HULL MATERIALS....3D Printing. Croatian Motion.

[Robert Grubisa]

materials shall not be: expanded, foamed, honeycombed"

Just to be a little academic (smile), this phrase must be understood to be talking about what the material *is*, not how it is processed. We are thinking that we ignore all matters about processing, that is, construction techniques, and we focus only upon material properties, so that is how this phrase must be interpreted.

If we do not ignore matters about processing, then this phrase can be interpreted to mean two things -- what the material is, and also how it may be processed. In this case, all my thought experiments fail, because they were exactly intended to take a material and expand, foam, and honeycomb it.

Lester,

Well, I suggested to make consensus about the meaning of the phrases used in the IOM Class Rules in order to better understand each others. So, my understanding is that it is prohibited to use foamed, expanded and honeycombed materials and to construct such features like honeycombed constructions. Voids, cavities etc as side effects of manufacturing imperfections should be tolerated just as they are -> imperfections.

This reminds me on my favourite interpretation (now Q&A) asked by GBR NCA regarding insects, bubbles, etc:

Question details:
Is workshop dust and other accidentally moulded in small bits like insects, air bubbles, bristles, hairs etc permitted in a moulded hull?

Reference to the old interpretation issued before year 2017
Interpretation 2003-IOM-4 on the IOM CR – edition 2002

Answer:

Having in mind IOM class rule D.2.1, we may presume that it is normal to have some imperfections in mouldings and it is not necessary to explicitly mention this in the class rules. Their presence should be noted by an official measurer if he feels it appropriate. However this would not normally prevent the Certification Authority from issuing a certificate. The presence of particles of foreign materials not permitted by the class rules but reported on a measurement form would not be a reason for the certification authority to decline to issue a certificate.
--------------------

All the best
Robert Grubiša
CRO 68

[Lester]

it is prohibited to use foamed, expanded and honeycombed materials and to construct such features like honeycombed constructions

Hi Robert

Sure, that is the current situation, I don't think there was any doubt. My understanding is that we are discussing a future situation, where some rule changes modify these prohibitions.

I thought you were suggesting that the rule changes should not deal with construction techniques and should only deal with materials and their properties. My point of view is that this is not possible. We are agreed, when we say, "D.2.1(b) [...] materials shall not be: expanded, foamed, honeycombed", we in fact are saying two things: (a) it is prohibited to use these materials, and (b) it is prohibited to modify materials to have such features. That is, we are dealing both with materials properties and with construction techniques in this rule. Perhaps I have not properly understood what you are suggesting.

But I think we can continue to discuss whether foamed, expanded and honeycombed materials are permitted for elastomers and thermoplastics, and we understand by this that it is also permitted to construct and use foamed, expanded and honeycombed elastomer and thermoplastic structures.

Just to move forward a little, I favour permitting honeycombed thermoplastics, but now think we need to add a rule which prohibits sandwich construction that uses foamed, expanded, or honeycombed elastomers or thermoplastics as the core.

This reminds me on my favourite interpretation asked by GBR NCA regarding insects, bubbles, etc.

Mine also!

[Robert Grubisa]

it is prohibited to use foamed, expanded and honeycombed materials and to construct such features like honeycombed constructions

Hi Robert

Sure, that is the current situation, I don't think there was any doubt. My understanding is that we are discussing a future situation, where some rule changes modify these prohibitions.

I thought you were suggesting that the rule changes should not deal with construction techniques and should only deal with materials and their properties. My point of view is that this is not possible. We are agreed, when we say, "D.2.1(b) [...] materials shall not be: expanded, foamed, honeycombed", we in fact are saying two things: (a) it is prohibited to use these materials, and (b) it is prohibited to modify materials to have such features. That is, we are dealing both with materials properties and with construction techniques in this rule. Perhaps I have not properly understood what you are suggesting.

But I think we can continue to discuss whether foamed, expanded and honeycombed materials are permitted for elastomers and thermoplastics, and we understand by this that it is also permitted to construct and use foamed, expanded and honeycombed elastomer and thermoplastic structures.

Just to move forward a little, I favour permitting honeycombed thermoplastics, but now think we need to add a rule which prohibits sandwich construction that uses foamed, expanded, or honeycombed elastomers or thermoplastics as the core.

This reminds me on my favourite interpretation asked by GBR NCA regarding insects, bubbles, etc.

Mine also!

