Hybrid NL Build

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Hybrid NL Build

Postby jfish1288 » Thu Sep 12, 2013 2:53 pm

Just bought Missed's plans and ordered FG and epoxy. I'm thinking of using 1/2 inch foam insulation board instead of plywood or luan. My thinking is that it will save on weight because it is lighter to begin with and won't absorb as much epoxy, and it should be stronger after fiberglassing because of the increased overall thickness of the sandwich composite.

Anyone have any experience using foam instead of wood to serve as the core for these boats?
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Re: Hybrid NL Build

Postby Lane » Thu Sep 12, 2013 11:28 pm

Don't do it..... UNLESS your willing to spend for structural foam made for fiberglass lamination. Airex, Divyncel etc. Even then you wind up with a heavier boat than if you had used wood. Or one that's very fragile. The wood gives puncture resistance and to equal that with glass laminations gets heavy fast. Construction foam, has a basically non existant shear strength so once laminated with glass, it will separate from itself right next to the glue line rather quick.
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Re: Hybrid NL Build

Postby jfish1288 » Fri Sep 13, 2013 10:58 am

Thanks for the advice. Is that based on personal experience, ie have you had foam core boats punctured or separate? Isn't foam board commonly used as the core when making sailboats, small yachts, and other handbuilt medium sized boats that have hull shapes that do not lend themselves to being made of plywood sheets?
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Re: Hybrid NL Build

Postby sharris » Fri Sep 13, 2013 12:21 pm

There is a guy that built a foam boat a few years ago. Here is the thread. You can PM him and ask how it held up. I personally wouldn't do the foam thing. Fiberglass on a wood core is very strong and light, and it is fairly forgiving to work with even when you screw up and split your boats deck :oops: .

viewtopic.php?f=72&t=90971
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Re: Hybrid NL Build

Postby jfish1288 » Fri Sep 13, 2013 12:24 pm

Thanks
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Re: Hybrid NL Build

Postby Lane » Fri Sep 13, 2013 2:24 pm

jfish1288 wrote:Thanks for the advice. Is that based on personal experience, ie have you had foam core boats punctured or separate? Isn't foam board commonly used as the core when making sailboats, small yachts, and other handbuilt medium sized boats that have hull shapes that do not lend themselves to being made of plywood sheets?


Without delving to far into boat design and stress factors, puncture resistance is the the hardest thing to get when the boat is
A-small
B- desired to be lightweight
There are many kinds of foam, and foam core boats are built with foam intended for the purpose. Airex or the like.
To get construction grade foam from the box store to work, you have to increase the fiberglass layup so nothing flexes because flexing is what starts the separation of the foam. Once you have the fiberglass so thick it doesn't flex..... you may as well loose the foam and just have glass boat.
And, yes all personal experience and mathematical formulas.

A Light and economical=ply core
B Light with cost no object= Airex or similar
If B is your option, just buy one that I build and get the best of both..... :wink: I just started a new mold for a 11 footer yesterday.
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Re: Hybrid NL Build

Postby MissedAgain » Mon Sep 16, 2013 12:24 am

Hi!

There are a handful of trains of thought that people encounter when thinking of better ways to build Hybrids. The first one is foam, the second one is aluminum. Others include needing to use thicker wood or heavier cloth because the builder is bigger than average - it just isn't necessary. Heavier wood is heavy and heavier cloth needs more resin and is heavier then two layers of lighter cloth, which is also stronger!

I have not built a Hybrid out of foam but almost... :huh: The blue & pink foam you see at Home Depot, Lowes, Maynards and everywhere else is not structural and actually off-gasses. What this means is that it is weak and will delaminate the eopxy resin/glass you have on it. The puncture resistance is not there and it may actually weigh more than the thin plywood & glass.

How can that be? The foam weighs a bit less than plywood, even 1/4 inch! Most of the boat weight comes in when you start putting resin and cloth on there. You'll need extra resin and cloth to do it right, at least double, possibly triple. I have done the research and spoken to some seasoned old boat builders who were nice enough to share their knowledge - the foam will weigh more! Basically after the third old boat builder told me this, I gave it up.

The aluminum factor is sweet. High tech welding, bending metal, sexy! :yes: Problem is the metal needs to be stiffer and if you add reinforcements or thicker gauge, it weighs more! I build a 75-90 pound 10 ft Hybrid depending on what goes into it - the lightest aluminum rig will be about 115 pounds. But they last forever! The jury is out on how long Hybrids last when taken care of - an epoxy boat should last in the range of 50 years. I'll be dead before my boat rots. It is comforting.

Please don't take this wrong, I'm just sharing.

If you want to do the foam, please use something like nida-core or core-cell. I have 1/2 a honeycomb Hybrid sitting in my garage because I screwed up on an $800 material purchase. Trying to figure out how to stiffen the 1/4 inch honeycomb. I used 12 oz bi-axial (18 oz strength) when I should have just used a couple layers of 6 oz cloth.

Oh yeah - I don't know where you are but make sure the honeycomb or foam will not freeze and shatter if you hit a rock or something. I heard that some of the building materials will get brittle in the cold - kinda like PVC does. I forget what I used was called, just wish I spent the $200+ on a sheet of 1/2-inch as it would have been stiffer and there wouldn't be a half-built boat sitting in my garage...taunting me :hammer:

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Re: Hybrid NL Build

Postby jfish1288 » Mon Sep 16, 2013 6:35 am

Thanks for the advice. My take away from all my classes when earning my engineering degree, which included a course specifically on fiberglass and carbon fiber composites, was that that the core material adds very little to the overall material strength. The core just serves as a spacer to increase the distance of the outer skin, where the stregth comes from, from the neutral axis. But I was not the best student, and it has been a while since those classe, so I could be off base some.

