Dunbrody by Mahuna - FINISHED - 1:48 - Cross-Section - Irish Famine Ship

[ggrieco]

Thanks Frank,

 

It seems like I learn a new technique each time I check in. Your posts are always very informative!

[Mahuna]

Thanks Frank,

 

It seems like I learn a new technique each time I check in. Your posts are always very informative!

Hi Glenn - that's one of the great things about build logs - we get to see new (to us, anyway) ways to do things.  Your Heroine build has given me lots to think about, and right now I'm thinking of trying your approach for building the deck structure.

[HIPEXEC]

Wow! What a nice job!

[Mahuna]

Wow! What a nice job!

Thanks Rich!

[Mahuna]

Part 26 – Planning The Accommodation Deck

 

In thinking about drafting the Accommodation Deck beam structure, one of the things that concerned me was having a good foundation for the drafting.  What I mean by that is having an accurate layout of the framing so that the beams can be laid out accurately. 

 

Even though the layout of the frames as I originally drafted in CAD is precise (because of CAD) I also knew that there were a lot of errors that crept in during the build and installation of the frames.  I needed a way to make sure that the plans for the Accommodation Deck took these errors into account. 

 

I decided the best way to do that was to measure all of the frames and the spacing between the frames at the level of the Accommodation Deck, and to use these measurements for planning the build of the deck structure.

 

I measured the span of each of the frames at their fore and aft faces, adjacent to the top surface of the deck shelf.  I also measured the sided dimension of each frame at the same location, and the spaces between each of the frames at that location.

 

I used these measurements to draw a layout of the actual model at the level of the Accommodation Deck, and I’m very pleased with the results – this will form a good foundation for accurately laying out all of the beams for the deck.  I printed the layout on a heavy card stock and laid it in place to see how it worked out.  I had to make a few adjustments to account for some errors in measuring, but after a couple of iterations I now have a workable base for planning the beams.

 

                        

 

                        

 

                        

 

So now I’ll start drafting the beams for the deck, and I should be able to get back to making some more wood dust fairly quickly.

 

 

Thanks everyone!

[Mahuna]

LOL - I just noticed a misprint on the layout - I have two frame #21's instead of a #19!

[AON]

misprint.... been there, done that!   

[PETERPETER]

G'day Frank,

Excellent photos of the method you used for replicating the lodging knees for the mast step. This is what we discussed during my visit Sunday. You must be using a tripod setup to take your photos, no?

Peter

[Mahuna]

Part 26 – Accommodation Deck Beams

 

After preparing the frame layout shown in my last post I spent some time drafting the beam configuration for the Accommodation Deck, using the Dunbrody construction plan as a guide.

 

The Construction Plan classifies the deck beams as Main Beams and Second Beams.  There are also Bulkhead Beams, but these are for the modern steel bulkheads, which won’t be included in the model.  I substituted Main Beams for these.

 

All deck beams have a moulded dimension of 10.5 inches.  The sided dimension of the Main Beams is 9.75 inches, and the Second Beams are sided 8.25 inches.  The small partial beams used in hatches and the mast partner are sided 6 inches.

 

The following photo is the plan for the Accommodation Deck beams for the sectional model.

 

                        

 

The small red numbers on each beam are the actual sided dimension of each beam, expressed in 64ths, and the small black numbers on the beams is the length of that particular beam.

 

NOTE – there are two hatches shown on the plan, both labeled FL Hatch – I have no idea what the ‘FL’ refers to, so if anyone has an idea of the meaning I’d appreciate hearing it.

 

The Dunbrody replica ship in Ireland didn’t seem to have any hatches on the Accommodation Deck, but since the original ship was designed to carry lumber and other freight it makes sense that there are hatches.  I don’t imagine that the ship’s captain worried too much about making the deck friendly for the emigrants, so I plan to make the hatch covers and associated hardware, rather than simply planking over the hatches.

 

 

Before starting on the deck beams I applied wipe-on poly to the deck clamp and shelf, stringers, ceiling, and keelsons.

 

                        

 

The first step was to mill all of the required lumber.  I then created each full-length deck beam, fitting the ends to the hull’s taper where necessary.  I pre-drilled bolt holes in the ends of the beams.

 

Using the bolt holes, I temporarily pinned each beam in place and marked the centerline on each beam using the setup shown in the following photo.

 

                        

 

This centerline will be a key in lining up the slots to be cut in the beams.

 

The four headers for the two companionways in the sectional model are all the same size, and the partial beams that intersect them are all located in the center of the header, so the notches for the intersecting beams were all cut at the same time.  The first step was to temporarily glue these headers together using Ambroid glue.  Since the narrow sided dimension needed to be glued together, a flat piece of thin stock that spanned all four timbers was used as a base, and was part of the glue-up.

 

                        

 

Another piece of thin stock was also used on the opposite surface, but was not glued.  The ‘sandwich’ that was created kept the timbers flush and level.  When the milling was completed, the pieces were separated by a quick bath in acetone.

