Boat Plans Stitch And Glue
Gday all,
I hope we all had a great week thinking of all things relating to boats..as usual !
World on Water latest News
This week we feature the finish of Thomas Covilles round the world attempt in his 105 foot Tri SODEBO, The Third ISAF regatta in Palma the 2011 Trofeo S.A.R. Princess Sofia MAPFRE, this weeks Fresh to Frightening featuring bashes and crashes in the Sydney 18 Foot Skiffs plus much more! An action packed 5 mins of all the best in Global boating last week.
Believe it or not, Wood is Best
Designing in metal, fibreglass, and other high tech materials, my favourite boatbuilding material is wood. Part of this is the aesthetic and pleasure of wood, but mostly its due to the fact that wood is, in many respects, actually stronger than any material known – even the space age materials. What’s more, wood is far less expensive and much more pleasant to work with.
Just What is Strength?
How can wood, plain ordinary wood, be stronger than Kevlar and graphite fibre’s (carbon fibre). I know it doesn’t seem possible, but it is the case. The confusion comes from the word “strength”. It’s important to understand exactly what’s being said when someone claims one materials stronger than the other.
To understand strength and how it’s compared, we have to understand the different kinds of strength. For basic structure applications, there are two critical types of strength: Tensile strength and stiffness (The modulus of elasticity – E), of which both are measured in pounds per square inch (psi) or kilograms per square centimetre (kg/cm^2).
Using common boatbuilding materials, let’s arrange a table, in order, from the “strongest” to the weakest” material.
Strength Versus Weight.
It appears, at first glace, that wood is anything but “strong”; it’s at the very bottom of the list. But remember that we have to be very careful about what we mean by comparing strength. Since boats – and most structures- require the minimum weight for a given strength, what we really need to compare is how strong each material is for its weight. You’ll notice that though wood has the lowest tensile strength, it also has – by far- the lowest weight of density, at just 32 lb./cu.ft or 512 kg/m^3. You can also see that although wood’s simple tensile strength is the lowest, its stiffness (modulus) is actually higher than E-glass, which weighs twice as much. How can we compare strength relative to weight?
Simple- divide the Tensile strength by density:
Doing this will give the following new table
Immediately, we can see that wood moves up in the list. Pound for pound, it’s stronger in tension than aluminium, ordinary E-glass-FRP lay-ups, and – even though your used to thinking of steel as being so strong – wood’s stronger than steel. Only the high tech, space age materials are stronger than wood in tension pound for pound. What if we do the same thing for the modulus or stiffness?
Example: Stiffness or E/ Density
This time – with regard to stiffness – wood had moved even further up the list. According to this simple analysis, wood is stiffer, pound for pound, than any fibreglass lay-up, any Kevlar lay-up and steel. Aluminium is a hair stiffer pound for pound, but the difference in stiffness is so slight as to be unimportant.
It still appears that wood’s less stiff than graphite fibre (carbon fibre), Spectra, and titanium but there is more to comparing strength. In fact, in most structures like buildings, airplanes, and boats, “stiffness” is more critical than pure “tensile” strength. This is because “stiffness” determines how much the structure bends under load. In most cases, if the structure’s stiff enough not to bend excessively, it’s far stronger than necessary in terms of simple tensile loads. Even more important though, is exactly how stiffness (the Modulus “E”) is used to determine if a structural member’s strong enough to resist bending of flexing is a certain application, when made of a specific material.
Structural Efficiency
For columns, structural stiffness is related to the materials specific stiffness (its modulus) and the square of the columns length. For beams and panels, it’s related to stiffness and the cube of the length. Doing some basic algebraic manipulations will show that for column’s structural efficiency’s equal to the square root of the stiffness divided by the density of a material. and that for beams and panels the structural efficiency equal to the cube root of the stiffness divided by the density
Column structural efficiency = (sqrt( stiffness or E)) / Density
Beam and Panel structural efficiency = (cubed root ( stiffness or E)) / Density
Wood Wins
Now that we know how structural efficiency- for stiffness- is determined, it’s a simple matter to generate new tables that give structural efficiencies as follow:
Amazingly, - and contrary to everything you’ve probably read and heard – wood is structurally far more efficient than any of the building materials known anywhere. It’s even more efficient than titanium and advanced carbon fibre and spectra composites. In other words, you can build a lighter structure out of wood than anything else, of the same stiffness.
