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Gaps or no gaps between the seams?

JEM

Well-Known Member
Thought this would be an interesting discussion. Hope it fuels a good discussion about building boats with plywood, resin, and fiberglass but not an outright raging fire.

As you may know, I demonstrated a technique to help with with panels alignment:



The spacers create a small gap between the panels so all the assembly pressure is on the spacers themselves and not the panel edges. This make it easier to control and keep aligned.

The gap that is created must be filled in. This is a good thing on larger craft that must withstand much greater forces and pressures than a paddle craft. On these boats built with modern methods (fiberglass and resin), hard contact between panels is not desired. The filling in these gaps can better distribute loads and dissipate sudden shocks evenly to the rest of the hull where as hard wood-on-wood contacts isolated shock pressures to a single, localized area and creates a greater risk of hull damage of failure. Kind of like the cartilage between you bones vs. bone-on-bone contact. Not quite the same but you get the idea.

But again, this is less important on small paddle craft since the loads and pressures are not as great.

There's a nice demonstration of this concept on a stitch and glue boat here:

http://www.bbkayak.com/kit.htm



They exaggerate things a bit in there "typical boat kit" picture as most designs call for interior hull seams to get fiberglass coverage and not just left bare. Most designs call for at least 4mm ply as well.

However, the bottom image shows a good example of how panel edges are captures and how you can get a more-rounded exterior seam. The draw back is that the density of filler in the seams is more than the density of plywood so it ads weight. Looks like they address it by using 3mm ply and 4-ounce s-glass.



So anyway, thought this might kick off an interesting discussion.


:D
 

Kayak Jack

Well-Known Member
Aug 26, 2003
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Okemos / East Lansing Michigan
I've built only four boats, so I'm not an expert. So far, I haven't crashed or ruined any of them, so have no experience in damage assessment. I built four boats from pre-cut kits, and one from plans where I cut the panels. (My panels were not anywhere nearly as nice looking as the factory stuff cut with lasers.) I did not use spacers in any of my boats.

Looking at it from an engineering point of view, I can see advantages to Matt's system. Anything that makes panel alignment easier seems a step in the right direction. Added strength is almost always welcome. Every step or technique has an accompanying set of characteristics. Under various circumstances, each characteristic may be an advantage, or a disadvantage. It depends.

I see the extra strength. I'm not at all sure I see any need for extra strength. And, I'm not sure I'd enjoy the bit of added weight and cost that will accompany use of extra epoxy. Many of us have built many boats, most, mostly without spacers. While I don't remember any of these coming apart, maybe some have. Builders who have built both ways would have their own thoughts about both techniques.

For my part at this point, I think it may be solving a problem that barely exists. But, I could be persuaded to change by hearing experiences of others. (I may also be bribed in either direction with beer or single malt......... or a visit with Bambii, the gymnastic nurse.)
 

Oyster

Well-Known Member
Dec 5, 2008
254
0
OBX North Carolina
Gaps and spacing for builds are fairly common for sure. I have read across several high profile plan seller forums that really fits are not important in these composite construction builds. I say that this is not a good practice to promote from the getgo to people entering into the madness of building their own boats. As people also enter the madness, forums that promote this also are not doing any favors either.

The more gap you use, the more material you use which adds wreight and costs to small boats that are usually engineered for portability or for small hp engines too. But also teaching a new comer that attention to detail in the original layup and cutting of the panels is not big deal promotes sloppy workmanship in future projects. I don't see enough of that being promoted, while replies are filled with just fill the gap with thickened epoxy. Its actually stonger than having joints that are close together.

IN numerous cases too, gaps are not always improper cutting and fitting either but are a result of funny shapes that can be trued up if you investigate further into how the rough in actually looks from a distance. ONce you fill and glue, you have in some cases built a distorted hull. my pennies worth.
 

oldsparkey

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Aug 25, 2003
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Central , Florida
www.southernpaddler.com
It appears to me that both styles have there advantages and there disadvantages. The designer knows which is the best for there design since it was planned that way.
But in reality it boils down to something really simple ... It is the builder who decides which is the best for there particular boat and building style.

I learned that the panels touch each other and to make a tighter fit the inside of the panel was lightly sanded to mate them up. The the outside was lightly sanded to round off the wood so the glass lays down nice for you. With the panels touching , it can be a pain if the cut is off , a lot of sanding the panels ( rise or bump ) to make them fit right.

