Steel Boat Build

Thanks Barry
Again, all solid points, just regarding the mig for aluminium, a mig that will weld aluminium well will cost me huge money, the new technology is fantastic and finds itself really at home with aluminium.

A friend of mine makes heavy aluminium lorry bodies, his mig was stolen,
he bought an identical model, it drove him crazy, none of his old or indeed
any of the settings he tried on this identical mig would produce the fantastic
welds he was previously doing, as luck would have it he got his old mig
back and what a relief.
Mig welding aluminium is no simple task, I have done it, and the tig is easier to
get good weld with, though in the meantime I will be testing out migs for this
purpose, but that will not happen in time for this boat.

I intend to build and learn from my mistakes, its how one improves.
As regard to the hull shape, I like it because it is soft and should not be too harsh in choppy water. I will attach a section when I get a chance.
And as far as me getting the shapes right, that will be a challenge indeed.
I spent some time inside the attached Steel boat (Tina) and got spoiled with her curves.
You could push her across the harbour and she just kept going, fishing of her deck was an amazing experience.

Regards & thanks, john

 

You said that you have a mig so assumed that you could use it for aluminum.
Different drive rolls and gas and you should be ok with your MIG, The distance from the rolls to the gun should not be more than maybe 10 feet with 5356 wire and 035 wire running through an ,040 or .045 tip
While Tig will give you nice looking welds, there is an issue with the amount of time that you have heat on a weld. Ie the longer you have the heat on, the more distortion, which, depending on the weld, can lock in the distortion

If you take two strips of aluminum, say 2 inches by 1/8, and 2 feet long
Butt them along the 2 foot side, and flat, ie side by side. Do not tack them, and just start a weld from one end. With Mig you might be able to get to the end of the 2 feet before the ends separate from distortion

Do the same with TIG, the longer heat will spread the far ends before you get there

Certainly you would tack such a joint but the amount of excessive distortion with TIG CAN be a problem and the above illustration will show the difference

And certainly, when you are doing fillets or welding pieces that have some rigidity to it, ie angles, channels and tubing, the effect is not as significant.

 

Regarding developable surfaces.
You did not comment on this but showed a round bilge steel sail boat.

Whomever built this would have required a sophisticated roll to get bends in two directions out of a sheet.

If you take a thick piece of paper and bend it into a U shape, it is difficult to then bend the U shape at 90 degrees to the original U. IE bending the paper in two arcs at 90 degrees to themselves

Because of this, most metal boat cross section is made up of flat sections, curved in one direction, which creates longitudinal butt joints, ( often called multichine) which takes away from a nice smoothly curved, in two direction, hull form

I am sure if you look on the internet, you might find a design for a small multichine steel or aluminum boat, or one that could be scaled down, that the design work is done

 

http://www.boatdesign.net/forums/at...s-26-28-ocean-cruising-steel-sailboat-tt2.jpg

Multichine cross section

 

Hi Barry, very informative, I will probably not be able to create the perfect curves required to form that hull, but I will probably try anyway just to see how well I get on.
I did in fact take a tape to the pier, and spend a day measuring a 21 foot aluminium boat similar to the one in your picture.

I in putted all the measurements to Corel Draw, made some small
changes, and was able to easily calculate all the panel shapes angles
dimensions etc with great ease.

I calculated all the required sheets, and other materials,
and put it all away in a folder for when the time would come,
but when the time came, wallop, computer hard drive crashed.
All my detailed and simplified calculations quantities and assembly
notes were all gone.
And what annoys me the most is, I intended to make the plans
available to anyone for free, I just wanted the feed back on how others
found the design, how they improved on it etc.

Anyway, I might do the same again as no one seems to be willing to
give anyone a helping hand these days, while I understand people need paid
for their work, those who can afford to give out such plans are bent on taking
then and their money to the grave, sad people.

Thanks for the information regarding the welding, but as of yet I have been unsuccessful with welding 3mm aluminium with a mig, I have no problems with steel or stick welding steel or tig, I have tried with different migs, some come close, but none made me happy, modern migs with pusle and electronic feed back and automatic compensation will of course change this, when I can afford one. Heavy aluminium welding I can manage, but am not using heavy sheets nor making a big boat which requires them.

Regards, john

 

Just another thought
Just about any boat that can be sheeted with plywood would be able to be made in either steel or aluminum
And there are lots of plans on the internet for plywood boats in the size that you are looking for

 

I will look into that too, the difficulty being deciding on what to replace the wooden support structure with when using steel, weight will become a big consideration.
I just like the idea of seeking advise, and putting a good stable boat together
that will be good enough to cope with the unexpected.