Wood Shortcomings
So why aren’t airplanes and spacecraft made of wood? Well, airplanes were for many years, through and beyond WW2 were made of wood. Wood, however, isn’t the perfect material – there’s no such thing. Supersonic aircraft and missiles experience high heat – as do spacecraft – which eliminates wood from consideration. Additionally there are other factors – abrasion resistance or hardness for one. Wood is very poor here. Aluminium and steel hulls can take a much greater beating against other objects, like rocks – than unprotected wood. Further, they can’t burn. Another consideration is fastening the material together. Wood falls down here too when compared to welded aluminium and steel. Before modern glues (epoxy and the like), it was the fastenings that limited wood hull strength, not the wood itself.
Wood’s also only moderately efficient in tension. For pure tension members structural efficiency is simply the tensile strength divided by the density – as we did in our first calculation. Here, high tensile materials like carbon and titanium are clearly superior. This is part of the reason why rigging wire, bolts, and tie-rods are made of metal. Finally we should consider volume.
Strength versus Volume.
Because wood is light you can use less of it pound for pound, but the structural piece required will be thick or fat – quite fat – compared to metal or high-tech laminates, which are denser. Wood standing rigging would be stronger pound for pound than steel or aluminium, but such rigging would be too fat, too much windage and interesting- it would be too stiff. It’s actually necessary for rigging wire to flex and bend with changing load direction. It’s this that keeps the rigging in pure tension. Wood standing rigging – assuming such a thing were possible – would be so stiff it would be subject to bending as well as tension, which would quickly lead to failure.
Wood/ Epoxy Composite
For modern one-off and semi-production boat hulls though, wood/epoxy-composite construction offers the lowest cost, the lightest weight, and the most control over hull shape possible. By gluing up and encapsulating wood in epoxy, the hull becomes essentially one unit, without structural joints or seams and weakness of local fasteners. Even better, the wood is protected from rot.
Finally, wood’s soft, easily abraded surface can be protected by finishing the hull with a few layers of unidirectional S-glass cloth or E-glass, which has great abrasion resistance. Overall, a hull of this construction is easy to build, light, strong, long-lived and with low maintenance.
So the next time your thinking of building your own boat and wondering:
"What materials should I use?"
Well... Ill let you be the judge
Have a great week !!!
Latest Weekly Builds
Grahams SportzMaster 19
On the way home from Brisbane , we dropped in to visit Graham and Helen and to see their SportzMaster 19. All I could say was WOW ! What a sweet looking boat ! After crawing around the outside, I finally climbed inside. Damn, Grahams photos do not give it justice as to just how big this boat is ! Its bloody huge ! As I couldnt stay for long, but we yakked about his boat for a while, swapping a few ideas around as to what he wanted in the design.
Today I ran all the wiring to make sure all would go through the loom with the heavy battery cable 2 B&S it was a squeeze but I managed. I have just glued the panel with the wiring looms showing down and will glass that section tomorrow.
You can see more of Grahams SportzMaster 19 in our BoatBuilding Forum
For more information about the SportzMaster 19, or any other of our range of designs,
please visit our website
Peters Mushulu 12
Just yesterday we recieved the latest build pictures from Peter and his Mushulu 12.
Last time we spoke, Peter was preparing to glass the exterior of his boat whilst it was still upside down and was in the process of making up all the internal joinery, seats etc.
Its great to see the progress so far and speaking last , hes now sanding the boat and preparing to paint her.
It wont be long now and well have another launching !!!