Hi all,

I hope that native English speakers are understanding that language problem is existing in our communication, and that this may be the reason why other are not participating more actively.
It seems to me that discussion on this forum is becoming dialogue between Lester and me which is not the intention (at least mine).

Put aside pure hypothetical/academic/whatever high intellectual discussion, the actual wording of the IOM Class Rules and CRO proposal and let's agree which hull constructions we want to permit and then draft the appropriate wording. I will try to list them:

1) Wooden hulls made by planks on frame or in similar way. All types of woods are permitted. Clear or coloured resin of any type, paint, lacquer or similar products could be applied on one or both sides. Thickness of hull skin along the hull is unrestricted. Fillers based on wood, metal, thickened resin etc are permitted. Hull may contain GRP and metal parts as well as thermoplastic parts made by additive material technologies.

2) Wooden hulls (sandwich construction). All types of woods are permitted. Clear or coloured resin of any type, paint, lacquer or similar products could be applied on both sides with glass fibres/cloth (sandwich construction). Thickness of hull skin along the hull is unrestricted. Fillers based on wood, metal, thickened resin etc are permitted. Hull may contain GRP and metal parts as well as thermoplastic parts made by additive material technologies.

3) Glass reinforced plastic (GRP) hulls made using any type of resin and glass fibres (cloth, matt, strings, etc). Resin may be coloured, thickened and gel coat is assumed as a sort of resin. Fillers like glass micro balloons of any size, glass microspheres, glass bubbles, metal talcum and powder, thickening agent for resins, coloured pigments are permitted. Carbon fibre milled powder, or anything like that is prohibited. Hulls may be made in male and female moulds, using brush, spray, infusion, by using heat and force. Pre-preg material is allowed. Hull may contain any number of layers of glass fibres. Hull may contain wooden and metal parts as well as thermoplastic parts made by additive material technologies. Thickness of hull skin along the hull is unrestricted. It is not allowed to use honeycombed construction of any material as a core between two skins made of GRP.

4) Moulded thermoplastic hulls
I am not an expert here. Please provide data. I do know that It is not allowed to use honeycombed construction of any material as a core between two skins and that fibres, if used, better than glass fibres should be prohibited.

5) Hull made of thermoplastic materials using additive material manufacturing -> 3D printing. Hulls may contain wooden and metal parts as well as GRP parts. Filament used for melting in the 3D printer and cured making hull shape may be coloured and may contain glass fibres. It is not allowed to use any filament "better than glass fibres" in the filament. Thickness of hull skin along the hull is unrestricted. Hull could be reinforced by any resin and glass fibres. It is not allowed to use honeycombed construction of any material as a core between two skins made of thermoplastic materials by infill method or any other method(s). Web frames and bulkheads may be printed separately or as integral part of the skin.

6) Hull made of other materials using additive material manufacturing other than 3D printing.
I am not an expert here. Please provide data. I do know that It is not allowed to use honeycombed construction of any material as a core between two skins and that fibres, if used, better than glass fibres should be prohibited.

7) Other hull constructions which I am not aware or I missed to list here. Please list it here.

In all above mentioned construction foamed and expanded materials like polystyrene, polyurethane and similar is prohibited. Glues may be used in all above constructions. Human hairs, insects, microbes and alike in the hulls are tolerated. Imperfections in any of the above constructions like air bubbles/voids/etc are tolerated.
----------------

At the end, the intention of the CRO proposal was to cover and permit above mentioned.

Your inputs/comment/agreement on above list are welcomed.

All the best
Robert Grubiša
CRO 68

[Mr Graham Elliott]

Everyone, do not be put off by Roberts and Lesters detailed discussion at the moment, they are both extremely educated on the IOM rules and the pitfalls of such possible changes as we have two subjects that are very closely linked, they will also be discussing these subjects with fellow experts that are not posting and gauging these thoughts aswell.

Materials allowed.

Building techniques.

When you break down there posts and take time to analyse these posts, they all make perfect sense, even to me.

[Antonio Campos]

Hi, Robert:

"Regarding your item 1), I don't see how servo/winch trays or similar hull structural items with openings are not in compliance with current IOM Class Rules and CRO proposal. Opening for servo or winch is certainly not falling under "expanded, foamed, honeycombed" as stated in the current IOM Class Rules and CRO proposal."

