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CObob
01-21-2014, 10:12 AM
Hello all, and thank you for the wonderful forum. I've been researching/lurking for a few months now, and just started a lutra laker build. Its my first wood build, but i did a lot of fiberglass/epoxy modification to a very small gheenoe a year back (fiberglass flat-back canoe). I think i know the answers i will get to this question, but will take the flogging anyways because i can't get the idea out of my head.

the mid-plank and shear-plank seem thin at 4mm. I like the idea of the 6oz + glass that will cover the outside of the bottom and garboard (i may go 9-10oz; i like oyster). I am tempted to pre-glass the exterior of the mid and shear plank prior to hanging/final trimming them. No the plans do not call for glass on the mid and shear plank. I have experience pre-glassing parts and think the weight added by 4oz glass (or less?) and a little extra epoxy will be minimal for the strength added. All posts i have found about glassing lapstrake talk about glassing after setting planks, which is just silly. I am planing to pre-coat each panel with epoxy anyways, and think a quick layer of light glass will add minimal time and weight. I'm even looking at some fabrics that are less then 4oz (any pointers there appreciated). This will not result in galss between the laps as the bevel on the lower plank will remove the glass, and set to the interior side of the upper plank. the exterior will have epoxy/graphite/silica for the bottom coat and a nice topside above that, so there will be a little extra fareing needed if i glass. Wood is Okoume. One last thought is whether the glass be better served in the interior for dent resistance..

No I have not yet asked the designer; i will if you all fail to convince me i'm a fool... Thanks, and i know what i'm getting into asking about fiberglass here. flog away!

capefox
01-21-2014, 10:23 AM
How will you get 9 oz cloth to bend around the sharp edges of a glued lap?

Rich Jones
01-21-2014, 10:23 AM
Welcome to the Forum!

I've built five glued lap boats (four of them 4mm Okoume) and just used paint or varnish inside and out. My first was a Tom Hill Charlotte solo canoe that did have fiberglass on the very wide garboard/bottom plank applied after the plank was in place. My concern with pre-glassing is that it'll be that much harder to bend/twist the planks at the ends of the boat, especially at the garboard. Let us know a little more about the design and that might help with advice.
Unless you plan on beating the hell out of this boat, I don't really know the reason for all that glass.

slug
01-21-2014, 10:33 AM
If you need chafe protection on the laps you might consider 6 oz , 45 by 45 biaxial tape. The biax will conform to the laps. Choose 4 inch tape. 6 oz is strong stuff.

The lap must have it sharp edge beveled before you tape.

naturally you must do some fairing to blend the tape in and rebuild the lap edges.

CObob
01-21-2014, 11:18 AM
How will you get 9 oz cloth to bend around the sharp edges of a glued lap?

9ox only coveres bottom and garboard, so the only edge is the aprox 90deg at bottom/chine to garboard. no overlap.

JimD
01-21-2014, 11:19 AM
I've always liked the idea of preglassing ply panels and planks although most builders don't. I also see value in using a very light cloth around 2 ounce and have done so on kayaks and dinghies. As already noted, getting any cloth to wrap over sharp corners will be a pain if not impossible. Whereas if you glass after assembly you will at least have a fighting chance at this. It may be that you do not intend to wrap the ply end grain and it seems perfectly reasonable not to. Also mentioned is the potential problems of tight twists of the planks. Glassed planks will take some twisting no problem but there are limits which are hard to predict before hand. A pic of the Lutra Laker so other posters know what boat we're talking about. Hope I have the right boat:
http://www.duckworksbbs.com/plans/nichols/laker/laker-5.jpg
http://www.duckworksbbs.com/plans/nichols/laker/laker-4.jpg

CObob
01-21-2014, 11:32 AM
Welcome to the Forum!

I've built five glued lap boats (four of them 4mm Okoume) and just used paint or varnish inside and out. My first was a Tom Hill Charlotte solo canoe that did have fiberglass on the very wide garboard/bottom plank applied after the plank was in place. My concern with pre-glassing is that it'll be that much harder to bend/twist the planks at the ends of the boat, especially at the garboard. Let us know a little more about the design and that might help with advice.
Unless you plan on beating the hell out of this boat, I don't really know the reason for all that glass.

