Composite Beams

[Thom delForge]

I will be interesting to see if these beams are strong enough -- I am not an engineer; however, I believe my beams are as strong or perhaps stronger than my original beams.  I decided to build my composite units to the same dimension as the timber.  Using four pultruded square 1/8" wall tubes laminated to a foam core (non-structural) shaped to match the original dimension.  I also laminated diagonal components to form a 'web truss' within the beams.  At the mast step additional pultrusions were laminated to the center of the beams to distribute any load.  I then began laminating two layers of 17 oz. bidirectional glass cloth on the entire outside Extra layers on all tube connections, and then several layers at around the lashing positions.  I feel that has more than made up the structural equivalent of the wooden units.  All in all they seem quite stiff, although I know they will have a slight degree of flex -- being encapsulated as they are I don't have any doubts at to their strength.  These too are over built -- just in composite.   

My plans now call for finishing all the 'mods' this winter and possibly sailing to Key West by winter -- ambitious perhaps, but getting close.

Thom

[Galway Bay]

Luckily it is not necessary to model the whole rang of motion. The max. loads can be identified and calculated.

1.  The first is the down force on the beam assuming a single mast on the centre of one beam at the point of lifting a hull.

2.  The second is to assume an extreme case - one hull held as if in a vice supporting the other hanging in mid-air.

These are both simple exercises in levers solvable with no more than a few sketches. For my boat the answers are  [ approx. ]     1. = boat wt.     2.  = boat wt. x 2.   Most W. boats will be similar.

Now you must exercise judgment. Should the value for 2. be divided by the number of beams or should we continue to assume an extreme case - all the weight on only one beam ? or a guesstimate compromise ? Incidentally this is also the max. value on lashings.

So once you have this decision made you can now calculate a beam to carry these loads. I cannot find my very useful book by John Teale but I seem to remember this involves no more than looking up a material value from tables and fitting this into a short formula.

A little tiresome perhaps but hardly a dark art.

I would be happy with a beam to these specs. and including the usual engineering margins.

I remember great excitement in the yachting press  when Japan announced it was going to make this standard mandatory on multihulls and apparently was actually proposing to TEST them !!

And now the really good news - all this work is superfluous !!

If all you want to do is substitute one beam for another and you accept the first as adequate then all you have to do is apply the simple formula to the first to establish a base value and ensure the new one at least matches it.

Hollow beams / I beams etc have been around for ages the calculations can be done on any pocket calculator , indeed good estimates can be done with a pencil. The formulas are in any practical boat building or even carpentry book.

Once more I recommend John Teale's book "How to build a boat". It is on Amazon.

[stella]

Even with some decay I could have sailed a bit more if the beams would have been made to plan. The hardwood (I go for oak) triangle under the bolt fixed to the hull keeps the lamination from splitting and is screwed into the beam, actually screwing into the different lamination layers. On an alternative beam materials  I would stick to this feature and consider the curvature - the arc absorbs many shocks. I have seen flat beams on a Pahi 31 do fine, but with a triangle allowing the movement. I love the lashing and the flexibility, which polyester or of course or even prefabs could deliver. I doubt alu could do it, although junked laser or hobby-cat masts could do for an instant fortune-repair. They are great for the non-flexing first and last net-holding beam.

The reason for the failure was the boat being given up by a professional skipper for about 6 years, which was not obvious on purchase. AS the picture shows, it is redwood. I would actually prefer pine, as it is a long fiber. Luckily I got the boat to sign that he guaranteed the wood and beams were impeccable. I'm not to blame for not painting or maintaining. Still I would consider oils instead of paint to let the wood breath and keep the wood structure visible.

Especially having the shapes and plans for plywood, I think a plastic hull, using Stella as a mold, may be a modern easy-to-build alternative. Wharrams are about making a cheap and easy do-it-yourself live-aboard evtl unsubmersible, easy to sail cruiser, backed by an interested community. I think plastic can do this.

[Jeremy Walker]

Yep, this is an interesting thread. What seams to characterize a Wharram is most definitely the de mountable beams with flexible connection, along with easy amateur construction.

Laminated wooden beams fit in well with this philosophy and composite construction is not so much more difficult or complex. Only real problem I think would be amateur builders trying to gain a lower weight advantage using fibre/matrix/foam composite, and in which case the result may be flimsy and unreliable.

