Author Topic: Scratchbuilt hull material  (Read 12865 times)

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des

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Re: Scratchbuilt hull material
« Reply #15 on: August 29, 2019, 04:04:07 »
Steve - photos coming soon, I hope.  Every time so far that I thought it was ready to photograph I found some issue that has required almost complete dis-assembly again;  all due to my own inexperience as a hull-builder, not due to the material.

I thought of you this afternoon - see my later post ref Kort nozzles.  I was hoping you might be able to give me some tips ref 3D design & printing.

Capt.Towline

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Re: Scratchbuilt hull material
« Reply #16 on: August 29, 2019, 12:13:20 »
It’ll be good to see some photos Des. I’ve often wandered about using that method but three possible issues always held me back. The first being accurate placement of pieces the second being twisting and the third finding a good way of glueing whilst avoiding 1 and 2.

I’ll be watching your progress with a keen eye.

Capt.Towline

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Re: Scratchbuilt hull material
« Reply #17 on: August 29, 2019, 12:14:47 »
But I really like the idea of building frames and shell plating as ship builders would with steel!

des

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Re: Scratchbuilt hull material
« Reply #18 on: August 29, 2019, 13:51:17 »
Surprisingly, accurate placing is not really much of an issue, as long as you use at least three "3rd hand" tools to hold a frame in position whill you measure it all up and make adjustments (which WILL be necessary).

But I made two mistakes before I even got to that stage.

Firstly, I cut all of the notches in each frame for the stringers - located at the top outboard corners, and at the chines.  (I had thought that placing the stringers at these locations would stiffen the hull, as well as giving me somewhere solid to cement the "plating" in place later, and provide a watertight seam.)  So I lost these corner setout points even before I started.

Secondly, a lot of the frames are "open top" - they are roughly U-shaped in order to leave the deck openings clear.  So I lost the top centre marks as well.

Good thing it's easy to fill and file styrene without causing distortion.

sea monkey

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Re: Scratchbuilt hull material
« Reply #19 on: August 30, 2019, 07:09:22 »
If you make the frames with closed tops the whole thing will be much stronger and more rigid when you put the plates on. It’s easy enough to cut the ‘tops’ off when finished and the hull is nice and true.
I usually attach the deck (with access holes already cut) before I start plating/planking. Really stiffens up the keel and ribs.
Warped hulls can be very difficult to fix.

des

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Re: Scratchbuilt hull material
« Reply #20 on: August 30, 2019, 14:34:28 »
Yeah - thanks.  I already worked that out.

I had to dis-assemble the whole lot.  I put some masking tape over the tops of the open frames and marked out the top centres.  Then I put the keel into a jig to hold  it straight (there's another lesson there, too), then used some milliners elastic thread to stretch a top centreline fore-and-aft, and re-assembled the whole lot again.  When it was all lined up I glued it all together again.

Then, when I tried to line up the next frame I couldn't get it right, so I measured everything, and found that one side of everything was 3 mm higher than the other, even though it was all lined up correctly along the centres top and bottom.  It took a while to work out that I had to ease the slots in the bottoms of the frames where they engage with the keel, in order that the frames could be "rotated" a bit to get each shoulder height right.  Then set it all up, measure it several times, then glue it all again.

I am now uncertain about whether or not the frames are still symmetrical, so I have made templates for each frame so I can ensure both sides are the same.  I have had to ease one side of several frames, and fill the other sides of those frames, to get them right again.

So, many lessons learned.  Whether or not my original reasons for using styrene were correct, I am still glad I used it,  due to ease with which I can carry out the reworks needed, at only the cost of another bottle of styrene cement.

Des.
« Last Edit: August 30, 2019, 17:53:08 by des »

des

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Re: Scratchbuilt hull material
« Reply #21 on: October 01, 2019, 19:48:04 »
I've had a couple of weeks off from working on this project, so not much progress has been made beyond rectifying mistakes made earlier.  But here are a couple of photos as it stands right now.

The first photo is clearly a "top down" view, showing the framing and partially clad bottom.

The second photo shows the hull set up within the assembly jig in preparation for installing the next frame.  The three "3rd hand" tools enable me to set the frame  to the correct height, and adjust each top corner separately to achieve the required spacing from the previous frame;  and to achieve the required "shoulder" height.  The bottom tool holds the frame in the keel and prevent unwanted rotation of the frame relative to the rest of the hull.

