Inexpensive hull construction materials

Well, I guess this somali boatbuilder is state of the art then.



What is cheap depends on where you are and what you want. Have you considered ferro?

 

I said foam is not cheap. I didn't say all foam construction is high end. But thanks for posting the video. I think it shows that foam (Or PVC or other) can be used to reduce cost. I don't think the Somali boatbuilder is using the foam to make the hull lightweight; they are doing be because making the frames and stringers out of straight CSM and Poly would cost more.

I have not considered ferro

 

The traditional cheap way of making GRP boats is timber inserts to stiffen the structure. Maybe treated timber would be the way to improve the durability of it, it is a shame to see boats that could have lasted indefinitely, not economically repairable because of rotted wood,

 

I thin PVC board, i.e. Azek would be a possible replacement for wood. It becomes brittle with age, but that is better than rotting I think.

Or cheap foam to create the shape. (coated with wood glue to stop it from melting. Then use acetone or gasoline to melt it all out, and leave it hollow.

*** edit I just read a lot of resins don't adhere to wood glue so maybe skip that

 

PVC isn't as stiff as wood, and likely not as strong, I don't know about the ageing issue.

 

Fpjeepy you need to be clear about what you want. Yes foam/wood/cardboard stringers can be used to stiffen the structure. They do not function the same way, wood only needs to be atached to the skin while the others are formers and you need a much heavyer laminate to take the actual load. Can you save resin and csm by doing it? I don't know, you would need an actual case study to see how much material for the same properties (panel stiffness, puncture resistance, etc.) and then make a cost analisys for a given location.

The somali builders are using cheap urethane foam because wood is more expensive/unavailable in the needed sizes. You can see in the video that they use wood only were they have to (longitudinal bottom stringers, transom).

 

PVC is not too stiff. If cost is an issue, cheap lumber is the way to go.

 

Build it out of cardboard and packing tape. Cheap.

 

In most of the places in the world; wood is the cheap material. Bamboo might win it...not here.

You are seeking a degree of stiffness.

PVC is not the cheapest. I have tried to abstain, but I must echo gonzo's sentiment.

 

I agree. Wood is the cheapest. But it will rot if not done properly, and doing wood properly is not cheap.

Assuming wood is the winner. What is second place?

 

The second is using a cheap form, like cardboard, and laminate over it. However, the OP indicated he wants to save on resin and fiberglass.

 

I stated I wanted to reduce the overall cost.

Cardboard will soak up water. What is the third place finisher?

Also, cardboard can't be used for sandwich style construction. What would be second place for that?

 

Cardboard is used as a form, it doesn't matter that it soaks up water. Sandwich construction material preference will largely depend on the shape of the hull. If it is a developable surface, plywood is a good choice. There is no best choice for every application. However, if cost is the driving parameter, solid laminate with a chop gun is the cheapest.

 

It does matter if you don't want wet, rotting paper and associated mold perpetually in your bilge.

Plywood will be the first choice, what would be the second?

I agree that a chopper gun may be the most well-established solution, but there has to be other outside the box solutions that are comparable. Recycled plastics sell for cents per pound polyester resin has compressive and shear strengths 10x that required for a core material. Do they make a hopper gun that shoots plastic pellets? Something like the popcorn ceiling guns?

 

Junkyard non rusting Wire mesh of the proper Gage and stiffness of the required strength for the panel areas?