Seeking info on structural members in composite boats.

[Splint]

Hi,
I've been searching around on the net to see how the different manufacurers design structural members under the floor and also to see how the transom ties into the hull. There isn't a lot of info on the style of boat I'm interested in which is 15 to 20 foot recreational outbord and inboard fishing/diving and ski boats. I'm more interested in but not limited to moulded grp type structures as I am in the process of building a cnc router which I could use to make plugs. I anyone knows any good online or other resources I'd be very interested to find out about them.

Cheers
Splint

[Karsten]

Look at Australian Standard 4132. It must be one of the worst standards for boats but it's pretty straight forward if you want to use polyester and chopped strand mat. Anything else is too hard to make comply with the standard.

For the transom they define plywood as core. Structural members under the floor are usually polyurethan foam (PU) covered with polyester. Some use pine wood instead of PU in higher loaded areas. You could also make a mould for the members and install the whole grid in one piece. That's a very good option if you want to make more than lets say 10 boats. Theoretically you have to connect the shear webs where longitudinal and transverse members cross if you use the moulded option. But I doubt this is done in normal production boats.

Cheers,
Karsten

[Splint]

Thanks Karsten, when I'm closer to designing the boat I'll buy a copy of the standard so I know the requirements.
One thing I need clarified is how dose the Uniform Shipping Laws (or alternately National Standard for Commercial Vessels) tie in with Australian Standards?

Cheers
Splint

[Karsten]

Under K.2.1 of the USL code it states:

"...detailid requirements of this sub section should be those of AS4132 Part 3"

This is for the construction of FRP vessels. For transoms with an engine attached the AS gives a table with the engine power in kW and the corresponding required plywood core thickness. Not very scientific but the whole standard is a bit like that. Your boat only has to meet the standard if it is used for commercial purposes. If it is used for private use you can do pretty much what you like.

Cheers,
Karsten