Project 945 - Sierra I (1/60 scale)

[cstranc]

Where to begin. I attended my first sub-regatta last year in Carmel. I was hooked on RC subs before. Now I am doubly hooked.

On the long drive home I started playing with the idea of putting a pitch control system into a model. so when I say down it will give me a nice smooth dive (even at low speeds).

I did some experiments and in the end submitted an article on the tests to SCR. Of course testing is nothing without application. So the Sierra began.

I got the plans from Deep Sea Designs. The plans are in 1/96 scale, but I have big fingers, and big plans for the inside of this hull so I took the drawings and had them scaled up. As it stands the model will be 67" long and have an inside diameter of 7 3/4". Plenty of space.



In this thread I shall follow the construction and outfitting of the hull. I shall start a separate thread that focuses on the actual pitch control system.

[cstranc]

Like so many models the

Like so many models the hull will start out as large foam blank. I used the "lost foam" technique, so no mold that I can create multiple hulls from. This is probably a good idea.

I may as well admit it now. I am not a perfectionist. I'm an engineer. So I tend to over build things, and can ignore the occasional detail in the pursuit of functional elegance, durability, or getting this model in the water before Carmel 2007

I chose the Sierra I for my model because I really liked the shape. When it came time for fabrication I really appreciated how easy life is with circular hull cross sections.

I used 2.5" insulation foam for the majority of the hull where the diameter was consistent. The areas with significant tapering I switched to 1" foam.

I marked out each foam section on the plans, then took the diameters and used a compass to mark the foam for cutting.

I have used hot wire for cutting foam before. This time I used my bandsaw. It is more messy, but I find it gives a better result. Especially for thick foam the wire does not stay straight. Instead the wire in the center of the foam "falls back" a little due to friction, then as you turn a corner it cuts into the radius. Also if you don't move at a constant speed can melt back the foam... None of those hassles with the bandsaw.

When I had the sections all cut to shape I glued them. I actually did the bow and stern separately, then when they had set I glued these assemblies together.



When I was gluing the individual foam sections together I was careful to reverse every second one (top of sheet / bottom of sheet). Sometimes the foam board has a slight taper to it, and reversing every second section tends to prevent a cumulative bow.

So now I had my foam ready for sanding. sand, sand, sand... Hmmm.

Something did not look quite right. Sure enough along the length of the hull I had a curve/wobble....



Ahh well foam is (relatively) cheap and experience is priceless.

Foam blank one was relegated to "official test hull" and I started the whole process again.

This time I took a length of 1/2" copper pipe and the center of each foam section was pre-drilled to accept the pipe. As before I was careful to glue everything together standing on end. You do not want gravity to give you a curved hull.



With the help of the copper pipe the alignment was perfect. Under 1/32" along the entire hull before sanding and filling.

And so it was on to sanding... If you look closely in the following picture you can see the 30" sanding block my dad made for me (thanks dad). It did a fantastic job smoothing the hull.



At the front you can see hull taper ready to be sanded to shape.



I had the copper pipe extend when I was gluing up the sections. I had to pull it back flush with the front of the hull for sanding. I did not remove it though. It was too handy being able to stand the model on it's tail, put the pipe into a stand and them be able to coat the entire hull with resin in a single shot.

[cstranc]

Soon enough both hulls were

Soon enough both hulls were sanded to shape. We have this large granite slab on the island in our kitchen. I noticed quickly that it was perfectly smooth and just a little bit bigger than my model... A perfect dry dock. I have used it frequently to check the hull is true, and when I am marking lines.

I use packing tape to protect the foam from the polyester resin. This worked on my last model. But it never hurts to test...



I go back and check. Sure enough I am using a different manufacturer for the packing tape. Apparently all packing tape is not created equal.

I tested a few more brands until I found one that did actually protect the foam.

Applying the tape to the hulls took a certain touch to prevent it from creating wrinkles on the curved surface. Always working along the length of the hull, I would take a 24 to 30" piece of tape. Starting at one end I would lightly press down the center of the tape for a 2" length, then go back and spread out from the center to the edges over that 2" length. My other hand would hold the tape with no tension. I found that applying tension with the other hand tended to cause more wrinkles by forcing the edges to contact and stick to the foam before I was ready.

