Pre-Project Questions

I was looking at some of the public domain designs and ran across the 25' Seacraft plans that appeared in Popular Mechanics long ago. I really like the boat and was wondering if anyone could answer some questions pertaining to this design.

First off. I have seen where people have modified the overall size of a design, primarily the length. My question is, can I uniformly scale this design up to about 150%? The end result is the same hull shape just bigger. While 37' is a little longer than what I want I would like the Beam to be about 12'.

The second question I have is can this design be converted to a FRP build instead of wood? Ideally making a female mold and laying up the composite sandwich inside.

The next question is this. Has anyone evaluated using a construction methodology advocated on the following URL, http://www.fuellessflight.com/matrixphoto.htm

In general, I would say that any foam that is flexible would not have the strength necessary for hull construction. However, if you used 1" X 2" strips of rigid EPS that was hot formed into the curvature, I could see some real benefits. Standard insulation running at 2lb density has extremely high compressive strength. In the neighbor hood of 25psi. Wouldn't this work when used for its compressive strength and floatation within a cross braced fiberglass reinforced epoxy matrix? I know EPS and fuel do not mix but in this case you would have each piece encapsulated and unless there was a huge failure only those strips exposed to the failure would be vulnerable. I plan on build a prototype panel like this but wanted to get additional input before I started to spend any time or money on this path.

Thanks in advance for any input.

 

The method is similar to this...

http://patft.uspto.gov/netacgi/nph-...50&s1=4495884.PN.&OS=PN/4495884&RS=PN/4495884

that I just posted here in post #6...

http://boatdesign.net/forums/showthread.php?t=18467

I have thought of doing it like shown, with the dual axis. I think it would make a real strong boat. I have heard of Carolina Skiffs (made according to the patent) becoming waterlogged, which would be very hard to remedy with that type of construction, but epoxy would cut down the probability of that. I also don't know if the problem is widespread. I would try hard to avoid the small hollow channels that you can see at the corners of each strip of foam.

 

Vaccuum

I was thinking of using a vacuum pump and work the layout in sort of a quasi-resin-infusion fashion.

Generally you would layup a wet-strip next to another dry-strip. Then lay a bladder over it that you could apply pressure to the outside and vacuum to the inside.

I have seen this done in gutar construction were they use vacuum clamping to apply pressure and draw out air bubbles when gluing a bridge on an acoustic guitar.

Applying this process with some standard composite layup methodology would allow you to clamp the piece in place and "wick-off" excess epoxy while evacuating all the air from the joints.

This is why I need to test my ideas. The thing is I have a fairly broad knowledge of useless information. I am trying to thread together some disparit ideas that may integrate well together. A.K.A., I'm board and I am doing a lot of "what-if"ing.

 

No you can't scale this 25' boat up to a 37' 6" boat. For what it's worth, the hull shape used on this boat is not particularly good.

Yes, you can make it out of 'glass, but it will need to be converted (re-engineered) by a skilled designer. Without using GRP composite construction methods, it will likely be heavier then the wooden version, but you'll have to wait for the designer's scantling calculations to be completed, before you know how much so.

Frankly, this "Matrix" method doesn't offer much for the one off market and wouldn't be especially amateur friendly. It will take much longer to make the mold then the hull, probably cost a bunch more as well.

Your assumsion about foam is incorrect. It's function, in an engineered cored structure needs to be fully understood, before you can grasp the concept. The strength comes from the skins, which are separated by the well bonded, usually high compressive qualities core. Standard insulation foams aren't suitable for marine core applications. You'll need a closed cell structure, not the open cell variety, typical of construction insulation.

Cored composite structures are highly engineered. The principles, concepts, chemistry, physics and applications need considerable study, before reliable pieces can be asked to carry you and more importantly your loved ones, farther from shore then they can swim back to.

There are many, much more backyard builder friendly methods to build 'glass hulls from. Several of these don't require a mold, nor rely on less then well proven material applications. Pick up Geer's book "Elements of Boat Strength" as a start to understanding what you're up against and to get a good start at understanding it.

I'm not trying to insult you, it's just that Matrix method looks terrible. It has voids inherent, is resin and fabric rich, has more laminates and requires more effort then necessary to construct an adequate panel of known qualities. It's a bit like buying a car that comes with 6 tires and an extra fender on each corner. Where are the savings in this revolutionary process?

 

Insite

Thanks for the insite and no insult taken. I am a firm believer in asking questions, no matter how dumb they may be perceived in order to prevent dumber mistakes.

I understand your comments on Matrix construction. It is over-engineered in some respects and under thought in others. That is what I was trying to figure out. As a construction concept is seems fundamentally sound as it is in effect a structure comprised or cross-braced I-beams. To me it seams that the use of the foam is for filler so that the lattice can form properly. With the Matrix the foam isn't acting as the web of an I-Beam as in a composite sandwich. The formed webs in between the foam is functioning as that. This seems plausible and I thought it had been a hallmark of building construction. At the very least it seemed to be a "poor mans" honeycomb core.

My biggest issue with this construction had been the voids in the joints. That is why I thought that there might be a way of crossing over some un-related technology that could be used to augment the resin-infusion process in order to reduce/eliminate the voids and excess resin.

Be that as it may, I will look up the recommened book and do further reading. I still do not understand why the hull will not scale or the reason reducing the weight of the hull would be an issue but hopefully the but will illuminate the answer.