Regards & thanks, john

 

With steel, you will have to deal with painting it to inhibit corrosion. A further cost that you should factor in when deciding between aluminum and steel.
You will need to sand blast it or grind it with a flapper disc to remove the mill scale, prime, finish coat etc.

You mentioned Tina a Steel Sailboat that was stable. This sail boat would have probably had a heavy ballasted keel which prevents heeling/rolling. Your design does not. I would be extremely concerned about roll stability with the shape of your hull. Your hull and Tina's are very different

Say you take a 5 meter telephone pole that weights 500 kg and put even a small weight on the edge of it, the pole will roll.
Or a canoe. Without a keel which will produce a righting moment, your boat will not have a lot of stability. Nor will you have a heavy engine near the keel to provide some resistance to roll

 

Hi Barry

Yes Tina, has about 7 ton of lead inside the fin for balance.
Am not comparing the design that FreeShip threw out with Tina, that is world
class ocean going boat, http://afloat.ie/blogs/sailing-satu...sic-yachts-traditional-boats-wheres-the-truth

I have no sail or such leverage to contend with, but of course I realize the shape of the boat will play a major role in stablity.

The calculations thrown up by FreeShip do however indicate the boat is quite
stable, less I read them wrong.
I also plan to test the hull / boat for all of this, and add to the keel if and where necessary, I don't know the name of the fin like structures that run length ways along the bottom of such a keel to add stability, but I will know how to fabricate and add them where required.
I will keep in mind that you mention you have serious concerns regarding the boats stability, and also I will be making a scaled model before I build anything to get some idea of stability, I also will be adding flotation as earlier mentioned, and will be sealing up the decks, I think filling it full of water wont sink it when all I plan is in place,
The engine will be outboard of testing, future plans are to put angine
down low for propulsion and stability.

 

Greenerpastures:
You are at the very beginning of a great adventure. There is lots of good advice already there for you. Here's a bit more. Consider only a single chine hull, anything else is too difficult at this point. 5m is ok if you use 11 gauge cold rolled steel. 16 gauge is easier to cut with a small electric shear but very floppy. Cut 11 gauge with a nibbler or abrasive blades in a portable saw for precision. Consider a frameless hull design for fair shapes. Remember that with any metal hull, if you do not curve it one way it will curve the other, therefore no straight cuts. This probably means a displacement hull, cute, a bit plump, and slow. In Alu, the same applies except 3/16 is the best choice as it is easy to cut and weld. Mig is the only choice but you must have a spool gun. My first small group of boats started out as above with steel to start and then switch to alu. Lots of luck.

 

Hi and thanks you for your advise.
11 gauge sheet steel is quite heavy, I certainly wont have a problem welding it.
Regarding curving or not curving, are you saying I need to ensure each sheet has for example an inward or outward curve to it so it will resist being pushed with the water the boat is submerged in.

I have seen many boats with angles and flat sheet surfaces, they must have been supported well as they were straight to look at.

Below are links to two boats I think could be built in steel or aluminium,
perhaps people could offer their opinions as to which is more suitable to
build in steel, and secondly which one is the most stable on a choppy water.

Boat #1
http://www.selway-fisher.com/Mc2130.htm#POW (just the green boat) with these specs,

Power 2 Particulars

LOA 21' 6.41m
Beam 7' 2.13m
Hull Mid Depth 2'9" 0.84m
Draft 14" 0.36m
Maximum Headroom 6' 1.83m
Approx. Dry Weight 500 lbs 227 kg
Engine Up to 150 hp outboard
Speed 30 knots with 80 hp
Hull Shape

U - flat bottom with 2 planks per side
Construction Methods Stitch and tape
Major plywood requirements for hull 13 x 9mm sheets
5 x 12mm sheets
Guidance Use Coastal
Drawing/Design Package 4 x A1 drawings + 6 x A4 instruction/spec sheets
Additions and alterations included with the plans Mark 2 version with 21' length and 3 planks per side.