Yea, i need to describe the build a little better. the flat bottom and garboard go togeter first with a seam of 4" tape feathered. Then one solid piece of glass across the bottom and up the garboards. Next are the mid and shear plank, both pre-treated with epoxy but un-glassed per plans. I'm considering adding a light layer to one side of the mid and shear plank.

mid and shear plank receive less twist so i don';t think glassing 1 side will give me too much trouble. I don't plan to be hell on horses and women, it just turns out that way. The design is a 10hp freighter-canoe style workhorse and it will get used.

jimL55804
01-21-2014, 11:39 AM
My son and I built a BayCruiser 20 from a panel kit provided by Swallow Boats across the big pond. Building sequence photos available at: https://plus.google.com/u/0/photos/111091018237930049744/albums/5493241981946375665. We pre-glassed the interior side of the upper strakes with 1.5oz cloth (if I remember correctly, it might even have been lighter) and outside after assembly with either 4 or 6oz (I cant quite remember). The garboard strakes had a much heavier lay-up (12oz bi-ax inside and out, I think). We used peel-ply on everything. We did this more to get a good finish than for strength, although I am sure that the glass on the outside does add strength as well as abrasion resistance. I don't think that I have ever seen plywood simply coated with epoxy that doesn't end up with cracks and crazing five or ten years down the road. I'm not so sure that it is actually encapsulated anymore at this point. It also make refinishing a much bigger job than it out to be, since at the least, all of the paint needs to be removed to re-coat with epoxy. I'm sure that the additional weight added from the glass vs. three coats of epoxy was minimal.

https://lh5.googleusercontent.com/-4f4GSZWLcBc/TIcVL5PrCnI/AAAAAAAAFU0/OcET7170ZbM/w912-h684-no/P1010509.JPG

Tom Robb
01-21-2014, 04:32 PM
How much abrasion resistance do you imagine "light glass" will give you?
My thought is, "What's the point?"

jimL55804
01-21-2014, 07:30 PM
The point isn't abrasion resistance, the point is to avoid all of the crazing and little cracks that I see on epoxy coated plywood (without glass) some years down the road. A modest level of abrasion resistance is just a bonus.

Jim

James McMullen
01-21-2014, 09:17 PM
. .. .f you all fail to convince me i'm a fool...

Hey, I'll give it a shot! :D

So then, CObob. . .what in particular makes you think you have the skill, knowledge, experience or credentials to redesign the structural scantlings of you very first ever boat build? Do you think the designer of the boat did it wrong? Is it a bad design that needs modification in order to make it work at all? Are there lots of stories out there of people who are in despair because they didn't beef up and overbuild this formerly light, handy and manageable boat? Do you have enough experience to even know whether you're actually working towards solving a genuine, real-life issue or offering up a waste-of-time-and-money placebo for an imaginary ailment?

You don't have to answer me, just answer the questions for yourself, amigo.

almeyer
01-21-2014, 10:27 PM
My suspicion is that all the crazing and cracks you've seen is from the quality of the plywood, which may be something less than marine grade. If you're using BS1088-rated occume, that shouldn't be an issue. You're in Austin, so you've likely got a limestone bottom where you'll use the boat, so glass/epoxy on the bottom and garboard seem justified. But I don't see anything to be gained with glassing the mid and shear strakes.
Al

CObob
01-22-2014, 01:12 AM
Hey, I'll give it a shot! :D

So then, CObob. . .what in particular makes you think you have the skill, knowledge, experience or credentials to redesign the structural scantlings of you very first ever boat build? Do you think the designer of the boat did it wrong? Is it a bad design that needs modification in order to make it work at all? Are there lots of stories out there of people who are in despair because they didn't beef up and overbuild this formerly light, handy and manageable boat? Do you have enough experience to even know whether you're actually working towards solving a genuine, real-life issue or offering up a waste-of-time-and-money placebo for an imaginary ailment?

You don't have to answer me, just answer the questions for yourself, amigo.


Now thats what I'm talking about!

All I can say is if I were afraid of getting into something I wasn't fully experienced with I wouldn't be building a boat in my friggen' garage in the first place. beyond that; I think I may have different goals and expectations then the designer; nothing wrong with the design at all, I'm just a different soul. Perhaps more prone to drop an anchor, run up on oyster, back into a tree, whatever. Any-who, some substantive criticism could actually help, that was pretty unconvincing

CObob
01-22-2014, 01:24 AM
How much abrasion resistance do you imagine "light glass" will give you?
My thought is, "What's the point?"

