Hey! Gimme my thread back! I'm still looking for concrete designs, with dimensions.
Wouter, I actually like your design, what thickness for the timbers (planks), how about maximim width? Aluminum strips on the 3 edges? Thickness? The same width as the thickness of the timbers?
I'll consider an aluminum pole, What dia, and wall thickness?
A 4" dia carbon tube has been suggested, anyone agree with that? Wall thickness? Most affordable source of such a pole?
Any other thoughts or considerations on my original T proposal?
Other designs?

Dave

Carbon, Aluminium and now CONCRETE <img src="http://www.catsailor.com/forums/images/graemlins/confused.gif" alt="" /> <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

Quote:Gato are you reading this?

Would not like to miss it for all the carbon in the word. I will try Wouters solution for the boom. There is for les than 50€ in timber for a 4 meter spar and I have time enough to give it a try. At least I will not be doing something stupid in stead.

Jake,

I like you as a person, so it is not about that.

But I do think a great definition of "unwiseness" is to first state that you didn't read all of my inititial posting and then follow-up with claims about what you feel I failed to mention.

You could at least do me the honour of actually reading the article you are about to critize ? Fact checking and that sort of stuff.


Lets look at what we wrote okay.

You wrote :




When I had already written in the post you replied to :




To copy the expression you used first : "no $hit Sherlock".

I had already stated in my first posting that the diameters wouldn't be the same. Add to this that such an observation is trivial (obvious).

A component having the same weight, same stiffness AND same dimensions as another component would practically have to be made of the exact same material, wouldn't it ?

Pardon my emotional outburst. I got a little annoyed chasing wraiths created by a person who clearly didn't read the whole posting. And the "INCOMING" picture and "No $hit Sherlock", "Mr tensile strength" and "Mr density" quote's aren't much justification to calling you dumb, or are they ?

I hope you can now understand my use of descriptions in line of the word "stupid".

If you just had read all my posting and took a little time to reflect on what was written then you would have recognized the "uselessness" of your comments before you wrote them down.


Wouter

Dave,

I can't give you dimensions unless I know what loads are acting on your boom. Magnitude and direction. Contrary to what some people believe, I don't do guesswork.

>>Wouter, I actually like your design

Which one of the two ?

After some though I would personally do it even simpler in your case. Just two vertical planks and alu strips as top and bottom. And have the the outward facing corners of the timber plancks rounded at a woodshop. That should be sufficient to score "good" on the hurting your head aspect.

The sides of the boom can then still be given a non-constant contour optimizing for load baring and weight.


>>Aluminum strips on the 3 edges?

I really doubt wether you'll need that. Just alu on top and bottom (can also be carbon of course)


>>Thickness? The same width as the thickness of the timbers?

Probably not. Alu (carbon) is much stiffer then timber and also weights significantly more per volume. So you are looking at relative thin alu strips compared to the timber. And that is all you'll need anyway.


>>I'll consider an aluminum pole, What dia, and wall thickness?

Also for this I need to know the loads and such. However 80x2 round sections are pretty much commonly available and should hold. Such a section should only weight 3.40 kg (7.5 lbs) per 2.5 mtr (8 feet) length. This is probably bigger then needs be but it will give you a feeling of what we are talking about. If such a section is made out of carbon then it would still weight about 2.30 kg (= 5 lbs). So how much are you willing to spend on 2.5 lbs weight savings ?


How long is the foot of your mainsail ? And what kind of purchase are you using on your mainsheet ?



>>A 4" dia carbon tube has been suggested, anyone agree with that?

I find that a larger diameter. I think you can do with less. Note that 8 foot 80x2 mm alu tubes (about 3 inches outer diameter) are also as rearbeams on homebuild Blade F16's. There it handles sheet loads of about 300 kg at midbeam. Surely it will hold up as a boom.

But lets give you a proper design, so allow some time to get the laod data of your boat and run them through some calculations.


>>Wall thickness?

If going for a pure aluminium tube then you never need more then 2 mm walls. If you can get 1.6 mm then that would be perfect as that would be 25 % weight savings.


>>Most affordable source of such a pole?

Without a doubt your local alu supplier.


>>Any other thoughts or considerations on my original T proposal?

It can be done better.


Wouter

Thanks Gato,

Can you send me the pics of the building and its completion ?

Or just signal me that they are on your blog.