With the spaces the cut can be a hair off and the boat will fit together like it should. The other benefit is a lot stronger junction which would be a large benefit if your are going to give the boat a hard time. You have the epoxy in the spaces to round off and not the wood when applying the glass.

As the Lawyers like to say , Seams like we are discussing Apples and Oranges , which do you like ( works for you) and are happy with. :D

Chuck.
 

oldsparkey

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Aug 25, 2003
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Central , Florida
www.southernpaddler.com
One other benefit of having a gap between the boards. If , for some reason you were paddling and cracked a section of a panel it would be a lot easier to replace that cracked section then with the boards touching each other. The epoxy in the gap would make a fine line to cut that piece out. Then replace it and fill in the gap. :D

Chuck.
 

gbinga

Well-Known Member
Nov 7, 2008
736
2
Hoschton, GA
Oyster said:
...But also teaching a new comer that attention to detail in the original layup and cutting of the panels is not big deal promotes sloppy workmanship in future projects. I don't see enough of that being promoted, while replies are filled with just fill the gap with thickened epoxy...
I think that's a great comment. If you want a gap as a design feature, then you should put a gap there on purpose, and cut the parts properly, and have a constant consistent gap that will accomplish whatever sort of objective you were trying to accomplish. We shouldn't ever give people the idea that sloppy cuts are ok - they'll make a mess of their project and get frustrated with the whole undertaking.

GBinGA
 

beekeeper

Well-Known Member
Mar 4, 2009
1,807
49
Since building my one and only boat, I have had a question. It seems some what related to this topic to me because the issue of adding weight if the gap and larger fillet method is used. If asking here is wrong, I apologize and will ask in another post.
My boat was built with screws, 3m5200 glue, and chine boards (logs?). After adding the fiberglass tape, cloth, and epoxy resin, seems the weight increased considerably. I have not weighed it. The boat seems over built. My question relating to this post is; would a 3/4" x3/4" clear yellow pine chine and screws weigh any more than a large fillet reinforced with fiberglass?
This question is part of my pondering of how would a boat built with plywood (3/8" bottom,1/4" sides), chines, screws, glue,and one epoxy saturation coat compare to one built with Luna (5mm common size?) or 1/4"plywood, 6oz cloth, tape, and epoxy (common stitch & glue)? I am not pondering about extreme criteria like white water or having to portage long distances. In practical terms(for me; load, unload in truck & fish slow flowing creeks or protected lake coves), how would they compare in regards to longevity, durability, weight, and strength? This not an attempted start an argument about old(traditional) vs new method. I'll state up front I prefer to work with wood not epoxy and glass (more experience). I added epoxy and glass to my boat because I was worried about longevity. After my struggle with the fiber glassing, and the added weight, I question if it was needed.

Tried to move this to a new post after I typed(pecked) it, but it woud not copy and paste there for me. Too much typing (pecking) to redo, sorry

beekeeper
 

hairymick

Well-Known Member
Dec 8, 2005
2,107
2
Queensland, Australia
G'day Beekeeper, I think you question is a valid one here mate.

Chine logs and glue and screw work fine in a boat of uncomplex design - like a pirogue where there is one bottom panel that is joined to the side panel at allmost a right angle.

Where things become more challenging is in multi panel designs as in many kayaks and canoes.

I think a chine log for each seam in such a boat is outdated and has pretty much been replaced by the epoxy fillet method.

Re the gap thing, I have built a few with the spaces as described and more recently, without them.

I think the gap makes a stronger joint but the spacers hinder eyballing the lines of the hull before tacking to ensure smooth, consistent curves. And it takes longer to stitch using spacers.

Either way, I usually wind up cutting a few tacks here and there to get the lines to a point where I am happy with them :oops:

Oyster has made tome very valid points in that we should be encouraging each builder to be doing a fine a job of his build as he can. Our woodworking doesn't need to be furniture quality but To encourage sloppines in a build is downright dangerous.
 

JEM

Well-Known Member
beekeeper said:
My question relating to this post is; would a 3/4" x3/4" clear yellow pine chine and screws weigh any more than a large fillet reinforced with fiberglass?
Depends on how large is "large". But generally, a boat with appropriately sized fillets covered with fiberglass will be lighter than screws, glue, and chine logs.
 

