Layup schedule help

A 15.5 oz dbm?

 

Yes. My build is on another site. I am building in a full female; developable panel, hard chine cat.

I am using much heavier no mat cloth 22oz triax and epoxy and have been told if I post cure and fair that print through will be minimized. It is also minimized by using a barrier coat or high build. And further by avoiding dark paints.

I don't know if tansl (Ignacio) has had experience with print through on an epoxy post cured no gel coat boat. But my supplier seem to think I'll be okay. (Systems 3 via a reseller, but in direct consult with S3.

I would do exactly what you are doing. Use epoxy and no mat glass. Phooey on a veil coat.

But make sure you resins are right for the job.

 

Tansl I believe the 1715 is 17oz dbm with a 1.5 oz mat? I don't find that anywhere I do see the 1708 which is the same but with an 8oz mat backing

Interesting Fallguy the second layup I have is 24oz woven roving which uses several layers of mat. How thick of a core are you using?

 

I thought 1715 meant 17oz glass with 1.5oz mat. So, he could just use a 17 or 18 oz stitched db cloth right?

I never thought the mat was part of the total weight. Was I wrong? And didn't the mat mean per sqft?

My core is 12mm Gurit Corecell M. I will try to get you a link to my build blog, but would rather not publish the blog here; so email?

I would do your build with 18oz stitched db cloth. Tansl can advise if I am right or not- for sure.

Don't like the roving idea much. And my glass would be overkill for yours I think. Again, tansl will tell you best despite the 15.5 oz? I have no experience with roving, but it seems bulky.

 

@fallguy , I tried to give an answer, which I thought logical, to the existence of an external layer of MAT, a layer that we already know that from the structural point of view is not necessary. But whatever my opinion, the opinion of a manufacturer / distributor of fibers will always be more authoritative than mine.

@Scuff , I have studied a panel of 350 x 500 mm and I have applied the following schedule (in metric units):
WR 500 + 16 mm PVC (36 kg / m3) + WR 500
That combination could replace another similar to the one originally had your boat:
MAT 450 + 500RV / 300MAT + 16 mm PVC + 500RV / 300MAT
(I have searched for the existing mat and fabrics in my country, which I think are more similar to those used by your designer)

 

Scuff-if you want a tougher outer layer; you could put a light cloth, say 2-6 oz woven on the outsides of the outer hulls for dock dings.

 

Tansl, what about the 17 oz dbm schedule? That is the one I wanted to evaluate and remove the mat if possible

 

What I wanted to show you is that in the combination that I have prepared, that I have tried to be similar to yours, for the boat I have studied as an example, the mat can be eliminated.
Apparently, what you want could be done. But it would be very imprudent on my part, with the data I know, to tell you to do it. Consult the designer who knows why has placed the initial schedule and what he wanted to achieve with it.
I'm sorry, I do not dare to go further.

 

Scuff, there is no definitive answer. If you want to change the original designer layup schedule, you have to run the stress analysis. Very briefly this is what the layers do;
1. Outer layer mat- This resin rich layer in conjuction with the gel coat acts a water barrier. It also acts as a cosmetic/aesthetic layer to prevent print thru. It can be ommited if;
a. It is less than 300 grams/m2 as it is not structural (including the gel coat) and therefore not included in the stress analysis.
b. If the boat is sans gel coat, to be primered and painted.
More than 300 gr/m2 (>0.7 mm), it becomes structural and becomes part of the stress analysis, that of being the first outermost layer.
2. The second layer DBM being at +45 -45, I have doubt. If loses 88- 90% of its strength once the axis is rotated (see ISO calculation). It is possible the loss of strength was factored in the calculations, otherwise this is a "hot spot" as the outermost layer receives the greatest stress. The same goes if the outerlayer Mat is greater than 0.7 mm.
3. The mat underneath the DBM serves as an interface of shear stress between the outer layer and foam core. No matter what they say about epoxy not needing a mat interface, the shear is great having only a 16mm core. This is critical as the shear transition from the outer layer to the core may exceed that of the resin properties (epoxy). You can eliminate it only if the core is thick as the stresses are greatly reduced.
4. Core sizing takes all of the shear.
5. Balanced laminate is important for thin laminate single skin. For thick laminate, the outer skin is made thicker than the inner as it is in compression. Making it thicker or (higher modulus) compensates for the loss of mechanical strength in compression properties. This is common practice for panels.

All of this can be analyzed using ISO tabulation method, including the loss of strength in the +45-45 orientation. ISO tabulation includes the shear strength analysis in the laminate interface.

I believe Tansl has the software (or ISO tabulation) and this can be analyzed.

 

#2 above and the op's post #7 are not in agreement. OP said designer cited single layer, so he'd lay the 45s on the diagonal to the WL.
Or am I confused?

 

A DB or double bias is a +45-45 single layer. It is a bias cut. A BD or bi dircctional 0-90 is also a single layer. A BD can also be a WR, cut at an angle of 45 and laid down at 45 orientation is also a +45-45. Only a Uni or UD can be laid down at 0, 45, or 90 singularly.

 

Oh, sorry, when you referred to a second layer; I assumed you meant a different fabric, but you mean within the original schedule. My mistake. I thought it was already determined the mat was not needed.

 

Unless some expert says otherwise, in my opinion, the first layer, from the structural point of view, in that total thickness of the laminate we are talking about, could be eliminated. Regarding the other mats that are combined with fabrics, I have not dared to say anything.

 

Rx, the schedule I have shows the dbm at 0 degrees .. 0 is the waterline? Since the dbm has no 0 degree are you saying the hotspot would be due to no reinforcement in the 0 axis. The 1.5 oz mat used as the outer layer is listed as being .051" thick .. wouldn't that be more or less a standard thickness for a single layer of the 1.5 oz mat?

Would a composites supplier be able to assist me with substitution if I'm purchasing from them?

 

Okay, I'm confused by that.

But I have a question for Tansl and RX

So, correct me if I am wrong, but the 1715 spec would result in a fabric that is roughly 30 ounce fabric, right? I mean it'd be like 17oz per sqyd and another 13 oz or so for the mat. Even more for the gelcoat.

Couldn't he just build the boat in a better laminate like a 900g triax and call it a better boat and lighter with less abrasion resistance than a gelcoat boat, but more abrasion resistance than the 17oz? I realize there is no factual calculation to support my question, but please remember, it is a question.