Beams weighing possibly a bit more than wooden laminates could no doubt be less rot prone, which of course raises the question about using composites for hulls......... as an answer to the same problem there.

[Thom delForge]

The beams I built for my Tiki 31 using foam core and pultruded (4 x 1" x 1" square tube) to the original designed shape then laminating the tubes, warping the entire structure with 2 layers of 17 oz. cloth. The building method is straight forward, time consuming, but straight forward. The results with my beams are that they are lighter by half, and seem to be as strong. There is an almost undetectable amount of flex - something like 1/4" to 3/8" per 18'. Combined with the lashings flex I feel quite comfortable.
I showed these beams to James and Hannke -- Hannke thought these were just fine -- I just remembered I was meant to send her some samples of the pultrusion (forgot until now) -- I will be getting those in the post soon.
If anyone care to inspect my set up here in SW Florida -- you are welcome -- just call.

[Galway Bay]

Thom-

I have been looking at your photos.

However I have a concern. I see a good truss structure vertically and therefore good strength / loading this way. I do not see any  truss horizontally so I wonder about this. Horizontal beam loads can in fact be high when sailing. Also these are point loads at the lashings / beam trough ends not spread out.

These beams need to carry the weight of a car. I could see you driving a car over one held vertically but would you be confident of being able to do it if the beam was laid on it's side ?

[Robert Hughes]

I suspect the saving factor for the horizontal loadings in Thom's beams is the two layers of 17oz cloth they're wrapped in.  Probably just a good idea to check for any horizontal deformation in the areas where these loadings are applied next time the beams are off though.

People often forget about the horizontal loads on beams.  Although they're significant they're not as great as the obvious vertical loads.  Years ago I knew some young guys who sailed a Raka from England to the Caribbean (in the first ARC), and before they left they got quite worried about how much the hulls moved horizontally, like one trying to overtake the other!  They were so concerned that they fixed a pair of diagonal rigging wires from the bow of each hull to the stern of the other.  This triangulated the structure very well, but they still joked about whose hull would reach Barbados first!

[Thom delForge]

Robert Hughes said:

I suspect the saving factor for the horizontal loadings in Thom's beams is the two layers of 17oz cloth they're wrapped in.  Probably just a good idea to check for any horizontal deformation in the areas where these loadings are applied next time the beams are off though.

People often forget about the horizontal loads on beams.  Although they're significant they're not as great as the obvious vertical loads.  Years ago I knew some young guys who sailed a Raka from England to the Caribbean (in the first ARC), and before they left they got quite worried about how much the hulls moved horizontally, like one trying to overtake the other!  They were so concerned that they fixed a pair of diagonal rigging wires from the bow of each hull to the stern of the other.  This triangulated the structure very well, but they still joked about whose hull would reach Barbados first!

[Thom delForge]

I guess I am not that concerned -- years ago an engineer created a computer model to create a greater understanding as to loads and the requirements for materials and dimensions.  As I recall, the fore and aft beams on the Classic designs did approximately 80% of the work.  One of his sons rebuilt his Tangaroa with just two beams in steel.  David Coe's Windchime was built 20 years ago (undergoing a total refit in SW FLORIDA).  The beams have been replaced and lengthened to a total just under 23'.  The lashing system is through a series of eyebolts through the hulls.  The boat has been through the mill -- but still very much together.  It will be complete in the next 6 months and ready for the Bahamas. 

David Halliday at BoatSmith has beed building composite beams for his production Wharrams, I believe he has incorporated a triangler shape (Tiki 21/26 style)  -- I believe that would be better in terms of horizontal structure, but in my case I was refitting all my deck arrangements therefore kept the same dimensions as the original timber beams.  I see now I could have built the fore and aft beams with the triangle provision.  Still the loads seem to be within any serious question. The Wharram design philosophy of being extremely conservative and redundant. 

Thom delForge said:

Robert Hughes said:

I suspect the saving factor for the horizontal loadings in Thom's beams is the two layers of 17oz cloth they're wrapped in.  Probably just a good idea to check for any horizontal deformation in the areas where these loadings are applied next time the beams are off though.