Kayak Jack

Well-Known Member
Aug 26, 2003
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Okemos / East Lansing Michigan
And, a point that hasn't been addressed is thickness of wood. I use 4mm plywood for all parts of the boat. A bottom of 3/8" and sides of 1/4" are definitely overbuilt for any uses I've read about on this forum. Or, for which I would want to use a boat. And, it would be overweight.
 

jdupre'

Well-Known Member
Sep 9, 2007
2,290
38
South Louisiana
From my limited experience and from what I've learned on this forum, 1/4" and 3/8" plywood is probably overkill. I think if you are going to use glass and epoxy, chine logs are just unneccesary weight. You can't have a light boat if you START with 50# of plywood and an extra 25' or so of chine lumber. As far as durability, full glass inside and out on medium thickness ply seems the way to go. 6" tape on the seams would be nearly as strong, but might leave unglassed wood subject to checking in the future.

In the end, every one of these methods will make a great boat. The builder decides what most suits him. I chose nostalgia and the challenge of old time carpentry method for my pirogue. Might be different on the next boat.
 

beekeeper

Well-Known Member
Mar 4, 2009
1,807
49
JEM said:
The 3/8" and 1/4" do sound like overkill for a paddle craft. Lot depends on the overall design.

But if it's a power, sail, or row boat, then thicker wood is generally needed.
My Croc by Gator Boats is designed for power use, however the 3/8" bottom is reassuring when I step my 300lbs. in and its not entirely in the water. If 1/4" would be adequate that would be great. Just trying to learn. The over build I thought came from adding epoxy, fiber glass tape and cloth. I was shocked at the weight when my epoxy and fiberglass supplies came. For my comparison question, I only was only thinking of boats that would work with either method of construction (example pirogue), and for paddle.


beekeeper
 

Tor

Well-Known Member
My first canoe I used the paddlepop spacer method, the canoe I'm currently building I didn't use spacers.

The next boat I build (yes dammit) I'll use spacers because I like the extra security of knowing and seeing the glue squeeze through between the panels. When I've made test pieces with no gap I have found these fail more than joints with a gap, it may be my technique but as I'm not undertaking a ship building apprenticeship I'll use the more forgiving method for a gap.

I'll be using packing strapping to keep the gap to a minimum and the weight down but that's for 2010 (I think :roll: )

Tor
 

JEM

Well-Known Member
beekeeper said:
Just trying to learn. The over build I thought came from adding epoxy, fiber glass tape and cloth.
That's the most important part! The beauty of this hobby is you can always take another crack at it or just build it anyway you please.

There's really no absolute "wrong" way...unless it sinks or you don't enjoy it. :p
 

seedtick

Well-Known Member
Jul 22, 2006
1,161
7
Denham Springs, LA
interesting to see the various opinions here on "overbuilt" and "stronger" etc.

The reality is that , unless your boat breaks up in use, it's overbuilt and you could've made it not as strong as you did

no question that the more epoxy and glass you add to a joint, the stronger it gets. But is it stronger than a well attached inside chine? I don't know as I've never seen destructive testing for comparison. I know from my experience that it doesn't NEED to be stronger than the inside chine.

Is 1/4" (6mm) sides and 3/8" bottom (no glass) overkill ? Probably as I've seen 1/4" by 1/4" pirogues hold up quite well.

Is 4mm sides and bottom encapsulated in glass and epoxy overkill? Is it stronger than 6mm sides and bottom with no glass? If so by how much? Any hard data out there? or is it all anecdotal information based on our own experiences?

How much safety factor (overkill) do you want in your boat ?


I think Matt's statement about no absolutely wrong way unless it breaks up is correct






/
 

beekeeper

Well-Known Member
Mar 4, 2009
1,807
49
My launch sites don't allow me the luxury of having the bottom of the boat floating completely when I step in. I try to be as careful as possible and not stress the boat unnecessary. But in the real world ( or at least in my world) that is not always possible. I'm not stirring the pot, just trying to learn what is best for me. I'm reasonably sure 3/8" saturated with epoxy is strong enough. Would 1/4" saturated be strong enough? Would 1/4" saturated and glassed be strong enough? Would 1/4" saturated and glassed be lighter than saturated 3/8"? If heavier how much, estimates stated as such accepted? I may could compensate in another area. Not trying for ultra light weight, just put it in the bed of truck easily light weight. :)
Thanks to all for your input.

beekeeper