Wood-fiberglass Mast (ideas to improve it in 2022?)

[Richard_F]

I messed up my excell drawing that time. Most time it is better.

You could use other than H80. Depends on the design (spacing of ribs). Can even be a light foam core, no ribs. Just relying on biax layers and unis. The core takes up the compression stress.

For a nodeless (no rib design, tapered, differing cross section), lay up can be 90/0/+45-45 with the uni 0 degree taking up most of the bulk. The ratio is about 15% biax on the outside to take care of shear, 70% 0 degree uni for bending strength, and 15% 90 degree fibers to prevent collapse/buckling. This is filament winding method.

Carbon uni is a necessary evil if you want bending strength approaching that of alloy. Eglass can be used for the 90 and +45-45 degree. The author cautions about using Eglass uni with +45-45 because of differing strain. Apparently the +45-45 Eglass has low strain compared to Eglass Uni. I haven't found any reliable data yet to confirm. Anyway, design is always a compromise. Bulk of 1 direction can be increased, thus Eglass uni can be used. For comparison, Carbon uni and certain species of wood has similar strain.

I need to look into this with more details to see what I can change and leave the same strength as the original. I would leave the ribs and stringers as necessary, if I can switch on most parts (ribs, ply, etc) from wood to divinycell is already a big improvement on my view (no rot).
The good point is that I have one reference to compare to.

 

[rxcomposite]

I need to look into this with more details to see what I can change and leave the same strength as the original. I would leave the ribs and stringers as necessary, if I can switch on most parts (ribs, ply, etc) from wood to divinycell is already a big improvement on my view (no rot).
The good point is that I have one reference to compare to.

The spacing of the ribs depends on the stiffness of the skin. If you use sandwich structure, you can eliminate the stringers. You can beef up the main spar using a C or box beam, stiffening the caps with lots of Eglass uni. The nose or leading edge does not have to be beefy. It handles only shear flow, thus solid fiberglass, No birdstrike at high speed is suffered by the mast. The trailing edge handles the induced torque. Needs to be solid biax and WR construction.

You can build the skin using a pair of mold and resin infusion. Add flanges with alignment tabs so that the finished part can be mated together accurately. You need to have build in joggle (depression) so that you don't build up laminate during assembly.

Ribs are sandwich laminate. Tab/glue/align then fit the upper and lower skin. You may have to grind some part for a perfect fit. For a perfect fit, we place release tape on the inside of the skin and apply thickened epoxy on the edge of the ribs. Flop the skins (upper and lower), clamp and allow to set, It will align naturally if you have the flange with corresponding alignment tabs. Release when cure and you have perfect fit.

Trim the flange leaving only the joggle. Assemble using industrial epoxy such as 3M 2216 or Hysol. Complete the tabbing on the edges/ joggle.

Lastly, you can build only a section, fix the end part to a wall, effectively a cantelever and sandbag the part with an equivalent force the RM dictates. Measure the deflection. If you want, you can test it to destruction and see where it fails. It is only a part and not too expensive.

 

[rxcomposite]

If you are comfortable with math, this is a combined load and the detailed explanation on the site best describe it.

It is basically the weight of the sail and riggings bearing on the mast (compression), the torque induced by the force acting on the sail (torsion), and the off axis horizontal load. The "push" (bending) exerted by the sail perpendicular to the mast.

 

[wet feet]

Borrowing the drawing from rxcomposite to show how they built their second mast:

View attachment 183226

I'm seeing 21mm of glass,in total and can't really understand where the 5cm of carbon comes from.I don't think I have ever seen a carbon laminate more than about 40% of that thickness.That in itself was an outlier and efficient design with due regard for the properties of the material and anticipated loads ought to save a lot of cash and laminating time.

The other question that crosses my mind is whether,like most wing masts,it is intended to rotate?If it is,how will the rotation control be applied and will the torsional rigidity be sufficient?Certainly an interesting project.

 

[wet feet]

Thats much more rational.I had hoped you weren't referring to a 5cm thick laminate.For a fixed mast,will you be using spreaders and lower shrouds?If so,the attachment points will need careful engineering.Has a post just disappeared?

 

[Richard_F]

I'm seeing 21mm of glass,in total and can't really understand where the 5cm of carbon comes from.I don't think I have ever seen a carbon laminate more than about 40% of that thickness.That in itself was an outlier and efficient design with due regard for the properties of the material and anticipated loads ought to save a lot of cash and laminating time.

The other question that crosses my mind is whether,like most wing masts,it is intended to rotate?If it is,how will the rotation control be applied and will the torsional rigidity be sufficient?Certainly an interesting project.

sorry my bad explaining at first, they have built two masts, the first one it was a Kurt Hughes project and it had a 5cm carbon fiber layout (not sure if this is 100% true, I´m saying what they told), this mast has less wood and less E-glass + the 5cm of carbon fiber. The project indicate a 5cm width strip of carbon fiber but they laminate someting like 60cm width (taking the measurement from the picture) of carbon fiber, pic bellow:

The second mast, they add much more wood and E-glass, no more carbon fiber, that´s why they had 7 mm thickness of E-glass on the surface and it was double on the front and back of the spar (laminated one over the other)

I do not plan to have a rotating mast, by the way their second mast it was not rotating, only the first one. My intention is only use geometry to get stiffness avoiding carbon or at least reduce it as much as I can, maybe only strips for the box spar as rxcomposite suggested.

Probably I will have something like an ellipse section, not really a wing. I was trying to estimate the weight by meter of this mast, the wood they used is Freijó, 0,59 g/cm3. The cross section of mast had roughly 300 cm2, so 17,7Kg/m just of wood, need to add the 7mm hand laminated of triaxial of E-glass for the surface (roughtly 2m length) and need to add the ply. Not light weight but I think is good enough for a DIY + wood/fiberglass mast, I was checking the weight of aluminium mast for a multi around 50ft and found this webpage bellow, it does´t look too bad as the aluminium mast has almost half of the cross section.