I didn't mean the openings (holes) for servos in servo trays, but hollow trays, bars, tubes or any reinforcement, that are today allowed as long as they are made with permitted materials. I have checked my Crocanto and Britpop and there are hollow fiberglass reinforcements in the foresail attachement point, for instance.

"I strongly believe that we should not list any construction techniques."
"It is not allowed to use honeycombed construction of any material as a core between two skins made of thermoplastic materials by infill method or any other method(s)"

I would agree that construction techniques should not be listed, but there is a contradiction in excluding infill, which is a construction technique that is intrinsecal to 3D printing. Furthermore, if I am correct, you are the only one in this discussion that proposes to forbid infill, all the other opinions where in favor of allowing infill or didn't express any opinion about infill.

I think Lester provided a brilliant document to demonstrate that thermoplastics are strongly handicapped compared with other materials in weight/modulus. There is no need to change the rules, as written today, that allow in principle infills, as long as they are not honeycombed. In that sense I think the last interpretation that prescribed "no infill allowed", guessing that all infills are honeycomb shaped (which is not correct as per the images I posted) goes beyond what an interpretation can do and rewrites the rules about thermoplastics, which an interpretation cannot do. I think therefore that this interpretation should be retired and the issue about infills should be solved by this rule modification we are discussing.

Also, as I have 3d printed many parts, I do not see how you could have two skins with no infill in the hull. That cannot work mechanically, and if this is written this way in fact you are forcing to have a single, solid layer (which is maybe your intention with this paragraph?).

Finally, as already said, it is impossible to check if infills are used without destroying the hull, which is a very important practical consideration.

I certainly would vote and recommend others to vote that infills are not forbidden, so as not to add more handicaps to 3d printing.


"Other hull constructions which I am not aware or I missed to list here. Please list it here."
I am not sure what is the intention of this request you make, as the rules today allow other constructions techniques or combinations of materials which maybe are not used today, but could be used. For example, you can imagine aluminum structure with beams and ribs, and wood strips over them, or an aluminium foil laid over parts of the hull. You could construc hulls with aluminium, hammering a foil over a mould, although this is not used practically. Would you like to restrict the possibilities to keep only what is actually in use?

Hope this helps, regards,

Antonio

[Lester]

I do not see how you could have two skins with no infill in the hull. [...] in fact [...] a single, solid layer (which is maybe your intention with this paragraph?)"

Hi Antonio

Yes, I think two skins with nothing between them is intended to be the same as a single solid layer.

[Torsten Kass]

It doesn't matter how many perimeters are printed. I also build a laminated fuselage with several layers of glass. Perimeters are not an infill, but the outer skin of the parts. Infill fills the area between the perimeters and could be printed with less than 100 percent ... which I personally would not allow. It is just not necessary! If infill is used, the parts are drawn oversized. It is better to use a bead or other formative elements to get the necessary stability. That is the decisive advantage of printing - we are relatively free in terms of design, as we do not have to worry about possible problems with laminating.

[Robert Grubisa]

Hi, Robert:

"Regarding your item 1), I don't see how servo/winch trays or similar hull structural items with openings are not in compliance with current IOM Class Rules and CRO proposal. Opening for servo or winch is certainly not falling under "expanded, foamed, honeycombed" as stated in the current IOM Class Rules and CRO proposal."

I didn't mean the openings (holes) for servos in servo trays, but hollow trays, bars, tubes or any reinforcement, that are today allowed as long as they are made with permitted materials. I have checked my Crocanto and Britpop and there are hollow fiberglass reinforcements in the foresail attachement point, for instance.

RG: Ok. I now understand that what you mean but I think that a tube (circular or rectangular) could not classify as expanded, foam or honeycombed parts.


"I strongly believe that we should not list any construction techniques."
"It is not allowed to use honeycombed construction of any material as a core between two skins made of thermoplastic materials by infill method or any other method(s)"

I would agree that construction techniques should not be listed, but there is a contradiction in excluding infill, which is a construction technique that is intrinsecal to 3D printing. Furthermore, if I am correct, you are the only one in this discussion that proposes to forbid infill, all the other opinions where in favor of allowing infill or didn't express any opinion about infill.

RG: I am not a 3D printing expert but what I can see on the Internet, it is possible to 3D print the boat without infill so the statement that 3D printing is not possible with infill is not true. As I explained in earlier posts, in my opinion, 3D printing is construction technique, while honeycombed construction is just that -> construction which may be produced by various construction techniques. You will easily find out that I am not "the only one proposing to forbid infill"...

