[stefan]

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.

The is intended to be no wood except for decoration - but this may change in some areas

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


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[sschefer]

There is a lot of opinions on the subject of boat building with Al. Go get a copy of this book: http://www.boatdesigns.com/Boatbuilding ... fo/12-442/

It will answer all of your questions if you allow yourself to believe it rather than the scuttle-butt you hear. The writer knows his stuff and writes in an understandable manner. I read my copy about a dozen times before I bought my plans and I'm glad I did.

[stefan]

Many thanks for that, will have to try to locate.
the specific things I'm trying to ascertain are

is it possible to alleviate warpage using a jig.

would it be better to do intermittent welding i.e 2inch weld with 8 inch space until next weld

will the pulse mig resolve this for me

will the edge of the sheets be best ground at a 30 degree angle for max fill/penetration and strength?

[sschefer]

Many thanks for that, will have to try to locate.
the specific things I'm trying to ascertain are

is it possible to alleviate warpage using a jig.

would it be better to do intermittent welding i.e 2inch weld with 8 inch space until next weld

will the pulse mig resolve this for me

will the edge of the sheets be best ground at a 30 degree angle for max fill/penetration and strength?

Q. is it possible to alleviate warpage using a jig?

A. Roughly speaking, no. In order for jig style small boat building to work, the materials have to be precisely cut to fit. There are some folks building boats from water jet cut parts that are so close in tolerance that they can build them on the floor without a jig.

Q. Would it be better to do intermittent welding i.e 2inch weld with 8 inch space until next weld?

A. It all depends, most certainly tacking is the key to distortion elimination. Chain welding can be used in some areas as well as stitch but the plating seams need to be fully welded on both sides. The technique of laying down a few inches of weld and then moving to the opposite side of the boat for the next weld is one that works the best. The result of that can be a continous weld and be very effective at reducing shrink warpage.

Q. Will the pulse mig resolve this for me?

A. No. Use the pulser to improve the quality of your welds but use the same best practice techniques. Sometimes your can get away without back welding and sometimes you can eliminate using run in, run out tabs. It all depends on the situation.

Q. Will the edge of the sheets be best ground at a 30 degree angle for max fill/penetration and strength?

A. That all depends on the thickness of the material. Testing that I did showed that a 60 deg bevel on both plates was best for welding. That bevel is on the inside of the hull. The plate is first tacked in place from the outside and then full welded on the inside. The outside of the weld is then back chipped to remove contamination and then also fully welded. This is equivelant to a 100% penetration.

I have either MIG or TIG as options for welding my boat. I've made up a number of sample joints and have determined that TIG will be my welding method of choice and MIG will be used only when TIG is not possible. I'm not in a production shop where TIG is too time consuming to use but if I was, I would use one of the new pulser MIG's like a Miller 350p.

Here's another question you're going to ask I'm sure:

Q. Can I use a plasma cutter instead of a Skill Saw..

A. Yes, but if it's going to be on a welded joint, you must leave the cut 1/8" proud and them remove that by planing or routing inorder to meet code. The worm drive Skill saw with a 0 deg rake carbide blade cuts the stuff like butter. A reciprocating saw with a non-ferrous blade lubicated with WD-40 also works great. WD-40 is a water dispersant that has great surface tension making it act like a lubricant. It is not a penetrating oil and is easily removed with warm soapy water or Acetone. You can also use PAM cooking spray, they're about the same but taste a little different.

Hope that helps.

[stefan]

Many many thanks, gives me a lot to think about, can see it will end out as a bit of everything as I go through.

Given the info you've provided I'm considering making sure the strakes are part of the welded area... similar to a lap joint. they should provide some support as well as a minor heatsink. This should work if I leave a 2 to 3mm gap between sheets (horizotal welds) and using the frames for the verticle welds.

Your opinion?

[sschefer]

I would go get a copy of that book I mentioned in my earlier post. It has all the info you need. You can order it directly from the Glen-L site. It will definitely keep you from making some costly mistakes. I can almost recite it word for word and as soon as I can, I'll start building my boat.

[stefan]

Many thanks Steve. As you can tell I've got this post in 2 areas. One for overall project (welding project ideas) and one in welding tips for specific help. My apologies if this is confusing. I have difficulties in NZ trying to locate tech books so am picking the brains of every engineer/novice and aluminium supplier I can find.

I'm going against some convensions when it comes to the rudder and power supply. Those problems will come later down the track.

