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

[Browndog]

Welcome to the forum. Congratulations on considering a boat building project. The access to experienced boat builders and the designers along with continuing support is extremely helpful along the way.

Many boats have been built or are being built by folks with less experience than you have. The forum has many wonderful examples that have been documented by the young, old, men, and women builders that participate in sharing their work here.

The boat plans assume some familiarity with the use of the materials and boat building in general and are not a how to manual. There are numerous tutorials though and many build threads that help to fill in the step by step details.

There are many different features and benefits to the differing core & hull skin materials and the various construction methods. Cost is one component, weight is another, ease of use, ability to be formed into developable surfaces, tolerance of joints required, susceptibility to rot, UV resistance, ready availability, toxicity, and strength are just a few of the many considerations.

There are so many choices: Wood, aluminum, fiberglass reinforced plastic, steel, ferrous cement, epoxy fiberglass marine plywood composite, cold molding, stitch & glue, foam sandwich construction, skin on frame, male or female molds, cedar strip.

Your experience, location, construction facilities, existing tools and comfort with the different materials and most importantly the requirements you have for the boat you plan to build will help to steer you towards the best combination of materials and methods.

The cost of the hull materials is only one component to consider.

The cost of the trailer, motor, steering, controls, gauges, fuel system, pumps, fittings, primer, paint, tools, sandpaper, brushes, rollers, gloves, et al, adds up quick. Even if you value your labor at $0, your time is worth something and the time spent on this project is time away from paying work, home maintenance, other recreation, etc.

If you want an inexpensive boat, you will be better off buying a used, but in good condition, production boat that meets your requirements. Most people do not use their boat very often as you acknowledged and they tend to depreciate fast. There are many good deals to be had.

On the other hand if you want to exercise your creativity, use your knowledge of aircraft composite building and experience the pride of building and owning a high performance custom one off hand made boat then you are in the right place pursuing the right project.

Best wishes to you as you embark on your project.

[OneWayTraffic]

There's not a carefree boat building material in the world.

Balsa core: rot, especially around hull penetrations.
Foam core: Impact strength, unless you put thick skins on, water ingress around hull penetrations can ruin foam just as easily as wood.
Marine plywood core: Water ingress and rot.
Polyester glass: Water ingress (osmosis), heavy poor long term fatigue strength for its weight.
Aluminium: Galvanic Corrosion, welds pop, rivets loosen and leak, noisy slapping against waves, cold and condensation.
Steel: Heavy (especially for small boats) and rusts.
Wood: maintenance heavy and will not forgive neglect.

Most of the issues come down to workmanship and neglect. If you build a plywood core boat well, seal all penetrations, and look after it, then it will outlast you. So will a foam core, though it would not be my choice in that size.

I would not even consider building a one off polyester boat. All the work, more cost to build a plug, then a mould and no advantages in terms of weight savings.

An alternative to buying a second hand boat in good condition is buying an old one in less than good condition. There are a lot of rebuilds in the forums. That way you have both a solid symmetrical solid glass hull, and custom features and layout.

[Fuzz]

Over the years I have owned and or fished a ton of different boats. I have built a wood epoxy boat, a foam cored boat and three solid glass boats. They have ranged from 18 to 36 foot. You have received good advice from all the guys. Do like Browndog said and add up all the costs to get a boat on the water and then look at the cost to build the hull. On a 15 foot boat the hull will be way less than 25% of the total cost no matter what you build it out of.

[fallguy1000]

Over the years I have owned and or fished a ton of different boats. I have built a wood epoxy boat, a foam cored boat and three solid glass boats. They have ranged from 18 to 36 foot. You have received good advice from all the guys. Do like Browndog said and add up all the costs to get a boat on the water and then look at the cost to build the hull. On a 15 foot boat the hull will be way less than 25% of the total cost no matter what you build it out of.

You can say that again. A 60hp Merc new is about $8 grand. Makes the $3k hull look cheap.