I think Lester provided a brilliant document to demonstrate that thermoplastics are strongly handicapped compared with other materials in weight/modulus. There is no need to change the rules, as written today, that allow in principle infills, as long as they are not honeycombed. In that sense I think the last interpretation that prescribed "no infill allowed", guessing that all infills are honeycomb shaped (which is not correct as per the images I posted) goes beyond what an interpretation can do and rewrites the rules about thermoplastics, which an interpretation cannot do. I think therefore that this interpretation should be retired and the issue about infills should be solved by this rule modification we are discussing.

RG: Well, if you don't need glass fibres in the filament which you are using for 3D printing, then the class rule change is not necessary... But the interpretation stated that it is not allowed so CRO proposal propose to allow it. I believe that the infill is not allowed according to the current wording.

Also, as I have 3d printed many parts, I do not see how you could have two skins with no infill in the hull. That cannot work mechanically, and if this is written this way in fact you are forcing to have a single, solid layer (which is maybe your intention with this paragraph?).

RG: True. The CRO proposal, as well as current class rules, is allowing "solid layer" of hull skin, the same for all construction techniques used.

Finally, as already said, it is impossible to check if infills are used without destroying the hull, which is a very important practical consideration.

RG: True. Building declaration is needed. It is needed today for the GRP hulls, as well. Not the best solution, but I think we may live with it.

I certainly would vote and recommend others to vote that infills are not forbidden, so as not to add more handicaps to 3d printing.

RG: I understand your intention, an NCA needs to propose such improved wording and at the end voting will be needed within the IOM ICA on the next AGM.


"Other hull constructions which I am not aware or I missed to list here. Please list it here."
I am not sure what is the intention of this request you make, as the rules today allow other constructions techniques or combinations of materials which maybe are not used today, but could be used. For example, you can imagine aluminum structure with beams and ribs, and wood strips over them, or an aluminium foil laid over parts of the hull. You could construc hulls with aluminium, hammering a foil over a mould, although this is not used practically. Would you like to restrict the possibilities to keep only what is actually in use?

RG: Antonio, I tried to list possible, feasible, useful constructions which I believe that are IOMs as we want to sail which will not make existing fleet obsolete in any way having in mind all possible new additive material construction techniques (NOT only 3D printing).

I am curious is it possible to use new technologies for IOM hulls building such as making hulls with ELEGOO Mars machine and similar devices/technologies.

Why you and Lester are fascinated with metal hammering over mould, precise putting of parts of woods between metal parts, I don't know I am joking, I really appreciate your valid input and the discussion!

All the best

Robert Grubiša
CRO 68

Hope this helps, regards,

Antonio

[Robert Grubisa]

Hi all,

I just received this photo from a friend of mine from one of the Facebook groups dealing with the 3D printing of radio sailing boats. Maybe some of them know the source. Sorry, I am not on Facebook

https://photos.app.goo.gl/f8J9wECCrPzEacqr7

I am kindly ask the 3D printing guys to let us know whether such constructions could help them to produce better hulls. The construction shown on the upper part of the photo is permitted by the current wording of the Class Rules. Shell stiffeners (ribs, frames, web frames, bulkheads, stringers) are common on the wooden boats and on some GRP boats. I am not sure about the compliance of the construction on the lower part of the photo regarding the "honeycombed construction clause".

Since the honeycombed core is not permitted in the GRP hulls and I believe that it should be prohibited regardless of the construction techniques, maybe shown constructions should be allowed for all construction techniques provided that they are of some benefit for 3D printed boats.

All the best.

Robert Grubiša
CRO 68

[Hiljoball]

Hi Robert,

My impression of that picture is that the 'honeycomb' is not a honeycomb, but an hexagonal pattern surface texture, and serves little difference than the picture with strips.

From Wikipedia, (and I underlined the key piece)
Honeycomb structures are natural or man-made structures that have the geometry of a honeycomb to allow the minimization of the amount of used material to reach minimal weight and minimal material cost. The geometry of honeycomb structures can vary widely but the common feature of all such structures is an array of hollow cells formed between thin vertical walls. The cells are often columnar and hexagonal in shape. A honeycomb shaped structure provides a material with minimal density and relative high out-of-plane compression properties and out-of-plane shear properties.[1]

So to be a honeycomb, requires two skins separated by an internal web.

