Alternative framing for discussion

[2farnorth]

Will it work? Maybe its been discussed before. PVC pipe for framing with plywood panels. Cheap, readily available, strong, easy to construct, waterproof, filled with expandable foam for flotation. Attached is a quick overview of a proposed frame for a simple design. Looking for devils advocates and open minds.

[Eric Sponberg]

Maybe on small boats only, not for an ocean-going boat.

Eric

[2farnorth]

How about a 40 foot LOA with a 12 foot beam for use on rivers and ICW?

[2farnorth]

Eric, Nice website by the way. Thanks for any input from true professionals such as yourself.

[Eric Sponberg]

How about a 40 foot LOA with a 12 foot beam for use on rivers and ICW?

PVC is not a very strong material, nor is it very stiff (has a low modulus of elasticity, bends easily), particularly compared to plywood. Also, a pipe shape is not necessarily the best shape for a frame where strength and stiffness are required, at least in your suggested application. Frames are usually made with edge-on flat panels and perhaps even with T or L flanges for very good reason--more strength and stiffness for the least amount of weight and cost. For plywood construction, you would be able to build a stronger, stiffer, cheaper, and lighter boat simply by using plywood frames. These can be easily cut to shape, even in pieces and glued together to maximize material usage and minimize waste.

Eric

[2farnorth]

Thanks for the input Eric. So plywood frames, epoxyed (sp) to the panels huh? Lightweight is very imortant for this project as it will be electric propulsion.

[PAR]

2farnorth, you can't design a boat just yet, as much as you'd like to, you just don't have the knowledge required.

There are several good books that will get you started understanding the concepts, principles and engineering involved. Try the library here at BoatDesign.net.

[apex1]

Ohh gawdelpus.................

[2farnorth]

Ohh gawdelpus................. Are we feeling a little high and mighty? Look, I just threw something out there for discussion. I got the idea from a very accomplished boat designer in Australia at Compu-Craft. They are using round and square tubing as framework on some of thier boats. So gawdelpus if we all just stick to the norm and never think there may be a better way to do things.:)

[2farnorth]

2farnorth, you can't design a boat just yet, as much as you'd like to, you just don't have the knowledge required.

There are several good books that will get you started understanding the concepts, principles and engineering involved. Try the library here at BoatDesign.net.

I can design a boat. Whether it floats or not is another story :confused:

[daiquiri]

I don't see any structural advantage of using PVC pipes for reinforcing this composite pannel. A reinforcement needs to have a better mechanical behaviour under a given load then the structure it is supposed to reinforce, or otherwise it is just a useless weight on board. The elastic modulus of PVC is only 30-50% of plywood's so it is a more probable candidate to become a reinforced part of the structure, not the reinforcing one.

That said, I have some objections on your actual pannel/foam setup.

What you are trying to create is a sandwich of plywood/rigid foam, and you have correctly concluded that the two outer plywood skins need to be connected transversely in order to obtain a more efficient structure.
But thru-bolts are not a correct way to obtain that goal. Instead, those holes are a good way to introduce humidity in between plywood pannels, creating conditions for their rapid decay.
A hull structure is in continuous movement, and sooner or later a leakage through bolt-wood interface would occur. And once a leakage has started, it can only get worse with time.

A more correct way to connect those ply pannels would be to glue them tightly to the foam core. In that way you give a sense to the presence of the foam pannel in between, which is now not very clear.
Glueing the foam to the ply pannels provide at least three important functions:
- first, under bending loads it would stabilize the compressed ply pannel, giving it much higher resistance to buckling.
- second, it would keep ply pannels separated by some distance, which would give the sandwich structure a higher rigidity. A bigger separation between the outer skins means higher bending rigidity.
- third, it would prevent humidity form condensing on internal plywood walls, which could create conditions for bacterial and fungal growth and wood rot.

Once you have created a correct sandwich structure, it will have much more strength than a practical PVC framing can provide.

What remains as a problem is the thickness of the outer ply skin. It takes a relatively thin plywood sheet to make a rigid sandwich structure, but a thin sheet can be easily perforated by floating objects. So a (much thicker) ply-on-frame (but not a PVC frame) becomes competitive again here...

If something else comes up on my mind, I'll get back. ;)

[2farnorth]

Daiquiri, Thats what I am talking about. Good discussion that will inform more than just myself. From what you are saying, after the sandwiching of the skins, the pvc would just be useless weight. Thank you for your expert opinion.

[apex1]

Daiquiri, Thats what I am talking about. Good discussion that will inform more than just myself. From what you are saying, after the sandwiching of the skins, the pvc would just be useless weight. Thank you for your expert opinion.

You had already expert opinions mate! No, you had ONLY expert opinions, because all the contributors by so far are professionals in the boatbuilding business. ALL

And not just to contradict you. YOU CANNOT DESIGN A BOAT! period............
Maybe you can draw a picture of a boat, but that is another sandbox to play in.

[2farnorth]

Apex1, I didnt hear your expert opinion, and I am sure you have one as I looked at the pictures in you public profile. Very nice, but why do you have to be such an ash hole to someone just looking to discuss different ways of doing things. Also I guess you didnt notice the sarcasm when I stated I could design a boat.

[apex1]

Apex1, I didnt hear your expert opinion, and I am sure you have one as I looked at the pictures in you public profile. Very nice, but why do you have to be such an ash hole to someone just looking to discuss different ways of doing things. Also I guess you didnt notice the sarcasm when I stated I could design a boat.

Well, my comment was´nt really supportive, touchez! Your a..hole in this case (not nice but) understandable. Pari...