Thanks Again

 

I think it's as you say about the foam being mainly a form for the glass. In the patent posted, 2 lb density foam is suggested as plenty for the process, and the type of foam used is a readily available, widely used, closed cell construction roofing foam, impervious to polyester resins or epoxy and 1/4 the price of conventional 'marine' 'structural' foams.

At the 'Matrix' site is an extruded carbon fiber product that seems to take the foam process shown to the next step and eliminates the foam.

 

The design shown is surely conically developed for plywood build. It would lend well to strip building, which is similar to cored construction with fiberglass inside and out.
It would be so much easier to purchase a set of plans designed specifically for your building method. The cost of plans is a pittance against the cost of building---- and the right plans can reduce building time and material costs so drastically as to offset the cost of the plans many times over.
Also, the plans in Popular Mechanics will favor building methods of the past, not considering the advantages of epoxy laminations and the changes in structural details involved.
Engines are lighter as well nowadays, outboards far more feasable due to quieter and smoother operation (as well as fuel economy), and so that option will often be available as applicable to a retro design if you look around.
All those advantages and an efficient hull too, with the look you want.

Alan

 

Plans

A good point on the plans. Most plans I have seen run in the neighborhood of 1K-3K for cabin cruisers. I certainly like the idea of using plans that are designed for a GRP construction.

I did a little more research last night and found the rigid EPS insulation is a closed cell foam that will not absorb water. Additionally polyurethane foam regardless of how it is made does absorb some water but, however much, it has a higher absorption coefficient than EPS. This is offset slightly by using a higher density foam.

I also found out the polyurethane foam has less compressive strength than EPS foam. By a whole lot!!! The offset to this is again to use a higher density foam.

From what I have been able to determine, pound-for-pound EPS is stronger, more resistant to water, and is significantly more resistant to compressive forces that polyurethane. It also seems that the need to increase the weight to get the properties desired also greatly increases the price. this is why EPS is used in al most all engineered panels like SIPs and GEOFoams. Structured Insulated Panels really have come a long way in the construction industry and the use of EPS in this area has repeatedly proven itself.

Polyurethane however is fuel resistant where EPS is not.

The matrix construction methodology isolates the potential failure of the EPS to the location of failure. I guess it is like rip-stops in sails or canvas. A failure is bad but the EPS is not there solely for its' compressive strength as other more dense foams are in standard GRP construction.

Ok lets do a little math. If you used 2lb EPS instead of 5lb marine grade foam you could double the volume and still be 4/5ths the total weight in foam. If you used a layer of woven roving on the outside, inside and between, you would have the same volume and weight as any three ply lay-up. Add in the use of a 1.875D woven tube to slide over a 1"X2" strip of EPS and you effectively add four more ply's to the lay-up. So we now have a seven ply lay-up with a 2 ply web cross braced on 2" inch centers. Wouldn't the additional ply's and epoxy offset the 1lb per cubic foot weight saving in the foam almost one-for-one? Would it weigh significantly more and by how much? Couldn't the use of lower weight roving for the tube be used without sacrificing any of the compressive strength it is intend for?

Lastly, wouldn't a hull made this way be significantly stronger than the traditional foam core construction? Certainly thicker but not significantly heavier I would presume. Isn't a mrginal increase in the hull weight worth the additional strength? It would also seem that you have a triple-hull that individually would not be feasible but combined would be practical, stronger, and albeit safer than traditional construction.

Lets say I want to give this a try. Can anyone recommend a cruiser design that would be best suited for this process?

 

Here is the foam Carolina Skiff used...
http://www.elliottfoam.com/tech.html

 

" . . .Ok lets do a little math. If you used 2lb EPS instead of 5lb marine grade foam you could double the volume and still be 4/5ths the total weight in foam. If you used a layer of woven roving on the outside, inside and between, you would have the same volume and weight as any three ply lay-up. Add in the use of a 1.875D woven tube to slide over a 1"X2" strip of EPS and you effectively add four more ply's to the lay-up. So we now have a seven ply lay-up with a 2 ply web cross braced on 2" inch centers. Wouldn't the additional ply's and epoxy offset the 1lb per cubic foot weight saving in the foam almost one-for-one? Would it weigh significantly more and by how much? Couldn't the use of lower weight roving for the tube be used without sacrificing any of the compressive strength it is intend for? . . ."

Quartxeye, your example panel is considerably heavier, thicker, more costly and more time consuming to construct. You can't "engineer on the fly" without a reasonable grasp of the concepts, of which this format is a poor place to gather them. Not that there isn't much to be learned on this forum, but starting your education and getting the necessary information absorbed, so you can indulge informed "envelope expansion" of the techniques and methods employed in cored structures, is quite limited in this arena.

Sure you can build a panel as you've suggested. It will be heavier then necessary, cost more to produce, require much more effort to build, it will use more materials and decrease interior volume available in the yacht. Typically, these things are what we try to minimize, not arbitrarily increase. The same panel can be made thinner, lighter, less costly, require fewer materials and take less labor to produce, with standard practices. Isn't this the goal, to engineer or build lighter stronger, less costly, less bulky, less labor intensive structures? Other wise what's the point. What has this to offer, in spite of the additional materials, labor weight, thickness, increased construction time and labor?

 

stitched, non woven fabrics are stronger, lighter, and cheaper than woven roving.

Also to consider is if you can get a strong enough core/skin bond.