This is a honeycomb structure https://tinyurl.com/y3j5o5u2

John

[Lester]

I think it would be useful to bring us back to the two key questions of this thread. One is whether to permit fibre reinforcement in thermoplastic, the other is whether to permit cellular structures in thermoplastics.

I deliberately do not mention construction techniques, 3D printing, honeycombing, or infill, I think we can give some answers to these two questions without trying to explain to each other what honeycombing really means, or what 3D printing really involves, or how you can or cannot 3D print without infill, or how you can have unrestricted construction techniques without any danger of changing the nature of the class....

I think it is better to talk here about "cellular structures". We may define a "cellular structure" as a number of closed cavities. We consider a cavity to comprise some walls, and a top and a bottom which we call skins that close the cavity. If we have some walls and just one skin, the cavity is not closed and it is technically a shell. In a shell, the walls simply strengthen the single skin. When a second skin closes the cavity, we have a structure with much more interesting properties, because the walls now allow the skins to carry far more stress than otherwise, and in different directions, usually one skin in tension and the other skin in compression. The walls between the two skins allow lighter and thicker structures with much better stiffness and strength than we would see if the walls were merely strengthening. The walls also provide much improved resilience to impacts and some degree of fail-safe -- one skin may fail yet the structure may still retain overall integrity.

To anticipate, my guess is we are mostly happy with the idea that thermoplastic may have added materials whose modulus does not exceed that of glass fibre, let's put a number to that, and say not larger than E = 80 GPa.

But the real question remains unclear. I'd like to invite you to reply with a simple Yes or No, and if you really must, a Maybe (!):

Shall cellular structures be permitted in a hull made from thermoplastic?

Many thanks!

[Robert Grubisa]

But the real question remains unclear. I'd like to invite you to reply with a simple Yes or No, and if you really must, a Maybe (!):

Shall cellular structures be permitted in a hull made from thermoplastic?

Many thanks!

No.

Robert Grubiša
CRO 68

[Zvonko]

But the real question remains unclear. I'd like to invite you to reply with a simple Yes or No, and if you really must, a Maybe (!):

Shall cellular structures be permitted in a hull made from thermoplastic?

Many thanks!

No

Zvonko Jelacic CRO 35

[Torsten Kass]

No

[GAVIN WATSON]

But the real question remains unclear. I'd like to invite you to reply with a simple Yes or No, and if you really must, a Maybe (!):

Shall cellular structures be permitted in a hull made from thermoplastic?

Many thanks!

NO..............................
Gavin Watson
GBR 44

[Zoran]

No.

Zoran Grubisa - CRO 69

[Funci]

No

[Mr Graham Elliott]

NO.......

GBR 9

[Gabriel Le Duc]

NO

[Bruce Andersen]

no

[Antonio Campos]

Yes.

[Antonio Campos]

I would like to answer two questions asked by Robert:

I am curious is it possible to use new technologies for IOM hulls building such as making hulls with ELEGOO Mars machine and similar devices/technologies.

Yes, but in a resin 3d printer bigger than the Elegoo Mars, like the Elegoo Saturn. Here are some photos of a tests I made with an IOM 3d file. As you will see I an trying to print the fittings as part of an integral hull, instead of gluing them later.






I am kindly ask the 3D printing guys to let us know whether such constructions could help them to produce better hulls

I think the two structures in the image you link are pieces printed with only "infill" and 0 mm thick walls (in the image you can see the base, which has one or more solid layers and a number of layers of the part made only of infill, no walls, probably the top of the part is not represented, or it has been defined also as 0 mm). You can program the printer to build that way by specifying 0 mm walls and a percentage of "infill", say 20%. In this case"infill" may not be the right word (because it would not be enclosed), but that is how the the software that creates the file for the printer ( the slicing program) would call it, as that is the role that it plays in normal parts with walls.

At this point of time I cannot figure how you could use this kind of structure practically. With some imagination, maybe it could be used to reinforce internally the hull without being enclosed. You would be producing a geodesic structure inside the hull, I suppose, and would not be forbidden by the prohibition of infill, if that is the way that the rule goes. Obviously geodesic structures are not forbidden now, or ribs, stingers, etc.
3d printed aeroplanes tend to have some kind of geodesic structure these days, so it would be natural to have it in hulls too, but my first approach would be to design them in the CAD program, no to program them in the slicer software.