People often forget about the horizontal loads on beams.  Although they're significant they're not as great as the obvious vertical loads.  Years ago I knew some young guys who sailed a Raka from England to the Caribbean (in the first ARC), and before they left they got quite worried about how much the hulls moved horizontally, like one trying to overtake the other!  They were so concerned that they fixed a pair of diagonal rigging wires from the bow of each hull to the stern of the other.  This triangulated the structure very well, but they still joked about whose hull would reach Barbados first!

[Thom delForge]

Thom delForge said:

I guess I am not that concerned -- years ago an engineer created a computer model to create a greater understanding as to loads and the requirements for materials and dimensions.  As I recall, the fore and aft beams on the Classic designs did approximately 80% of the work.  One of his sons rebuilt his Tangaroa with just two beams in steel.  David Coe's Windchime was built 20 years ago (undergoing a total refit in SW FLORIDA).  The beams have been replaced and lengthened to a total just under 23'.  The lashing system is through a series of eyebolts through the hulls.  The boat has been through the mill -- but still very much together.  It will be complete in the next 6 months and ready for the Bahamas. 

David Halliday at BoatSmith has beed building composite beams for his production Wharrams, I believe he has incorporated a triangler shape (Tiki 21/26 style)  -- I believe that would be better in terms of horizontal structure, but in my case I was refitting all my deck arrangements therefore kept the same dimensions as the original timber beams.  I see now I could have built the fore and aft beams with the triangle provision.  Still the loads seem to be within any serious question. The Wharram design philosophy of being extremely conservative and redundant. 

Thom delForge said:

Robert Hughes said:

I suspect the saving factor for the horizontal loadings in Thom's beams is the two layers of 17oz cloth they're wrapped in.  Probably just a good idea to check for any horizontal deformation in the areas where these loadings are applied next time the beams are off though.

People often forget about the horizontal loads on beams.  Although they're significant they're not as great as the obvious vertical loads.  Years ago I knew some young guys who sailed a Raka from England to the Caribbean (in the first ARC), and before they left they got quite worried about how much the hulls moved horizontally, like one trying to overtake the other!  They were so concerned that they fixed a pair of diagonal rigging wires from the bow of each hull to the stern of the other.  This triangulated the structure very well, but they still joked about whose hull would reach Barbados first!

Funny!

[Galway Bay]

Thom some of this conversation is out- of - sequence, crossed in the post so to speak. Obviously I was typing while others were posting.

I have great respect for David Halliday and his construction methods. Also I like what he does to the sails although I feel this is better suited to his wind area [ and wallet ! ] than mine. But David designs his beams or else hires in an engineer to do it. I would be surprised if they were only laid-up with 2 layers of 17oz [ 600g/m ?] glass cloth.

Why do you seem to think the vert. side needs a truss but the hor. not ? If the encapsulation is good enough for the horizontal forces why is it not good enough for the vertical ones ? It is worth stopping to think about this. It is essentially what bothers me.

Perhaps over -cautious but that is what we all would like to be ?

I like the idea of alternative beams including alternative materials. I think lashings are the best attachment for a home builder.

Happy sailing. I do not think you will come to grief in any way. But I would need more convincing - including at least SOME estimates , some figures before I was happy.

[Galway Bay]

Sorry Thom - I managed to delete a post by accident. My own so no harm ! Fat fingers !

Basically I was fessing up to having sailed into the pier end once at about 5kn. Truly. Now stop laughing !! 

Stopped one hull dead and the beams took the shock of the momentum of the other. Probably something like this would be a good max. load situation to consider. Easy enough to calculate - we know the momentum from the weight and speed and we know the lever length. So we have figures for a worst case point load at the lashings.

Probably you will never meet this load in sailing. Possibly a racing boat might not survive it. I think a cruising boat should.

[Penn D]

Speaking of one hull coming to a complete stop... A friend of mine in a tiki 26 was landed on by a Hump Back Whale off Noosa, Qld, Aus. He was doing 8 knots so the story goes when the Whale breached and came down on the Starboard bow. The little Tiki came to a complete stop bow diving down, then, proceeded on it's coarse as though nothing had happened.

I dont think it would cost too much to get an engineer to punch some numbers for you. Biggest hurdle would be finding the right engineer. Be good to hear from boatsmith in regards to this.

I love the idea of composite beams, but with my lack of working knowledge, I myself would be getting someone who really knows what they are talking about to calc them for me.

Peace