Is there any way of having a educated idea of knowing if your Hull is any stronger or weaker than a comparable hull built of differing materials.?
in particular , Is a strip plank hull inferior Or stronger than a glass hull if both are the same age and condition?

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MAGNESIUM said..
Is there any way of having a educated idea of knowing if your Hull is any stronger or weaker than a comparable hull built of differing materials.?
in particular , Is a strip plank hull inferior Or stronger than a glass hull if both are the same age and condition?

The USS Constitution earned the nickname "Old Ironsides" after battling the British ship Guerriere on August 19, 1812. British cannonballs bounced off its thick wooden sides, which were comprised of three layers of oak, and fall into the water.

Maybe you could fire cannonballs at them.

Yeah there is but it is complicated. Weight for weight chop strand glass laminate is pretty weak and flexible. So to get enough stiffness production boats often had thick non cored hulls that were a little heavy but strong enough for all loads. If they were not, the boat started getting soft in a few years. You can see this in a Laser dinghy. After hard sailing over a few years the glass gets micro cracks and softens up, getting slower. Old glass yachts with soft decks are common, they have been pushed into their fatigue zone because the laminate was highly loaded hundreds of times.

There are many different types of strip plank. The Gougeons did one where they stripped over double diagonal, others use lots of frames inside the hull and the more modern version - popularised in the mid 80s by kiwis like Malcolm Tennant - used stitched glass fabrics laid across the grain of cedar strips. The cedar strips in my cat are 12mm thick with 600 gm double bias outside and 350 uni inside. It is still rock hard and stiff 23 years after launch and many many thousands of coastal miles. So plenty strong, but you would not want to be tee boned. Be careful of wanting "more" strength. You want a structure to have enough strength. This could be enough to not start getting stressed so highly it fatigues more quickly, but being "stronger" is not always better. In boats, weight can never be ignored and more weight is not always a good thing, especially in decks, masts, the ends of the boat and rigging.

A very broad question. Assume "textile" should have been "tensile". Shear also needs to be accounted for - so the stress state through the panel thickness will be normal stresses from axial and bending (axial giving same stress through the thickness, bending giving tensile and compression each face linear through the thickness from zero at the neutral axis, all this in the 2 directions) and shear from lateral and vertical (external wave impact or smashing into waves or falling down them or internal flying objects..........) and torsional (hull twisting) loadings.

Assuming you are looking at strip planked cedar suggest google the below and many good informative links will come up from designers and epoxy resin and cloth suppliers. If you have strip planked oregon the timber strength grade is greater. The fibre laminate type each side needs to be known - e or s glass, kevlar or carbon fibre?

boat hull panel strength strip plank cedar compared to solid laminate grp

Not sure if "the bible" on epoxy cold moulded and strip plank as here includes such comparisons but it probably does.

www.westsystem.com/app/uploads/2022/10/GougeonBook-061205-1.pdf

If you are looking at a Jon Sayer designed and built yacht just buy it.

sayerdesign.com/about-us/

Same for Robert Hick designed and built yacht.

I have the book "The Elements of Boat Strength for builders, designers and owners" by Dave Gerr which is superb for grp, wood, wood-epoxy composite, steel and aluminium. If you have specific details of the yacht you are looking at I could respond more. Never heard of Gerr before I got his book 2nd hand but his book and website is an absolute treasure trove;

gerrmarine.com/

Select to expand quote

Kankama said..
Yeah there is but it is complicated. Weight for weight chop strand glass laminate is pretty weak and flexible. So to get enough stiffness production boats often had thick non cored hulls that were a little heavy but strong enough for all loads. If they were not, the boat started getting soft in a few years. You can see this in a Laser dinghy. After hard sailing over a few years the glass gets micro cracks and softens up, getting slower. Old glass yachts with soft decks are common, they have been pushed into their fatigue zone because the laminate was highly loaded hundreds of times.

There are many different types of strip plank. The Gougeons did one where they stripped over double diagonal, others use lots of frames inside the hull and the more modern version - popularised in the mid 80s by kiwis like Malcolm Tennant - used stitched glass fabrics laid across the grain of cedar strips. The cedar strips in my cat are 12mm thick with 600 gm double bias outside and 350 uni inside. It is still rock hard and stiff 23 years after launch and many many thousands of coastal miles. So plenty strong, but you would not want to be tee boned. Be careful of wanting "more" strength. You want a structure to have enough strength. This could be enough to not start getting stressed so highly it fatigues more quickly, but being "stronger" is not always better. In boats, weight can never be ignored and more weight is not always a good thing, especially in decks, masts, the ends of the boat and rigging.

Select to expand quote

r13 said..
A very broad question. Assume "textile" should have been "tensile". Shear also needs to be accounted for - so the stress state through the panel thickness will be normal stresses from axial and bending (axial giving same stress through the thickness, bending giving tensile and compression each face linear through the thickness from zero at the neutral axis, all this in the 2 directions) and shear from lateral and vertical (external wave impact or smashing into waves or falling down them or internal flying objects..........) and torsional (hull twisting) loadings.

Assuming you are looking at strip planked cedar suggest google the below and many good informative links will come up from designers and epoxy resin and cloth suppliers. If you have strip planked oregon the timber strength grade is greater. The fibre laminate type each side needs to be known - e or s glass, kevlar or carbon fibre?

boat hull panel strength strip plank cedar compared to solid laminate grp

Not sure if "the bible" on epoxy cold moulded and strip plank as here includes such comparisons but it probably does.

www.westsystem.com/app/uploads/2022/10/GougeonBook-061205-1.pdf

If you are looking at a Jon Sayer designed and built yacht just buy it.

sayerdesign.com/about-us/

Same for Robert Hick designed and built yacht.

I have the book "The Elements of Boat Strength for builders, designers and owners" by Dave Gerr which is superb for grp, wood, wood-epoxy composite, steel and aluminium. If you have specific details of the yacht you are looking at I could respond more. Never heard of Gerr before I got his book 2nd hand but his book and website is an absolute treasure trove;

gerrmarine.com/

Thanks for the posts very interesting information, I wonder how much real strength our old Fiberglas yachts have really lost a bit frightening when you think most modern yachts are built to the minimum .