[Robert Grubisa]

I would like to answer two questions asked by Robert:

Hi Antonio,

Thanks for providing details and photos!

I don't know whether the proper wording for making products using "Elegoo printers" is "3D printing" or not However, construction techniques are unrestricted, some sort of resin is used in the process, so hulls made in that way seems permitted.

Lester asked for opinions regarding permitting cellular structures in a hull made from thermoplastic. It is resin which is used in "Elegoo printers" so cellular structures are prohibited in hulls made in that way....

You already know my views regarding cellular structures in IOM hulls

Robert Grubiša
CRO 68

[Olivier Cohen]

Sorry I have not read that forum for 2 weeks, and I was 3 pages behind !

Thanks Lester and Robert for giving life to this forum !

I have now read it all, and if I am not wrong, we all agree on one point :
- Not plain structures shouldn't be allowed. So this is already in rules. So no change needed.

One point to be corrected for 3D printing is the result of interpretation not allowing filaments reinforced with glass fibre. Reading Torsten comments, it is mandatory to avoid brittle hulls after some time.

Interpretation was based on rules, especially on the fact that on D2.1/8 glass fibre was not considered as a permitted material.

So my proposal for a new wording would be to change D2.1/(8) Thermoplastic, which may be moulded, containing only permitted materials and glass fiber reinforcement.

Robert or Lester would certainly find a better wording, but I believe this would help building competitive hulls with 3D printing.

Your views ?

[Lester]

[...] we all agree

Hi Olivier

Not too sure about that (smile). Of course, the decision makers will need to consider a wider range of opinion than is represented on the forum, and will need to understand the reasons for the opinions expressed. An executive summary of a stakeholder analysis, as attached.

Stakeholders
Who are the people or organisations which have an interest in, or are affected by, proposals to change the IOM? A partial list includes:
IRSA, IOMICA, National IOM Class Associations.
Potential owners of IOMs, Existing front-of-fleet owners of IOMs, Existing back-of-fleet owners of IOMs.
Existing commercial builders of IOMs.
Promoters/managers/administrators of racing events for IOMs, Promoters/managers of individual IOM competitors, Promoters/managers/administrators of national IOM teams

Stakeholder interests
Questions to ask about a stakeholder to understand their interests and how they might be affected by IOM changes.
Do they have a financial interest? Do they have an emotional interest? Do they have a fiduciary duty? What motivates them? Do they have religious or political interests or motivations?

Stakeholder risk perception
Given the various interests of a stakeholder, what are the risks that may concern them? Note there is no discussion whether a risk is real or apparent. In a stakeholder analysis it is only necessary to determine stakeholder perception. Some risks include:
Make or lose money; gain or lose value of current possessions; gain or lose status, reputation, esteem, credibility, honour.

Stakeholder power
What is the power and influence of relevant stakeholders, that is, how are decisions made?
Do they have a vote? Do they exercise their vote? Is their vote constrained by regulation or convention, or by leverage and/or influence from advocates?
Do they contribute to voting? Do they exercise their ability to contribute to voting? Is their contribution by regulation or convention, or by leverage and/or influence through their advocacy?

Stakeholder situation
Now we begin the analysis of what can be done to bring stakeholders towards agreement or support.
Do they have accurate information?
Do they have informed understanding?

And now over to those who wish to bring about change.

[Art Prufer]

Despite coming in late, I am throwing my hat in the ring to further this discussion.

Firstly I would like to applaud this detailed technical discussion on this forum. I think this is what was missing from the proposed motions.
I believe a thorough discussion and understanding of any proposed changes on a public forum, well in advance of creating a motion, is the first step to a successful change.

As we know the Croation motion was not confined to only 3D printing but also included changes for all construction materials.
So based on this there are 2 distinct changes to discuss.

1) Existing construction materials - are changes warranted and if so, what are they?
2) 3D Printing - rules must be updated to include and provide clarity for this technology

Furthermore the discussions must include both materials and construction techniques.
In many instances, one cannot be separated from the other.

I quote the following from a discussion on page 2

LG: In some sense, all materials have properties given to them by construction and manufacturing techniques, and the difference is only whether we purchased them already modified and called them "materials", or used our own techniques at home to modify them.

RG: Agree. Why we should be worried about that? Maybe I am missing something important here.