This was one of the good things about having a "test hull". You can test, perfect techniques, and generally do what you want with it.

Finally it was time to apply the resin and fiberglass. I was worried that the taper at the front and back of the model would give me wrinkling issues as the hull changed diameter. So I chose the glass the center, then either end.



To get the right shape for the cloth I cut out a paper template, adjusted it to the hull then used that to mark the cloth.



Once I had the whole hull covered I would sand it smooth and then put down another layer of cloth. I would vary the location of the seam where the pieces of cloth overlapped.

Looking back on it, I wish I had used the technique that Kevin McLeod describes. It seem to generate excellent results with a lot less fuss.

I used 3 layers of cloth and 4 layers of straight resin to do the production hull. I also glassed the test hull, but only 1 layers of cloth, 2 layers of resin. When I was doing the main hull I would apply any left over resin to the test hull rather than just discarding it.

I had meant to finish the hull using only resin. In the end I broke down and used some bondo to fill some areas before doing my final 2 coats of resin.

Then it was time for the final sanding... I would take my 30" sanding block and hold it against the hull, noting any high spots. Rotate the hull more notes, ... Then after marking the entire hull I would sand the markings off.



At this stage I worked up to 600 grit paper. That gives me a good finish for now while I work on the inside of the hull.

[raalst]

nice and fast !



nice and fast !

keep on going (and posting)

[tmsmalley]

Very cool Chris - keep

Very cool Chris - keep it coming! It's good to have somebody demonstrating the lost foam process for one-off hulls. It's faster and cheaper than making moulds if you aren't planning on multiple copies.

For those who haven't received your copy of the SCR yet, Chris Stranc has an interesting article about building an automatic pitch controller in the March 07 issue.

I have a couple of questions, Chris - what adhesive did you use to glue the foam together? Some types will melt builders' foam. Also - what brand of packing tape did you find worked best?

Even though a barrier isn't 100 percent necessary when using epoxy resin, polyester resin will attack foam that is not well protected. Jeff Jones employs multiple coats of water-based house paint so that's what I used when laying up my Hunley.

[himszy]

There is Dan's Storm build

There is Dan's Storm build (though he probably doesn't want me reminding everyone about that) that used the lost foam method....

I've also found that Duck/Duct/Gaffer tape works best - the cheaper the better (has less glue on which means if you get it right you can pull out the former intact).

Michael

[JWLaRue]

Very nice, Chris!

....I think I

Very nice, Chris!

....I think I can see another excellent article for the SCR coming in the near future!

-Jeff

[cstranc]

Ronald,
Alas I'm not this

Ronald,
Alas I'm not this fast. I started the model in November. It's just with that SCR article coming out I thought I should hurry up and get my follow up information on putting pitch control into a model. I have been taking pictures, so you get to see the accelerated build.

Tim, I am using Bondo polyester resin and I find that Tartan tape worked well. I still am carefull to put two layer over the entire hull. It's hard to trust something that thin after putting hours of work into the foam.

For gluing the foam together I just used Welbond. It should be available everywhere. But I am very glad you mentioned it...

When gluing the foam sections together I found two things. Initially I used to make a spiral of glue on each face being glued, then put them together etc. On my test hull I found this did not always set as well as I would like. It seems that Welbond needs the air exposure to set. For the real hull I would make little dots of glue in a radial pattern. This way each dot had the air contact to set. It was much more reliable.

Another thing about the gluing was to keep the glue 1/4" away from the edge of the part. If it's too close to the edge it squeezes out and then you have to trim it before your start sanding. If you don't trim it then the sanding can dislodge it and it makes a nasty scar in the foam....

Michael, you mention saving the form. Wow, that never occured to me. When I say "lost foam" it is truly lost, converted into tiny little piece flying everywhere as you are about to see

It's interesting to think about lost foam versus master & mould techniques...

Lost foam should certainly get you to a working hull faster but it has possible drawbacks...

In Kevin's Oscar article he mentioned saving weight on the upper hull by going lighter on the cloth / resin that the lower hull. I suppose this might be possible in a lost foam approach, but it's not as simple / elegant.

