Author Topic: Scratchbuilt hull material  (Read 8041 times)

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des

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Scratchbuilt hull material
« on: March 08, 2016, 18:51:43 »
Has anyone tried to build a hull using the frame and plank method, using styrene strips and sheets?  Any ideas how such a hull would compare with a similar hull made in fibreglass from a mould - weight, quality of finish, amount of work involved, durability of the finished hull, etc

Or is this such a dumb idea that I should forget it now before I spend too much time and effort on it?

Des
« Last Edit: March 09, 2016, 02:13:16 by des »

2tugboats

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Re: Scratchbuilt hull material
« Reply #1 on: March 26, 2016, 19:44:25 »
Hello Des,

I am surprised that there are no replies, 70 readers, to your important question here.
I personally would like to know which approach, frame and plank or fiberglass has,
in the opinions of the many experienced here, the most favorable attributes towards
less work and energy put out and finished product looks and strength.

Personally, I have always avoided fiberglass but the fact is, fiberglass hulls look
"knock-out" beautiful, are strong, and light weight.  And I would love to get
involved the the fiberglass tugboat "mold" world. . .or would I?

Part of what I would like to hear about is if I am right in that a "fiberglasser" has to build
their tugboat with a frame and plank anyhow to have the form to fiberglass. I don't
even know if I have that right because I have never worked with the glass. With out
some input here, which would be quite simple for many to give, I only know what
I don't know.

One of my friends sent me this picture of their fiberglass start on their tugboat. Is it
really that simple?



And below here is one of my approaches. . .ambient it rough, very rough, but it worked
out alright. A lot of work, wood filler, and I never did achieve the "right" tugboat hull look.



Again, a perfect and strong question Des, thank you very much,
Michael
Yet another case of why men and women go down to the sea in ships. . .A pleasure to be here and smell the salt air. Thank you Tugboat Forum. . .Michael in Anacortes, Washington www.twotugboats.com

Tiny69

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Re: Scratchbuilt hull material
« Reply #2 on: March 27, 2016, 00:46:59 »
The point of the original question is the use of plastic strip and sheet a viable use of materials to build a plank on frame hull compared to a fibre glass hull.  In my own experience I have only built plank on frame hulls using plywood for the frames and limewood for the planks.  I have not come across anyone building a plank on frame hull using plastic so I guess this is why there have been no replies to the question.  To build a fibre glass hull a mold has to be constructed first to lay the fibre glass matting into and apply the fibre glass resin.  This is time consuming and probably not the best way to construct a one off hull, but if more than one is required then more copies can be made form the one mold.


NickelBelter

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Re: Scratchbuilt hull material
« Reply #3 on: April 06, 2016, 23:58:49 »
The fibreglass hull would be superior in all aspects except ease of construction.  Moulding a skillful and time-consuming practice which is why so few people make moulds of hulls that aren't going to go into mass production. 

Styrene won't take fibreglass as nicely as wood planks will and the fibreglass is a key component to keep the planks from separating along the edges.  It's also softer than a wooden hull with resin and 'glass applied.  Vac-forming is a better method to produce a styrene hull, but the equipment needed to vacform a bigger hull is beyond what most model builders can justify. 

des

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Re: Scratchbuilt hull material
« Reply #4 on: April 07, 2016, 15:37:40 »
Thanks for that, NickelBelter.

Firstly, I have no intention of mass producing a hull, which is the main reason I am reluctant to build a hull as a plug, then make a mould, finally to get ONE fibreglass hull.  It's a lot of effort.  And vac-forming is out of the question (I had never considered it).

It seems to me that if I have to make a plug (in effect, a hull in itself) in order to then make a mould and then finally lay up a fibreglass hull, then why not simply eliminate the second and third steps?

From building an AZIZ kit using a fibreglass hull, one of the things I found is that there are NO reference points anywhere on a plain fibreglass hull;  and it is difficult to measure anything accurately either around curves or in tight spaces.  A lot has to done by eye alone.

On the other hand a frame and plank hull has references everywhere - you have a keel running full length, from which you can accurately measure side to side;  and you have a number of frames and / or bulkheads from which you can measure fore and aft.  Hence why this time I am considering a frame and plank hull.

You seem to be implying that a wooden frame & plank hull should be sheathed with fibreglass, presumably for water sealing and strength, and that a styrene hull would probably need the same treatment but would not "take" the fibreglass as well as the wooden hull.

