IOMICA Forum

I'm am new to the IOM and plan to build a one-off of a IOM that I have designed. I was looking for information on the best materials to use for the construction of the hull. I was considering glass over balsa because the balsa is easy to form and develop the final shape, and the glass would give me the hardness for the bumper cars out there. But in reading the class rules I'm not sure this is legal because once the exterior is painted the glass would not be visible for inspection. Can anyone tell me what are proven or successful methods of construction, which will maintain minimum overall weight. I only have production boats made from molded fiberglass in the area, so I don't have any other examples to look at. I would appreciate any insight you all might have.
Thank you.

Hi and welcome to the class.

Glass over balsa is allowed. I have built several this way. The rule about being able to inspect the layup applies to 'all-glass' hulls.

John

John - Thanks for the information regarding the hull. Could you tell me if you used balsa for the deck too, or did you use something heavier.

I use thin plywood .079mm (1/32nd) and seal it (both sides) with a thinned coat of clear epoxy resin.

John

is it allowed to use spectra or dyneema cloth in place of fiberglass cloth?
edgardo

Hi Edgardo

The short answer is: No

Only wood and/or fiberglass reinforced plastic and/or plastic are allowed. And for fiberglass it's only pure fiberglass that's allowed.
So, for example Texalium is not allowed, because it's fiberglass coatted with alluminium.

Best regards

I think that the issue of spectra or dyneema is a bit more complex than just a 'no'.

According to Wikipedia, they are brand names from two manufacturers for the same thing.

Also from Wikipedia, they are thermoplastics (long chain polymers).

The closest document that I could find was the rules interpretation 4-2003 but that does not seem to address this flavour of the issue.

John

John - Can you tell me more about your method of building the hull and deck.
Also, do you build the keel foil and rudder foil, or do you buy those from somewhere.
Thanks

I found the AMYA US1M construction guide the most useful.

http://www.theamya.org/boats/us1m/us1mcons.php

While I have made a fin out of a balsa, ply sandwich covered in glass, the CF fins are much better. Unless you get into vacuum bagging, it is easier to buy the CF foils.

John

Hi John

Some times one has to read the rules more careful
And you are right John, it seems that this question is more complex, than just a no.

So if it's legal or not, I can't say.

Best regards

The interpretation of the GRP only rule has been pretty strict. Texalium was banned because it's not (just) fiberglass despite strong support to the contrary.

That probably sets a precedent to continue to ban anything other than good old fashion fiberglass for hull construction, despite the eloquence of your argument in support of spectra.

I can't speak for VC Tech, but I imagine that liberalizing the hull construction scantlings after the Texalium affair would be a bit of a battle.

How to enforce it is another question. Texalium looks different than fiberglass. Spectra looks pretty much the same when covered with resin.

Hi Bruce,

I am not arguing for or against spectra. The hull materials list allows thermoplastic. I did a google search and found a reference that Spectra may be a thermoplastic - I don't know, I'm not a chemical engineer. Are there different kinds of thermoplastic? Are only some allowed? Is thermoplastic allowed or not allowed if in cloth form and combined with a resin layup?

It sounds like we need another interpretation from the tech committee.

John

Having been there before, please don't go down the road of "Isn't specta really a thermoplastic" or "Isn't spectra really fiberglass". The IOM class rules were meant to promote inexpensive construction methods and basically limits hulls to be made from fiberglass and/or wood. (Thermoplastic was put in the rule when it was hoped that someone would mass produce vacu-formed hulls.)

Unfortunately, when you try to write rules, the language is never perfect. Yes, there is an argument to be made that what is really "fiberglass" is unclear. I'm sure if people are so inclined there can be numerous posts here making more and more esoteric arguments in support of one position or another. (Frankly, sometimes I think with enough effort someone can make a case that day is night or vice versa.) However, for the sake of the new person here, and to save us all a lot of effort, let's just say for now that practically and simply, no--spectra cloth is not fiberglass or thermoplastic and not permitted in IOM hull construction.

Right on Roy!!

If you go into a store to buy fiberglass I am pretty sure the conversation won't turn to whether you should use Spectra instead. It is not specifically authorised so until there is some request to visit it formally it is out, I would say.

The better idea is likely to revisit the possibility of vacuum formed plastic hulls coming into existence and reverse that addition.

Besides, fish can probably smell Spectra and will start biting your boat.

Regarding Dyneema & Spectra vs. fiberglass, Dyneema & Spectra are fibers made of ultra high molecular weight polyethylene and fiberglass is made of silica. They are distinctively different materials and most importantly have different mechanical properties, with Dyneema/Spectra being much stronger and lighter. They are sort of in between fiberglass and carbon fiber, being even stronger than aramid (Kevlar) fibers.

which is cheaper per square meter? fiberglass, carbon or spectra/dyneema?
edgardo

fiberglass is by far the less expensive material