Massive Stem bars ..........Why

Ships may have a relatively small solid round bar bent to the profile shape. It's called a stem bar but it's not a structural member . Many don't have a stem bar at all. Some have a centre line web. Some just have extra floors and Breast hooks further up. There's lots of potential designs. You can make it as strong as you want and carry any load you want. Whether it's breaking ice or carrying a sailing rig fore-stay load. There's never only one way to achieve strength.

 

does this make you salivate, it should this is real boatbuilding--at its very best and most skilful
Yes there is your stembar
built by Bos and Carr NZ

 

Well to recap.

If you have a stem bar as the primary structural member it's quite large and heavy in a steel boat. It's sized as though the plating has no structural input. It's one way of framing but it's not the only way.

The bar is not mandatory and can be safely omitted or reduced considerably in size providing the plate in the bow and stem are of sufficient thickness and is adequately shape supported. That thickness is often already inherent in a steel sailboat and if not is easily achievable unless relatively thin plate is being developed for a complex bow shape.

The bar is favored in fabrication as a strongback to carry and position the frames prior to plating and as such it does aid construction and define the limits of the bow plates.

But if the bar is present it does not need to match the dimensions given in the class rules for a stem bar and can be as small as you like if you specify that you are using an all plate stem. That's the crux otherwise the plan approval process will mistakenly reject your stem bar size as inadequate if you label it a stem bar in the materials list. If you label it a stem softening bar or a profile definition bar there's no problem.

A round bar used as a nose softening at the stem can suffice as both a construction aid and local collision reinforcing. I think you'll find it's a lot stronger than you imagine.

It is a very common misconception and leads to the use of a lot of unnecessary material in small boats. I think a lot of this confusion arises because plan approval see's 'stem bar' specified as say 25mm round and say "no that has to be 150 by 20" !

In the pic: That's an acute enough angle to make a very simple and strong plate stem. The webs are what give it strength to stop buckling, It can be lighter and stiffer than using a big heavy bar and it can have just as good a collision strength if you want.

If you still need convincing I can calculate the strength for you. Or take two plates of 1m by 300 by 6mm use a 25mm round bar at the apex and weld them at 45 degrees, add a triangle web at each end and one in the middle to keep the shape then try and dent it with your sledge hammer ! And that's only a small part of the strength since the stem is also backed up by framing and adjacent plate as well, so the real strength is closer to tack welding the base of the triangle to a base plate. You could run over it all day with a 20 tonne excavator and it wouldn't budge a mm.

 

and for a boat that will lock a lot and be in heavy river traffic, what else would you do?
The topside plate is 8mm al al. I have never seen a barge or river ship without a bar and they date from turn of 20th century til now

 

Lock a lot, don't know what that means....can you explain. New terminology for me.

Totally depends upon the SOR and hence where it is opertaing and how. If collisions are likely and frequent, you ascertain what type of collision. A collision between a submerged container, is different to that of a quayside. Thus, where is your risk coming from and then design to suit.

But you also need to weigh up the balance between designing for a nominal "collision" and a full on "crash case". It has major weight and hence cost implications.

Topside increase in plate thickness is a throw back to "old days" and wooden boats. Although on container ships/tankers etc this is common owing to the higher stresses that occur round the deck-side shell connections.

Only if you have large fenders and/or rubbing streaks, otherwise an increase in plate thickness as "top side" is unnecessary.

 

Lock, Sluice slisen call it what you will , a place where ships go to go to next river level

 

Mike, my whole life I have been constructing in metal.
I am not convinced and round bar is a messy thing to use, Welding into a flat bar stem from inside is hard near bow unless you are soft nose, but welding into a round bar a big one, pray tell me how are you going to get the gun nozzle in there
NZ is not staffed by just NZ,ers, the guy we used was from Croatia , from the times they were heavily into shipping
You have overlooked the massive loads carried on megayacht forestays although I did mention it
The bow structure you see in the rhino was approved in UK, they did not alter my dwgs and I am content to carry on that way
I can then out a single jack under any point if I want to life there. Now tell me you can do that with 2 plates meeting at 10 degrees
good day to you

 

Ahh..i wasn't sure if this was a verb or adjective or a noun.

So you mean technically "Lock through". To take a boat through a lock.

If that is all your concerned with, with regards to collisions, then there is nothing to worry about. The speed at which you shall be traversing going into and through a lock is slow, very slow. Therefore the impact shall be minor. Unless your scantlings are so light, in which case a minor jolt against the jetty would cause damage. As the impact is roughly the same.

 

<removed>
I have been at sea in tugs sailed and built boats all my life
Please try to to not be superior and I am sure we can communicate, and believe it or not just maybe we can learn off each other
<removed> no I do not mean Lock through, You in UK may call it this but the rest of the world does not

 

I’m sorry but you seem to be reading a totally different post to that which I have added.

There is nothing superior in my postings, only your interpretation and approach in reading them. Since to reply in such a manner suggests you feel you know more than anyone else, ergo, why should you be questioned, as the implication is you know more than everyone else?...otherwise, I simply haven’t the foggiest what you’re on about.

And you seem to be calling me John…for such a personal salutation do I know you??.

Then please explain what it is you mean. Unlike you seem to be, I am not a mind reader, I can only reply to a post that is written not sent via ESP.

 

Please, let's try to keep this discussion polite to one another so it can remain productive and focused on the topic at hand.

 

Some stem bars running from the stem head to the keel base are often so overbuilt it appears an obsession with the designer.

I was at the boatyard this afternoon to get some measurements for alterations I'm designing on a sailboat, I found one frustrated shipwright !

This stem bar was frankly bordering on a FOS of around 25.

The 8mm plate with a couple of transverse webs would have been far more than adequate on it's own. It's a good example !


Dean
I've never seen any problem with welders with round bar. In all my steel design work I always check access for a Mig gun. You wouldn't be very popular if you didn't consider the welders.

 

Just use another class and surveyor like they do here in Asia so you can build the boat how you like, after all you are paying them/him

 

ok Mike
those pics, all I see is a mess, that tube ? what is it doing? the plate is miles fromit in a place that often strikes bricks first. I am quite sure neither you or I designed that
i do not think I overkill . I asked Dubois and Frers if I could do my own structure . they were ok with that IF I DID NOToverbuild
In a 17m sailing yacht I may use 130x16 stem ,cut from 5083 which is the cl bar and then climbs to up to 300 by way of the mast step Often in a modern yacht with U sections you can plate OVER the bar in other words you will have your bottom plate run maybe 500 wide each side
the aim is to maintain continuity of the bar and step .I was fortunate to build under Lloyds for an owner who was a very eminent engineer and founder of a firm that employed 700 design engineers. I learnt so much. It was funny to see him cover reams of A4 with blue ink arguments and fire them off to London. His arguments were always accepted. He was older, passed away 2 ,3 years back. He was also a very good sailer. Rambling and remembering

 

often people aren't aware that specific design is an option. If you think some structure is redundant then a NA/ME who does structural analysis can give you and the class society a workable alternative.

Currently they are more interested in seeing what's called a Finite Element analysis which gives a very clear indication of whether an alternative is strong enough or not. I do this commonly and it gives me a lot of work. There's nothing like design to first principles to teach anyone just what structures are redundant.