Construction of a cutter

[dskira]

Originally Posted by MikeJohns

Daniel
I'll add :

Or add the rider that the welds in those locations are critical, ie should be defect free with no stress risers, But it looks like you might have a bit of overkill in the web width anyway. Class rules are usually pretty forgiving as well.

in the ballast area the inner end of the floor-frame weld will be in tension when the vessel is heeled. This is the fatigue load that needs consideration, either a doubler plate or a bracket might be advisable in high load areas with that 90 degree butt.

An alternative is to cut the floor straight across the top and bevel the joint. This staggers the welds rather than having them all in line, Particularly if there's a flange (face bar). Sometimes a little more welded join obviates the need for another part (like a bracket). See the pic below.


But steels much easier to detail than alloy or wood which would have (messy ) joins overlapping and tapering all over the place.

I know, the builder unfortunately after giving me the scanting, I find he didn't follow the plan schedule. I started to mention what Ad Hoc mentioned, and I ends up receiving the new scantling with the frames far wider. I am on a pickle, the weight distribution as to be redone. When the builder change the schedule, it is not good news.

The ballast reinforcement been inside was taking care very carefully. It seams not going that direction, but we have long telephone conversation and he will make the change to go back to the plan. He is a good guy, and I hope he will continue to send pictures, the only way for me to follow his work.

Thank you for you input

[dskira]

Originally Posted by Ad Hoc

Indeed this is a critical area. This was addressed in this thread here:
metal frame detail

But unfortunately the image that was in the first post is no longer there, it is ostensibly the same as that shown in Mike's above.

Personally i don't recommend a doubler, for the reasons noted in the thread, despite the debate being about aluminium (different characteristics). In this instance, steel, because you still have a sudden change of modulus, despite the forgiving nature of steel, compared to ally. The stiffness in the side frame changes too quick over a short distance.

Even though most Class societies say any joint greater than 150 degrees is considered continuous, thus may obviate the need for a bracket, i still recommend it, as does LR too, in these regions:
Attachment 48785

The system designed was the one on the right of your drawing Ad Hoc




It was not intended to be web system at the beginning, I designed with separate pieces and all welded, like I always do. He was on the trip to web and weld, since he find a way to have the offset put on a computer, and use the computer to cut the steel.
My intention was for him to loft and the then do the framing the classic way, with the welding at the floors, at the gusset, and separate beams and floor.
I am now trying to reconsider the whole plan since the builder put me against the wall. it is not fun, but it is always challenging to work with a builder at 3000 nm from my home. (I don't travel)
Thank you for helping me, I will certainly come back with some specifics questions.
For the moment I have to extract from him all the element already done, and redo the weight estimate.
Then from there I will see the necessary changes.
Thank you for your input.
Daniel

[Ad Hoc]

Originally Posted by dskira

... but it is always challenging to work with a builder at 3000 nm from my home. (I don't travel)

It is not so easy working such distances for the first few times. I have been working remotely from yards for many years now. At my previous shipyard, we licensed out our designs to other yards, some being over 8,000 miles away. But once you recognise the pit-falls and establish and clearly define the scope and who has responsibility/authority, it all falls into place. So, whether you’re 3,000miles away or 3metres shouldn’t make any difference.

If you have any questions, we're only too happy to assist

[MikeJohns]

Daniel hope you don't mind a bit of hijacking We don't get much opportunity for good technical discussion these days.


John

Yes that's one bracketed method, What does that Llloyds guide say about floor to frame non-bracketed, do you have it there?

For others reading this; there is a distinction depending on the frame Z as to whether the ends require fixity or not. A lot of smaller vessels the web depth is dictated by other factors and they are beefy enough to not require fixity brackets. Then its more a matter of making sure the angles are less acute, or adding smaller curved brackets.

John

I think you'd be quite shocked to see some small boat framing that shipyards built and approved 100A1.

The doubler on a web frame I meant as alongside the web across the weld as a cover plate fully fillet welded. Like normal commercial builds which just overlap the frame web over the corner bracket with fillet welds. The full butt welds take longer but will be stronger. Yes an insert bracket fully welded would be better still, if required. There are other doublers too, oval shapes circles and rectangles that are welded across as stress relief at the join.

But with deep web frames on small vessels the loads are quite small. I've often shaved brackets off designs following analysis that would not be applicable in a larger vessel. I did a lot of analysis for one design of a very lightweight steel sailing vessel, it was quite illuminating to see just how much of the standard shipbuilding requirements were overkill when we looked at the actual reactions in a small vessel frame closely.

