4mm steel hull

hi there can anyone tell me if it would be possible to build a 55ft boat out of 4mm steel

[EmilSB]

Hi,
I belive is possible to build a 55ft boat with 4mm thikness steel shell plate.
You can cheack this with formulae which you can find in ship rules from Lloyd's Register or DNV Register or other register (maybe ABS).

[Polarity]

You might find the www.metalboatsociety.com a usefull rescource as well as this forum.

Paul

[Dragonfire]

Do you want to go to sea, with the cheapest and thinnest hull ? I sure you can, will it be safe?? will it look as good?? and when you are sitting on a reef will it make any different?? I am building a 32' with 5/16th, I could go with 4/16th but who am I cheating. My saving would be about $432 for the complete hull, NOT worth it. Be smart , follow the plans, the disigner wants the fastest design boat, but a safe one too. BUT it is up to you

Dragon

[terhohalme]

Sure, just keep the stiffener spacing low, say below 400 mm and allowable speed under 20 knots. And use a numerate designer!

Terho

How fast does 4mm corrode to an unsafe thickness?

I should think that corrosion on boats isnt very desirable, the metal must be protected from it. even slight corrosion cant be good news, so i wouldnt think of it in terms of 'when will it be too thin', more 'how can i stop it corroding at all'. All IMHO of course.... ;-}

[MikeJohns]

Your plating thickness depends on the spacing of the framing (longitudinals and or transverses) I would not recommend it. We design 56 foot boats that require 6mm for scantling rules but we specify 8mm bottom plates and 6mm for the topsides.
The total amount of steel may not vary that much (I havn't done the numbers) but my instincts say avoid thin bottom plating at all cost.

[Dutch Peter]

I don't believe thickness is the problem, strenghtwise. as said by Mike, it depends on frame spacing. But that is only looking at it in general. When looking at high stress points, you will run into trouble.
An other problem is weldability, with 4 mm plating, your boat will look like a very hungry horse.


Peter

[Gaspereaux]

I don't know about a 55' boat but I have a 30' steel sloop built with 4 mm steel in Holland in 1954 - I think that makes her an antique. As old as she is, she still has that hourglass look - I guess we can say that she has fared well . Anyway, we had a 100 point ultrasound survey performed in January 2003 and the steel thickness was basically 4 mm.

You may also want to check out the oragami boat group at yahoo:

http://groups.yahoo.com/group/origamiboats/


Regards,

Rich Murray
North Weymouth MA

Hi,
I have built an Alan Pape designed 57ft Stays'l Schooner,basically 6mm garboard strakes and 4mm up to the cap rail.Unusually - I have used 15" wide x50" (4mm) plates and laid them diagonally (like double diagonal Vosper launches,etc- but only one layer!)The hull is round bilge and the results are fantastic - lots of welding tho-welded once from the outside with full thickness V prep.
The frames are 6mm T bar, the tail being outwards and approx 15" spacing.these could be flat bar.
Mostly tho - if you buy plans from a reputable designer - all the guesswork is out!AND yu have the on going support during the build.
It's taken me 5 years to build the hull,decks and superstructure (PART TIME!!!) Now I have 3 years of woodwork to lay teak decks and interior,build hollow masts with Sitka Spruce (from Alaska!)She will look fabulous!!
All the best,
Dave (S.Wales - UK)
PS I had EVERYTHING shot blasted and primed BEFORE delivery (Shot blasting is a nightmare (I did the completed frame work-NEVER again!!!)

I professionally build steel yacht to Dudley Dix designs in South Africa. As most sailers are aware, we have the most treacherous waters around the cape of storms, hence we build strong and safe boats.
Dudley is without question the foremost designer in steel, and renowned world wide for his excellent boats. I had build to his designs the Dix 38 (a boat I commisioned 1990 - ex FM) Dix 57ft and the Dix 65 ft. All of these boats were build with 4mm mild steel plate hull with 3mm deck plating.
Remember friend, it is not the hull plating that give a yacht its inherent strenght, rather a symphony of factors, mainly the framing and stringer design.

[MikeJohns]

No

Thin plate is just nice to work with for the round chined hull builder. Apart from that it has little to recommend it.