More then no glass?

Seems like a minimal addition if I'm epoxying anyway, and the damn wood seems soft too.

dbrown
01-22-2014, 01:34 AM
If McMullen can't convince you that you're being foolish then you must not be listening. ...If you have "different goals and expectations than the designer" ,maybe you should choose a different design. What does friggen' mean ?

CObob
01-22-2014, 01:51 AM
My suspicion is that all the crazing and cracks you've seen is from the quality of the plywood, which may be something less than marine grade. If you're using BS1088-rated occume, that shouldn't be an issue. You're in Austin, so you've likely got a limestone bottom where you'll use the boat, so glass/epoxy on the bottom and garboard seem justified. But I don't see anything to be gained with glassing the mid and shear strakes.
Al

hum. There must be abrasion resistance and some added strangth/ ragidity from it (not saying stiffness; it will only be one side)... Your "nothing to be gaind" argument is the best so far. This is just a cost/ benefit question for me. Boat will likely be drug off the trailer for hand-launching and some dragging, will get drug and rubbed through mangrove and god knows what, and will be generally well loved/used/abused. I'm a fly fisherman and this is a tool; not looking for a showpiece to be babied.

anyone going to tell me that weight is an issue? That's my biggest concern. The planks will be 7-10" wide an 17' long. And i can't find a good estimate for total weight added.

Oyster
01-22-2014, 02:07 AM
hum. There must be abrasion resistance and some added strangth/ ragidity from it (not saying stiffness; it will only be one side)... Your "nothing to be gaind" argument is the best so far. This is just a cost/ benefit question for me. Boat will likely be drug off the trailer for hand-launching and some dragging, will get drug and rubbed through mangrove and god knows what, and will be generally well loved/used/abused. I'm a fly fisherman and this is a tool; not looking for a showpiece to be babied.

anyone going to tell me that weight is an issue? That's my biggest concern. The planks will be 7-10" wide an 17' long. And i can't find a good estimate for total weight added.

Google west system and system3, both sites will tell you laid up weights for a given cloth weight.
Royce

James McMullen
01-22-2014, 08:59 AM
Any-who, some substantive criticism could actually help, that was pretty unconvincing

Ha ha! That's what I get for being subtle rather than direct.

Well, enjoy your overweight and needlessly costly boat, CObob. It's your boat, you're the only one who has to be satisfied with it. And this is where your lack of experience in having other boats for contrast should come in handy towards lowering basic expectations.

There, was that any better? :D

Watch out for the bats under the bridge there in Austin, amigo.

Breakaway
01-22-2014, 09:17 AM
I am with the it folks who say: will be more expensive and time consuming to build, plus heavier than needed, all for not a lot of gain.

This is not to say that the way you will use the boat, and the environment you'll use it in, isn't rugged. With that in mind, have you considered adding a sacrificial keel piece and/or bottom runners? Screwed onto the bottom and bedded in something non adhesive they can take the brunt of the bottom dragging and simply be replaced if needed. These would add some weight and will likely slow you down when rowing. But they are cheap, quick and effective.

Kevin

Kevin

CObob
01-22-2014, 09:23 AM
My son and I built a BayCruiser 20 from a panel kit provided by Swallow Boats across the big pond. Building sequence photos available at: https://plus.google.com/u/0/photos/111091018237930049744/albums/5493241981946375665. We pre-glassed the interior side of the upper strakes with 1.5oz cloth (if I remember correctly, it might even have been lighter) and outside after assembly with either 4 or 6oz (I cant quite remember). The garboard strakes had a much heavier lay-up (12oz bi-ax inside and out, I think). We used peel-ply on everything. We did this more to get a good finish than for strength, although I am sure that the glass on the outside does add strength as well as abrasion resistance. I don't think that I have ever seen plywood simply coated with epoxy that doesn't end up with cracks and crazing five or ten years down the road. I'm not so sure that it is actually encapsulated anymore at this point. It also make refinishing a much bigger job than it out to be, since at the least, all of the paint needs to be removed to re-coat with epoxy. I'm sure that the additional weight added from the glass vs. three coats of epoxy was minimal.



pictures 26 and 27 show exactly what I am thinking. Beautiful build. Ill go read up more on peal-ply.


i have seen numbers for weight of glass set with epoxy but have no reference point for the 3 coats already called for. Ill keep looking


EDIT:
I did the math with for epoxy coverage after finding numbers for coverage no-glass here: http://www.systemthree.com/sys3news/the-epoxy-book/appendix-a-estimating-usage/
Amusing: each mid plank is 9sqft, and each sheer is 12sqft. Epoxy is 9lb per gallon. 4 coats total; 1 soaking and 3 re-coats. okoume is hardwood.