[Lakesurfer]

4. Im not concerned with the overall weight of the boat.

That's like not being concerned with the overall weight of an airplane. Boats operate in a different medium, but weight and balance are still important in the design. When you get the PH15 planing, it's essentially "flying" on the surface of the water. Just like an airplane, extra weight in the hull is going to mean either less useful load or more power (bigger engine) to get the same performance. TAANSTAFL.

Being in aviation I completely understand the importance of weight, drag and thrust. I use the "i'm not concerned with weight" statement very loosely. Im a complete amature dirt bike rider and I've watched so many people spend so much time and money on weight savings and just completely waste it. people asked me where they should cut weight on their bike and i always told them to forget about the weight and use the money for gas. the people with more gas tend to ride more and get better in the end.

that being said, I definitely do not want to jeopardise or compromise the boat in any serious way. if the boat is designed to carry 3 adults or whatever, and I add 200lbs throughout than im ok with only carrying 2 adults. not that it works that way exactly. so im not concerned with adding weight but ill definitely pay attention to the added weight and compensate if needed.

-Mark

[Lakesurfer]

LS I think you are missing something on the performance side, Draft. The heavier you are the more you draft, and the deeper the water you will need to not only float, but to get up and plane out.

You will also most likely spend more making the plug and thickening the lamination for strength then you would on the cored version. There are some price conscious foam and pvc cores out there now that will help you out, like carbon core. Good luck.

For sure I agree with ya here,

Im really trying to find a way to avoid building an expensive (relative) home built boat. my confidence and abilities, I believe are up to the challenge but i can fade in and out of projects at times. as it stands with the divinycell foam, im looking at, maybe $6,000 for a completed hull?

Ive been looking at carb core for a while now and it looks like a potential option for PVC foam and even seemingly better is there carbon core PE foam. its a polyester foam in 5lbs density that is said to have better properties than PVC and PU foams and is quite a lot cheaper. I've been using US Composites epoxy resin for a long time without issues and can be had for a little over $600 for 10 gallons. so if the PE foam is what it is and with the cloth and epoxy i could be looking at maybe around $3,000 for a completed hull, ish. still have a lot of questions to answer though.

Don't sell yourself short. I get the concerns very much, hell I currently have three unfinished boats and I just started another one not to mention the four vehicles in various stages of restoration. I am VERY ADHD and have a hard time staying on task. If I take even a single day off from a project there is a chance that I don't start back on it, but rather bounce to something else.

With that said, I think one big mistake you're making mentally is looking at it as a "home built boat". You are mentally implying that it will be inferior somehow to a store bought boat and so you feel bad about spending money doing it right. A better way to look at it is a "custom built" boat, one that is carefully hand crafted to exacting specifications using premium materials and stringent quality control. Once you can wrap your head around that way of thinking then you will have a much better time with the project and not look as closely at the price of each component. That may be harder on the wallet, but it will be better on the finished product and may even keep you focused longer to the point where you actually finish something you started (not a slam at all, like I said before: I'm the same)

Please don't take this post as negative criticism, just an offering of advice from someone who suffers the same snags in building that you do and is working to overcome the same.

solid advice, I appreciate it.

-Mark

[BB Sig]

Welcome to the forum! Nothing to add except we look forward to your build! Keep us fed with lots of pictures!

[bklake]

If I read correctly, you like a design here but want to build it differently with a material you are more familiar with?

I have participated in experimental aviation for 50 years, went to Oshkosh for the first time when I was 5. I have seen many build planes exactly as designed and everything worked great. I have also seen dreams come crashing down when someone changed something in a design because they thought they knew better or wanted to do it the way they knew. Steve Wittman was a genius designer but he refused to change his ways when he used Dacron fabric on his plane. He used the glue and dope he always used for cotton fabric. It worked fine for a few years until it didn't.

These boats are designed by an experienced designer and engineer. A seemingly simple change has huge implications down the line. Build it as designed and have many happy years with a boat that works as described and is safe. There is probably a design out there in your material of choice. Go with that rather than adapt something. I can't speak for the designer but he has vast experience in just about all building materials and methods. He could competently design or adapt a design. All it takes is money. His designs here can be made by anybody with basic tools. Not everybody has a full composite shop and the experience to make usable parts. Is it a better use of his time to design something hundreds will buy or spend the same amount of time on something 3 people will buy?