I know next to nothing about fibreglass at all.  And I have limited experience in working with wood.  So it never occurred to me that sheathing a hull would be necessary.  I had thought that styrene itself is water resistant, so sheathing would not be necessary.  Wood also swells and shrinks, which styrene doesn't, so expansion or shrinkage at joints probably should not occur.  I would expect that joints in a styrene hull would be permanent and watertight, without swelling or shrinkage.

I accept that styrene would result in a softer hull material - but I don't intend to drop the hull, or run it onto rocks.  But even if I did, I would expect it to be easier to repair.  Also, the softer material makes it easier to work, which is one reason I am considering styrene as a hull building material.  But I am concerned about the ability of a styrene hull to support 10 - 12 kg total displacement without bending or hogging.

I am not rejecting your advice - nor have I settled on styrene as a hull material.  I'd certainly like to continue this discussion with other members to get more opinions and ideas.

Des.

sea monkey

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Re: Scratchbuilt hull material
« Reply #5 on: April 07, 2016, 20:40:42 »
Not sure about costs in Aus but styrene is much more expensive that plywood here so cancels itself out for hull construction. I have seen some German models made with styrene hulls but they were hard chine so easier to make from panels. Styrene also warps very quickly in sunlight.
I've used ply ribs and balsa strips before and that was quick and easy. Wood is very forgiving and easy to sand and fill. A coat of epoxy or polyester resin makes the hull much stronger and resistant to minor knocks. Usually best to coat the inside as well.

2tugboats

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Re: Scratchbuilt hull material
« Reply #6 on: April 07, 2016, 22:29:15 »
Well Des, you received lots of ideas and thoughts about making your tugboat hull
and for me, I also now have my eyes much more open with new ideas and approaches.
Styrene strips didn't get much support here. Using them in my mind's building mode,
I can't see the strips working out very well. Wood strips are the way to go if I am
planking a hull. Tiny recommends "Limewood".

I will confess that I quickly learned that plastic or vinal window bind strips don't
work at all. I still throw used blinds in the dumpster and sense that there is a tugboat
part there somewhere.

For my first tug several years ago, I took the time to fill all the spaces between the
frames with Styrofoam. The foam was just for flotation, however, looking at the filled
and flush "hull", I did think about the mysterious fiber glass. I quickly figured that
because of the cost of fiberglass, the mess and glass particles, my inexperience
and the smell. . .I would pass.

One main point that I learned from several of the replies here is that I can now see
how to make a production mold. Just thinking. . .maybe I will have to get us't to
the smell.

A pleasure to be here on the Forum and thank you to all who have shared. For sure,
now I know what I don't know about fiber glassing and all.

Michael



Yet another case of why men and women go down to the sea in ships. . .A pleasure to be here and smell the salt air. Thank you Tugboat Forum. . .Michael in Anacortes, Washington www.twotugboats.com

des

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Re: Scratchbuilt hull material
« Reply #7 on: April 07, 2016, 22:57:48 »
I had thought to make a plug by shaping polyurethane foam, then coating it with plaster, then make a mould from that.  I still haven't completely discarded that idea.  At least it's fairly easy to free-form the hull shape.

Sea Monkey - what type of plywood?  Can I get it at Bunnings?  Also, what type of epoxy or polyester resin would be suitable?  What about polyurethane (Estapol)?  Do you put it on before painting, or after?

I'm considering a hull approximately 1100 - 1200 mm length, by around 250 - 300 mm beam;  guessing a total displacement around 10 - 12 kg.  One reason I am considering styrene is its light weight, so I don't have to worry unduly about how heavy individual components and sub-assemblies are likely to be.  Has anyone any idea how heavy a hull this size would be if built in wood?  (For American readers, these dimensions are 43 - 47 inches length, 9.5 - 11.5 inches beam, 22 - 27 lbs.)

Des.
« Last Edit: April 08, 2016, 21:42:41 by des »

NickelBelter

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Re: Scratchbuilt hull material
« Reply #8 on: April 17, 2016, 21:45:01 »
If you're going to use foam, you can just fibreglass over it once you've carved it to shape.  Here is a build log from RCGroups showing just that method of construction.

http://www.rcgroups.com/forums/showthread.php?t=1337980

Easier still is to build a conventional keel and frames hull but fill the spaces between with foam and sand them all down to the frames. 

