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heavy wood vs light wood

jdupre'

Well-Known Member
Sep 9, 2007
2,313
40
South Louisiana
This just popped into my mind from something I learned years ago. We spent a week in Colonial Williamsburg and toured all of the trade shops. Something the wagon builder said just struck me as counter-intuitive. They made heavy, cargo carrying wagons as well as small, light personal wagons and buggies. It seems they use the heaviest (and strongest) woods for the lightest vehicles and the lightest ( less strong??) woods for the big , heavy wagons. The rationale being that heavier, stronger woods could be smaller overall and therefore lighter in the long run. Lighter woods could be used for the heavier vehicles and made somewhat oversized to compensate for lesser strength. Put in those terms, it makes perfect sense. How that translates into boat building is yet to be known.........but the wheels are turning.
 

oldbuffpilot

Well-Known Member
May 13, 2014
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Central Kansas and Central Texas
This just popped into my mind from something I learned years ago. We spent a week in Colonial Williamsburg and toured all of the trade shops. Something the wagon builder said just struck me as counter-intuitive. They made heavy, cargo carrying wagons as well as small, light personal wagons and buggies. It seems they use the heaviest (and strongest) woods for the lightest vehicles and the lightest ( less strong??) woods for the big , heavy wagons. The rationale being that heavier, stronger woods could be smaller overall and therefore lighter in the long run. Lighter woods could be used for the heavier vehicles and made somewhat oversized to compensate for lesser strength. Put in those terms, it makes perfect sense. How that translates into boat building is yet to be known.........but the wheels are turning.
That may be our problem, the wheels are always turning! Wouldn't have it any other way.
 

Kayak Jack

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Aug 26, 2003
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Okemos / East Lansing Michigan
Joey is a very creative thinker. I like to volley ideas back and forth with him. He makes statements, and ask questions that set me back. My guess is that he used to do that to his folks and teachers too? They may have graduated him from 12th grade at the age of, say, 9 or 10 - just to getbrid of the pesky little twerp?

In boats, cedar has been a popular choice for a lot of years, for a lot of reasons, for a lot of boats. It rates well for strength, lightness, rot resistance, and appearance.
 

jdupre'

Well-Known Member
Sep 9, 2007
2,313
40
South Louisiana
Daddy used to say I asked so many questions when I was young.........many of them he couldn't answer. :D

Cedar has been used in paddlecraft primariy with a epoxy/glass covering. Same principle.......heavy and strong glass used very thin so it's strong but still lighter than solid wood thick enough for the same amount of strength. Carbon fiber, the miracle material, can be as strong or stronger than other boat building materials, not because it's necessarily lighter, inch for inch, but because you can use a lot less of it to do the same job.
 

jdupre'

Well-Known Member
Sep 9, 2007
2,313
40
South Louisiana
I little nugget I learned from building glass/wood longbows and all- wood selfbows. If you double the width of a board, you double the bending strength. Increasing the thickness, you increase the bending strength exponentially. If you double the thickness of a board, it has EIGHT times the bending strength. On my longbows, .003 of an inch increase in thickness increased the draw weight by 1#. A 20# draw weight increase (REALLY noticeable) is hardly noticeable when looking at the bow. So, in looking for strength, go thicker rather than wider.
 

beekeeper

Well-Known Member
Mar 4, 2009
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Lots of data on this site.

Comparing Western Red Cedar to White Oak it appears WO weighs about 2X as much and is stronger. The question becomes will it be strong enough, or remain stronger than the WRC if you reduce the size to 1/2 the thickness?
 

jdupre'

Well-Known Member
Sep 9, 2007
2,313
40
South Louisiana
On paper......yes. In practice......it might be hard to determine. When you're talking thousandths of an inch, you're probably getting out of the realm of our simple boatbuilding. Some things just don't make enough of a difference. You know, if you run your truck with a quarter tank of gas all the time, you will get better gas mileage because of the weight savings. Is it enough to make a difference and is the difference worth the effort? Questions only the person involved can answer.
 

beekeeper

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Mar 4, 2009
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Take a look at Eastern White Pine compared to WRC. It only weighs a little more and is "stronger" in all aspects. I have used it for chine logs and gunnels because it was lighter than yellow pine or ash. The box lumber stores have it in the 2X? lumber. It does take some searching to find some boards "clear" enough and you will have to mill it to what sizes you need. I think I recall Ron may have posted about a stripper boat built with it. It is also less $$$ than cedar but probably not as rot resistant.
 

jdupre'

