Alternate build methods?? long winded post, you've been warned

[TomTom]

It's actually technically challenging to make foam cores with REPEATABLE material properties. Even the best cores vary by +/- quite a few %. That sort of expertise does not come cheap. If you struggle to pay for the materials, maybe it's just not going to happen....

I have a friend who used to work for Martin-Baker - they make ejection seats for fighter planes. We were having this very same conversation and he said the reason they still aluminium is because they are working with a known quantity and it is much more repeatable than composites. I thought that was interesting.

Lakesurfer - you may enjoy reading parts of the Gougeon Manuel on epoxy. Maybe it will give you some ideas. Maybe it will also help you to understand how epoxy resin really revolutionised wooden boat building and was the missing link that took a superb boat building material that wasn’t superb because it could rot, to one that really now has pretty much everything going for it!

Read the appendix C for starters. Maybe like many of us on this forum who started out sceptical of wood because we had been brainwashed, you will change your mind and come to realise what the rest of us - and many, many great boat builders did as well - that wood is a pretty darn good material and a whole lot simpler than all your alternative suggestions...

https://www.westsystem.com/wp-content/u ... 1205-1.pdf

This from appendix C...



I have a 20 year old plywood and epoxy OD 18 - Built from plans on this site - and it had water under the sole for 5 years - and it doesn’t have an ounce of rot because everything was epoxy coated. I live next to a boat yard that has plenty of fiberglass boats in various states of disrepair that have soggy osmosis riddled hulls.

Ultimately if you own a boat - whatever it is made of - you have to look after it in a manner appropriate to what it is made of...

[Lakesurfer]

It's actually technically challenging to make foam cores with REPEATABLE material properties. Even the best cores vary by +/- quite a few %. That sort of expertise does not come cheap. If you struggle to pay for the materials, maybe it's just not going to happen....

Let's compare cores. One of the most important figures for foam cores is the core shear strength:

The Carbon Core is 60 kg/m3 nominal density so has lower shear strength than H80 Divinycell at 80 kg/m3

It only lists one value for shear strength - 0.82 MPa. We might assume that this a peak or nominal amount
H80 has a nominal value of 1.15 MPa and a minimum of 0.95 (notice the variation by the way). So let's compare the highest number with both products.

The CC has only 70% of the shear strength of the H80 (shear strength is closely related to density).

Therefore you'll have to buy a thicker CC core to make up the difference in shear strength. So if the plans call for 1/2" H80, you might need to use 3/4" CC to have similar strength in the core. This does negate some of the cost savings.

H80 has a shear strain of 30% before failure. This is pretty forgiving. CC is 13%. Ah ha! So the way they are getting high numbers is to make the foam stiffer, but it's a lot less damage tolerant. I'd be a little bit worried about using it on the hull bottom where slamming loads are so high. I would be OK using it with bulkheads, decks etc. where I just need enough stiffness but high loading rates are not present. Divinycell has been around a long time with an excellent track record. CC is a new kid so I just don't know how good it is.

Boat builder is selling 1/2" H80 for $157, Carbon Core is selling 3/8" 60 lb density for $99 which are roughly comparable in shear strength. Not quite 1/2 price.

Dang thanks for the research, good info.

I will be vacuum bagging as much as I can. I’m not worried about ultra consistent results because the same methods and materials I would employ would be the same methods that have been approved to use on the wings the airplanes that I’ve previously repaired. The amount of divination between panels would be negligible in my experience and opinion. Please remember I’m not trying to build a production, bullet proof mass production boat. I’m planning on building a solo skiff to toot around the flats and beach it on a sandbar ounce and a while.

Let’s say I pick up the CC 1/2 core material fo $75 per sheet and add a layer of 1708 to the hull bottom. This might add?? 20-30 lbs and I’d save over $1000. I have a 2 stroke yamaha roller motor on the back burner and do not plan to build a center console so the added weight would or should be negligible again.

Please don’t mistake my questioning as argumentative. Just trying to save a few dollars.

Thanks again.