Boat #2
http://www.selway-fisher.com/Mc1620.htm#POWER (top boat on page)
this boat can be welded up, its shorter beamier and deeper hull.
Specs

Power 1.3 Particulars

LOA 17'2" 5.23m
Beam 7'6" 2.28m
Hull Mid Depth 3' 0.92m
Draft 10" 0.25m
Approx. Dry Weight 595 lbs 270 kg
Engine Up to 100 hp
Speed 25 knots with 20 hp
Hull Shape

U - flat bottom with 2 additional planks per side
Construction Methods Aluminum (or stitch and tape ply)
Major plywood requirements for hull 14 x 9mm sheets
1 x 12mm sheets
Guidance Use 6 adults +
Drawing/Design Package 5 x A1 drawings + 8 x A4 instruction/spec sheets
Additions and alterations included with the plans

Hope to hear from you all regarding which of the above boats would be most stable in a chppy sea, and which will be most suitable to build in steel or alloy.

Thanks & regards, john

 

Greenerpastures
They state the #2 boat is designed for alum. Steel would be too heavy for a planing hull if you used 1'8" (11gauge) at 5 lb per square foot. I still prefer a single chine for simplicity of construction. The extra chine means lots more work in alum, stitch and glue ply might be easier. Note that the 21' boat has a beam of 7 feet while the 17' 2" boat is wider at 7' 6'. The plan view shows it is fairly stubby, and all else being reasonably equal will trim bow up while getting onto plan far higher than the the 21'. They note that the aft sections are all parallel and straight so that you can extend the hull easily. This is also the best for a planing type hull. The ply hull will not distort like an alum hull when you weld it. With an alum hull there should be bottom longitudinals at proper spacing for support, plus to prevent distortion. Stability? Good question for an owner of this shape of multi-chine boat.

 

Thanks Kenora Kid
Noted that boat 2 will plane easier, it has less draft and is also heavier, and can be extended as can 1.
They state though that someone extended boat 1 to 24" and is using it in the Irish sea and the Bristol chanel.
The hulls remind me of a few Bayliners that I saw, they were definitely more suited to lakes than the sea, having said that they did good on flat seas.
I think I will keep looking for a slightly more sea worthy design, and am realizing that with the amount of work required to do the boat right, aluminium will pay in the end.

You mentioned frame less designed boat, I have not come across any just yet, sounds appealing though, as long as they are designed to stay in one piece as the absence of frames means you loose a lot of reinforcing.

That Boat Tina in my picture has the slimmest frames ever, well spaced apart, not a trace of weld where the plates were joined, can not tell where the joints are at all, inside or out, and the steel is like the day she was made, over 50 years ago.

Regards, john

 

If you want a planing boat and stability, throw away any multichine designs as in the first link. I don't think that I have ever seen a twin chine hull whose purpose is to get on step. Bayliner tried even rounded chines with quite a few of their boats and found increased instability and more power required to get it up on step, ie more fuel consumption per mile at planing speeds.

So single chine, mono hull, ie last 2/3rd same deadrise angle.

Width is king for planing hulls, our 21 foot jets were 7 feet at the chine, mind you 12 degree deadrise which is way too flat for a big water boat.

Weld on some reverse lift strakes and turn the chine down and you will have the best of both worlds.

Bottom could be 3/16 ( 1/4 easier to keep fair) aluminum with 1/8 inch sides. Weld in longitudinal stringers to the bottom and to the sides. If you need some framing, weld theses to the stringers

We used 1/4 bottoms because our all up weight, full load, was around 4,200 pounds, 400 hp, 35 mph boats that frequently hit rocks in rivers. We used 1/8 sides

I would think that 20-22 degree would be ok, but perhaps others will have a better idea.
We have built to 18 degrees but can still pound in big waves, but better than 12 for sure

 

Thanks Barry.
Good advise re the 1/4 inch for the bottom, keep a bit of weight down there too.
So if I got this right, #1 boat above is not as stable as #2 on a choppy sea, I think this is because it has an almost flat bottom and is narrower.
#2 Boat will be stabler because of its wider beam and slightly more V shaped hull.
#2 will also plain easier because of its width and shorter length and its smaller draft.

Although I am not taken back by either of these boats for the sea, I think either one will be fine for the lake I will be on, I might rig it out to cruise on the inland waterways here in Ireland for few weeks during the summer.

I think I will contact the designer and ask which of the two boats he thinks will suit me best, and see if the plans will be detailed to construct either from Aluminium.

Although I feel the smaller boat will suite me ok, the bigger one at 30 knots with 80 hp is not bad for its larger size and carrying ability and shape which goes against proper plaining.

If anyone wishes to comment on my assumptions or either of these two boats please feel free to give me your opinions, its always good to learn form those who know.

Regards & Thanks, john