a Crackerbox step by step with lots of pics!

Yes he has a good point there,put it on a building board then sheet it.I would add all the side sheets too then id get some thin glass cloth and some resin and cover the whole boat ,bottom and sides in one.Once the bottom,sides and transom are done glass the top the same way once the sheets are on.You dont need thick cloth its just to seal the boat and add a little strength to an allready strong boat asuming you use good glue lol.One layer of 2.5 oz cloth should do ,then seal the inside with the same resin but no need for cloth inside unless you want to but might be tricky ,maybe just a few strips in places you feel need them.
Mart
something like this might be what your looking for ,enough here for a cpl of layers if need be.
[link]http://cgi.ebay.com/ebaymotors/FIBERGLASS-CLOTH-2-5-OZ-5-yds-FINE-CLOTH-17-50_W0QQcmdZViewItemQQ_trksidZp4634Q2ec0Q2em14Q2el1 262QQhashZitem4a93a7aa8cQQitemZ320304818828QQptZBo atQ5fPartsQ5fAccessoriesQ5fGear[/link]
Old 07-29-2009, 08:01 PM
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CrackerboxSydney
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Default RE: Building a Crackerbox step by step with lots of pics!

Tidnab, that's a great idea!I wish i'd thought of that before. To be honest, i'm just making it up as i go along. But i'll suggest it to my brother-in-law, he'll benefit from my hindsight.
Certainly explains how you're meant to get it all lined up - i had a hell of a time figuring it out without that.

My next question: How thick plywood should i use for the bottom/side sheeting? Ican only get 3mm locally. Will that do?
Old 07-29-2009, 08:55 PM
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Default RE: Building a Crackerbox step by step with lots of pics!

According to Aircraft Spruce's plywood list http://www.aircraftspruce.com/catalo...nnishbirch.php the 3mm is 1/8" which is what you want.You can use it for the hull bottoms as well as the deck.What are your frames made of? The 3mm would work for them also. You'll have the 3mm transom frame and when you get all your stringers in and all the hull bottom and deck sheathing on,you'll sand the transom down and put on 3mm cap over that,a little larger than the transom to cover the ends of the stringers and trim and sand it down till it's even with your deck and hull bottoms all around the edge of the transom.This will give you a 1/4" thick transom.Also before you put on your bottom plywood,use a straight edge and check to see if your bottom is flat from the transom to about,I think it was 8"or 10"forward.I straghtened mine out before I put on the bottom ply instead of doing it later and using putty.I would also put some holes in the forward frames that will be inclosed by the front deck to not so much lighten the hull up a little ,but to let trapped heat out and provide ventilation to dry any water that gets in.If you inclose the front and heat builds up ,it may split your forward hull open.Don't forget to put some pool noodles or other floatation in there.
Old 07-29-2009, 09:46 PM
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Default RE: Building a Crackerbox step by step with lots of pics!

Some good tips there, tidnab.
In answer to your question, i've used 3mm ply for everything so far. In parts where the plans indicate to use thicker ply, i've simply doubled up multiple pieces of 3mm ply.
I've already done the second piece on the transom, too. Maybe should have done it later. Oh well.
Its good to hear that 3mm will do for the sheeting - great.
Thanks
Old 07-30-2009, 01:49 AM
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Default RE: Building a Crackerbox step by step with lots of pics!

You want to use 3mm for all your sheeting & frames except for your transom & stringers, for those you want to double up. Looking good so far, use the tips above to help keep a straight hull. For cheap epoxy resin try FGi (Fibre Glass International, local Aussie dealer) or your local marine shop. You can get some epoxy resins cheaper than others. I'm not sure about Sydney, but here in Adelaide you can get Boat Coat brand at a lot less that West System and it does just a goos a job, I suggest you shop around.
Old 07-30-2009, 02:27 AM
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Default RE: Building a Crackerbox step by step with lots of pics!

Ok great, i'll stick with 3mm ply then. And i'll ring around to see where i can buy resin. Question: How much resin do you think i'll need?

Well, i've been busy with the stringers - see pics. Notice i'm using string to hold them into place whilst glue drying. Itie the string near to the joint, then spread it out to make theV, which tightens the string and holds it tight.
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Old 07-31-2009, 01:31 AM
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Default RE: Building a Crackerbox step by step with lots of pics!

OK i've been working on bending the front stringers into position.
Firstly i got some paper towels, dipped them in boiling water, and draped them on the stringers. Then i poured boiling water out of the kettle onto them occasionally for a few minutes. Then they were nice and bendy, so i could bend them into position, where i fixed them with a zip tie, and then a couple of tiny screws. I'm really hoping that the PVA glue will hold tight once its dry, because i think i'll need to remove the screws in order to fit the outside stringers as well.

Question: Can anyone give me a closeup photo of how their stringers meet at the nose so i can see if i've got the right idea? It'd be useful for my brothers build.
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Old 07-31-2009, 01:38 AM
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Default RE: Building a Crackerbox step by step with lots of pics!

Question: Can anyone give me a closeup photo of how their stringers meet at the nose so i can see if i've got the right idea? It'd be useful for my brothers build.
Answered my own question:
http://www.mariosrcmodels.com/images...ilding_1lg.jpg

Bummer!Iwish my work was as neat as that!

Oh wait - i'm an idiot!Only the side stringers are meant to go all the way to the front... doh! Oh well, i might leave them there, a bit of extra strength cant hurt.

Old 07-31-2009, 02:29 AM
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Default RE: Building a Crackerbox step by step with lots of pics!

Maybe leave those screws in untill you get the bottom sheets on ? also if you have a small nail gun you can fix them with that and leave the brads in thats how i do it sometimes .If you have a boatyard near you why not pop in and see if they can spare some epoxy resin they might sell you some cheap?, then id fillet all joints with it and glass with it too its less smelly than poly resin too.
Mart
Old 07-31-2009, 08:37 AM
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Default RE: Building a Crackerbox step by step with lots of pics!

Hi m8 i been bending stringers into position with the use of steam .And here the way i bend wood my wood/stringers. first i draw and layout the line on paper the i put finish nail in 1/2 ply on the outside of line then i take a pvc pipe and cap one end then i put the wood into it then i use a 1300 watt monster steamer to steam the wood for 5Min then take it out and put it into the building jig and let dry over night or you can bend it on the boat and clamp it down it bean very easy .hope this help anyone ,here some picture of it.
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Old 07-31-2009, 08:42 AM
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Default RE: Building a Crackerbox step by step with lots of pics!

Here more picture of my Zipp Kits boat
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Old 07-31-2009, 07:33 PM
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Default RE: Building a Crackerbox step by step with lots of pics!

That looks awesome, Kenny! I kinda wish i'd known about the zipp kits before i'd started. Not to worry. Also some of your pictures are only thumbnail size even when zoomed, which is a pity because i wouldn't mind a better look at how you've done things.
I like your idea of using a steamer. The guys who make the real-size boats use those, unfortunately i don't have one. Although i could fit part of the timber in the baby's steriliser when the wife's not at home... that'd do the same trick...
Cheers
Old 07-31-2009, 11:19 PM
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Default RE: Building a Crackerbox step by step with lots of pics!

Do you have a heat gun? They work pretty well too. It's not really the steam that makes the wood bend easily, it's the heat. In fact if you leave a piece of wood in a steam box too long it can dry it out and make it harder to bend right. Doug
Old 08-01-2009, 12:07 AM
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Default RE: Building a Crackerbox step by step with lots of pics!

Don't have a heatgun, but would a hair dryer work?

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