—Mark

[Lakesurfer]

It's actually technically challenging to make foam cores with REPEATABLE material properties. Even the best cores vary by +/- quite a few %. That sort of expertise does not come cheap. If you struggle to pay for the materials, maybe it's just not going to happen....

I have a friend who used to work for Martin-Baker - they make ejection seats for fighter planes. We were having this very same conversation and he said the reason they still aluminium is because they are working with a known quantity and it is much more repeatable than composites. I thought that was interesting.

Lakesurfer - you may enjoy reading parts of the Gougeon Manuel on epoxy. Maybe it will give you some ideas. Maybe it will also help you to understand how epoxy resin really revolutionised wooden boat building and was the missing link that took a superb boat building material that wasn’t superb because it could rot, to one that really now has pretty much everything going for it!

Read the appendix C for starters. Maybe like many of us on this forum who started out sceptical of wood because we had been brainwashed, you will change your mind and come to realise what the rest of us - and many, many great boat builders did as well - that wood is a pretty darn good material and a whole lot simpler than all your alternative suggestions...

https://www.westsystem.com/wp-content/u ... 1205-1.pdf

This from appendix C...



I have a 20 year old plywood and epoxy OD 18 - Built from plans on this site - and it had water under the sole for 5 years - and it doesn’t have an ounce of rot because everything was epoxy coated. I live next to a boat yard that has plenty of fiberglass boats in various states of disrepair that have soggy osmosis riddled hulls.

Ultimately if you own a boat - whatever it is made of - you have to look after it in a manner appropriate to what it is made of...

It’s a brain thing for me having a wooden cored boat. It makes me uncomfortable. I know it’s a proven method and if done right and maintained it can last longer than a full composite boat. But I would feel super uncomfortable to the point where I just wouldn’t build it. Maybe with my background I just trust composites more, either way it doesn’t matter as it’s something I’m just not going to do.

I may be stubborn or ignorant and I’m not trying to disagree with anyone because I actually agree but for now I just can’t change my feelings and I can’t justify spending thousands on something that I’m not into and uncomfortable about. Hope that makes sense.

Thanks again.

-Mark

[bklake]

As an A&P, this will make sense. Say a wing is designed to skinned with .020 6061. The builder thinks that is way too thin and decides to skin it with .035 because it only adds 10 pounds. Seems reasonable. The designer says don't do it. Why? The wing is designed as a unit. It no longer flexes the way it was designed. The skin is stiffer and takes too much load while the spar is doing nothing. The skin fails because, it alone, is not strong enough. Then the spar fails because it is not strong enough alone. .020 with the designed spar is stronger as a unit than the thicker skinned wing.

Another example. You are building a wing for a Rutan design and want to substitute carbon fiber for a spar and skin it with fiberglass. Sounds like a plan and you save 15 pounds. Problem is the carbon is much stiffer than the fiberglass. It fails before the fiberglass because the load is not shared. Same problem as above, 2+2=1.5. All CF wings have been designed and engineered. Much better to follow that than substitute materials.

Wood and E-glass share a similar stiffness and strength profile. Put CF where it wasn't designed for and stuff starts breaking before bending. Each component of the system has to work with the others. The designer knows this and plans it out accordingly. You start mixing stuff because x is so much stronger, lighter, better than y and you are asking for trouble. Don't get lost in a forest of specs and numbers for components. Each one is impressive but they have work together.

Where you can go crazy with exotic materials or processes is the add ons. Benches, seats, consoles, polling platforms, cabins etc. Leave the basic structure as designed and experiment with the extras. Get a quote from a designer for the material you want to use and you will find that building this way is a true bargain. You can build a hull, as designed, very quickly then get to the fun stuff. It may be that by using exotics on the extras will spur development on an entire boat. It all depends on if the common builder can do it too. 10 years ago, a CNC mill was $100,000. Now you can get a small one on Amazon for $200 and do a lot of small parts.

I would love to see glass work done by an experienced composite person. You probably have tremendous experience with glass/resin ratios and staging a process. It would be very educational for the community to see your work and see what proper glass work looks like.