Well-Known Member
Sep 9, 2007
2,313
40
South Louisiana
I would think white pine would be strong enough to do the job. I'll look for some for this next boat. I don't even consider rot resistance when building a pirogue. The way I use one, I don't think that comes into the picture. Our boats are protected by some kind of finish, used for 6-8 hours at a time and then dried out for days, weeks or months. Mr. Rot doesn't have time to get his grubby hands on the wood.
 

beekeeper

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Mar 4, 2009
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Not to hijack Joey's thread but this may help any interested south Louisiana builders. Stine's Lumber in Walker has "exterior" rated Luan plywood. They only had the 5.2mm the day I was there but they do carry 9mm. I boiled a couple of scraps and they did not delaminate. I would advise testing any future purchases before using it for a boat.
Luan is lighter than pine but not as strong. Each builder must decide if it is strong enough for their application.

 

oldbuffpilot

Well-Known Member
May 13, 2014
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Central Kansas and Central Texas
JD that's real interesting I'm still on the lookout for a lightweight Plywood for kids to kids to build Uncle John type pirogues with minimum use of epoxy and cloth. I know it's early but do you have an opinion if that might be viable ?
 

beekeeper

Well-Known Member
Mar 4, 2009
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I have not been a big fan of Luan plywood mainly because of rot and delaminating issues. The exterior rating should solve the coming apart issue. The 5mm seems weak compared to 1/4" pine. With adequate framing and light use it could work for the sides. The 9mm I used for the bottoms of a couple boats worked fine. Stronger/stiffer than 1/4" pine with equal weight.
Another side to your question and project is, do you want to put kids in boats built with marginal wood? The main advantage of a lightweight boat is it is easier for one person to load/carry. Will these kids be using their boats by themselves.
That being said the first boat I built for my grandson was 5mm sides and 9mm floor. It worked with no structural issues until it developed a rotten spot and started to come apart. It was finished with marine varnish, no epoxy or glass. It was listed as underlayment so I assumed it was water resistant. I was wrong.
 

oldsparkey

Well-Known Member
Aug 25, 2003
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Central , Florida
www.southernpaddler.com
Beekeeper said..." I have not been a big fan of Luan plywood mainly because of rot and delaminating issues."

Very true in most cases. Like all things there is way to get around it. I found if you epoxy saturate the wood it really helps to stop any problems. I like to mix epoxy with some Acetone to thin it. Then apply that to the wood and it will be adsorbed by the wood. By doing both sides the greater majority of the wood is epoxy cured for better words.
( It's the same trick builders use to repair dry rot wood. They drill some holes in the boards , then apply a diluted mix of epoxy in the holes so it saturates all of the wood , preserving it and solidifying it with epoxy.) I learned about it and treated some patches of dry rot that way , it works.
In my boats I only used 1/8 Th inch wood so I felt like 99% of it was saturated just by brushing that mix on it. Then I would do a normal epoxy saturation before glassing the boat.
 

jdupre'

Well-Known Member
Sep 9, 2007
2,313
40
South Louisiana
Chuck, unforturnately the idea that epoxy penetrates deeply into wood does not coincide with the testing. I've looked at multiple sources and the finding is that epoxy, no matter the viscocity, penetrates less than .004 of an inch...........about two thicknesses of notebook paper. I tested a few pieces myself years back and found that to be the case almost exactly. Now expoxy does increase the strength of the wood. Approximately .008 " of penetration (both sides) of a piece of .125" ply adds considerably to it's strength.
 

beekeeper

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Mar 4, 2009
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Not to drift into the "strong enough" discussion, but I have questions.
How much strength does a saturation coat add? I'm curious how the increased strength compares to heaver species of plywood. I can only find test for plywood and fiberglass.
 

oldsparkey

Well-Known Member
Aug 25, 2003
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Central , Florida
www.southernpaddler.com
Without questions we would never have any answers to think about.
I can't answer with a definite response , all I know is it adds strength and protection to my boats. I do a very diluted ( could call it a watered ( Acetone & Epoxy ) down mix ) mix at 1st , then a more normal one before glassing. I cheat , for better words , and apply the mix at the end of the day when the air in the wood is warm and contracting and not early in the day when it's expanding. I think it helps to adsorb the mix rather then expelling it and causing bubbles. I'm referring to 1/8 Th Luann. ( Door Skins )
As far as the dry rot I had in some of the porches lumber it made it like a rock.
The sheets of ply for the boats , jdupre did a article on it , what he refereed to in his post.
 

beekeeper

Well-Known Member
Mar 4, 2009
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Seems to be established epoxy applied to wood will seal the wood and add some? strength. Andy's question about the Luan plywood being suitable for kids building a boat stipulated a minimum use of epoxy and glass. Based on my limited experience with my Luan built boats I can not answer his question.