I get just over 4 lbs epoxy for these components without glass, and 6.3 with. Also need to add the weight of glass in (about 1.2 lb).

I guess you can look at it as only 3.5 lbs or a 2.3% increase it total wight of the boat (around 150lb)... or you can also look at it as nearly double the weight of just epoxy finish. Here are the calculations by weight in lbs:



epoxy weight for 4 oz galss









1
2
3
4




mid
0.54
0.27
0.27
0.27

1.35


mid
0.54
0.27
0.27
0.27

1.35


sheer
0.72
0.36
0.36
0.36

1.8


sheer
0.72
0.36
0.36
0.36

1.8











total epoxy
6.3







total glass
1.125







total
7.425
















Epoxy Weight no glass









1
2
3
4




mid
0.25
0.204
0.204
0.204

0.862


mid
0.25
0.204
0.204
0.204

0.862


sheer
0.33
0.27
0.27
0.27

1.14


sheer
0.33
0.27
0.27
0.27

1.14











Total
4.004
















difference
3.421

Phil Y
01-22-2014, 03:41 PM
Seems like a good idea to me. I've even heard of people laying up some glass on the full sheet of ply before they cut out the planks. Hard on your edge tools I guess but ply is pretty hard on them anyway. If you do your bevels with a sanding disc on an angle grinder that's not a problem anyway.

James McMullen
01-22-2014, 03:54 PM
If you do your bevels with a sanding disc on an angle grinder. . . .

Sweet Jeebus!!! http://www.sherv.net/cm/emoticons/shocked/crazy-smiley-emoticon.gif

Todd Bradshaw
01-22-2014, 04:23 PM
If you're already going to epoxy coat it (figure two coats unsanded [ugly] or three coats sanded smooth [much better looking]) to get the needed 10 mils or so of epoxy coating thickness that are needed to properly seal the plywood, I don't thing you'll gain a noticeable amount of weight by stuffing a light layer of fiberglass cloth in there. You can also use it as a thickness guide, to be sure that you have sufficient resin thickness. As far as adding strength, don't count on it for most impacts if it's on the outside, other than when you drop an anchor on it. It needs to be put in tension, not compression to get strength, and objects impacting the outside of the hull will not put outside glass in tension. For cases like that, inside glass would add better strength.

The checking problem is also not that easy. Fiberglass will only prevent checking on plywood if it is heavy enough to do it by brute force. The fact that a good epoxy resin resists delamination so well pretty much assures you that the glass won't delaminate (which is good) but there still have to be enough glass fibers present that the force it takes to rupture them is greater than the forces which are making the plywood want to check. A plywood application that might not check with 6 oz. cloth, might split open with 4 oz. or 2 oz. cloth instead, so just sticking a layer of some sort of fiberglass cloth on can't guarantee that the plywood will never check. I'm not aware of anyone putting out figures suggesting which weighs and weaves of glass are sufficient to stop checking on various types of plywood. I suppose the best bet is to start with really good plywood.

It would also be possible to micro-fracture (from stretching) flat plywood planks which were glassed on their outsides as you bend the planks to shape - depending on how much you have to bend them. The fractures show up as uniform, regular patterns of tiny white spots, down in the weave where originally you had good clarity. They aren't a big deal, but do indicate that you have lost some of the strength of your laminate. The curves on this boat aren't too severe, but it's something to keep in mind, even while handling the unmounted planks.

So I think it could be done, but my inclination would be to stick with the original scantlings, skip the upper glassing, assume the designer knows his stuff and has had success with the design, do a good paint job and maintain it well.

Tom Robb
01-23-2014, 04:16 PM
I hear you can lead a horse to water, etc...
A wise man would listen to Jim & Todd.

WI-Tom
01-24-2014, 01:24 AM
A wise man would listen to Jim & Todd.

And what's especially appealing about their good advice is that they're telling you to less work rather than more! (Without giving up quality). What could be better than that?

Tom