One of the things I have found is that everything must be assembled without applying any force at all.  Using plywood, if a joint is tight then you would just give it a tap with a hammer until it fitted;  not so with styrene, as styrene does not have sufficient internal strength to resist any such force, and so some distortion WILL occur.

Des
« Last Edit: October 01, 2019, 19:58:19 by des »

Capt.Towline

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Re: Scratchbuilt hull material
« Reply #22 on: October 07, 2019, 01:50:50 »
Great progress Des and thanks for posting. So much to take in from the pictures and makes it even more evident that accuracy is key! Using your “helping hands” to keep everything in place...I imagine a lot of cross checking.

I see you’ve doubled up on some of your transverse frames which I assume gives a bit more rigidity. I wandered whether starting out with some sort of deck plate jig would have made it all easier but as you have different deck angles and heights, even getting this right would be a task in itself.

Good luck going forward and keep us up o date!

CT

des

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Re: Scratchbuilt hull material
« Reply #23 on: October 07, 2019, 13:05:40 »
Hi CT - thanks for the comments.

I doubled up on those frames where I thought they'd be subject to some extra load - eg at the rudder post, where the prop shafts penetrate the hull, and where some gear will be mounted (motors, electronics, etc).  But once I started actually assembling the bits I found also that these doubled frames were also easier to work.  I'm thinking that if I do this again I'd double them all.

I did form up the aft deck area upside down over some graph paper, starting from the deck hatch edge beams and working outwards;  then adding the frames to the deck support structure, then finally adding the keel into the frame notches.  This gave me a solid assembly that I knew  to be "right";  so when I rolled it over and set it into the assembly jig I could use this section as a reference point to set up the other "loose" frames into position prior to cementing them in place to the keel and stringers.  But it took me 4 or 5 "wrong" attempts before I worked out the "right" way to do it all.  All very time consuming, and lots of rework.

Des.

Capt.Towline

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Re: Scratchbuilt hull material
« Reply #24 on: October 08, 2019, 09:33:50 »
Aye, we all live and learn Des....you’ve obviously got a practical mind which will always find a way.

Keep up the good work....and the pictures!

CT

des

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Re: Scratchbuilt hull material
« Reply #25 on: October 28, 2019, 17:36:39 »
I've now got the hull framing completed, and about half of the hull sheathing added.

After I had initially completed the framing I found there was excessive flex in the region where the keel sweeps up to form the stem post, even after the stringers had been fixed in place, and even with the keel still held in the build jig.  This is because the stringer material doesn't have sufficient rigidity to resist this movement, partially due to the material itself, and partially because there is insufficient spacing from side to side in this region.  To overcome this flexing I installed a shelf spanning 4 frames up to and including the final frame right at the bow.  (I know that I could have achieved the same result by installing the foredeck, but I wanted to the keep the area clear until after I have completed cladding the bow area.)

Here are some photos.


des

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Re: Scratchbuilt hull material
« Reply #26 on: October 28, 2019, 17:40:56 »
More photos

mike_victoriabc

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Re: Scratchbuilt hull material
« Reply #27 on: October 29, 2019, 05:33:25 »
Interesting build - looks very tidy!

sea monkey

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Re: Scratchbuilt hull material
« Reply #28 on: October 30, 2019, 16:45:44 »
Good work Des.
Will you give it an internal coat of resin to water tighten everything. That should also help with removing any flex.

des

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Re: Scratchbuilt hull material
« Reply #29 on: October 30, 2019, 17:18:29 »
Hi Steve

No, I hadn't planned on epoxying the hull, either internally or externally.

I was intending to rely on getting an adequate water seal along the seams between cladding sheets by using a "putty" made up by dissolving styrene scraps in liquid solvent / cement.  All of the seams are slightly filleted so that they leave a partial gap along the seam, while still fitting snuggly together;  the putty flows along and into these seams and fills and seals them.  When the solvent evaporates it deposits the dissolved styrene into the joints, and filling the fillets and seals them.  Then later I will rub back and fill any blemishes (and there are plenty) with a commercial putty prior to painting.

This is the first time I've used this cheap form of putty.  It's also very useful for sealing the gaps between butchered joint halves.

As for stiffening the hull, I am expecting the external hull sheathing and deck will do this adequately - it's already quite rigid except just behind the forward bulkhead where there is still some minor flex due to the local geometry, but I expect this will  go away once the deck is laid.