 

The beams and partners were normally joined using a lap joint, but since only the top of the joint would be visible I decided to use a full slot for these joints, cutting the slots on the milling machine.  The following photo shows the setup used.

 

                        

 

The beams needed joints as well.  The centerlines marked on each beam were used to align the beams for milling.  First the centerline was carried around each beam so that it was visible from each side of the beam.

 

                        

 

Every beam, header, and partner on the plan has a midline marked.  The beam being worked on was then laid on the plan with the centerlines aligned, and the location of the midlines of the associated timbers was marked on the beam.

 

                        

 

                        

 

The two beams that will be slotted were then clamped together with the centerlines aligned.

 

                        

 

The milling was done on a tooling plate, and I used screws inserted in the tooling plate as a ‘fence’, since these screw holes are already aligned.  The first action was to align the milling head with the line for one of the slots.  This was done using a laser centering device.  I find this tool to be extremely useful and accurate, and worth the cost.

 

                        

 

                        

 

With the head properly aligned the x-axis was locked in place, the laser was replaced with an end-mill, and the slot was milled.

 

                        

 

All of the beams and associated timbers were cut to size and the appropriate slots cut.  All pieces were then dry-fit on a copy of the plan.

 

                        

 

After seeing Glenn’s work on the Heroine deck I was hoping to glue the hatch assemblies together off the model and to then install them as ‘modules’, but the slight tumble-home prevented me from doing this.  I was able, though, to make some ‘sub-assemblies’ off the model.

 

                        

 

                        

 

Seven of the deck beams each have a pair of hanging knees.  Since the knee will cross the deck shelf, deck clamp, and bilge ceiling – all of different moulded dimensions – creating these knees was fairly complicated (and error-prone).

 

                        

 

There are also 4 hold stanchions (pillars) in the model – these were more straight-forward.

 

                        

 

The stanchion knees are held in place using a restorer’s clamp (from Lee Valley).  The moulded dimension of the knees is smaller than that of the stanchion, so I needed a way to ensure that the knees were correctly centered. I milled a piece of aluminum stock so that the groove is approximately the same width as the stanchion, and the depth is one-half of the difference between the stanchion size and the knee size. – the assembly is resting on the jig in the above photo.

 

The following photos show the current status of the model – the forward hatch assembly is in place, including three pairs of hanging knees and two hold stanchions.

 

                        

 

                        

 

                        

 

Thanks everyone for following, and for the comments and ‘Likes’ – all are much appreciated. 

[GuntherMT]

Beautiful and precise work as always Frank.  Looking great!

 

Maybe "FL Hatch" is for F'ing Large Hatch.  

[mtaylor]

Beautiful and precise work, Frank.  Very cleanly done.   

 

Where did you find the laser centering device?  

Edited June 22, 2016 by mtaylor

[druxey]

Lovely work, but usually hanging knees attach to the sides of beams, not under them. Are you sure that this was not the case here?

[EdT]

Fantastic work, Frank.  The precision is extraordinary.

 

Ed

[Mahuna]

Beautiful and precise work as always Frank.  Looking great!

 

Maybe "FL Hatch" is for F'ing Large Hatch.  

Thanks Brian.  Hmm, I hadn't thought of that for the hatches.

[Mahuna]

Beautiful and precise work, Frank.  Very cleanly done.   

 

Where did you find the laser centering device?  

Thanks Mark - I found the laser at LittleMachineShop.com

 

Fantastic work, Frank.  The precision is extraordinary.

 

Ed

Thanks Ed.  Your books and logs have been a marvelous help in the learning process.

 

Lovely work, but usually hanging knees attach to the sides of beams, not under them. Are you sure that this was not the case here?

Thanks Druxey.  The construction plan shows the knees under the beams.  Also, Crothers says "The Hanging Knees, installed under the beam ends ..." - so I think they're in the right place.  

[Mahuna]

Lovely work, but usually hanging knees attach to the sides of beams, not under them. Are you sure that this was not the case here?

Druxey - I checked Ed's Naiad books (only books I have on Age of Sail warships) and found that the hanging knees are indeed installed as you said.  I then checked the Desmond book on later period wooden ships and found the following: "The hanging knees are fitted to the underside of beams and to the side of vessel and fastened with through rivets driven at varying angles".

 

So it seems to me that the method of installing hanging knees must have changed sometime in the 1800's.  It's odd that neither of the books I'm using as references refer to the change.

 

Thanks for bringing up a very interesting point.

[captainbob]

Beautiful work, Frank.

 

Bob

[thomaslambo]

Hi Frank,

 

So glad I came across your superb build...it'll be a pleasure watching you work 

Edited June 22, 2016 by thomaslambo

[druxey]

Rivets imply iron or steel construction, Frank.

[Elijah]

She is looking more and more like a ship!

[GuntherMT]

Rivets imply iron or steel construction, Frank.

 

I think Frank mentioned that the replica ship had steel/iron in the construction.

[Mahuna]

Rivets imply iron or steel construction, Frank.

