Sleeving a bit more on the end of a boom?

[BenR]

What is the best way to go about this and what sort of layup goes into a boom?

My initial thought was to make an equivalent section to the boom and make a piece the same section except the thickness of the laminate smaller bog it all together and hey presto...longer boom.

How long does the inner bit need to be for this to be as strong as a continuous boom?

[Phil Alderson]

You could do it like you suggest so that the sleeve takes all the load, in which case you probably need a sleve that is 4-5 x the diameter of the tube, and as strong as the tube..

Or you could use a smaller, thinner sleeve 2-3x the diameter, and add carbon to the outside of the boom to take the loads. If you taper the ends of the boom, and new section  you can do it so that the OD does not change. A simple bandage on the outside also works but looks a bit ugly.

[kokopelli]

Here is a thought, this might work for you and is very simple. (probably not the in the way i have written i though). If it is the clew end you want to extend; at the end, mark the 1/2 height, cut tapered section through, then use the cut off by turning it round and marrying it to the existing boom and that gives you a longer tapered section. how you stick it together is just butt it, 'instant mitre' together and then laminate strengthen as neatly as poss.

[BenR]

Thanks Guys,
I think I am going to go with the sleeving method and turn a mandrel on the lathe as I think I can get the section needed by turning a circle and cutting it in half. then inserting a plank in between.
What sort of layup goes into a boom (I was going to use biax in and out then UD in the middle. How much weight of carbon is necessary?

[roland_trim]

The reciepe used recently with the "Paul Croote" boom mandrel uses a reciepe coined as 3-2-1. It uses a uni tape athat is 2x the boom length, one full length piece, one cut into 2/3 and one 1/3 length (thicker at the kicker/gooseneck end). This refers to how many uni layers you find as you head along the boom length - although there is a extra strip bit made from the "waste" from a 300mm wide tape (a 25mm offcut).

So in short - at the end of the "Paul Croote" mandrel boom it is only (from inner to outer)
-1 layer weave (200g?)
-1 layer uni (300gsm)
- 1 extra 25mm wide strip uni top and bottom (300gsm)
-1 layer weave (200g?)

The section of Paul's mandrel is a bit deeper, but you get the point that it is not alot of cloth there...

[phil_kirk]

And because the Croote boom mandrel section is oval you get a lot more bending strength by adding fibres at the top and bottom of the boom.

For your extension biax or weave can be used for the inner and outer layers. 

From experimentation successful stiff carbon tubes have a minimum of 3 layers (1 weave, 1 uni, 1 weave) and usually 200 gram material.
Leave 1 of the layers of weave out at your peril.  So this is the minimum for your boom extension but it's worth adding the extra strips top and bottom. 

[roland_trim]

Is the boom off Paul's mandrel - if yes then we can save you needing to make a mould...

The other option would be to use the inside of the section you have to make the formwork. i.e. insert something formable like polymorph into the end, slide it out and use it. Depending on the extension length you could use it stand alone or not pull it all the way out and cast the extension insitu (the polymorph will flow out with hot water, even if it gets stuck and you don't then have to bother joining old and new).

But if we are really playing there is always - wedge an insert of blue foam into the end of the boom, sand to shape (long board will find the section very easily), cover in carbon and then dissolve out core with acetone.

[BenR]

The boom is a C-tech maybe 80x60 flattened oval.


Ok so crazy new plan:
the boom is always in compression by virtue of having a mast at one end and a sail tied to the other. Would it be a thoroughly stupid idea to have a removable section of boom therefore leaving the old one totally intact?

thanks for the laminate schedules. Hopefully my boom is long enough, this is just in case we cant get the area on the new sails any other way.

[Stuberry]

The other option would be to use the inside of the section you have to make the formwork. i.e. insert something formable like polymorph into the end, slide it out and use it. Depending on the extension length you could use it stand alone or not pull it all the way out and cast the extension insitu (the polymorph will flow out with hot water, even if it gets stuck and you don't then have to bother joining old and new).

I really like this idea!

Would it be a thoroughly stupid idea to have a removable section of boom therefore leaving the old one totally intact?

If you are conserned about keeping the old boom intact, do not over-estimate the time involved in making a new boom. It's all done in one hit. The class own a mandrel you can borrow. And we have a tried and tested recipe.

[phil_kirk]

When the main sheet is puled on it can oppose the upward pull of the clew tie down so yes the outhaul is then putting compression load into the boom. At all other times the boom is under bending from the kicker and gooseneck and clew, hence why we use oval sections.

[Tom K]

I'm not keen on the look of a nice shiney pro boom with a DIY extension.

I'de much prefer a smaller round section of pre made tube bogged and carboned in.

Like this,

http://www.yachtsandyachting.com/photos/skiff/yandy84693.jpg

[BenR]

That looks good actually. I think we have a winner.
Thanks Tom aesthetics are obviously the most important thing here