Carbon Boom Design

Howdy

As has been much fraught over here, the 505 class allows carbon booms and poles. I'm in college and my partner in the boat isn't rich, so we can't quite afford the upgrade.

Just completed a course on mechanics of composites and am considering applying my knowledge to the design and construction of a boom and some spin poles for the old battle axe.

What I hope you all can help me with is two fold.

1) After the requisite research here and elsewhere I have not really found a solid source on boom design. Do any of you have a reference you could direct me too? Really its just a beam with applied loads, and any kid that's a sophomore in engineering can sort it out but the issue here is calculating leech and vang loads so I have a number to put into the engineering analysis. I can design the spar theoretically, but I don't want to go through a big iterative process of not making it strong enough and breaking it because I didn't begin with a good assumption of the applied load.

Along the same lines, what are the commonly accepted "design standards" that apply. Please don't say that if it breaks that I should build it stronger, I know that. What would help here is some standard deflection (which should be small) or safety factor to apply which accounts for an ultimate limit state (like broaching and trying to ease the main into the water....)

2) Can you recommend a laminate schedule that you've found to work well empirically? I've contemplated just making a laminate which will mimic the stiffness of my aluminum section and this is plan B, but my concern is that I won't properly account for buckling or local stresses due to fittings. If any of you have homebrewed your own booms or spar sections and can give me some advice on design details with fittings into composite tubes, that'd be sweet.

Thanks alot for your time.

 

Phil S

Super Anarchist
2,603
230
Sydney
Best measure sectin size and thickness, weigh and look at some existing carbon spars. Calculate how strong they are from the dimensions, and gain some idea what loads are applied.

Assume 2/3 of the strength is in the front half where the BM is max. and do not forget the latteral loads when the boom hits the shrouds out square, plus all the shock loads from waves and collisions.

And if you are wet wrapping you will be weaker than prepreg, and tape wrapped prepreg on a mandrel will be weaker than vacuumed female molded prepreg because of fibre kinks. No idea of the derating factors though.

I only know enough to accept that the better the materials and tooling the better the product, and that good tooling does not come cheap. So small runs are either very expensive due to good tooling or poorer standard. You take the choice.

I have tried a few home builds but buy my tubes now.

 
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another 505 sailor

Super Anarchist
7,497
184
Yeah thanks man
I've seen that and am not concerned about build process. Its more of an engineering question so that I don't build something thats just gonna break and waste my time and money.
It's going to break and you're going to waste money. It might be a fun project, so it won't be a waste of time. If it breaks in the first race of a 2 race day at Worlds, you're going to be bummed. Over the years I've been in, it's usually the home built stuff that breaks on a 505, like rudders. A home built carbon pole broke at the last regatta, underbuilt and operator error.

Do you need a new boom? If your aluminum one is fine, and as you said money is tight, spend the money on sails or accomodations this August. If you need a boom, and since money is tight, why not buy a used aluminum boom from someone who upgraded to carbon?

Unless my boom breaks, I won't replace it for a year or two. I'll let others sort out the issues.

edit:

As to the vang loads, try to bench test an aluminum boom. they bend a bit under vang load, so load it up until it bends, calculate the load, then add more.

 
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mwonnacott

Member
60
0
If you're determined to give it a go, you can get the moments of inertia (Ixx and Iyy) from the Proctor website for their aluminum sections. That would give you a starting point.

 
Yeah thanks man
I've seen that and am not concerned about build process. Its more of an engineering question so that I don't build something thats just gonna break and waste my time and money.
It's going to break and you're going to waste money. It might be a fun project, so it won't be a waste of time. If it breaks in the first race of a 2 race day at Worlds, you're going to be bummed. Over the years I've been in, it's usually the home built stuff that breaks on a 505, like rudders. A home built carbon pole broke at the last regatta, underbuilt and operator error.

Do you need a new boom? If your aluminum one is fine, and as you said money is tight, spend the money on sails or accomodations this August. If you need a boom, and since money is tight, why not buy a used aluminum boom from someone who upgraded to carbon?

Unless my boom breaks, I won't replace it for a year or two. I'll let others sort out the issues.

edit:

As to the vang loads, try to bench test an aluminum boom. they bend a bit under vang load, so load it up until it bends, calculate the load, then add more.
He's right. Those that have been there and done that, will say the same. This is especially true in carbon spars. In my fleet, we have the DIY types and they usually are the ones spending the most time in the boat park repairing their work. Not all, but many. Sure it's fun at first, you learn some techniques, and it makes you proud about doing it yourself, but it just is not worth all the effort IMO. The work almost always fails, they miss out on the racing, and the parties afterwards. The fact that it's a boom means it's not really going to improve your performance very much at all. You're much better off saving your time and money with an aluminum version and making sure it's totally bomb proof for the city front conditions at Worlds. Remember the Bay in Summer has no mercy on you or your craft - DNF's don't help your overall results either. Go metal or go home (this is coming from a carbon junkie).

 

xpatriota

Member
244
0
Howdy
As has been much fraught over here, the 505 class allows carbon booms and poles. I'm in college and my partner in the boat isn't rich, so we can't quite afford the upgrade.