I think overall you lose control over fine tuning the strength / weight of the hull with lost foam. As you may have noted from the nose on picture of the hull there is not a lot of cloth there. It was correct to the profile, so I did not want to build it up more, but it was thinner than I like (3/32"). In the end I re-enforced it after removing the foam.

There is a difference in the results of detailing the hull too. For example in both scenarios you can add features by taping and then priming. But in the mould technique the raised areas end up made of resin. But in lost foam you just have extra layers of primer. I have no idea on the relative hardness & durability of that primer.

Then, of course, then there is the "you get one hull".

[cstranc]

While the hull was still

While the hull was still filled with foam I decided to put in the flood and vent holes. Taking the model to a flat working surface I marked all the locations on the hull in pencil. Of course the side and top views in the plans did not agree on the vent hole locations. Thankfully I had a picture that clarified...



After marking where the vents would be I used my drill press and made multiple holes in each vent to remove most of the material. The picture below is "simulated" the holes do not come out that clean!



After the drill press it was time to use the dremmel tool to bring each vent closer to it's outline, and then finally finishing with a square file.

I liked to use the drill press first because sometimes the dremmel can skitter across the surface when you expect it to dig in. The drill press is a lot less effort and quite precise.

As usual I perfected the technique on the test hull. When I was happy with the technique I shifted to the real hull.



Here you can see the real hull with the vents done. You can also see the guide lines used to position the vents.

One interesting note is the vent holes on the tapering section of the hull. From the side view they look rectangular, but by the time you project that onto the curving hull they are not... As I duplicated the "rectangular from the side view" shape I had to wonder if on the real hull they don't just make them rectangular and ignore what happens when you project a rectangle on the curve of the hull. I did not have any picture to guide me in this area.

When you look at the drawings, and in real life you can see the vents are frequently paired together with very little hull between.



Clearly the resin would not support that thin strip of material between the vents... I suppose I could have done the two vents as one larger hole, and then inset a piece of brass to simulate the divider. As you can see from the hull photo before I decided not to. I went for increasing the width between the vents and adjusting the overall pattern to compensate.

I know all the purists are kringing and will never read another of my posts...

This must be a common situation. I would love to hear how people deal with it.

[cstranc]

It's time to split the

It's time to split the hull! The basic idea is to cut on the horizontal centerline until about 6" from the stern. I wanted to leave the last 6" as a single structure so it could support the control surfaces, etc.

It was relatively easy to mark the cut lines, but the cut. ohh what a pain that was. Lost foam is not ike a moulded hull where you can leave yourself 1/4" or more extra hull in the mould to trim off. In lost foam anything you cut is gone. If you take a saw that has a 1/16" blade width then when you mate the two halves after the cut they will be 1/16" short (unless you build it up again with a very careful resin pour). Ouch.

But I did not want to do that. So I looked for my finest saw. You know that balsa saw that cuts through balsa wood like it is a ultra low density soft wood. But you would not really think of using it on any material with a strength greater than butter.

That balsa saw, with it's 0.013mm blade, does cut through fiberglass very slowly...



I have tried to block this cut from my memory. When I say it was slow I mean it. I would saw and saw and saw and see a little progress. That was on the thin test hull. On the real hull with 3/32" hull thickness I kid you not it took me over 4 hours to complete the cut. I stretched it out into multiple sessions on multiple days. After the cut I had a numb spot on my index finger for over a month! Brrr.

But it was worth it. You had to be really carefull because you did not want the saw to jump out of the cut and scar the hull. The blade would heat up and then start binding more and cutting less.

But because it was such a slow process you had fabulous control over the cut. Over the full 60" length of cut I am sure that I was always within 1/2 a pencil mark width of perfect. If I had a finer pencil the cut would have been even more accurate. You did have to be careful because even the slightest course correction could create a little force that would tilt the blade off vertical. But you get used to that.

But in the end I got a cut like this:

I know it's out of focus, but even if it was in focus you could barely see it and it was true.

