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Old 04-03-2021, 13:04   #76
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Re: How many layers fiberglass on new deck

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Originally Posted by Scubaseas View Post
With all due respect Sir, Gerr's book is exactly what the OP should be reading. It would correctly address all his questions and the discussions that have followed from that.

You have someone advising using pure uni or biax which is not a good idea as it tends to crack up.

The OP asked"

Gerr's Book "The elements of Boat Strength for Builders, Designers and Owners" exactly answers all of these questions.
OP is talking deck patches for cryin' out loud. It ain't rocket surgery.
No finite element analysis required.
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Old 04-03-2021, 13:18   #77
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Re: How many layers fiberglass on new deck

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Originally Posted by boatpoker View Post
and completely irrelevant to the OP's query.
I think he was asking about thickness. What does he need a bunch of structural strength for skinning a deck. Yes some is required and I think his layup schedule looks good with the exception of the cloth. Matt can be sanded for fairing.
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Old 04-03-2021, 13:32   #78
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Re: How many layers fiberglass on new deck

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Originally Posted by Chotu View Post
Clueless


Yet another one who thinks Jamestown distributors and everyone who sells 1708 doesnít know what they are talking about.

How does a square yard of 1708 weigh 25 ounces then? Can you answer that? Simple arithmetic

As to the wasted material, do you not even understand the concept of directional forces? None at all? Tell me. Why do you think a chopper gun boat is a piece of junk? Go ahead . Answer that one. It will help clue you in as to why directional fibers do all of the work in 1708.


Frankly, this thread scares the hell out of me. Iím asking for advice on this forum in a lot of boat building areas. Granted, itís all fit at work because the whole is already built, but still. Iím getting some good stuff, but to see something this simple completely misunderstood and then have people arguing it to the moon. Thatís nuts.
Per Hexcel Knytex who makes 1708 the 17oz or 8.5 oz per YARD (two directions, 2X8.5) and the 08 is .75oz per sq.ft. So yeah the mat part, the angel hair part or the CSM part weighs about 6.75 oz per sq yard of material.

Read Gerr's book. I am only stating what Gerr says and what I have read on manufacturers sites. If you want to laminate strictly biax fine but it may be better overall if there is some mat in there.


If you want better directional strength best toss in some 1808 or at least try and rotate the 1708 so you get fibers lined up at 0, 45, 90, 180, 225, 270 etc...
Read Gerr's book.

The OP should be asking what does it take to equal or exceed the original laminate. He should read Gerr's book.
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Old 04-03-2021, 13:33   #79
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Re: How many layers fiberglass on new deck

The 6.75 oz per square yard of CSM is correct by the math. My bet would be that the extra 1.25 oz that's not accounted for comes from the stitching holding it all together.
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Old 04-03-2021, 13:35   #80
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Re: How many layers fiberglass on new deck

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Originally Posted by boatpoker View Post
OP is talking deck patches for cryin' out loud. It ain't rocket surgery.
No finite element analysis required.
How big is the deck patch? Where is it?

Quote:
We are replacing a few large areas of the deck that are shot and causing sponginess and water leaks in the cabin. Boat is 45' Dufour.
Large, deck and leaks sounds kinda structural to me. Especially the large part. Hell why not just trowel in some kitty hair/gorilla hair Bondo and call it a day? Why not do it right as long as your doing it?
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Old 04-03-2021, 13:38   #81
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Re: How many layers fiberglass on new deck

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Originally Posted by Cadence View Post


I think he was asking about thickness. What does he need a bunch of structural strength for skinning a deck. Yes some is required and I think his layup schedule looks good with the exception of the cloth. Matt can be sanded for fairing.
Without knowing how big he's repairing . where and or what the original laminate schedule was who knows? So how thick is good?

Read Gerr's book.
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Old 04-03-2021, 13:48   #82
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Re: How many layers fiberglass on new deck

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You forgot to look at the REST of the Jamestown page. LOL. Says I was right all along.

Here is the copy/paste from the page you linked to. Open ďInfo and guidesĒ for the actual weights of 1708

ď 1708 signifies the weight of each layer.
+/- 45 biaxial weave cloth is 17 ounces per square yard.
mat backing is 8 ounces per square yard
yields a total weight of 25 ounces per square yardĒ

Go back to your link and check. Building anything except small repairs with 1708 and epoxy is a HUGE mistake and extremely poor engineering.

Itís 1/3 heavier and untold amounts of wasted epoxy.

It was invented ages ago for polyester.
The mat is .75oz per sq foot. It is about 6.75 oz per sq yard NOT 25 oz/sq.yard.

OP says:
Quote:
We are replacing a few large areas of the deck that are shot and causing sponginess and water leaks in the cabin. Boat is 45' Dufour.
How large is large? Where is it? Water leaks?

If he copies his original lamination schedule he would probably be fine. Or if he wants to figure out what will work and what is engineered right then I would get Gerr's book. Or just take advice from some idiot like myself.
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Old 04-03-2021, 14:02   #83
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Re: How many layers fiberglass on new deck

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Originally Posted by rslifkin View Post
The 6.75 oz per square yard of CSM is correct by the math. My bet would be that the extra 1.25 oz that's not accounted for comes from the stitching holding it all together.
More likely the bidirectional cloth is a bit over 8.5 oz. A lot of the many, many yards of 1708 I've used looked a lot closer to 1808. The stitching is negligible. Some could easily be from the CSM being heavier than .75oz/sq.ft too but it's not 26oz/yard.
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Old 04-03-2021, 14:04   #84
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Re: How many layers fiberglass on new deck

The 25 or 26 oz / sq yard being quoted was as the total weight, not just the weight of the CSM.
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Old 04-03-2021, 14:37   #85
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Re: How many layers fiberglass on new deck

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and completely irrelevant to the OP's query.
My point was why not use 1708 instead of the OP using roving as it's twice the strength for 1/2 the thickness and probably close to 1/3 less resin. Plus it works easier and lays flatter.

