USS Cape (MSI-2) by Dr PR - 1:48 - Inshore Minesweeper

[Dr PR]

Here is another "sea tale" about the Cape - and minesweepers in general.

 

We went out once while I was aboard to sweep magnetic mines. Our forward engine room had two large generators to produce current for our "magtail." This was a two wire cable - the wires were 1 inch (25.4 mm) diameter copper cables (probably the most valuable part of the vessel) - that was strung out behind the ship. It had two electrodes that were spaced 50-100 feet apart. The current from the generators was fed to these electrodes and then flowed through sea water. The current through the water generated a large magnetic field several hundred yards behind the ship. This magnetic field simulated the change in the Earth's magnetic field that a large iron ship would create, and this would detonate mines that had magnetic sensors.

 

But the minesweeper itself should create no change in the Earth's magnetic field if it wasn't to be blown up. As I have explained earlier, our engines and other large metal objects were all made of non-magnetic materials. We had a few magnetic things aboard, like the magnetic compass, but these things had degaussing systems to cancel the magnetism.

 

While we were in port (most of the time for the Cape) we had all sorts of magnetic items on board. Metal office chairs, typewriters, some tools, personal belongings and such. When we went out to sweep magnetic mines all of these things had to be off loaded and stored in a locker on shore. It was a real pain in the posterior to get all of these things off the ship and in storage, and then to have to move them all back aboard after the sweeping exercise.

 

We went to San Diego for a yard period (when they screwed up one of our engines) and afterward passed through the Navy's degaussing station off Point Loma. This was a series of under water "metal detectors" off to the side of the channel into harbor. We made several passes through these and adjusted our degaussing system to cancel all magnetic fields from the ship. However, there was one magnetic field we couldn't cancel. As we passed through the array yet one more time the station ashore radioed us and said there was a metallic object in the bilges and gave us a frame number.

 

Our enginemen pulled up the deck plates and looked around in the bilges. Sure enough - we found a small crescent wrench one of the yard workers had dropped, right where the degaussing station operators said it would be!

 

That really impressed me! After losing the wrench over the side the ship had no magnetic signature.

Edited December 8 by Dr PR

[Ras Ambrioso]

Great stories Phil. I am learning a lot about minesweepers. Thanks.

[Dr PR]

Another of the hull details to be completed is the garboard strake. I have installed the first layer flush with the other hull planks. Now I need to add the second layer that is built up on top of the first layer.

 

The blueprints do not show the details of this strake clearly. However, thanks to photos from Austin Cox (the current owner of the Cape) of the vessel on blocks I can see what the strake looks like and where it ends.

 

 

 

 

 

 

As you can see in these pictures the strake tapers down to match the contour of the other hull plating just aft of where the stem starts to curve upward, This is about bulkhead 2 on my model. The taper at the aft end is a bit harder to see.

 

 

 

It is clear that the strake tapers down to the contour of the hull planking a bit forward of where the planks fair into the deadwood, forward of the stern frame and propeller. This is just aft of bulkhead 15 on the model.

 

To help visualize the shape of the strake I made a series of paper templates from the drawings of the bulkheads.

 

 

You can see the gaps in the templates where the keel and planking come together. These show the shape of the garboard strake. I think the strake can be carved from a 1/4 x 1/8 inch (6.35 x 3.175 mm) basswood stick. I will cut the angle at the corner between the keel and planking first. This will be on the "inside" with the glue where it won't be visible so the angle doesn't have to be precise. Then I will use heat to curve the plank to the shape of the hull. After that I will use the templates with files and sandpaper to shape the exterior surfaces.

 

At least that is the plan. We'll see what Murphy has to say about it!

 

Edited December 9 by Dr PR

[Dr PR]

The garboard strakes are finished - well, I may do a bit of retouching before I paint the hull.

 

 

 

I may taper the front and rear ends a bit more.

 

These "planks" had to be about 0.080 inch (2 mm) thick, so I couldn't use any of the 1/16 inch (1.59 mm) planks. I started with a 1/4 x 1/8 inch (6.35 x 3.175 mm) basswood stick and shaved it down to 0.080 inch with a plane. Then I used wet heat to bend it into the shape of the hull. I used a file and sanding blocks to make the angled edges and shape the piece to fit in the angle between the hull planking and the keel.

 

Next will be the bilge keels, and then the "guards" (rub rails) around the edge of the deck.

Edited December 11 by Dr PR

[Jim Lad]

Looks good, Phil. Now you need to tackle to bilge keels!

 

John

[Dr PR]

After "completing" the garboard strake I was looking at the photos of the current day Cape and realized I did not carry the strake forward enough. I was going by the blueprints, and they don't show the strake extending forward of frame 7, just forward of my bulkhead 2. But the photo (below) clearly shows the strake running forward to where the planking is starting to turn up at the stem. I should have been paying more attention to the photos!

 

 

I cut off the most tapered part of the strake (left below) and added a new piece to extend the strake forward to just past my bulkhead 1 (right below).

