glassing coves fillets etc

Topics pertaining to fibre glassing, finishing issues, concerns and tips, epoxies and epoxy problems/resolves
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DungBeetle
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Joined: Sun Sep 26, 2010 3:46 am
Location: Toowoomba

glassing coves fillets etc

Post by DungBeetle » Sun Sep 26, 2010 3:49 am

how many layers and what width/grams of tape do different people use on their main bulkheads? ie mast, transom

and on normal bulkheads?





onya,

mal





ps. hello all. lurking here for years. finally surfaced.

Jim
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Joined: Fri May 19, 2006 8:25 am
Location: Cairns

glassing coves fillets etc

Post by Jim » Sun Sep 26, 2010 4:30 am

What are you building, as the answers will vary.

Jim.

DungBeetle
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Joined: Sun Sep 26, 2010 3:46 am
Location: Toowoomba

glassing coves fillets etc

Post by DungBeetle » Sun Sep 26, 2010 4:42 am

i'm building my own, so i'm looking for all the varied answers,



m.e.

mahnamahna
Posts: 580
Joined: Wed Aug 02, 2006 4:48 pm
Location: Gosford NSW

glassing coves fillets etc

Post by mahnamahna » Sun Sep 26, 2010 7:08 am

Schionning specify 2 layers of 457gm double bias for their duflex balsa core boats, 150mm and 100mm, but there is debate over which should be laid first, schionning say wide tape first then thinner tape but I have met 3 different professioanl shipwrights that all claim the thin tape should be first then the wider tape over it.

Trev
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Location: Moruya NSW

glassing coves fillets etc

Post by Trev » Sun Sep 26, 2010 10:09 pm

I was shown the thin tape 1st and the wider one on top? I think the theory is that this way both tapes have contact with the surfaces being taped?

Trev

teamROAM
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Location: Beaumaris, Tasmania

glassing coves fillets etc

Post by teamROAM » Mon Sep 27, 2010 12:09 am

From a purely structural point of view the widest tape should go on top. Reasoning behind the widest tape first as it was explained to me was so if during sanding the builder got a bit excited and over sanded the most critical one being the widest would not be the first damaged…



I’m sure if it made a big difference structurally then the engineers would not allow the plans to be drawn thinner tape on top.

mahnamahna
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Location: Gosford NSW

glassing coves fillets etc

Post by mahnamahna » Mon Sep 27, 2010 9:15 pm

teamROAM wrote:From a purely structural point of view the widest tape should go on top. Reasoning behind the widest tape first as it was explained to me was so if during sanding the builder got a bit excited and over sanded the most critical one being the widest would not be the first damaged…

I’m sure if it made a big difference structurally then the engineers would not allow the plans to be drawn thinner tape on top.


This was also how Schionning explain it saying that it is very easy to sand through the ridge created by the smaller tape under the wider tape and therefore more likely that a stronger bond will result in amateur builds if they stack the wider one first. Also there is a much greater chance of getting air bubbles under the wider tape created by the edge of the narrow tape below it, also resulting in a weakening.



However perhaps there is also a second structural reason. By having a stepped effect loads are dissipated out through the layers of glass. There are many instances on my build such as the uni stacks each side of bulkheads (that are stepped 500mm apart on the ends) and the mast step on my cabin sole and the 4 layers of glass attaching the mast post to the decks are stagger stepped with smaller glass above bigger glass, so as to transmit the loads out to the edges of the pancake.



Perhaps having the smaller layers under larger layers does not have the same dissipating effect and ultimately puts more load on the point in the middle so effectively whilst it seems having both tapes in contact with substrate maybe this is not as structurally effective?



Any engineers wanna have a run at this one?

44c
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glassing coves fillets etc

Post by 44c » Mon Sep 27, 2010 10:48 pm

Bob Oram uses 750 gsm weft triaxial tapes. From an engineering standpoint this is superior to using 2 layers of 440 gsm double bias, since weft triax has a third of it's fibres oriented at 90 degrees to the join.

Trev
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Joined: Thu Jan 15, 2009 2:56 am
Location: Moruya NSW

glassing coves fillets etc

Post by Trev » Mon Sep 27, 2010 10:56 pm

Remember it's not the size that counts, it's how well its used :D

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