Just completed a course on mechanics of composites and am considering applying my knowledge to the design and construction of a boom and some spin poles for the old battle axe.

What I hope you all can help me with is two fold.

1) After the requisite research here and elsewhere I have not really found a solid source on boom design. Do any of you have a reference you could direct me too? Really its just a beam with applied loads, and any kid that's a sophomore in engineering can sort it out but the issue here is calculating leech and vang loads so I have a number to put into the engineering analysis. I can design the spar theoretically, but I don't want to go through a big iterative process of not making it strong enough and breaking it because I didn't begin with a good assumption of the applied load.

Along the same lines, what are the commonly accepted "design standards" that apply. Please don't say that if it breaks that I should build it stronger, I know that. What would help here is some standard deflection (which should be small) or safety factor to apply which accounts for an ultimate limit state (like broaching and trying to ease the main into the water....)

2) Can you recommend a laminate schedule that you've found to work well empirically? I've contemplated just making a laminate which will mimic the stiffness of my aluminum section and this is plan B, but my concern is that I won't properly account for buckling or local stresses due to fittings. If any of you have homebrewed your own booms or spar sections and can give me some advice on design details with fittings into composite tubes, that'd be sweet.

Thanks alot for your time.

I think you are getting ahead of yourself. You want to do some small projects, like tiller extension or a spinnaker pole before you jump into a possible expensive mistake. The cloth will cost you about 30-40% of the cost of purchasing a CF boom without rigging. You will need probably seven layers of sock to make your boom. Soller is a good source, and will help you with strength (unofficially). However, I recommend you have more experience with carbon fiber, and vacumm bag before attempting it. You get one chance to get it right.

G

 

BalticBandit

Super Anarchist
11,114
2
Yeah thanks man
I've seen that and am not concerned about build process. Its more of an engineering question so that I don't build something thats just gonna break and waste my time and money.
It's going to break and you're going to waste money. It might be a fun project, so it won't be a waste of time. If it breaks in the first race of a 2 race day at Worlds, you're going to be bummed. Over the years I've been in, it's usually the home built stuff that breaks on a 505, like rudders. A home built carbon pole broke at the last regatta, underbuilt and operator error.

Do you need a new boom? If your aluminum one is fine, and as you said money is tight, spend the money on sails or accomodations this August. If you need a boom, and since money is tight, why not buy a used aluminum boom from someone who upgraded to carbon?

Unless my boom breaks, I won't replace it for a year or two. I'll let others sort out the issues.

edit:

As to the vang loads, try to bench test an aluminum boom. they bend a bit under vang load, so load it up until it bends, calculate the load, then add more.
You can use the AL boom to figure out your loads as well. get a laserpointer as a sight. rig up the sails statically at the dock, and then sheet on the main as hard as your skipper can - Doesn't matter if the wind is blowing because the limiting factor is your skipper's strength.

Now measuer the deflection and its maximum points. Repeat with the vang by itself.

Douse the sails. take a spring loaded scale and hook it between boom tip and main halyard. Have the skipper whale on the mainsheet again until you get matching deflections at the tip. Read the Scale. You now have the static max load the boom will see. From that you can also calculate the vang's max static load.

Shockloads? Well 2x isn't a bad safety factor, 3x is safe, and 150% is aggressive. But you can also improve on the aggressive by modding the layup based on the deflection pattern you saw.

Odds are though that the hand laid up boom will NOT be cheaper than buying just a stock blank tube and mounting fittings on it.

 

ExOmo

Best Anarchist Ever
2,061
228
The Great Void
The design/analysis of composite structures is one thing but your limiting factor is likely actually manufacturing the boom and accurate material properties for your particular material set/manufacturing method.

As a rough start, you could design a composite boom that has approximately equivalent stiffness (EI) to your current Al boom.

Does the 50 class limit materials or process for rigs/booms?

 

johnbillings

New member
1
0
Howdy
As has been much fraught over here, the 505 class allows carbon booms and poles. I'm in college and my partner in the boat isn't rich, so we can't quite afford the upgrade.

Just completed a course on mechanics of composites and am considering applying my knowledge to the design and construction of a boom and some spin poles for the old battle axe.

What I hope you all can help me with is two fold.

1) After the requisite research here and elsewhere I have not really found a solid source on boom design. Do any of you have a reference you could direct me too? Really its just a beam with applied loads, and any kid that's a sophomore in engineering can sort it out but the issue here is calculating leech and vang loads so I have a number to put into the engineering analysis. I can design the spar theoretically, but I don't want to go through a big iterative process of not making it strong enough and breaking it because I didn't begin with a good assumption of the applied load.

Along the same lines, what are the commonly accepted "design standards" that apply. Please don't say that if it breaks that I should build it stronger, I know that. What would help here is some standard deflection (which should be small) or safety factor to apply which accounts for an ultimate limit state (like broaching and trying to ease the main into the water....)

