thinkness of hull steel

[kingofcary]

Hi Folks .. first time question on this forum. Appreciate any and all input. My question is related to the thickness of steel hull. I know there is no true answer but what is an optimum gauge. I see a 60' sailboat with 1/4" for the hull. It's a blue water vessel. I have also see 3/8" on other boats. Certainly seems thicker is better up to a point of diminishing returns. Seems 1/4 is small number. Thanks for feedback ... Dennis

[Keel Scraper]

Originally Posted by kingofcary

Hi Folks .. first time question on this forum. Appreciate any and all input. My question is related to the thickness of steel hull. I know there is no true answer but what is an optimum gauge. I see a 60' sailboat with 1/4" for the hull. It's a blue water vessel. I have also see 3/8" on other boats. Certainly seems thicker is better up to a point of diminishing returns. Seems 1/4 is small number. Thanks for feedback ... Dennis

From my time own steel boats the builder started off at the keel with thicker steel and the thickness decreased as the boat was built up. Cabin tops and cabin sides do not require much thickness unless your going to use the boat for other than recreational use. Access to inspect the steel for corrosion is more important than having thicker steel.


Sent from my iPad using Cruisers Sailing Forum

[mako]

The thickness per the designer depends on the spacing of frames and longitudinal as well as the service requirement. But to give you an idea, my 65' was 3/16" throughout the hull. In general 1/4" plating on a 60' is excellent. Have not ever seen 3/8" except on specialized commercial vessels. Are you sure you didn't mean to say 3/16"?

[barnakiel]

Originally Posted by kingofcary

Hi Folks .. first time question on this forum. Appreciate any and all input. My question is related to the thickness of steel hull. I know there is no true answer but what is an optimum gauge. I see a 60' sailboat with 1/4" for the hull. It's a blue water vessel. I have also see 3/8" on other boats. Certainly seems thicker is better up to a point of diminishing returns. Seems 1/4 is small number. Thanks for feedback ... Dennis

Thicker is better? Why?

I think thicker is heavier and heavier structures are more loaded.

Then again think about steel vs. steel. Are you comparing the same material and construction methods?

I think that both 3/8 and 1/4 are heaps. You simply give more structural support to 3/8 so it all may ballance out (or not). Unless you opt for 'stiffer' steel on the 3/8 and thus get a lighter and stronger structure.

The above my opinions, not facts.

b.

[kingofcary]

Great feedback all .. thx .. the 60 I am looking at is 1/4 .. the 3/8 could have been as suggested a more specialized hull. Also the point as to the structure that supports the steel is key. U gave me what I need in that all things equal the 3/8 is good ..


Sent from my iPhone using Cruisers Sailing Forum

[StuM]

Originally Posted by barnakiel

I think that both 3/8 and 1/4 are heaps. You simply give more structural support to 3/8 so it all may ballance out (or not). Unless you opt for 'stiffer' steel on the 3/8 and thus get a lighter and stronger structure.

The above my opinions, not facts.

b.

3/8 is half as thick again as 1/4. Why do you need to give it more structural support?
How can adding more structural support to heavier plates "ballance [sic] out"?
How can you get a lighter structure with 3/8 compared to 1/4?


Did you mean 3/16?

[StuM]

Originally Posted by kingofcary

Great feedback all .. thx .. the 60 I am looking at is 1/4 .. the 3/8 could have been as suggested a more specialized hull. Also the point as to the structure that supports the steel is key. U gave me what I need in that all things equal the 3/8 is good ..

And 50% heavier than 1/4

[Pauls]

As one of the other posters said, steel thickness typically is reduced higher on the hull. On a 60 footer the keel bottom will probably be 3/4", the keel sides will probably be 3/8" to 1/2", 1/4 to 3/8 on the bottom, 3/16 to 1/4 on the sides, usually I'd expect 1/8" on the decks. Strength where it's needed and the lowest practical center of gravity.

[bsurvey]

1/4 inch plate is 10 lbs per sq ft


3/8 inch plate is 15 lbs per sq ft.


so why do you need the extras weight

[SV DestinyAscen]

Structural keel and the frame(ribs) are what gives a steel boat strength - not the thickness of its hull. Thicker hull plates, unless needed for ice protection, is pointless beyond what's needed to prevent deflection at expected loads with the designed ribbing. Adding thickness unnecessarily just increases keel and frame design requirements without adding any performance or safety.

[tkeithlu]

My 44' 60,000 lb dry trawler is 6mm in the hull and 4mm in the superstructure, built on 30" frame spacing and 16" stringer spacing. It will crush anything made of fiberglass and most docks as well. Rusting really is only a problem above the waterline - with a generous supply of aluminum anodes and a resulting >1.0 volts on the test electrode, even bare metal under water does not rust.

[Sailorbob8599]

Unless you're designing the boat yourself, the plate thickness will be specified by the NA who considers all aspects of the vessel and its future use when first he sets out to design it.

[hpeer]

Plate thickness is a function of size and strength needed and. Instruction practices.

Small steel boats will use down to 10gage steel. I'm told that below 10 gage the welding heat distortion becomes too difficult to control. 10 gage is a wee bit thicker than 1/8".

At about 38' - 40' you will typically see 3/-16" plate, although I've seen boats up to 50' in 10 gage.

Our 33'er is 10 gage, the 44'er is 1/4" below the water line and 3/16" above.

Small steel boat in 10 ga, say below about 35', will be overbuilt for the required scantlings.

60' is a whole pile of steel boat. So many questions come to mind.

[Manos1955]

I have seen last year in Curacao a steel sailboat about 55feet on deck with its side plates so badly bended - deformed because of the waves that I passed the opportunity to buy her for 12,000 USD
Thin plates and a wide spacing between the ribs created the problem.

[UNCIVILIZED]

Once you get past the point where the hull is strong enough to keep out the water, as well as survive some moderate knocks, weight becomes the enemy. With the exception of having a tiny extra bit o thickness in the plating for losses to corrosion over time. But this applies priarily to commercial steel vessels.

So then 1/4" plate weighs 6lb/sqft, plus; frames, stringers, insulation, fairing, primer & paint, & the boat's interior. Thus the all up weight of a section of the hull ill be well above this 10lb/sqft figure. Whereas with a boat made from cored composites can easily be as little as 2-3lb/sqft, including; fairing, primer & paint, & the interior. In other words, about what the interior, plus paint, etc. weighs in the steel boat, once it's hull's built.

That kind of weight differential makes it impossible to have a small steel vessel (under 40-50ft) perform at anywhere near the levels of boats made from other materials. Which is why small steel boats are uncommon, & my comment on weight being the enemy comes from.
You just can't make something that heavy sail well in less than 15-20kts of wind.