Are Bulkheads Necessary?

[LBG]

I'm building a 33' steel yacht and plan to build it outside without a gantry to lift the 4mm bulkheads, so I'm building those sections out of the same mat as the rest of the frames, 50 x 6 flat, if they are necessary I will put them in later when the hull is turned over. So what I want to knows is do I put them in now, later or not at all?.

Any advice is most appreciative.

[DaveB]

It's generally best to stick to the plans when building a boat... assuming of course you have plans...

Some kind of stiffening/framing might be useful when flipping your hull... they tend to be quite wobbly without anything... The framing that you use to jig it up may be sufficient.

Bulkheads are fundamental primary structure and I think you'd be hard-pressed to find anyone worth talking to that would tell you that you don't need them... Without them your boat will have a tendency to fold up... They're also pretty handy for longitudinal subdivision... keep you floating if you're holed...

You could likely do something fancy and get away without most bulkheads... just use more frames, but I'd highly recommend a collision bulkhead at least... also nice to have one near the mast and aft separating the engine compartment... Very hard to say what's best/possible without more information (drawings).

Cheers,

Dave

[LBG]

Thanks DaveB, I will probaly put them in when the hull is turned over, the plans dont show water tight bulkheads, one up front, one on the mast line and one aft. Do I weld the hull plate to the longitudinal stringers or to the bulkhead itself as I don't want the hungry horse look.

[webbwash]

you follow the plans -- where it calls for a staggered weld you stagger the weld and where it is shown continuous you lay it down continuous.

keep away from "hungry horse" by laying your welds down intermittently and not all at once, as nice an idea that may seem. check your weld heat and pre-heating for the plate if required.

it sounds as tho you welded your hull upside down to make use of all the down hand welding you could get. when you roll your boat make sure you have enough deck/cross beams to maintain the proper spacing of the hull.

Have fun --

[djwkd]

so wahts a bulkhead then?

[jam007]

http://www.answers.com/main/ntquery?s=bulkhead&gwp=13

[djwkd]

cheers.whats the best size,type,thickness (yes, i am a newbie) etc for a 17' shantyboat to go to sea with?

[webbwash]

Shantyboat going to sea?? -- hopefully that is being metaphorical -- shantyboats, or barges with houses on top rarely "go to sea" maybe hang around the local marina OR at most travel the inland canals -- it is not a trip for the uninitiated to go out of the harbor.

As for thickness -- ply equal to your hull sides is a good start, they both are designed to keep the water out. From the Deck to the hull.
As for distance, maybe 3'-6" aft of the bow and forward of the stern -- this is standard "barge" construction with a little rounding off.

That leaves 10 feet for the lower portion of the house and sufficient overhangs to get a deck chair on and enjoy the out of doors.

The ends of the barge mean you can store some things FROM THE DECK with watertight access -

Have fun and give us some pictures when you are well along --

[djwkd]

thatll be a while yet,i rarely have a day a week to get it done...........with hand tools!also,if it cant go to sea,i wont build a shanty,and just a sharpie or something.

[Crag Cay]

Bulkheads are fundamental primary structure and I think you'd be hard-pressed to find anyone worth talking to that would tell you that you don't need them...

Dave Gerr? "Unlike FRP hulls and some forms of wood epoxy hulls, even so-called 'structural' bulkheads referred to on metal boat plans aren't required for strength. The basic framing and plate alone are quite robust enough by themselves. Bulkheads on aluminium and steel craft are principally to divide the vessel into compartments to separate machinery, accommodation and cargo spaces, and to increase watertight integrity in case of hull breach.

For strength purposes, full structural bulkheads are called for under exceptionally heavy deck machinery, such as cranes, dredges and similar heavy lifting equipment.'

Obviously, when you turn the boat over, you will need it to be braced heavily, but this is normally done, as has been said, by the building frame. If it doubt weld a bit more in.

I have never designed a metal boat with a structural bulkhead, and have never even specced a steel bulkhead in a steel boat. You do not have unlimited weight carrying capacity in a 33ft steel boat, so I wouldn't waste it on using steel for bulkheads. Plywood makes entirely satisfactory hull dividers.

Water tight bulkheads are a slightly different story. However I have never seen a really satisfactory installation of one in a 33ft boat, let alone 2. For boats I have done that were 'heading into high latitudes', we have used scantling rules to build foam/frp bulkheads that have been bolted on, but the doors have always been heavy, costly, elaborate and inconvenient. Not one of the three owners would fit them to a subsequent boat.

We did experiment with ideas for incorporating watertight compartments into the forward v-berth structure as a way of doubling the hulls in the most vulnerable area, without intruding into the livability of the boat. However all the boats (admittedly frp) I have seen with this sort of system and which have had a collision, have usually had sufficient damage to displace the mini bulkheads and rupture their water tight integrity. However it might be a idea I would pursue with an aluminium boat as the elasticity of the material might survive a major impact.

[djwkd]

oh crag,where abouts in england do you live?and is it N,NE,NW,S,SE,SW?

[webbwash]

So what do the plans say about bulkheads -- They are useful to hold the mast partners or the chainplates - They make a fine support for the cockpit - or maybe you want a lazarette -- a collision bulkhead in the bow would give you some measure of safety, but don't go bumping into any supertankers, not only will it crush your bow, it will probably drag you under, or at least into the propwash and make for a very undesirable effect. At the very least, it may be enough to ruin your whole day.

Kidding aside, it is important to follow the plans that have been laid out by the designer -- theoretically they have done the math and have produced the requirements for your design.

The bulkheads can be used for STRENGTH or for subdivision and may or may not be watertight -- follow the design and only modify if you have someone to help you, like a naval architect OR a yacht designer, both with the reputation for working in the medium and with a proven history.

[Crag Cay]

The bulkheads can be used for STRENGTH

Just for my information, can you let me know which scantling rule for a 33 foot steel yacht, requires full steel bulkheads for strength?

[webbwash]

As I said in previous thread -- they CAN be used for strength. If there is no design need for one then don't put one in -- However -- if there is strength required, say in the area of the Mast then they provide a nice divider as well as strength under the mast for the chainplates and partners.

Do what you feel is necessary and what is designed for -- but don't overbuild.