Cheapest and easiest building material

This is an awkward set of differing subjects to pin down. The principle problems I see here are the numerous styles or types of molding, plywood and strip construction methods, of which several combine elements from some of the other methods.

I think it boils down to core density, verses sheathing attributes and how the bulk of longitudinal, athwart and compression loads are transmitted and dispersed throughout the hull structure.

You can go quite light with a very low density core, which by its nature offers little to the structure then the separation of the load bearing skins it keeps apart. These methods, generally aren't inexpensive, have a high "goo factor" and require (in many cases) high tech fabrics to pull off a design successfully. In the same vain, you could go with a slightly stiffer core, which could impart some, if not a substantial amount of help with the structure, and thinner, less gooey and less costly fabrics skins. Taking it further, you can employ a very light construction grade wooden core, skinned with stronger, denser wooden veneers as your skins with just some fabric to offer some abrasion resistance and waterproofing. See where this is going . . .

I can think of a dozen different molding methods, each using slightly different approaches to the loading issues imposed underway. The same is nearly true of strip planking, and plywood methods. Plywood being the densest of the bunch (as a core) will have a weight disadvantage, but if it's used as the structure with or without additional protection or support, this decreases it's burden. I personally, don't see any advantage to plywood used as a true core. Used in a laminate, incorporating different structural needs (like the bulk of planking concerns), certainly and cost, make us come back to it often.

Matching build difficulty, with material choices, labor elements that vary from technique to method, can be daunting. This is why the really engineered structures ('glass, composites, goo and screw, etc.) have gained popularity in recent decades. Along with the new found process are the folks needing to sell the bits and pieces for it and their marketing teams.

Maybe a spread sheet could help. I can see values placed (individually specific of course, based on many things important to you) and a simple ranking system, which could be adjusted for changing needs, skills, materials availability, labor, types of support provided, strengths, weaknesses, budget and a host of other qualifiers.

 

Hello PAR,

You have summed up the situation with regards to modern boat building very effectively, especially how the differing methods of construction can be used in one vessel, such as epoxy ply composite for the hulls and foam core composite for the superstructure perhaps? There will always be wood boat traditionalists who prefer to work long and hard, with lapstrake, carvel or sheathed strip construction and long may they continue (although they are completely cuckoo ). It's not for me.

You mention a very light construction grade wooden core, skinned with stronger, denser wooden veneers. My concern is that there are generally a number of unseen voids in cheaper WBP plywood, which could make their presence felt in a finished boat. It's likely even the marine fir ply that Jarrett Bay use for the bottom of their boats is a non-starter as far as Lloyds Registration Type Approval is concerned. Using Joubert marine ply, with the added benefit of 3100 x 1530 mm as well as 2500 x 1220 mm, would ensure that approval. That said, I'd be proud to own one of their vessels.

http://www.joubert-group.com/UK/Range/Range_Marine.htm

My attitude is that the cost of the best grade of BS 1088, is insignificant compared with the cost of the finished vessel that barring accidents and with proper maintenance, could still be in service in 2100 AD.:?:

I like the idea of an epoxy ply composite monocoque hull being heavy, because the weight is in the hull itself, rather than having the multitude of frames as incorporated in the Sculley and Jarrett Bay hulls. Hull skin thickness is the key to a self supporting structure, with the proviso that the internal fit out units are bonded to the hull as longitudinal bulkheads.

The comments above presuppose the craft is ocean going.

Design Categories
Category Significant Wave Height * Beaufort
A - Ocean Exceeding 4m** Exceeding 8
B - Offshore Up to & including 4m Up to & including 8
C - Inshore Up to & including 2 Up to & including 6
D - Sheltered Up to & including 0.3m Up to & including 4

* Significant wave height means the average height of the highest 1/3rd of the waves over a given period. Waves of double that height may occasionally be experienced.

Your ideas for a spread sheet approach to design and build are absolutely correct for commercial construction: there being so many variables, that can affect profitability, it's essential to know the ramifications of all the decisions taken during the build. As a matter of opinion, I think a spread sheet would confirm that epoxy ply composite monocoque construction has a great future in the right hands.


Pericles

 

The lighter the material usually the weaker and requires more framing. Example one the lightest boats are stamped steel. A light boat can be made by combing the best of all materials. A composite boat is best.
I like aluminum, it is half weight of fiberglass and better in damage control.

 

Aluminium is good, but noisy - and I can't weld!

Ok - let's take a different tack. Cost aside, my material of choice would be foam core/epoxy FRP sheathed. (I'd be interested to know what the difference is likely to be too...). So from a practical point of view, is foam core that much harder to build with than ply or strip plank? My understanding is that you can do it in much the same way.... foam is laid over temporary frames, glassed outside, then inside. Permanent frames/bulkheads are installed, followed by 'normal' fitout. If the shapes are developable, then the foam can be laid on in large sheet-size pieces, in much the same way as ply is. Am I right? And are there any good "how-to-build" books about this style of construction?

Once again, thanks so much for all of your input - it really is very much appreciated

 

The goo factor is much higher in a foam core FRP hull the a plywood build.

 

err.... sorry... but what's the goo factor?

 

Goo factor? The amount of resin needed to saturated the foam core and the glass cloth used to reinforce the core. Jacques has his tutorial here.

http://bateau2.com/content/view/160/28/.

He wrote it to accompany the plans for this.

http://www.bateau.com/studyplans/LB26_study.htm?prod=LB26

There is more work in building the jig for a foam core, because more frames, plus ribbands, are needed to build a plumb hull. The pressure of applying the resin can distort the foam core if there is not enough support. On the other hand, you could build a series of boats on the more substantial jig.

Whilst you're considering methods, there is a 5 minute video here.

http://www.sintesfiberglass.com/id74.html

It describes the C-Flex method, a combination of longitudinal glass rod reinforced cloth and a non shrink (casting) polyester resin, finishing with CSM and bias woven fabric and faired with a plaster type resin containing glass bubbles and industrial talc. The hull is painted with 2 part LPU.

You pays yere money, you takes yere choice!!

Pericles