Its the plating that stretches, tears, distorts and corrodes. Remember its the plating that keeps the water out, no matter how strong your frames and stringers 4mm plate is just not sensible. Sure it will work but there is absolutely no insurance.

65 and 57 foot boats of medium to medium heavy displacement are only going to meet the designers rule. Try getting a Loyds A1 rating with 4mm bottom plate on a 65 foot boat!

There's a reason for this.

[Wynand N]

Nice of having your views on 4mm hull plating Mike

However, I beg to differ from you. Point in case, you mentioned that thin plate is just nice to work with for the round chined hull builder. Not so, thin plate is difficult to work with and to create a fair hull. Especially welding the hull and not cause the hull plate to warp, dent, wobble etc. Thick plating eliminate this problem. I should know, by trade I am a qualified boilermaker before I took the plunge to yacht design.

I have build hulls with 4mm plating that were so fair that no filler was nessecary to fair the hull prior to painting. As for Dutch Peter's remarks that a 4mm hull will look like a hungry horse after welding, I just smiled. If you have a hull in that condition, and I have seen a few, the blame must go to the designer and in a lesser degree to the builder.

As with Dudley Dix designs and my own, the transverse frames do not touch the hull plating except in high load and stress areas like the bottom plating around the keel, mast step, main floors etc. The longitudinal stringers are half way slotted into the transverse frames, then welded to the frames. The stringers are then space welded along the length of the hull to the hull plating. In effect you have a hull with longitudinal framing. This completely eliminate the "hungry horse look" effect.

Rust and wear should not be a problem on a well built steel yacht. In fact, if a hull is shotblasted to spec SA2.5 and immediately primed with an epoxy paint, and overcoated with the same paint system as per manufactures notes, you should have a boat that will outlast any tupperware hull. Needless to say, should you damage your hull, repair it properly without any delay. The same applies to fibreglass boats.

The Dix 57 I have build was approved aby ABS (American Bureau of Shipping) and build under their supervision. The Dix 65 was designed (as with all of Dudley Dix designs) in excess of ABS specs. Sadly, only because of the financial burden (South Africa's poor US$ exchange rate 1990) the hull was not build under ABS or Loyds supervision. Perhaps this will answer your closing statement.
By the way, go to Dudley Dix home page and view the 65 footer under construction and afloat.

Something to ponder about, I am laying out the frames of my "retirement" boat that in three years time will carry my old lady and I to the South Pacific via Cape Horn and then to down under. We are very safety concious and carefull people and would not take any risks with our lifes.

The boat: (Touch Wood)

Radiused chined steel hull, pilot house, properly designed by myself.
Aft cockpit double head sail sloop
LOA: 12.7m
Beam: 4.0m
Draft: 1.7m
Disp: 11200kg
Hull plating: 3.5mm
Deck plating: 2.5mm

You said the hull plating only keeps the water out of the boat Mike.

Fair winds to all
Wynand

[MikeJohns]

Yes Wynard the rules do vary a bit an you will find rules that allow thin plating, but I wouldn't recommend it for your bottom plate, 6mm has 50% more Ultimate Tensile Strength when it comes to a collision with that log, rock reef. Even though you can make that thin plating stiff enough with close stringers you cant make the plating UTS higher.

I didn't imply that thin plating was easy to weld, just easy to bend and form, these are not attributes you want in you bottom plating
I can see no detriment and only advantages to work in at least 6mm below the waterline.

The vessel set down on a rock or colliding with a large floating object will often experience a load in excess of the vessel mass on 1 square inch of her plating . Once a hole is made there can occur a tin-opener effect.

Whether you want a tear or a dent is simply down to the plating thickness. If you make the vessel safer with watertight bulkheads there are many who say it would be far better to put that material in the hull plating to start with, although I advocate both.

The fear induced when you collide with a log in a sea at night has to be experienced to be beleived. A fibre-glass boat here sank after a collision with a fridge! Odly enough I once found a large fridge foating out in the Tasman sea. I have seen the result of collisions with large logs.

If you intend to go south beyond the ice line then you had better re-read those scantlings.

Do you have a start date for your hull ? It would be good if you could put some pics in you gallery of the concept drawings.

cheers