On a larger vessel it's an entirely different story.

[Ad Hoc]

Concur with Mike, sorry for taking over the thread, but not often we do get the opportunity to discuss technical issues.

Originally Posted by MikeJohns

What does that Llloyds guide say about floor to frame non-bracketed, do you have it there?

LR generally don’t allow connections without brackets, as their rule state in Part 6 Ch.3. Sec4.,


but not necessarily consistent with their guidance notes, as they also provide alternatives:

Originally Posted by MikeJohns

I think you'd be quite shocked to see some small boat framing that shipyards built and approved 100A1.

Sadly no, I have seen some shocking stuff, but this too, is all slowly changing.

Originally Posted by MikeJohns

I did a lot of analysis for one design of a very lightweight steel sailing vessel, it was quite illuminating to see just how much of the standard shipbuilding requirements were overkill when we looked at the actual reactions in a small vessel frame closely.

Indeed.

Small vessel tend to be at the ends of the “envelope” of Class rules and thus, the rule minimums do not generally produce meaningful results. However, if you have previous supporting evidence to reduce the minimum, they will review and generally accept this. I have done this on numerous occasions. Having a large database of previous designs and history does help though!

[dskira]

John and Mike please continue talking technical issue in this thread, it is very interresting and informative.
Thank you both for your input and lets continue
Daniel

[Ad Hoc]

Originally Posted by dskira

John and Mike please continue talking technical issue in this thread, it is very interresting and informative.
Thank you both for your input and lets continue
Daniel

We'd be happy for this to be a Q&A, we (Mike and I), and any others too (if they wish to chip in), would be more than happy to answer any questions anyone has, just ask away.

[Jack Hickson]

Looks like a flat plate for keel and deadwood. I read an article in Latitude 48 a few years ago , about how racers were increasing their speed , by rounding of keels , and giving them a more airfoil section, to minimize stalling when sailing in rough water. When beating to windward , or sailing downwind in rough water, the sharp leading edges, and flat shape of some keels led to a huge amount of increased drag when they stalled.
You could drastically reduce drag by giving this keel a bit of airfoil shape. This would enable you to drop your ballast a lot deeper, enhancing stability. When, as kids, we play with model boats, we quickly realize that the deeper the V, the tippier the hull. This boat has a super deep V shape ,and will need all the help it can get, when it comes to stability.

[MikeJohns]

Originally Posted by Jack Hickson

Looks like a flat plate for keel and deadwood. I read an article in Latitude 48 a few years ago , about how racers were increasing their speed , by rounding of keels , and giving them a more airfoil section, to minimize stalling when sailing in rough water. When beating to windward , or sailing downwind in rough water, the sharp leading edges, and flat shape of some keels led to a huge amount of increased drag when they stalled.
You could drastically reduce drag by giving this keel a bit of airfoil shape. This would enable you to drop your ballast a lot deeper, enhancing stability. When, as kids, we play with model boats, we quickly realize that the deeper the V, the tippier the hull. This boat has a super deep V shape ,and will need all the help it can get, when it comes to stability.

Brent / Jack
Lattitude 48 isn't really a quotable authority on Naval Architecture.

Unfortunately you confuse a few issues in that post.

Racing boats have had aerfoil sections for their foils for many decades becasue they have a lower drag while providing lift.

Aerfoil shapes are not applicable to low aspect ratio keels since the flow has a high spanwise rather than chordwise component. For low AR foils flat sections are perfectly ok providing you round the corners on the leading edges.

For example a full keel on a sailboat can have a flat leading edge and straight run sides and only a taper aft with a with no discernable difference to an expensive rolled parabolic LE . Just so long as you round the corners.

As for flat plates; they can provide more lift and a delayed stall relative to an aerfoil section, just at the cost of greater drag.

[Jack Hickson]

Not much rounding you can do on a plate edge

[MikeJohns]

There is, you don't leave it sharp square edged.
You round those corners too even on a flat plate and it makes a significant difference in leading edge vorticity. Something most people would feel intuitively.

[Jack Hickson]

It would be far sharper than a proper airfoil . You still have your ballast much higher, in a very slack bilged , tender hull shape, lacking initial stability.
How many of these boats have been built? How many sailing craft of this size have you designed and built ? How many have done extensive ocean cruising ?