Cross beams/aka's for a 6m (20ft) trimaran

Thanks for the replies, based on your feedback and other research and conversations I've settled on 100mm aluminium tube with a 3mm wall. Plus a reduced beam from 5.5m to 5m.

Next I'd be keen to hear your thoughts on waterstays vs. fixed aluminium struts.

Here's what I've been thinking about so far... (please correct any of my thoughts if necessary)

Weight
Waterstays are obviously much lighter, a good thing for any sailboat.

Waterstays win

Strength
The fixed struts provide up & down vertical support, while waterstays only provide tension preventing the ama's from upwards movement.

I understand, however, the mast shrouds would provide opposite support to the waterstays although I want to limit mast compression where possible.

Struts win

Ease of assembly
Waterstays would be made from dyneema with a simple purchase system for tension. Installing eyes to the hull and aka's for dyneema is fairly straightforward.



I found reasonably priced 8mm quick release pins for the fixed struts with a breaking strain greater than 63,000 Newtons. To pullout the pin without depressing the button requires 3000lb+ of force. I believe the Ultralight 20 by Warren used quick release pins.

Struts win (just)


Cost
The manufacture of the aluminium struts plus the mounting brackets to hull sides and aka's will require professional help.

Off the shelf hardware is available so cheaper and faster to build using waterstays.

Waterstays win

So far it's neck and neck so the last factor is...

Sailing performance
This is the real unknown for me. What are the thoughts from those in the know?

Thanks.

 

Hi Aaron,
Boat speed has been good, very quick to accelerate, best to date is 14kts (2 sail close reach) in about 16knts of breeze. When boat is doing better than about 8kts it feels very smooth and out of the water. At 14kts it feels just as nice, amas sitting high in the water and not pushed at all. I sail 2 up only. I don't think 20knts is out of the question give how easy it gets to 14knts and how smooth it is.

My struts do splash in waves so to try and eliminate that I have wrapped them in a type of foil (wing) section so as to go through the water smoother. It seems to work ok.

Cheers