2) Can you recommend a laminate schedule that you've found to work well empirically? I've contemplated just making a laminate which will mimic the stiffness of my aluminum section and this is plan B, but my concern is that I won't properly account for buckling or local stresses due to fittings. If any of you have homebrewed your own booms or spar sections and can give me some advice on design details with fittings into composite tubes, that'd be sweet.

Thanks alot for your time.

Hey Russell,

I was looking over a variety of booms at PCC's. The larger sections make sense to me - they leave some room for rigging inside. Mike Jue (another 505'er) is a composite guy. I beleive he did bike forks and such & has a number of qualifications from UCB in composites & marine engineering. I can put you in touch with him & he might help get you going. - John - in San Diego.

 

Pete M

Super Anarchist
8,778
3
So Cal
ICE in the Columbia river gorge makes I 14 filament wound bowsprits & booms (same section), to P. bieker specs - job done

 
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GybeSet

Super Anarchist
Howdy
As has been much fraught over here, the 505 class allows carbon booms and poles. I'm in college and my partner in the boat isn't rich, so we can't quite afford the upgrade.

Just completed a course on mechanics of composites and am considering applying my knowledge to the design and construction of a boom and some spin poles for the old battle axe.

What I hope you all can help me with is two fold.

1) After the requisite research here and elsewhere I have not really found a solid source on boom design. Do any of you have a reference you could direct me too? Really its just a beam with applied loads, and any kid that's a sophomore in engineering can sort it out but the issue here is calculating leech and vang loads so I have a number to put into the engineering analysis. I can design the spar theoretically, but I don't want to go through a big iterative process of not making it strong enough and breaking it because I didn't begin with a good assumption of the applied load.

Along the same lines, what are the commonly accepted "design standards" that apply. Please don't say that if it breaks that I should build it stronger, I know that. What would help here is some standard deflection (which should be small) or safety factor to apply which accounts for an ultimate limit state (like broaching and trying to ease the main into the water....)

2) Can you recommend a laminate schedule that you've found to work well empirically? I've contemplated just making a laminate which will mimic the stiffness of my aluminum section and this is plan B, but my concern is that I won't properly account for buckling or local stresses due to fittings. If any of you have homebrewed your own booms or spar sections and can give me some advice on design details with fittings into composite tubes, that'd be sweet.

Thanks alot for your time.
rewind .. reset cache ... deep breath .. then buy a carbon tube

other than the vang area reinf./sleeve there ain't much rocket science in a boom that size

(as opposed to a mast for instance)

--------------

Odds are though that the hand laid up boom will NOT be cheaper than buying just a stock blank tube and mounting fittings on it.
yessiree bob

.

 
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usa7606

Member
195
0
Howdy
As has been much fraught over here, the 505 class allows carbon booms and poles. I'm in college and my partner in the boat isn't rich, so we can't quite afford the upgrade.

Just completed a course on mechanics of composites and am considering applying my knowledge to the design and construction of a boom and some spin poles for the old battle axe.

What I hope you all can help me with is two fold.

1) After the requisite research here and elsewhere I have not really found a solid source on boom design. Do any of you have a reference you could direct me too? Really its just a beam with applied loads, and any kid that's a sophomore in engineering can sort it out but the issue here is calculating leech and vang loads so I have a number to put into the engineering analysis. I can design the spar theoretically, but I don't want to go through a big iterative process of not making it strong enough and breaking it because I didn't begin with a good assumption of the applied load.

Along the same lines, what are the commonly accepted "design standards" that apply. Please don't say that if it breaks that I should build it stronger, I know that. What would help here is some standard deflection (which should be small) or safety factor to apply which accounts for an ultimate limit state (like broaching and trying to ease the main into the water....)

2) Can you recommend a laminate schedule that you've found to work well empirically? I've contemplated just making a laminate which will mimic the stiffness of my aluminum section and this is plan B, but my concern is that I won't properly account for buckling or local stresses due to fittings. If any of you have homebrewed your own booms or spar sections and can give me some advice on design details with fittings into composite tubes, that'd be sweet.

Thanks alot for your time.
installing a side launcher would be a better investment of your time and money.

 
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heidiv

New member
38
0
With all this new found interest in carbon booms for the 5o5. Are there any guideline/tricks you need to follow when fitting one out? How different is it than Aluminum other than you need to keep your bits really sharp?

 

BalticBandit

Super Anarchist
11,114
2
With all this new found interest in carbon booms for the 5o5. Are there any guideline/tricks you need to follow when fitting one out? How different is it than Aluminum other than you need to keep your bits really sharp?
Huge difference.

Carbon doesn't deal well with point loads, and sharp metal contact So where on AL you'd mount a fitting with machine screws or poprivets, try that in carbon and you will soon end up with a fitting that has chafed out a larger hole that then fails explosively.

So if you are going to mount fittings on the boom, they either need to have strain relief guides glassed in as part of original construction, or you need to have some sort of backing plate glassed in, or fitted on the other side of your fittting for load distribution.

The simplest way to do this on a generic tube is to carry the primary load on a webbed strap.

CST composites has a great "how to" guide for rigging out your boom http://www.cstcomposites.com/How%20to%20fi...your%20boom.pdf

 

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