Help Needed to design a curved beam for 21 foot sailing yacht

General Composites Discussions Engineering Talk
#1

Hello Everyone

I was wondering if anybody would like to help me design a curved beam for a sailing boat I am building.

The beam will support a metal track for the mainsail. The track could have a force on over 1100 kg at worst and normal working loads will be 250 kg.

I need to find out the best size of beam, what to make the core out of, I was thinking a plywood box section. I will them reinforce the box section with carbon fibre and vac bag it.

I am only guessing here from what carbon work I had done so far,
I would put 3 mm of uni carbon on the top, them 2 mm of Biaxle carbon on the sides and not to sure what to put on the bottom as it will be in compression because the loads are trying to pull the beam up.

If anybody is interested to help I will post some photos

Thanks in advance

Tony

#2

Hi Tony sounds interesting I am not an engineer but have been involved in a fair bit of boat construction if you want to bat a few ideas back and forth.

A couple of questions

Not sure how to word this but is the orientation of the arch of your beam as it crosses the boat like an arched bridge stood upright or laid over on its side.

What sort of distance is it free spanning?

Could it have a support leg at its centre to the deck?

I am guessing it’s a high performance sail plan. Something like a mini?

Things to consider like track fixing bolts how many and how they will penetrate your carbon reinforcement on the beam.
How might the track fixings be secured nuts, tapping plates, captive fastener (big heads).
Compression tubes for fixings if passing through a core.

Rather than a box section a channel section might be better it has some advantages less work to make with a top and sides. If you overlay a ply former you will be able to easily get to all your traveller fixing bolts underneath without adding compression fittings for a core. Bolts are shorter less weight and no inserts or tapping plates. Just easy to get to nuts and washers.

Something along these lines overlayed with carbon.

#3

Hi Wightmarine

Thanks for your interest,

I have had a bit of help from another forum and was pointed to a good PDF document which has all the formula’s to work out the laminate needed.

I have decided to go for a cedar core (its what I had in the shed, its cut in strips and bent around a former to the desired bend.

I wanted to have the beam without any central suports but I am constrained by the beam thickness so would need too much carbon to make it stiff enough (too expensive). So I have decided to have 2 posts supporting the beam. I need 2 because the tiller is in the middle.

Tonight I have offerered up the curved core to the deck and have seen the area for the beam to sit on is small I really will need the 2 supports.

I was going to make the beam like your photo (i think the photo is a dix mini in USA ?) but have been advised to make the beam like a sandwhich construction, this way it uses less carbon and very stiff.

The span is 1.7 M and your right its for a mini.

Cheers Tony

#4

Tony,

Any way you might be able to post that up here? I’m always interested in reviewing different documents in this regard.

Thanks

#5

OK, it is for the traveller! I was confused at first.

The bottom in general has the same laminate as the top. Your general idea should do the job.

And indeed, share as much as you have, the PDF, but also pictures of the boat and exact situation.

Is Leo Voorneveld still active in Mini land?

#6

Westcountry when you make your two support struts you may be able to use a couple of your traveller track fixings to double up and also secure the struts in positions on the underside of your beam.

All the best with your mini project and if you get the chance to post a few pics of your mini that would be great.

#7

Hi there

Here is the link

http://www.hexcel.com/Resources/DataSheets/Brochure-Data-Sheets/Honeycomb_Sandwich_Design_Technology.pdf

I vac bagged the beam this weekend and tonight have put some filler on it. It would be neater to use a mold but I didnt want the extra work and expense of that.

With the track I have I could get away with just a couple of supports near the middle but I want a really bombproof strong setup without any creaks and groans.

Wightmarine, I had the same idea, I am going to use two of the track fixings and take them down to the xxxxpit floor and tie into the deck stringers, I have some carbon tube which I can hide the fixings in.

In the end I made up a curved core out of some strips of cedar I had, the core size was 45 x 45 mm. I covered the core with a layer of 400 g/sqm biaxle carbon. Then the top and bottom had 2 mm of uni carbon and then I covered the whole lot in 1 layer of 400 g/sqm biaxle carbon.

Cheers Tony