The overall hull concept will have NO through hulls of any description. The reason is my son broke a skin fitting on a previous yacht and flooded the compartment. To answer some questions before they arise.
Water is always pumped either by foot or power in a yacht. the only exception is grey water out which is not allowed to be discharged in a marina anyway - hense again pumped. All intakes and outflows can be mounted wherever you want so will be over the stern. Will make them easier to clear banicles and other obstructions as well

The Propeller will be mounted in the rudder and driven by hydraulics. The engine will be an APU from a swinglift (Self powered container trailer). This will give flexibilty in usage and positioning, but these units are self contained including cooling by standard radiator. For additional Hydraulic fluid cooling a pipe will run over the stern and back up also run oil fin heaters during the winter months. The issue will be the mounting of the rubber and reinforcing of stern. I've been told by some I'm a fool and other marine engineers a genious. hard to get a straight answer

[sschefer]

Ah I see what you're up against. One of the reasons that we float frames on all but the necessary water tight compartments is to provide flex and eliminate hard points. Usually the frames aft of midships float but the forward bulkheads are fully welded and can be watertight. Sinking the stern in heavy seas and raising the bow is critical to the vessels survival. The sunken stern acts like a sea anchor and keeps you into the wind while the raised bow helps to keep breaking swells off the top of the bow and out of the main compartments. I've been in some sea states that blew all that out of the window but it is supposed to be a good practice from what I hear.

When creating watertight spaces it is normally done with floatation in mind so if you calculate the displacement of the vessel you can figure out how much water tight space is required to achive the level of floatation desired.

On the subject of cooling, keel coolers are pretty common and effective. They don't work in a performance environment but they do quite well in vessels like yours. Cooling directly into sea water is o.k. up to about 10 knots but after that the water does not stay on the cooling fins long enough to pull off the heat. I'm really not sure how much heat you're dealing with so your method may work just fine.

[stefan]

Heres the link to the yacht. is a PDF file.

The beams have to be strong enough to enable the boat to be lifted in/out. and minimize twisting. I will be following the glass/ply design which will give me overkill in strength ONCE I've figured out what's necessary alternative for Keel and cross beams.

The plans call for a (in glass/ply design) two beams (one curved)with a meshed board in between. I have been looking at 100mm square beams with 4mm sheet in between (sperating the beams vertically). if additional supports are required I would use 50mm box (6mm thick) either vertically or as a diagonal similar to designs for building rooves.

The keel - have been considering the following profiles
100mm Tophat 6mm thick though the flatter areas and even considered for the Strakes. would give a wider spread but limited support at the point of contact should I put yacht up on a beach. the alternative is 200mm flat formed to curve of hull (both longitudinal and transverse) backed by 50mm box.

In the nose - 50mm box (6mm thick) with either 6mm sheet out to enable forming of bow(s) shape and/or tube higher up at toward the nose as it flares out. Reinforcing it all by bracing to provide strength for the forestay and rigging.

By keeping to same profiles/thickness of extrusions and panels I should be able to reduce costs due to bulk buying and staying with common products should have the same effect. The only costly impact is the welding and any forming required by a third party.

The plan is a radius design mainly affecting the AMAs with a small amount in the main hull and roof of saloon. I am making enquires with designer to see if I can get away with straighter lines. This too will reduce costs and make life a lot easier.

[stefan]

oops

http://www.edhorstmanmultihulldesigns.c ... _3view.pdf

the link
cheers
S

[stefan]

Had been considering using 6.1M x 2.2m Sheet but unsure how to handle. Would reduce welding considerably, At worst will use 2.4m x 1.2M sheet - easy handling but significant increse in welding. Can get the 6.1M sheet 1.2m wide or at 1.8m wide.

the handling of the longer sheet is the problem so am designing a lifting system, if it's feasible will save me considerable time/ warping issues/ and consequently money

[Matt Sellers]

I used to be First Mate on Cuan Law a 110' Ali Trimaran based in the BVI. The owner/designer Duncan Muirhead's first Tri was a 65' plywood/glass design. He always claimed (and I don't doubt it) that at the time they were the biggest built. The last address I had: Trimarine Box 3069 Rd Town Tortola BVI, I haven't heard from him in a while but drop him a line, REALLY knowledgeable guy.

Did a haul out on Lammer Law the 100' Ali sister ship based in the Galapagos. The original welder, a Spanish born Canadian nick named the Aluminium sewing machine came out of retirement and met us in Guayaquil, guy was amazing, did all the welding using a spool gun off a big pipe welding generator.

Rather than drive through the rudder why not use the outer hulls? Just a thought.

[stefan]

Thanks for the leed. Have been considering positioning props on AMA's and come up with the following

pros - if all else fails can use for steerage. particularly in marina
-

cons/ issues - balancing power output while underway
- power drain on hydraulic system (more you spread it the slower each part goes) May need bigger APU but can establish with hydraulics plan.
-drag ( is a cruiser - who cares) or could be made retractable

outcome
going to start with main prop in rudder main hull. Additionally have two smaller props on AMA's possibly with additonal rudders. will only use when neccessary then. Achieves all options.

For the props will source some broken outboard motors (blown motors). Remove motors and add hydraulic drives. Keeps crown above waterline (for leakage and inspection purposes, keeps waterpumps intact for pumping salt water holding tank and or flushing grey/black water systems. easily attach/build into rudder as they're usually alloy.. Parts are readily accessible and keeps costs down.

Still trying to figure cross members and keels.