Welding Tips and Tricks

I am new to welding but someone has had a bright idea that I build a yacht out of Aluminium. The project is a 65ft cruising trimaran. This is planned to take about 6years to shell (fit out will be an ever ongoing - same as a house, once you finish, her indoors wants a change to decore). If your going to do a 14ft boat it will require the same skill, techniques and equipment for manufacture as a 65ft boat - so why not have what you want and not waste your money making 2 boats

The plan is for glass over ply which i am changing to Aluminium. Will be significantly lighter and cheaper to make. Less fairing time, no glass cost and price of aluminium is compareable to Ply of similar strengths.

The Ali sheet will be bonded to the frame/straiks using carbond/ metal bond and similar which will reduce welding time/costs.

The framing will be 50mm box section (6mm thick) - 6061grade
The straiks will be Angle ali 50mm x 25mm 4mmthick. 6061 grade
Skin and external fitting will be 5083 grade minimum 4mm thickness

The beams - still working on
The keel will be a mixture dependant on the region of the hull.

I need some advise for the following

1. The best technique including prep for seem welding 4mm marine grade aluminium sheet. I need to prevent warping and will be taking the welds back to a smooth finish so must have full penetration.


Any and all advise/comments are welcome.


I have the plans in paper form

stefan wrote:I am new to welding but someone has had a bright idea that I build a yacht out of Aluminium. The project is a 65ft cruising trimaran. This is planned to take about 6years to shell (fit out will be an ever ongoing - same as a house, once you finish, her indoors wants a change to decore). If your going to do a 14ft boat it will require the same skill, techniques and equipment for manufacture as a 65ft boat - so why not have what you want and not waste your money making 2 boats

The plan is for glass over ply which i am changing to Aluminium. Will be significantly lighter and cheaper to make. Less fairing time, no glass cost and price of aluminium is compareable to Ply of similar strengths.

The Ali sheet will be bonded to the frame/straiks using carbond/ metal bond and similar which will reduce welding time/costs.

The framing will be 50mm box section (6mm thick) - 6061grade
The straiks will be Angle ali 50mm x 25mm 4mmthick. 6061 grade
Skin and external fitting will be 5083 grade minimum 4mm thickness

The beams - still working on
The keel will be a mixture dependant on the region of the hull.

I need some advise for the following

1. The best technique including prep for seem welding 4mm marine grade aluminium sheet. I need to prevent warping and will be taking the welds back to a smooth finish so must have full penetration.


Any and all advise/comments are welcome.


I have the plans in paper form

I swear I just answered this... It's a 60 degree chamfer on all Butt welds. Welds are tacked on the outside then full welded on the inside with short welds alternating from side to side until complete. The outside is then back chipped and continous welded with a slightly wide bead that fills in the weld depression so that it can be ground flat. Watch the temp using a temp crayon. Stop and rest frequently to keep warpage to a minimum. Pulsed MIG is the best process, TIG is second and spray MIG is third. My boat is a 1/3 your size and will be mainly TIG.

I asked my instructor on the best way to prevent warpage when welding under 1/8" material and he told me to use chill bars. Try to get copper, failing that aluminum I believe is second to copper in terms of heat conductivity. All you want em to do is absorb heat from the surrounding metal, that'll help with the warpage. Other than that, just gotta keep your heat to a minimum.

thanks for that idea. had been considering but cant figure out how to hold it in place for the verticle welds. hense thinking that positioning the welds over the strakes/framing may enable the strakes to become the heat sinks. Having seean the videos on heat sinks though, heat sinks appear that they need to be considerably sized for optimum effectiveness.

I am enjoying planning for this venture. Once I've nutted out the finer details I can start. The AMAs are a radius design and have found several places to get the curves done.

Once I've figured what profile/thickness etc the keel and Beams will need to be to give me the strength I'll need I can start.

The advise I've received has been immensely helpful. Many thanks guys