An example would be the interpretation for permitted fillers:

Questions
1. HULL D.2.1 MATERIALS: Is it permitted to use fillers that contain micro balloons?
2. HULL D.2.1 MATERIALS: Is it permitted to use fillers that contain bulking materials such as slate, talc
etc?

4. HULL D.2.1(b) (1), and (c) MATERIALS: Is it permitted to use epoxy gel coats that contain micro
balloons?

Decisions:
Items 1, 2 and 4:
Answers:
YES - in adhesives, NO - in glass reinforced plastic.
Discussion:
Fillers are permitted provided they are constituent parts of permitted materials listed in D.2.1. Fillers
supplied as parts of a resin for laminating or/and gel coat are constituent parts of laminating resin and/or
gel coat which are explicitly mentioned as parts of the glass fibre reinforced plastic. Another filler added
by the builder to laminating resin and/or gel coat is not a constituent part of laminating resin and/or gel
coat.
Fillers are a normal part of adhesives and therefore permitted.

As a material, the use of "off-the-shelf" adhesives and fillers are permitted
As a construction technique, adding your own filler material to resin is prohibited.
So is a filler a material or construction method?

To further confuse the matter the current rule D.2.1(a)(3) says:

(3) Resin, which may be coloured and/or reinforced with glass fibres,

So if one makes their own filler using ground or shredded glass fibres mixed with resin, is this permitted or prohibited?
I certainly think there can be more clarity brought to the existing rules and interpretations.

In the case of 3D printing I would vote "No" to honeycomb or infill, based on Torsten's assertions around hull strength and durability.

There is one more 3D printing technology which as not been mentioned and that is LW-PLA which uses PLA which expands when heated, thereby giving a thicker wall material (hence stiffer) which is the same weight as standard PLA. Torsten has built several (non-IOM) boats from this material and can provide more feedback on the suitability & durability for 3D printing model sailboats.

My suggestion is to draft up 2 separate motions once we have come to a consensus for the wording:
- One to address any shortcomings in the existing D2.1 Materials section including any previous interpretations.
- Two to specifically address permitted 3D printing materials and techniques.
Keeping these as separate motions means one is not tied to the other if one is not approved.

[Gabriel Le Duc]

Hello everyone,

I would like to make a comment about the LW-PLA (Light weight PLA) that Art Prufer has talked about and that I think Torsten has also named and uses in other larger RC boats.

To my understanding it is a PLA that foams transforming into a rigid foam allowing for equal weight to have a thicker wall and the consequent rigidity that goes with that.
According to current rules it is prohibited and I think that is why Torsten did not do any IOM on this material.

Now I wonder ... if we know that the construction of a hull with thermoplastic and 3D FDM printing technology without any type of internal structure in the form of honeycomb or other, results in a boat that is a lot equal to weight. weaker than a fiber / epoxy one, maybe it would be interesting to allow the LW-PLA, which would allow us to improve the rigidity of the boat and with that maybe its durability, bringing us a little closer to the performance of a classic construction boat.
I believe that even so it would never be superior to a fiber / epoxy boat, but at least it would allow us to get a little closer to the performance of these constructions.

As a designer and builder, I see the LW-PLA as something positive for this new construction technique that is 3D printing, which would favor the entry into our sport for many young or not so young people who are already familiar with these new technologies. .

Ahhh ... I forgot, I have also done tests with the LW-PLA and I really liked it a lot as material to make the helmets of my IOM, but finally I did not make any whole for the fear of being outside the rules, I preferred not take a chance, but maybe one day I will make a complete boat out of this material to compare in life size the performance of the PLA + I currently use with the LW-PLA.

[Nigel davies]

After reading the many postings, may I add my experience of 3D printing a hull for competitive IOM racing. Two years ago I made in little more than 10 days a very good looking and competitive IOM which following its success was repeated by a fellow club member. After approximately 6 months of use both boats started to leak and because of the extreme stresses of shrouds, fin and rudder started to show signs of delamination of the adjacent printed parts. Neither boat was able to be sailed after 12 months. We have however wrapped both boats with brown parcel tape and taken fibre glass hulls from the useless 3D hulls. These hulls which maybe a mm or so wider than designed have proven to be very strong and equally competitive. My conclusion has therefore been that 3D is a brilliant tool for producing plugs for moulding fibre glass hulls, or maybe occasional recreational sailing, but not for the serious racer.

[Olivier Cohen]

Hello Nigel, which material have you used to get this result ?

[Nigel davies]

I used Esun PLA +