Top One Pete !!
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I hope we all had a great week thinking of all things relating to boats..as usual !
Easter is now fast approaching with only 2 days, so no doubt many will be taking a short holiday over the 5 day break, so please take care on the roads and out on the water.
World on Water latest News
Believe it or not, Wood is Best
Designing in metal, fibreglass, and other high tech materials, my favourite boatbuilding material is wood. Part of this is the aesthetic and pleasure of wood, but mostly its due to the fact that wood is, in many respects, actually stronger than any material known – even the space age materials. What’s more, wood is far less expensive and much more pleasant to work with.
Just What is Strength?
How can wood, plain ordinary wood, be stronger than Kevlar and graphite fibre’s (carbon fibre). I know it doesn’t seem possible, but it is the case. The confusion comes from the word “strength”. It’s important to understand exactly what’s being said when someone claims one materials stronger than the other.
To understand strength and how it’s compared, we have to understand the different kinds of strength. For basic structure applications, there are two critical types of strength: Tensile strength and stiffness (The modulus of elasticity – E), of which both are measured in pounds per square inch (psi) or kilograms per square centimetre (kg/cm^2).
Using common boatbuilding materials, let’s arrange a table, in order, from the “strongest” to the weakest” material.
Strength Versus Weight.
It appears, at first glace, that wood is anything but “strong”; it’s at the very bottom of the list. But remember that we have to be very careful about what we mean by comparing strength. Since boats – and most structures- require the minimum weight for a given strength, what we really need to compare is how strong each material is for its weight. You’ll notice that though wood has the lowest tensile strength, it also has – by far- the lowest weight of density, at just 32 lb./cu.ft or 512 kg/m^3. You can also see that although wood’s simple tensile strength is the lowest, its stiffness (modulus) is actually higher than E-glass, which weighs twice as much. How can we compare strength relative to weight?
Simple- divide the Tensile strength by density:
Doing this will give the following new table
Immediately, we can see that wood moves up in the list. Pound for pound, it’s stronger in tension than aluminium, ordinary E-glass-FRP lay-ups, and – even though your used to thinking of steel as being so strong – wood’s stronger than steel. Only the high tech, space age materials are stronger than wood in tension pound for pound. What if we do the same thing for the modulus or stiffness?
Example: Stiffness or E/ Density
This time – with regard to stiffness – wood had moved even further up the list. According to this simple analysis, wood is stiffer, pound for pound, than any fibreglass lay-up, any Kevlar lay-up and steel. Aluminium is a hair stiffer pound for pound, but the difference in stiffness is so slight as to be unimportant.
It still appears that wood’s less stiff than graphite fibre (carbon fibre), Spectra, and titanium but there is more to comparing strength. In fact, in most structures like buildings, airplanes, and boats, “stiffness” is more critical than pure “tensile” strength. This is because “stiffness” determines how much the structure bends under load. In most cases, if the structure’s stiff enough not to bend excessively, it’s far stronger than necessary in terms of simple tensile loads. Even more important though, is exactly how stiffness (the Modulus “E”) is used to determine if a structural member’s strong enough to resist bending of flexing is a certain application, when made of a specific material.
Structural Efficiency
For columns, structural stiffness is related to the materials specific stiffness (its modulus) and the square of the columns length. For beams and panels, it’s related to stiffness and the cube of the length. Doing some basic algebraic manipulations will show that for column’s structural efficiency’s equal to the square root of the stiffness divided by the density of a material. and that for beams and panels the structural efficiency equal to the cube root of the stiffness divided by the density
Column structural efficiency = (sqrt( stiffness or E)) / Density
Beam and Panel structural efficiency = (cubed root ( stiffness or E)) / Density
Wood Wins
Now that we know how structural efficiency- for stiffness- is determined, it’s a simple matter to generate new tables that give structural efficiencies as follow:
Amazingly, - and contrary to everything you’ve probably read and heard – wood is structurally far more efficient than any of the building materials known anywhere. It’s even more efficient than titanium and advanced carbon fibre and spectra composites. In other words, you can build a lighter structure out of wood than anything else, of the same stiffness.