I would love to have those pics.

Wouter

Ok, it will probably take some time but I will not forget to send you the pics.

>>Wouter, I actually like your design

Which one of the two ?

I like them all, am most attracted to the 1st, which is closest to my T shape, but honestly, I think it's the appearance that appeals to me, and that's probably not the best reason to choose it.

After some thought I would personally do it even simpler in your case. Just two vertical planks and alu strips as top and bottom. And have the the outward facing corners of the timber plancks rounded at a woodshop. That should be sufficient to score "good" on the hurting your head aspect.

So, the vertical planks would have an elliptical shape (narrower near the ends), and the alum strips would be constant width and thickness? Maybe 2" x .25" alum strips? A max width of the side planks of 6" to 8"?

>>Aluminum strips on the 3 edges?

This question refered to the original T shape.

>>I'll consider an aluminum pole, What dia, and wall thickness?

Also for this I need to know the loads and such. However 80x2 round sections are pretty much commonly available and should hold. Such a section should only weight 3.40 kg (7.5 lbs) per 2.5 mtr (8 feet) length. This is probably bigger then needs be but it will give you a feeling of what we are talking about. If such a section is made out of carbon then it would still weight about 2.30 kg (= 5 lbs). So how much are you willing to spend on 2.5 lbs weight savings ?

Type of aluminum alloy?

How long is the foot of your mainsail ? And what kind of purchase are you using on your mainsheet ?

The main has a luff of 34', foot of 11', square top. Currently running 10 to 1 mainsheet, I think about 12 to 1.


Thanks Wouter, and others, I'm enjoying this education.

Dave

I suggested 4" tube, but if you look around you may
find the remains of broken carbon spinnaker poles of
the standard 3.5" size for cheap. They also sometimes
come with the fitting, making gooseneck fab a bit easier.

Another common source for carbon spars is broken Melges
24 masts. The original masts were weak at the spreaders
and many, many M24 owners have the pieces laying around
in their back yards. Great for makeing strong booms out
of.

Wouters design is pretty cool. One other thing lazy
designers do (besides use carbon fiber) is sometimes
they design elegant creations without regard to the
labor involved. They sometimes add 20 hours of labor
to save $300.00 in materials, those pesky critters do.
His design looks like fun to build for the hobbiest,
though, and I bet it works.

Thanks Mark, those are good ideas. Is there a Melges site? And nice to hear someone support Wouter on occaision. Anyone have thoughts on how to connect with those with broken spin poles?
Dave

>>So, the vertical planks would have an elliptical shape (narrower near the ends),


No, just straight but with rounded corners.


>>and the alum strips would be constant width and thickness? Maybe 2" x .25" alum strips? A max width of the side planks of 6" to 8"?

Are you still serious with this approach ? If so then I will run the math on it and try to get you the best balance between weight and stiffness.


>>Aluminum strips on the 3 edges?

>This question refered to the original T shape.

I don't think the side edges need any alyu. Just top and bottom will work. However if you want more side-to side-stiffness then the much efficient weight setup would indeed be to replace the alu strip on the top by two on each side (with same combined crosssection area)


>>Type of aluminum alloy?

Anyalu you can buy at your local hardware store will be fine. Anodising is not really necessary. Most commonly available alu types are of 6061, 6005 and comparable alloys anyway. There is not much difference between these alloys at all.


>>The main has a luff of 34', foot of 11', square top. Currently running 10 to 1 mainsheet, I think about 12 to 1.

All right, I don't oceans of time so which setup is preferred by you. Round alu tube or T-composite setup. If you want I will run the numbers on one of these setups this weekend.



>>Thanks Wouter, and others, I'm enjoying this education.


Well that is the whole intention !

Wouter

I think this debate about Alu or Carbon is all about perception ? Aren't all boats female and the really sexy ones seem to have more sexy Carbon than plain Jane Aluminium. To prove my theory have a look at the attachment.

Now, Answer this question: What colour shoes was she wearing.

If you don't know then I reckon you're into Carbon. If you said red then stick with Aluminium (and get a life)

My immediate thought was about hooter size and pole length. <img src="http://www.catsailor.com/forums/images/graemlins/wink.gif" alt="" />

That was too easy! Hahahahaha.

tack

Dave, Dave, Dave, you know that cats and concrete don't play well! Why would you consider concrete designs with all of the exotic material available these days?