I will skimp on comments about the structure shown in your drawing, Eric, PAR and daiquiry said it all.

[PAR]

I based my comments on the basic nature and general understanding that I gather you may have. Reasonable engineering understanding, that would cause these types of questions to be "self evident" was not forth coming (apparently), so it could be assumed you didn't understand why.

With this in hand, it's clear you have some studying to do. I would start with the basics in volumetric calculations, get a handle on the math there, then onto design theory and engineering fundamentals. This way you can be fairly sure the boat will float where you'd like and not break in half on launch day.

This isn't an insult, we all start at this point. You have two choices, give up or carry on. It's a lot easier to have these types of discussions, when you have a better understanding of how things work. There is no sense in designing a boat, that doesn't come as closely to your goals as it can. Floating, with the decks facing up and about where you painted the waterline would be a nice beginning on launch day, don't you think? 40' electric propulsion requires a very efficient hull form and some very clever engineering to pull off with any success. A novice has absolutely no chance.

[rwatson]

Will it work? Maybe its been discussed before. PVC pipe for framing with plywood panels. Cheap, readily available, strong, easy to construct, waterproof, filled with expandable foam for flotation. Attached is a quick overview of a proposed frame for a simple design. Looking for devils advocates and open minds.

Hi 2farnorth - apex1 is a bit liverish this week because I have been 'examining his assertions' - but he, and all the others are right on in this case.

Expanded foam itself is a problem, as it takes up water (unlike slabs of marine foam).

Compared to plywood, foam and PVC are not cheap. You can get a lot more value out of ply offcuts as ribs than foam and PVC.

If you wanted to do a plywood shell with hollow frames, you would be better off leaving them empty( but draining to the bilge), and you could use heavy plasticised cardboard as a former for fibreglass.

My experience is that there are some pretty damn efficient and optimised plans out here for plywood stitch and glue, and you will be hard pressed to make any savings of real value.

[apex1]

Hi 2farnorth - apex1 is a bit liverish this week because I have been 'examining his assertions' - but he, and all the others are right on in this case.
If you wanted to do a plywood shell with hollow frames, you would be better off leaving them empty( but draining to the bilge), and you could use heavy plasticised cardboard as a former for fibreglass.


You may examine my assertions, til the cows come home mate, I do´nt bother.;)

Right the next one here:
Hollow frames are a mad idea! Whenever possible they are avoided in all shipbuilding industry worldwide. A simple plywood frame in this case, adds the same or more strength (if profiled) than a tube, at less weight and less trouble.
Just forget about any tubed framing.
Regards
Richard

[2farnorth]

I am an a..hole because why? I compliment you on your work on your public profile and I am an a..hole? You are abviously a proffesional when it comes to boats but a novice when it comes to actual human interaction. Maybe you need to start a forum only for professional designers and builders who allready know it all, such as yourself.

[apex1]

I am an a..hole because why?

Who said that? You named me that way! I wrote: Your a..hole (comment) ..understandable. Calm down and try to understand comments not as a personal offense, especially not when made the way I did.

[2farnorth]

Sorry I misunderstood your comment Mr. apex1. Thank you to rwatson, par, eric and daiquiri for informed professional opinions. I am not set on building with any materials in particular, just exploring everything out there. To PAR: I do realize I am not ready to design a boat. I just have an active mind that that questions most everything. I will be deploying to the Midle East in a few months so I will bring some design books with me for my down time.

[Rick Willoughby]

Thanks for the input Eric. So plywood frames, epoxyed (sp) to the panels huh? Lightweight is very imortant for this project as it will be electric propulsion.

For a light weight one-off build it is hard to beat flat panel construction using structural foam in a fibreglass sandwich. Go to carbon fibre if you want to go as light as you can but it will be more expensive of course.

One big feature of foam panels is that you can buy factory produced panels that have good quality control. It overcomes some of the quality issues of normal hand layup. Even if you make panels in the local workshop you have easier and better control on the variables than a normal hand layup over a shell.

This thread shows the progression of a build using end grain balsa cored factory panels:
http://www.boatdesign.net/forums/boat-building/my-little-piece-peace-25962-7.html
It goes on for pages but you get the idea of how the factory panels arrive and how the boat comes together.

Some designers are very clever the way they get the panels to fit together.

This blog shows home made CF panels:
http://www.adventuresofgreg.com/HPB/2009_04_24_archive.html
If you work through the blog you will see the boat coming together. The boat is 8m long but quite slender. The formed hull without fittings is only 54kg.

The weight of some of the modern catamarans and trimarans built using this technique is incredibly low. Forty foot hulls that weigh 200 to 300kg.

It is worth your while to get some experience with this method if you have a build in mind.

On this page #295 and #296 I show a small boat I built using CF over 3mm Klegecell. The main hull is 6m long and quite slender:
http://www.boatdesign.net/forums/boat-design/pedal-powered-boats-23345-20.html
As noted the actual work was 38 hours. The hull weighed 11.5kg after painting. It is much firmer and more durable than a typical kayak hull of that weight.

This is a proven technique able to give good results for novice builders who are prepared to take the time to do it well. Playing around with unproven methods, even with cheap materials, can be very wasteful. You are developing the whole thing from scratch and you will not find a designer prepared to check any calculations you might make. Without this it will probably float but you will never have confidence in it. Also do not underestimate the weight of expanded foam even before it becomes waterlogged.

Rick W

[2farnorth]

Thanks Rick. I looked at a few pictures on that Oram designed boat build down under. I will check out the rest when I have a little more time.