The weight of a hull that size built in wood will be a minor consideration.  My current build is 36 x 11 x 5 inches and weighs perhaps seven pounds, but takes nearly three times that much to float at the correct waterline.  Build a hull too light and it will be stressed by all the ballast you have to dump into it. 

des

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Re: Scratchbuilt hull material
« Reply #9 on: April 28, 2016, 03:22:21 »
Okay - so it looks like everyone recommends NOT using styrene for hull building.

I've just been made aware of aircraft plywood, available in thickness from 0.4 mm to 6 mm;  hoop pine, with high strength waterproof bond, and high strength to weight ratio, with fine grained blemish-free surfaces both sides.

I just read an old thread on the forum which suggests that ordinary PVA white glue is adequate for hull building, but it seems that many modellers apply an epoxy to the hull for improved water resistance;  is this applied to the outer surfaces as well, or just to the interior?  If it is not applied externally then I assume that the paint covering provides adequate moisture resistance to joints in the hull sheeting which are immersed in water.  What type of epoxy is recommended?  Is applied only to the hull, or also to bulwarks, gunwales, superstructure, etc as well?

Des.

sea monkey

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Re: Scratchbuilt hull material
« Reply #10 on: April 29, 2016, 02:24:14 »
Des: I use modellers/aviation ply that comes in thicknesses from 0.4mm up to 3.6mm. Usually available from hobby stores that specialise in aviation. Best glue to use is superglue (CA). I give the completed hull a coat of resin inside and out to make it water and bullet-proof. You can use either epoxy or polyester resin (available from boating stores or Bunnings) but only use one type. Don't put one on top of the other Ė they don't mix or bond.

tug-arlyn-nelson

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Re: Scratchbuilt hull material
« Reply #11 on: April 30, 2016, 19:20:55 »
Oddly enough, epoxy will bond to cured polyester but not the reverse. You see it in boatyards all the time where especially in blister repairs, the blister is ground out, then layers of glass cloth are laid in with epoxy.

des

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Re: Scratchbuilt hull material
« Reply #12 on: September 05, 2018, 20:05:42 »
Okay - I know this is an old thread, but ...

I've decided to go ahead and build a hull using styrene.  Hull will be based on a Burness-Corlett designed hydroconic tug of the 1970's era, twin screw with kort nozzles, built in 1:35 scale.

I've finally made this decision (2 + 1/2 years!) to use styrene because of the reasons set out earlier - little or no experience with fibreglass or wood, vs confidence in my ability to get a clean finish with styrene.  Also, I've always gained more enjoyment out of building the model rather than operating it on the lake - so I'm not going to be broken hearted if it isn't a complete success (unless of course, it completely breaks in half).

I'll start a build thread shortly, but progress will be slow as I have to finish the one currently on the slips - another kit-bashed AZIZ.

Des.
« Last Edit: September 07, 2018, 03:40:48 by des »

des

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Re: Scratchbuilt hull material
« Reply #13 on: August 27, 2019, 18:36:20 »
UPDATE

I've now commenced building the hull for a twin-screw 105 ft harbour / berthing tug based on a 1970's Burness-Corlett hydroconic design, at 1:50 scale.  As indicated previously I am using styrene for both framing and sheathing.  I have had some problems, mainly arising from my lack of experience in building a hull at all, but in general I am happy with progress.

The model I am building will have a total displacement of only 4.5 kg, of which approx. 1 kg will be the hull itself - I expect that I will need around 1 kg ballast.  So strength of the model should not be a major issue.  But even so, I have been surprised by the strength and rigidity of the framework that I have completed so far.

I am glad though that I chose styrene for my first scratchbuilt hull, due to the amount of rework I have had to do, including complete disassembly of the stern section to fix a twist that had developed.  Also, as I was forming up the framing for the bow I found that the bow shape was not developing as I had intended, so a re-design and re-build of this area was needed;  use of styrene made reworking much easier for those frames that had already been installed, without the need to remove and rebuild those frames.

I have decided though that this hull will be a "training exercise" in order to develop the techniques that are required to build a straight hull, and that styrene will not necessarily be the material of choice for the next one.

Des.

sea monkey

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Re: Scratchbuilt hull material
« Reply #14 on: August 29, 2019, 02:32:08 »
Keep us posted with your progress photos.
Using styrene is a bold move - good luck. Iíve never got past using ply. Itís very easy to correct any mistakes, and I usually make plenty of them.