Hi Druxey:

 

The Desmond book deals primarily with wooden ships.  In his book, Crothers cites the Chatsworth, a ship-rigged packet built in 1854 as having between 11,000 and 12,000 'riveted bolts'.

 

Here is the cross-section of the mid frame, showing the hanging knee under the beam.  There are many similar pictures of various ships in the Crothers book - all with hanging knees shown the same way.  If the knee were to be attached alongside the beam I would expect the drawing to show the upper part of the knee (probably as dashes) in at least one of those drawings.

 

[druxey]

I've no wish to quibble, but the knees, fitted as shown, would be weak. My interpretation is that we are looking at the beam closer to the viewer and the athwartships arms of the knees are hidden. As modified, the illustration shows what was standard wooden ship practice. The bolts would run horizontally through the beam and the lodging knees would interlock with the hanging knees.

[GuntherMT]

I've no wish to quibble, but the knees, fitted as shown, would be weak. My interpretation is that we are looking at the beam closer to the viewer and the athwartships arms of the knees are hidden. As modified, the illustration shows what was standard wooden ship practice. The bolts would run horizontally through the beam and the lodging knees would interlock with the hanging knees.

 

Why would you feel that the knees directly under the beams, with the bolts holding them in position would be weaker than placing the knees along side the beam, and the bolts in shear now causing all of the beam weight to rest on a much smaller portion of the knee?  

 

The knee strength doesn't change if it's placed in either location, but the weight transfer from the beam to the knees is now much more focused, and bolts are much weaker in shear than when used longitudinally.  A bolt in shear will have approximately 60% of the tensile strength of the bolt, and that is with modern metallurgy.

 

While I don't doubt your knowledge of what the standard practices were on the ships of long ago, those practices were ever changing as people learned more about things and how to make them better.  My brain can't grasp how mounting the knees to the side of the beam could possibly be stronger in an way than mounting it below the beam.

[EdT]

I believe Frank's interpretation of the knee design for the ship in question is very probably correct given the practice at the time and the availability of strong riveted iron bolts that were not available to earlier ship structures.  I say "very probably" because most of my investigation involved American ships.

 

With the knees beside the beam the top fastenings would be in shear.  While this offers no advantage when considering the strength of the fastening itself, it would have be of advantage with early fastenings in tension because of their lower extraction resistance.  However, even with the knees side-bolted at the top, they were still bolted from the inside through the frames, raising the question of the reason for the side bolting at the top.  Perhaps it required less fitting of the knee (only one face vs. two.) or was better for headroom with the low deck heights of the time.

 

Anyway, I researched this issue when drafting the structure for Young America.  Bill Crothers was quite clear on the arrangement - see p 240 of American Clipper Ships and/or p 209 in his book on packets. These knees are clearly on the beam center line - ie bottom mounted.  Although I had great confidence in Bill's conclusions, I looked for further primary source data.  This can be found in the following diagrams extracted from the American Lloyds Registers of 1857 and 1867 respectively.  These documents defined acceptable shipbuidling practices at the time.  Although titled "American" I believe they were consistent with British standards.

 

 

 

 The third image is a photo from Desmond on Wooden Shipbuilding showing knees in the beam centerlines.

 

 

Ed

 

[Mahuna]

This has been a very interesting and informative discussion - thanks everyone - and it demonstrates one of the great benefits of this forum: the exchange of ideas.  It also illustrates the need for research when building a model.

 

I looked through my photos of the Dunbrody replica ship in New Ross, Ireland, and found this photo taken in the emigrants' living quarters on the accommodation deck.  It clearly shows the hanging knee under the beam and the lodging knee on the side of the beam.

 

Edited June 22, 2016 by Mahuna

[Mahuna]

Hi Frank,

 

So glad I came across your superb build...it'll be a pleasure watching you work 

Welcome, Boyd.

 

Beautiful work, Frank.

 

Bob

Thanks Bob.  By the way, it looks like I may get up to your area sometime in early July.  I'll bring Dunbrody with me.

[druxey]

I sit corrected, then! Replacing a knee of that type would involve removing decking to get at the bolts....

 

Thanks for an interesting exchange, everyone.

[Mahuna]

Thanks Druxey.  When I took the photo in the previous post I was mainly interested in the emigrants' sleeping quarters and wasn't even thinking about the knees (didn't know enough at the time to even consider it).

 

It would be very interesting if there were details of the changes that took place in sailing ships from the napoleonic wars to the age of the clippers.  The major changes in hull design and sail plans are obviously well-documented, but details like this one we wrestled with are hard to find - and it would be great to get answers to 'why' and 'when'.

[AON]

Being in mechanical engineering I found this last exchange quite intriguing!     

 

Thank you Druxey for explaining why (some or most) knees we installed with bolts in sheer as until you stated the obvious "ease of repair" reason I was swayed to the logical "mechanical strength of design" explanation.    

 

I hesitated to respond earlier because you are no rookie... even though all the evidence was stacking up against you (photos and figures and mechanical design logic).    

 

Now I understand why they were installed on the side in most builds... and as in life some will be different (diversity) for whatever reason.