Of course the hulls do not fall appart because there is still 7" of foam holding them together. No problem... Just run the hull passed my hot wire cutter and ta-da. Wrong. First the wire was too thick for the 0.013mm cut! I had to go back to the local music store and get the finest wire they had. Then I had to adjust the voltage on my cutter because it would burn out the thinner wire. But eventually I was ready.




Notice how the test hull goes first... I am glad it did. As I pushed the hull onto the wire it went smoothly for the first couple of inches, then the full length of wire was busy cutting 7" of foam and it started to slow down... Then it stopped. The wire had bumped into a peice of glue (used to join the hull sections). That did not just melt away. And as I looked and thougtht about it I noticed the wire start to cut into the fiberglass of the hull!



There was now way the real hull was going through that! So in the end I took one of my trusty balsa saws and cut the back edge support off it. This way I could actually insert the full depth of the saw into the hull and cut the foam.

Besides cutting all the foam I could I also used this tool to ensure that the corner at the back end of the hull where the longtitudinal cut hits the vertical cut was truly complete. I would have hated to have the hull at that corner break or fray as I pulled the hull sections appart. It was difficult to do this part of the cut with the un-modified saw because the back edge of the blade could not go into the cut the blase was always cutting at an angle, and I did not want to overshoot the intersection point, so that left a little corner un-cut. With the modified saw I could get a nice square and complete cut from both the horizontal and vertical.



After doing the full length of the hull this way there was still an inch or more of foam in the center that was un-cut. So I put on heavy gloves and grabbed that fine piano wire and pulled with a gentle sawing motion....



There you have it. The hull parted into halves.

You can see the outline where the copper alignment tube was.

You can see the tail of the hull as a single unit so that all the control surfaces can be mounted to it.

You can see the bottlecap in the end of the hull. I used this when I was marking the hull. It gave me a nice flat surface to mark the center point of the hull.

Well then it was "lost foam" time



That is a lot of foam to remove. I started off using an xacto knife with a circular carving blade on it. The dinosours would have been re-born before I was done. So I switched to a large utility knife and I would make cuts down the full length of the hull. The first cut would be vertical, the second on an angle so that it intersected the first. Then I could remove a long triangular peice of foam. Much faster.

I would work to get a thin layer of foam next to the hull, then I could just grab the packing tape and pull the rest out. For the end peices (where it is still a cone shape) I took a large drill bit and twisted it into the foam (just using my hands, no power tools). When that removed enough I could grab the packing tape and pull out the rest.

And that left...


I almost forgot to mention the best bit. When you take the two halves of the real hull and put them together. It's perfect. You cannot see or sense the missing 0.013mm cut from the balsa saw.

It was worth having a numb finger for that month.

[jeffrey j]

.....

Nice work,
looks like you have it down with the one off hulls. I used that exact same saw on my type II hull. I went through several of them, but like you said it worked out nice. Next time if you try this again, try putting a few drops of 3-in-1 oil on the saw blade as your going, it make all the diff. Great job. Jeff Jones

[KevinMC]

Hi Chris,

Fantastic build! I remember

Hi Chris,

Fantastic build! I remember toiling for many hours on the pros and cons of building up a hull with this technique vs. the master/female mold method... As you say, it really just comes down to is "How many do you want to make when the master is done?"

I also remember going through the same issues you described with the easy case vents- are they square or are they rectangular? On my hull, I came to the conclusion that the upper vents were slightly rectangular but clearly it varies from class to class. Fortunately, since the vents are always seen at an oblique angle and no two photos ever seem to "show" them the same as long as you're close I don't think anyone will question what you've done.

Doing a lighter layup above the waterline is possible with the lost foam technique but there is a drawback- you'll have to blend the thicker areas into the thinner areas with great care. As you've already made note, in a female mold layup the "outer dimension" is defined by the mold so differences in final hull thickness only change the "inner dimension" which we really don't care about. With a male mold the extra material builds up the outer dimension so places where the hull thicknesses differs will have to be blended together.

As far as detailing the hull, the rattle can high solids primer on my master is definitely not as hard as the epoxy/glass underneath, but there are also much harder primers available than what I used. (I wanted something a little softer for all the scribing work I planned to do.)

