Inexpensive hull construction materials

[fpjeepy05]

Discussion prompt:
Suppose you had a mold for a boat hull. (Shouldn't matter but say 25ft semi-displacement.) The control construction is woven roving and CSM w/ polyester resin. Supposing you wanted to reduce the cost of construction what materials could you use to do so.

For example, PVC pipe could be split in half and glassed to the hull for stiffening and the amount of CSM and resin could be reduced and since PVC is cheap the overall cost would be reduced. Or same concept, but with strips of EPS foam coated in wood glue or epoxy or Azek PVC lumber.

This is closing in on developing world construction, but for the purpose of discussion, lets assume it is in the US. And let's not include labor costs.

View media item 27241

 

[Blueknarr]

Can't beat poly roving and CSM. It simply is the cheep way.

 

[waikikin]

Hi Fpjeepy05,
Split pvc storm pipe can make a cheap & effective stringer. Would be even better with some uni fibre caps applied to the crown of the stringers and more continuity than shown in your picture, staggering the longitudinal sections doesn't seem good to me. If you want to add thickness quickly and easily upica or coremat are good- they need to sit in the middle of laminate but anything thicker than 4mm seems to get pretty hot, kind of resin hungry but easy and conformable & if using cheapest singapore ortho resin right up the path you want to travel..
Jeff.
U-Pica Mat | Japan U-Pica Company Ltd. http://www.u-pica.co.jp/en/products/products10
https://lantor.com/coremat/
Startseite - Spheretex GmbH patentierte Rohstoffe Kunststoffindustrie https://www.spheretex.com/de/

 

[TANSL]

@fpjeepy05,
The structure of the deck seen in the picture seems, just say it seems, very strong. Perhaps, in addition to trying to place cheaper materials one could study how to place much less material. A study of admissible minimums could be very interesting and, since it seems to be a series production, the cost of that study would be diluted among several constructions.
There may be combinations of layers or construction procedures that, in addition to reduce the cost of material, will reduce the cost of labor

 

[fpjeepy05]

Hi Fpjeepy05,
Split pvc storm pipe can make a cheap & effective stringer. Would be even better with some uni fibre caps applied to the crown of the stringers and more continuity than shown in your picture, staggering the longitudinal sections doesn't seem good to me. If you want to add thickness quickly and easily upica or coremat are good- they need to sit in the middle of laminate but anything thicker than 4mm seems to get pretty hot, kind of resin hungry but easy and conformable & if using cheapest singapore ortho resin right up the path you want to travel..
Jeff.
U-Pica Mat | Japan U-Pica Company Ltd. http://www.u-pica.co.jp/en/products/products10
https://lantor.com/coremat/
Startseite - Spheretex GmbH patentierte Rohstoffe Kunststoffindustrie https://www.spheretex.com/de/

I'm familiar with coremat, what is the difference with upica or spheretex? Also has anyone done a test to see if coremat can reduce the resin use enough to offset its own cost?

 

[fpjeepy05]

Just doing a little back of the napkin math... 12"x 12"x 1" is 0.62gal and 1 board foot. At $550/55gal drum (~$1/lb) for polyester resin. That is $6.20 per board foot. So for "stringerless design" or "sandwich construction" we should mostly be considering products less than $6.20/board ft

 

[Mr Efficiency]

Saving weight has to be balanced against whether there is a minimum weight the boat has to be, to fulfil the design assumptions. For example, a deep vee planing boat that is built super light, will flop around something awful, because it isn't sitting on the designed waterline.

 

[fpjeepy05]

No one mentioned saving weight. Only reducing cost.

 

[TANSL]

Useless weight is cost.

 

[Mr Efficiency]

No one mentioned saving weight. Only reducing cost.

You picture using PVC tube to stiffen is presumably designed to use less laminate, which would be less weight. If it isn't using less GRP, what is the point ?

 

[rxcomposite]

fpj - Are you talking only about the mold or the boat part? For the mold, we recycle the empty paper tube the fiberglass is rolled. We cut it half and use as stiffeners. No need to buy PVC.

 

[fpjeepy05]

Useless weight is cost.

To us boat designers, yes. But the average customer could care less. "heavy boats ride better" "I like a little durability" "If you want to go faster add another engine"

You picture using PVC tube to stiffen is presumably designed to use less laminate, which would be less weight. If it isn't using less GRP, what is the point ?

It is using less GRP, but the reason is to reduce the cost because GRP isn't free. The reason isn't to reduce GFP to reduce the weight, but that is a nice benefit. Four 10ft 2" PVC pipes could make a 6" grid on a 4x8 panel. They would cost <$30 at my local big box. So if they reduce the amount of resin required by more than 3 gallons, then its cheaper to build with the PVC pipe than without.

fpj - Are you talking only about the mold or the boat part? For the mold, we recycle the empty paper tube the fiberglass is rolled. We cut it half and use as stiffeners. No need to buy PVC.

I was referring to the boat itself, but this would apply even better for the mold.

 

[rxcomposite]

Building it light is the first thing the designer do while meeting the minimum standards. It just depends on the amount of time he is willing to spend. Different points on the boat have different pressures.

Building it cheap (fiberglass/foam) can sometimes be expensive. Using a material that is 80% of the standard value can sometimes lead to an additional layer to compensate= Heavy + additional cost + labor. The only thing cheap is the CSM + Poly but one whack with a mallet and it cracks. Better to use wood, it is cheap. There are no shortcuts to a good engineering.

 

[fpjeepy05]

Building it light is the first thing the designer do while meeting the minimum standards.

Which designers are you referring to? I know many designers personally, and clients' desires are typically where the designer begins. Sometimes its weight, sometimes its cost, sometimes it is something else.

Building it cheap (fiberglass/foam) can sometimes be expensive. Using a material that is 80% of the standard value can sometimes lead to an additional layer to compensate= Heavy + additional cost + labor. The only thing cheap is the CSM + Poly but one whack with a mallet and it cracks. Better to use wood, it is cheap. There are no shortcuts to a good engineering.

A lot to unpack here...
Fiberglass/foam is not cheap. That is the preferred construction method of high-end boats.
Rarely will adding a foam core to a composite make it heavier, if properly designed.
CSM + Poly is not the only thing cheap. See PVC above
Wood generally is cheap, but when done properly it is not. Marine-grade plywood is not cheap. Nor is the required epoxy, hardware fastener bedding, etc.

 

[rxcomposite]

This could go on forever with pre conceived ideas. Are you asking or looking for a debate?