MetalMast Performance Mast Sections https://www.rigrite.com/Spars/MetalMast_Spars/MetalMast_Masts.php

 

[Richard_F]

Thats much more rational.I had hoped you weren't referring to a 5cm thick laminate.For a fixed mast,will you be using spreaders and lower shrouds?If so,the attachment points will need careful engineering.Has a post just disappeared?

sorry I was unable to add a picture, so I just copied it and post it again adding the picture.
yes indeed, i will add spreaders and lower shrouds, good point to keep in mind.

 

[Richard_F]

If you are comfortable with math, this is a combined load and the detailed explanation on the site best describe it.

It is basically the weight of the sail and riggings bearing on the mast (compression), the torque induced by the force acting on the sail (torsion), and the off axis horizontal load. The "push" (bending) exerted by the sail perpendicular to the mast.

I can crunch some numbers, have you add the wepage? Just got a picture. I´m planning to run this on SolidWorks to see how it goes..

boy ..you´ve hit the nail on the head.... I just found another Thread that they had discussed this issue more than 10 years ago. They did had a I beam Spar and looks like carbon fiber strips where you suggested.

Gougeon Wing Mast Plans https://www.boatdesign.net/threads/gougeon-wing-mast-plans.32195/page-3

 

[Richard_F]

That looks very light compared to what I posted.. .

 

[rxcomposite]

I can crunch some numbers, have you add the wepage? Just got a picture.

The lecture of combined loading in YT is in part A and B. There are plenty if you want to find some more. In Imperial and Metric. System.

It is an old technology so you have to date your research.
Eric Sponberg has retired but has written numerous articles in BD Forum and PBB. He is one of the foremost and leading composite mast designer.

Martin Hollmann (passed away) has three volumes with illustrations. Although his book on composite aircraft design and wing design, the physics is about the same. It is a design book or ring bound book in late 80's (3 volumes) that you might find in the library. It is a design book so expect some math, and a lot of typo errors. Took some time working it out.

If you look closely at the picture, you will notice that the centroid is heavily reinforced, the leading edge not so, the trailing edge is a weaker version of the main. Because that is what the analysis will tell you.

I especialize in advanced composites. Sorry can't help you in wood construction.

 

[Richard_F]

The lecture of combined loading in YT is in part A and B. There are plenty if you want to find some more. In Imperial and Metric. System.

It is an old technology so you have to date your research.
Eric Sponberg has retired but has written numerous articles in BD Forum and PBB. He is one of the foremost and leading composite mast designer.

Martin Hollmann (passed away) has three volumes with illustrations. Although his book on composite aircraft design and wing design, the physics is about the same. It is a design book or ring bound book in late 80's (3 volumes) that you might find in the library. It is a design book so expect some math, and a lot of typo errors. Took some time working it out.

If you look closely at the picture, you will notice that the centroid is heavily reinforced, the leading edge not so, the trailing edge is a weaker version of the main. Because that is what the analysis will tell you.

I especialize in advanced composites. Sorry can't help you in wood construction.

Thank you rxcomposite, I have more information now to look for it, you already helped and I´m sure you are more than capable to help in the future. But probably I will ended up something like you already said:

Let me see if I get it right:

1_ build female jig to therm-form the foam, half skin and infuse it, like that:

2_build the I beam spar or box spar (not sure if it´s necessary to be all WR);
3_ glue/tab I beam spar on the first half skin;
4_ build the ribs, sandwich laminate
5_ glue/tab the ribs on both sides of the I beam spar and the half skin ( that mean each rib has two pieces, from each side of the I beam);
6_ to close it building the other half of the skin, not sure the easiest way to do it, if I infuse the other complete half I think that it´s going to be difficult to align and put it together, that it´s a 20 meter piece. Maybe I can break this in steps, build the foam with just one side with fiberglass, than it´s flexible, I can glue the fiber-glassed side on the spar and ribs, each section at a time then later fiber-glass the outer skin.
7_ add fiberglass layers if necessary on the outer skin (but I´m not sure if I can infused that....maybe it would be hand laminated, need to check )

 

[rxcomposite]

Richard-Why don't you post the max Righting Moment of your boat, sail plan, mast height/plan, the base root ribs and the tip rib, and your intended rib spacing. That way, other members can do parallel calculations or estimate. I know one member who says he has a software that can do composite mast calculations.

I do have written the code for a round mast and an ellipse but not yet for a D shape profile and I can tell you right now, strength will not be a problem. It will be deflection and twist that is hard to control. And that is your problem from the very start.

It is going to be a very expensive endeavor especially if you want to improve something that did not perform to your expectation. I doubt if Solidworks can crunch the numbers for you.

 

[Richard_F]

oh I could not even imagine that someone could do this. I uploaded the page with the information now. No need to be D shape, I was thinking more like elliptical or something easier to build. I´m still reading all the info I got here.

yes, I know that to run simulations you can only compare with something that has been tested, hard stuff to make sure that all is fine. If I understood right, this is one of the reasons why mast projects are not very popular nowadays for DIY, too many factors that can compromise the project and each sailboat will need a new design.

 

[Richard_F]

For the ribs spacing I was reading this Kurt Hughes paper.... but this I could easily over design... will add little more weight only...

 

[Richard_F]

I was just reading another thread about a wood wing mast .... then he build a wing composite foam + carbon mast and change the rigging with no spreaders.... very interesting...

carbon fiber wing mast for my cat https://www.boatdesign.net/threads/carbon-fiber-wing-mast-for-my-cat.25444/