Keep up the fine work!

[cstranc]

Jeff,
Thanks for the tip

Jeff,
Thanks for the tip with the 3in1 oil. It's suggestions like that that will keep me up getting this thread up to date with the model. I bet there are a lot of things I could learn by listening to you folks. I just need to get to the stage where I can post what I am doing, not what I was doing...

Kevin,
My plan is to hide the vents by submerging as soon as I leave the dock. It's a submarine after all!

[cstranc]

Ok, last time we got

Ok, last time we got the two halves of the hull seperated. Now it's time to get them to fit neatly back together again. For this we need some interlocking tabs.

The interlocking tabs are made of fiberglass & resin as you would expect. Note the slight curve to the tabs. The hull is cylindrical, so I could not use flat strip for the indexing tabs. Of course I happened to have a "test" hull of exactly the right diameter. So my test hull was cut appart and I used the peices for the indexing tabs.

Did I mention this is a Russian sub? I have heard they regularly borrow bits from one sub to keep another at sea. I can harmonize.

In the next shot you can see the indexing tabs installed in the hull. One on the top side, and the other on the bottom. The interleave keeps the hull nicely aligned. Using strips with the right curvature for the hull also minimized any stress and makes it easier to assemble.


It's good to note the spacing on the tabs. I left a 1/4" on either side. I did not think too much about it until later when I was installing tabs to hold the tail of the hull together...

Thank heaven for that 1/4" gap on the indexing tabs. It allowed me to place the top hull on the bottom, then slide the tail into place.

You can see in the picture above that the top hull has a tab that extends most of the way round. Then there are two little tabs mounted on the bottom hull to keep everything aligned.

This seems to work nicely.

I'm afraid that's all I have done to align the two hull halves. I really need to spend some more time here. I need to create and install a second strip of indexing tabs for the rear section of the hull. More importantly I need to get the nose properly mated top to bottom.

But there are so many other exciting things to do, these tabs can wait a little...

[cstranc]

Well next it was time

Well next it was time to get the tail of the hull ready. Up to now the fiberglass of the hull tapered down and was cut to a strait end. I needed to form a cone that would extend the appropriate length.

Sorry I did not take any pictures, but I took some paper, covered it in masking tape to form a barrier against the resin. Then I wrapped the paper around the tail of the hull to form the cone. Then it was all taped into place.

Here you can see the two hulls standing vertically while I pour the resin in and let it cure. I used a level to ensure the hulls were really vertical.



And the next day I removed all that tape and voila.



And the next day I read Kevin's post about Dave's way to fill the stern with resin while you have a simulated stuffing box in place and I cried. If only I read more and modelled less. Naaa. I just have to read more.

Wrapping paper around the hull did not give me a perfect cone. So I took one of those architectural stencils with 20 different circles on it. Working from smallest up I would place it on the tail of the hull, pencil mark any high spots, then sand away the pencil marks...

When I was happy the hull was round I measured the diameter I needed to mate to the prop and trimmed the hull appropriately.

Then it was time to make the hole for the shaft (it's stuffing box really). It's easy enough to find dead center of a circle, but drilling perfectly aligned to the axis can be tough. Still I had a plan...

I went to my supply of brass rods & tubes and picked out each size that I had from 1/16" up to the diameter of the stuffing box. Working on my test hull I took a 1/16" bit, drilled 1/2" an inch, rotated the hull 90deg, drilled, rotated, drilled until I was through. I thought the 90deg rotation would tend to cancel out any general alignment issue I had. Then I put in the 1/16" brass rod, and saw how close I was to true.

Then I repeated the process with the next size up of rod. Attempting to correct for the misalignment in the 1/16" drilling.

And so it went until I had the stuffing box slipped into place and it was perfect. No problem.

So then I started doing the same thing with the real hull... Eventually I got bored, or tired, and I stopped double checking everything all the time...

Aaaakk, it's not aligned. Sigh there is a lesson there if I'm smart enough to learn it. Probably 2 or 3 lessons...

I had to use the drill to route the hole out a little so I could align the shaft . Later I will have to install, align and then set the stuffing box in resin. Sigh.