Wood Shortcomings
So why aren’t airplanes and spacecraft made of wood? Well, airplanes were for many years, through and beyond WW2 were made of wood. Wood, however, isn’t the perfect material – there’s no such thing. Supersonic aircraft and missiles experience high heat – as do spacecraft – which eliminates wood from consideration. Additionally there are other factors – abrasion resistance or hardness for one. Wood is very poor here. Aluminium and steel hulls can take a much greater beating against other objects, like rocks – than unprotected wood. Further, they can’t burn. Another consideration is fastening the material together. Wood falls down here too when compared to welded aluminium and steel. Before modern glues (epoxy and the like), it was the fastenings that limited wood hull strength, not the wood itself.
Wood’s also only moderately efficient in tension. For pure tension members structural efficiency is simply the tensile strength divided by the density – as we did in our first calculation. Here, high tensile materials like carbon and titanium are clearly superior. This is part of the reason why rigging wire, bolts, and tie-rods are made of metal. Finally we should consider volume.
Strength versus Volume.
Because wood is light you can use less of it pound for pound, but the structural piece required will be thick or fat – quite fat – compared to metal or high-tech laminates, which are denser. Wood standing rigging would be stronger pound for pound than steel or aluminium, but such rigging would be too fat, too much windage and interesting- it would be too stiff. It’s actually necessary for rigging wire to flex and bend with changing load direction. It’s this that keeps the rigging in pure tension. Wood standing rigging – assuming such a thing were possible – would be so stiff it would be subject to bending as well as tension, which would quickly lead to failure.
Wood/ Epoxy Composite
For modern one-off and semi-production boat hulls though, wood/epoxy-composite construction offers the lowest cost, the lightest weight, and the most control over hull shape possible. By gluing up and encapsulating wood in epoxy, the hull becomes essentially one unit, without structural joints or seams and weakness of local fasteners. Even better, the wood is protected from rot.
Finally, wood’s soft, easily abraded surface can be protected by finishing the hull with a few layers of unidirectional S-glass cloth or E-glass, which has great abrasion resistance. Overall, a hull of this construction is easy to build, light, strong, long-lived and with low maintenance.
So the next time your thinking of building your own boat and wondering:
"What materials should I use?"
Well... Ill let you be the judge
Have a great week !!!
Latest Weekly Builds
Grahams SportzMaster 19
On the way home from Brisbane , we dropped in to visit Graham and Helen and to see their SportzMaster 19. All I could say was WOW ! What a sweet looking boat ! After crawing around the outside, I finally climbed inside. Damn, Grahams photos do not give it justice as to just how big this boat is ! Its bloody huge ! As I couldnt stay for long, but we yakked about his boat for a while, swapping a few ideas around as to what he wanted in the design. Graham comments:
Hi Mark,
Today I ran all the wiring to make sure all would go through the loom with the heavy battery cable 2 B&S it was a squeeze but I managed. I have just glued the panel with the wiring looms showing down and will glass that section tomorrow.Picked up a Tinka trailer yesterday 6.2 meters long with 26 rollers so the boat should fit OK.
Cheers
Graham
For more information about the SportzMaster 19, or any other of our range of designs,
please visit our website
Peters Mushulu 12
Last time we spoke, Peter was preparing to glass the exterior of his boat whilst it was still upside down and was in the process of making up all the internal joinery, seats etc.
Its great to see the progress so far and speaking last , hes now sanding the boat and preparing to paint her.
It wont be long now and well have another launching !!!
Top One Pete !!
You can see more of Peters Mushulu 12 in our BoatBuilding Forum
For more information about the Mushulu 12, or any other of our range of designs,
please visit our website------------------------------------------------------------------------------------
See you next week with our latest weekly news and other articles !
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