 

 

This is closer to what is on the real vessel. Maybe not perfect, but good enough.

 

I have also started working on the bilge keels, but that is a story for another post.

Edited December 12 by Dr PR

[Jim Lad]

Nice recovery, Phil!
 

John

[Austin Cox]

Your attention to detail is fantastic, Phil. I can look at your hull and recognize it! We're enjoying following this build. Regarding the garboard strakes, they may have been closer to the blueprints originally. The garboard and worm shoe were replaced several years back - this is worrisome because so far most recent work seemed to have been fastened with stainless steel, which doesn't mix with the old growth doug fir! Luckily the keel bolts are still bronze. I can't really blame anyone, given the price of these fasteners, but it's still annoying. I've spend countless hours removing stainless fasteners and replacing them with silicone bronze.

 

I can't remember if I replied to your last email. We've been very preoccupied with holidays and a sick puppy dog. I apologize if your last email went unanswered. The blueprint displays well on my screen. We have most of not all of the original paper blueprints and ship documents. Although there's not much room aboard to roll them out for viewing. We still use the original Docking Plan blueprint when planning and implementing a stay in the shipyard. Cape is due to be hauled again this coming August in Port Townsend, WA.

 

[Dr PR]

Austin,

 

Thanks. I think we are up to date on emails. I sent some propeller information.

 

Your photos are invaluable! They have simplified some of the problems in deciphering the blueprints. For example, I am planning the bilge keels right now, and your photos show the shape of the ends. The blueprints aren't very clear about that, but they do give the cross-section dimensions.

 

Hope you have a good holiday and a healthy puppy!

[Dr PR]

I have bilge keels. It took a while to figure out how to make these. Part of the delay for a few days was an annoying head cold. I made some paper templates using the drawings for the bulkheads with the keel positions marked on them.

 

 

I placed each template over the keel at the corresponding bulkhead and marked the bilge keel positions on the hull. I used the Table of Offsets to get the positions of the bilge keels. Oddly, two of the dimensions (bulkheads 11 and 12) were inaccurate. But the remaining positions lined up perfectly. I have seen errors in the Table of Offsets for other ships so I wasn't too surprised.

 

The cross section of the bilge keels is a trapezoid (truncated isosceles triangle) with sides angled 15 degrees from the base and a height of 0.208 inches (5.28 mm). I cut them from a 1/4 x 1/4 inch (6.35 x 6.35 mm) dowel from a local hardware store. The wood has no grain and sanded/filed/carved easily. If I had a milling machine the setup would have been trivial - but I don't have one. I figured out how to hold the dowel with some alligator clips and set the table on my disk sander to 15 degrees. I used this for the rough cut and finished it with sandpaper lying flat on the table.

 

 

The pieces were temporarily fastened to the hull in approximately the right positions with large rubber bands. Then I used the wetting/heating process to bend the sticks. Even though I was bending across the wide dimension the wood bent to shape fairly quickly.

 

 

Next I shaped the ends of the keels, using the photo above provided by Austin Cox. The blueprints do not show the overall shape of the bilge keels in any detail.

 

 

I drilled 0.041 inch (1.04 mm) holes near the ends and at the center Then I held the keels to the hull in the correct position and used the holes as templates for drilling holes into the hull planking. I made six small pins by filing and sanding a bamboo skewer until it just fit into the holes in the keels. These "pins" assured that the keels would be properly aligned while I was gluing them onto the hull. It worked perfectly!

 

 

The keels matched the curvature of the hull almost perfectly after gluing. At the ends there were slight gaps of 0.010 to 0.015 inch (0.254 to 0.381 mm) between the hull planks and the ends of the keels. I filled the gaps with Squadron White Putty.

Edited Wednesday at 01:38 AM by Dr PR

[Jim Lad]

Nicely done, Phil.

 

John

[TBlack]

Phil, How you figured out the cross sectional profile of the bilge keels is an art/science in itself. wonderful progress!

[Dr PR]

Tom,

 

This was the first time I have put bilge keels on a model. I have seen drawings like the Booklet of General Plans for many vessels and wondered how to translate the 2D hull profile drawing into 3D positions on a hull. Likewise, the fore/aft drawings often show the bilge keels as more or less straight lines around the curvature of the hull (like great circles), but I couldn't decide how to turn this 2D information into 3D curves. It was a puzzle!

 

So I would like to weave another long-winded tale (this is getting long) about the trials and tribulations of bilge keel design, but that would be BS!

 

 

This is from the MSI Lines and Offsets blueprint. All I had to do is scale it to 1:48. And the 3D curvature on the hull? Just follow the instructions in the Table of Offsets - go to the frame number and get the height from the baseline and distance outboard from the center line and you have an offset point on the hull for the centerline of the bilge keel. That is what the paper bulkhead cutouts were for.

 

Or, if you want, it was an arduous process full of missteps and endless rambling ...

Edited Wednesday at 04:40 AM by Dr PR