[Lakesurfer]

As an A&P, this will make sense. Say a wing is designed to skinned with .020 6061. The builder thinks that is way too thin and decides to skin it with .035 because it only adds 10 pounds. Seems reasonable. The designer says don't do it. Why? The wing is designed as a unit. It no longer flexes the way it was designed. The skin is stiffer and takes too much load while the spar is doing nothing. The skin fails because, it alone, is not strong enough. Then the spar fails because it is not strong enough alone. .020 with the designed spar is stronger as a unit than the thicker skinned wing.

Another example. You are building a wing for a Rutan design and want to substitute carbon fiber for a spar and skin it with fiberglass. Sounds like a plan and you save 15 pounds. Problem is the carbon is much stiffer than the fiberglass. It fails before the fiberglass because the load is not shared. Same problem as above, 2+2=1.5. All CF wings have been designed and engineered. Much better to follow that than substitute materials.

Wood and E-glass share a similar stiffness and strength profile. Put CF where it wasn't designed for and stuff starts breaking before bending. Each component of the system has to work with the others. The designer knows this and plans it out accordingly. You start mixing stuff because x is so much stronger, lighter, better than y and you are asking for trouble. Don't get lost in a forest of specs and numbers for components. Each one is impressive but they have work together.

Where you can go crazy with exotic materials or processes is the add ons. Benches, seats, consoles, polling platforms, cabins etc. Leave the basic structure as designed and experiment with the extras. Get a quote from a designer for the material you want to use and you will find that building this way is a true bargain. You can build a hull, as designed, very quickly then get to the fun stuff. It may be that by using exotics on the extras will spur development on an entire boat. It all depends on if the common builder can do it too. 10 years ago, a CNC mill was $100,000. Now you can get a small one on Amazon for $200 and do a lot of small parts.

I would love to see glass work done by an experienced composite person. You probably have tremendous experience with glass/resin ratios and staging a process. It would be very educational for the community to see your work and see what proper glass work looks like.

Can't argue with that.

[Evan_Gatehouse]

10 years ago, a CNC mill was $100,000. Now you can get a small one on Amazon for $200 and do a lot of small parts.

Wonder how quiet it would be in the living room...

Back to cores - I'd steer away from the CC core because it is so new to the market for the hull itself and for the low strain % it has.

I would consider using it for bulkheads, decks, seats, consoles etc. where failure is not as critical and where it is not subject to slamming loads.

[Lakesurfer]

10 years ago, a CNC mill was $100,000. Now you can get a small one on Amazon for $200 and do a lot of small parts.

Wonder how quiet it would be in the living room...

Back to cores - I'd steer away from the CC core because it is so new to the market for the hull itself and for the low strain % it has.

I would consider using it for bulkheads, decks, seats, consoles etc. where failure is not as critical and where it is not subject to slamming loads.

I actually spoke with CC today and what is on their website is a 4lbs density pvc foam and I think we’re comparing those numbers to the 5lbs divinycell . Carbon core does carry a 5lbs pvc foam that is almost number for number spot on to divinycell and it’s $60 less per sheet.

[bklake]

10 years ago, a CNC mill was $100,000. Now you can get a small one on Amazon for $200 and do a lot of small parts.

Wonder how quiet it would be in the living room...

Same as a 1/2 hp wood router because that is basically what the motor is. When I was single, I routinely used my router in my living room. Married with 3 kids now. Family not a fan of the noise and dust. Probably a garage/basement only item.

[Lakesurfer]

10 years ago, a CNC mill was $100,000. Now you can get a small one on Amazon for $200 and do a lot of small parts.

Wonder how quiet it would be in the living room...

Same as a 1/2 hp wood router because that is basically what the motor is. When I was single, I routinely used my router in my living room. Married with 3 kids now. Family not a fan of the noise and dust. Probably a garage/basement only item.

I worked at a small airport a while ago doing 100 hour and annual inspections on GA airplanes, my boss at the time built a biplane in his living room. my last living room project was a 2x4 easel for my wife to paint on canvas, well girlfriend at that time. a few weeks ago I vinyl wrapped a small trim piece for my car in the living room and she blew a gasket. times have changed.