It definitely makes sense that there could be issues with getting a good bond between the foam and epoxy, and how much epoxy is required. The other issue is the compressive strength normal to material surface. So if the the fiberglass won't bond to the foam, or if the foam absorbs epoxy than wood, or the foam requires more layers of fiberglass than wood, then there would be no advantage to the foam.

All of those concerns seem plausable. And the fact that everyone is suggesting using higher density foams and staying away from construction foams makes me believe that those concers are well founded, and a construction foam/fiberglass boat is a bad idea. So I will probably just go with plywood or luan. But I will probably do some experiments with the foam once my fiberglass and epoxy arrive, just to confirm that it is a bad idea. I will be sure to post the results of those experiments and updates ont the build.
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Re: Hybrid NL Build

Postby Lane » Mon Sep 16, 2013 11:20 am

The epoxy bonds great to construction grade foam. Just the foam doesn't stay stuck to itself. It delams right inside the glue line if there is any flex at all. Have fun testing.
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Re: Hybrid NL Build

Postby MissedAgain » Mon Sep 16, 2013 2:32 pm

From my research, the thicker the core, the more strength in the laminate - within reason of course.

I did find a freeze-proof honeycomb...just wish I went with 1/2-inch...

The thin plywoods really do offer the best strength to weigh ratio. They also provide good puncture resistance. Go figure.

I'm interested in your findings and advanced education. A couple of the guys who have built Hybrids are composite engineers or airplane wing builders and have provided some good info. I'm sure you will as well...BRING IT ON! :welcome:
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Re: Hybrid NL Build

Postby jfish1288 » Sat Sep 21, 2013 8:18 pm

Ok so I made a testing sampleI of 1/2" construction foam 6" by 10". I put two layers of 6 oz E-glass with an epoxy resin on each side and let it cure. It is important to note that the sandwich composite was 2 parallel planes of fiberglass separated by the foam- the fiberglass was not wrapped around the edge of the foam.

What I found was that when a significant bending moment was applied, the foam separated at the glue line on the compressive side due to the lack of shear strength of the foam-just like Lane said.

Below is a picture of that separation.

I do think that if the FG was wrapped around the edges of the foam the forces would be better distributed and this delaminatiomn would be somewhat less likely. Additionally if the separation did occur it would not have much impact on the overall composite's structural properties. However ensuring all the foam is adequately encapsulated in enough FB to distribute all potential loads, is probably more trouble than it is worth for the weight savings. So I'm just going to use luan.

I would like to point out that I took a standard screw driver and hammer to the test sample and no matter how hard I hit it, I could not puncture even the first layer of fiberglass. Below is a picture of the "damage" from the screw driver.
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Re: Hybrid NL Build

Postby jfish1288 » Sat Sep 21, 2013 8:18 pm

Can't post pics from my phone. I will put them up sometime this week when I get a minute at work.
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Re: Hybrid NL Build

Postby Lane » Sun Sep 22, 2013 5:17 pm

12 oz of E glass would most likely work for a self powered light weight boat, but could also be quite fragile even on a structural foam core. If I remember right layed up on 1/2" 5lb core, that would equal 3mm/1/8" ply. It is "stiffer" but that is roughly the strength against out of plane loads.
A backyard test of puncture resistance would be a 2'x2' lamination, hit with a straight claw claw hammer.
The formulas to calc it out with regards to hull shape, weight and speed, You may have learned in your composites classes.
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Re: Hybrid NL Build

Postby jfish1288 » Thu Sep 26, 2013 2:43 pm

Ok so here is the result of bending the sample as much as I could

Seperated.JPG
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Re: Hybrid NL Build

Postby jfish1288 » Thu Sep 26, 2013 2:52 pm

Here is the puncture test. I put the sample between two paint cans and then hit it as hard as I could with a Phillips head screw driver and hammer.

Puncture Test.JPG


Here is the resulting damage.

Puncture Damage.JPG


I would say that there is little danger of puncture. The problem, as lane stated, is the shear strength of the foam. This can be overcome by using higher density foam, but that negates the weight savings from using the foam instead of plywood in the first place, and can be cost prohibitive.
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Re: Hybrid NL Build

Postby jfish1288 » Fri Sep 27, 2013 1:59 pm

Ok so here is the actual boat build....

I decided to go with more narrow boat that will sit a little deeper and hopefully track a little better. The bottom is 20 inches wide, and the top is 41 inches, the sides are about 13 1/4 inches long, and overall length is about 94 inches. The other benefit of having it sit deeper is that I can get a little more foot room and still keep a low profile. I plan on having about 14 inches of foot room.

I expect that myself, boat, and gear will be around 260lbs normally, so I should float in about 5 1/2 inches of water (and it would take upwards of 700 pounds to make it sit 8 inches deep).

Here is a pic of the hull stitched together. As you can see I have also added a bow keel in hopes that this will make the boat track better. I made it from a 1 X 12. If I decide that it is cumbersome or unnecessary I can trim/remove it with a reciprocating saw and patch it up with some fiber glass tape.

Hull Stiched Top.JPG


I used 1 X 2s to make a frame to get the curve I wanted.

And here is the a pic of the hull stitched together but upside down.

Hull Stiched Bottom.JPG


Here it is epoxied, filleted, and bondo-ed.

Bondo.JPG


Here is a bit of a profile pic before the seams get taped.

Profile.JPG


And here it is after taping all the inner seams, not the cleanest job but it should get the job done. I am just doing one layer of tape on the inside.

Taped.JPG
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