And as far as reading Gerr's book it's an easy read, answers all his questions and could easily tell you what is OK structurally or not. Do we KNOW it's NOT a structural repair? Sounds like a "large" deck delamination that is causing a leak into the cabin. Is the leak from the hull/deck joint? You have enough deck soft that the hull leaks? And that's not structural? What do I know?
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Old 04-03-2021, 14:44   #86
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Re: How many layers fiberglass on new deck

For anyone with difficulty doing simple deck work you may wish to purchase this. Fairly cheap at only 36 Euros.

https://www.scientific.net/AMM.275-277.105
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Old 04-03-2021, 15:07   #87
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Re: How many layers fiberglass on new deck

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Originally Posted by rslifkin View Post
The 25 or 26 oz / sq yard being quoted was as the total weight, not just the weight of the CSM.
Jamestown distributors has their copy as saying

"1708 signifies the weight of each layer.
+/- 45 biaxial weave cloth is 17 ounces per square yard.
mat backing is 8 ounces per square yard
yields a total weight of 25 ounces per square yard'

Sorry but this is not a correct statement.

1708 does not weight 25oz/yard. It weighs more like 23 oz/sq.yard. The math and the argument about weights started with the assumption that the copy of the Jamestown website is gospel.
The CSM or Mat part is .75oz/ft sq. or 6.75oz/sq. yard


The OP is asking basically is this scantling OK? So you guys figure it out. How much do you need to fix "large" "soft" and big enough it causes "leaks in the cabin" . Do not look at Gerr's book which quite simply answers all the OP's questions, give thicknesses and scantlings.
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Old 04-03-2021, 15:23   #88
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Re: How many layers fiberglass on new deck

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Originally Posted by boatpoker View Post
For anyone with difficulty doing simple deck work you may wish to purchase this. Fairly cheap at only 36 Euros.

https://www.scientific.net/AMM.275-277.105
Indeed or for $21.49 on Kindle/Amazon you can read :

Acclaimed author and naval architect Dave Gerr created this unique system of easy-to-use scantling rules and rules-of-thumb for calculating the necessary dimensions, or scantlings, of hulls, decks, and other boat parts, whether built of fiberglass, wood, wood-epoxy composite, steel, or aluminum. In addition to the rules themselves, The Elements of Boat Strength offers their context: an in-depth, plain-English discussion of boatbuilding materials, methods, and practices that will guide you through all aspects of boat construction.

Now you can avoid wading through dense technical engineering manuals or tackling advanced mathematics. The Elements of Boat Strength has all the formulas, tables, illustrations, and charts you need to judge how heavy each piece of your boat should be in order to last and be safe. With this book, an inexpensive scientific calculator, and a pad of paper, you'll be able to design and specify all the components necessary to build a sound, long-lasting, rugged vessel.
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Old 04-03-2021, 20:02   #89
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Re: How many layers fiberglass on new deck

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OK, folks. Everyone else is wrong but you couple people right? Jamestown distributors? Clueless, right? They donít know what theyíre selling. Total boat? Clueless right? Me? No idea. Right? The two or three people here who donít know what they are talking about. You guys are the experts right?

A square yard of 1708 weighs 25 ounces. Cut it out. Drop it on a scale. Learn.

1708. Where do you think the numbers come from? 17 is the biax. 08 is the mat. Those are weights. In ounces per yard.

How can you even come on here and argue something that is just fact? This is absolutely ridiculous.

I think the craziest part, is not knowing what youíre talking about, and then saying that everyone who sells 1708 doesnít know what they are selling.

Jamestown distributors is one of the most knowledgeable groups of people selling marine supplies on earth. Yet, you are right and they are wrong.

Starting to make notes here to make sure I donít listen to any of you guys about other things that I might ask on the form. Because if you can get something so simple as this wrong and argue the hell out of it, what other bad advice are you giving?
Choto, YOU are the only person has has called anyone clueless.

I weighed my sample of 1708 and am convinced you are correct.
I thought you were mistaken because originally I just looked at my sample, didn't weigh it, and read my copy of Boat Strength, and on page 22, Gerr says;

"A typical stich-mat is Hexel Knytex DBM1708. This is a +45, -45 bi-axial (the "DB"), built from two layers of 8.5-oz./sq.yd. uni-di (totalling 17 oz./sq. yd - "17"), with a single layer of 3/4-oz./sq. yd. (0.75-oz) mat stitched to it. ( The "08" is for the 0.75-oz. mat rounded off.)"

I am now convinced (partly due to your effort) he is wrong here, but while you are making your list of clueless people to ignore in the future, you might add Dave Gerr to your list.
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Old 04-03-2021, 21:58   #90
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Re: How many layers fiberglass on new deck

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Originally Posted by fourlyons View Post
......Gerr says;

"A typical stich-mat is Hexel Knytex DBM1708. This is a +45, -45 bi-axial (the "DB"), built from two layers of 8.5-oz./sq.yd. uni-di (totalling 17 oz./sq. yd - "17"), with a single layer of 3/4-oz./sq. yd. (0.75-oz) mat stitched to it. ( The "08" is for the 0.75-oz. mat rounded off.)"

I am now convinced (partly due to your effort) he is wrong here, but while you are making your list of clueless people to ignore in the future, you might add Dave Gerr to your list.
Did it ever occur to anyone that there could well be differing weights of mat on different types of biax?

The biax 1708 I have and use has a very thin layer of mat - way too little to be 1/3 the total weight.
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