Take a chance and expand your skills on a wood core boat. There might be some valuable skills or techniques that will help you solve a future situation in your composite business.

[Lakesurfer]

If I read correctly, you like a design here but want to build it differently with a material you are more familiar with?

I have participated in experimental aviation for 50 years, went to Oshkosh for the first time when I was 5. I have seen many build planes exactly as designed and everything worked great. I have also seen dreams come crashing down when someone changed something in a design because they thought they knew better or wanted to do it the way they knew. Steve Wittman was a genius designer but he refused to change his ways when he used Dacron fabric on his plane. He used the glue and dope he always used for cotton fabric. It worked fine for a few years until it didn't.

These boats are designed by an experienced designer and engineer. A seemingly simple change has huge implications down the line. Build it as designed and have many happy years with a boat that works as described and is safe. There is probably a design out there in your material of choice. Go with that rather than adapt something. I can't speak for the designer but he has vast experience in just about all building materials and methods. He could competently design or adapt a design. All it takes is money. His designs here can be made by anybody with basic tools. Not everybody has a full composite shop and the experience to make usable parts. Is it a better use of his time to design something hundreds will buy or spend the same amount of time on something 3 people will buy?

Take a chance and expand your skills on a wood core boat. There might be some valuable skills or techniques that will help you solve a future situation in your composite business.

hey, im actually originally from Appleton, WI, not far from Oshkosh. I went to the EAA more after I left the state lol. from there I got my A&P and have been in various areas within aviation, most recently sitting at a desk manipulating excel spreadsheets. Building a Vans RV-8 was on my bucket list for a long time until I took a few flying lessons from my old boss who was an instructor rated pilot. I could barely make it off the runway before getting the most sick i've ever been in my life. I tried a few times with the same results and decided that building an airplane for me was a terrible idea.

During that time I stared building surfboards. i build a few with foam and glass to help me understand the shapes and designs a little better. then I made 2 cedar strip 8 ft funboard surfboards. with a ton of time and numbers I designed it exactly like the wing of an experimental AC. it has a central spar and several ribs spaced out every 12 inches with a cedar skin covered in epoxy and glass. local surfers thought i was ridiculous and told me it wouldn't work and to heavy and so on. well it was pretty heavy for a surfboard but it worked and has worked for 10 years now with moderate use of course and a few repairs along the way. it needs to be vented due to the air inside heating an cooling, I forgot the vent screw in it and the heated air inside popped a board and cracked the glass. it wasn't the best or most useful surfboard by far and I definitely have WAYYYY more time building it than riding it but it was an awesome experience. I recently started stripping it because I used epoxy that doesn't have any UV resistance and now its starting to look pretty rough and ugly.

that being said, the last thing I want to do is offend the designer(s) or builders(s) and I would never think for a second that I may have a better way of doing something that goes against a proven method. for me its about the entire building process, maybe go against the grain a little to see what happens.

I made carbon fiber tubes a long time ago with scrapes from the shop and tested them out by driving my truck over them. those tubes laughed at my truck. maybe one could build tubes, cuth them in half and glass them into the bottom of the hull to serve as stringers? not that I would consider that but it crossed my mind. I've also made little carbon fiber I beams for a failed project. the beams didn't fail and were insanely strong. but the forms to make them were relatively easy and wouldn't be that much more difficult for stringers and frames. but i'm not sure i wanna pay the price to test it out.

so at the end of the day I really would like to build it out of foam if my best options are foam or plywood. the plans call out for Divinycell PVC closed cell foam. at almost $200 for a 4x8 sheet, I really struggle to pay up for 16 sheets. there has got to be an alternative, they can't be the only company who makes closed cell PVC foam, right? I reached out to carbon core and was told that their closed cell PVC foam is a direct replacement for the divinycell stuff and at half the cost. this is the information im sort of looking for.

thanks for the reply

-Mark

[Evan_Gatehouse]

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.