Scratch-built 1/96 Oscar II

[gerwalk]

Over the course of my

Over the course of my conversations about this project, a new set of drawing popped up in my inbox last weekend. (Thanks again Pablo!)

[color=#000000]You're welcome! and thank you!]

[KevinMC]

In comparing my master to

In comparing my master to the new drawings I found that the centerline of the prop spines was on the order of 3/4" too low. Now 3/4" doesn't sound like much, but if you were to look at a side view of the hull with the prop-spines coming out as they do and compare that to how they should look the problem becomes pretty obvious. The way it is I have a banana! After quite a bit of thinking I decided the best way to correct this would be to cut most of the way though the hull from bottom to top and insert a wedge to "prop-up" the stern end. This will leave a discontinuity on the top surface that will have to be filled in, but that's okay as I have a fair bit of filling ahead of me right now anyways. Here are a couple of shots that show making the cut and inserting the wedge.

Here's the hull on it's back with the saw part way through. I actually had to do this twice to minimize the discontinuity on the bottom of the hull where I don't need to do much filling...



Cut complete. The end now has to be supported so I don't crack the stern right off.



Here's the balsa wedge used to prop up the spines to the right angle.



And here's the final fit check prior to being epoxied in place. Notice how slight the angle of the wedge is- with the total required angle split between two wedges it doesn't take much at all! (This one was about 1/16" on the thin side and 7/64" on the thick side.)



Next I'll have to do something similar to this on the bow. The tip of the bow bulge occurs higher on the new drawings than it did on the old. This time though I'll just grind away and the material on the bottom and add filler to the top...

[gerwalk]

Major surgery! Hey! Drinking and

Major surgery! Hey! Drinking and using that big saw at the same time is a bad idea!! (beer bottle in the first and second shots)

[PaulC]

Hi Kevin,

Great job on the

Hi Kevin,

Great job on the boat, and thread. What will the dimensions of this boat be when finished?

[KevinMC]

Pablo- I would argue that

Pablo- I would argue that the beer was a necessary first step before being able to start hacking in to my not-yet-even-finished Oscar!

Paul- Thank you. The finished whip will have a length of 63" and a beam is 7.4". I can't remember the height of the interior off hand but I can get that measurement tonight.

[KevinMC]

Hey guys!

Despite not adding anything

Hey guys!

Despite not adding anything in the past week I have been making progress. (Slow though it may be!)

Contrary to what I'd indicated in my last post I decided I'd tackle getting the girth of the hull right before cutting the bow down to shape. It occurred to me that if I were to start on the bow I'd have to reshape it first, and then re-blend it again after adjusting the cross-section of the hull. This way I tackle the hull first and fix the bow in one shot at the end...

Since there are some places on the hull where my master is 3/8" or more too small I've gone back to using drywall compound to build it up. Here's the bottom side of the hull where the difference between the original and new cross sections were greatest.




And the top side




I still have some final filling to do, but the general shape is now what it ought to be. In case anyone's wondering, the strips that are inlaid into the d/w compound are just balsa, used to indicate when I've sanded the compound back down to the right depth.



Edited By KevinMc on 1133184386

[KevinMC]

While waiting for d/w compound

While waiting for d/w compound to dry (which has eaten up a considerable amount of time in the last week) I also got going on re-making the fin. (I'll have to make the ventral fins anew as well.) Construction was by the same process as last time but with one twist- I made the leading edge of the fin by inlaying a piece of brass tube. From the few close-up photos I've found of the fin I've noticed that the leading edge has a very blunted (cylindical) shape to it. So instead of trying to carve this I used something that would automatically give me the correct shape. The next step, as before, will be to vac-bag the part.

[pirate]

Kevin,
Nice step by step documenting.

Kevin,
Nice step by step documenting. Looks like you're moving down the right path.

One question though; you started with one set of plans, and have switched to another halfway through; how do you know the second plans are more accurate than the first? Not to put a crimp in your process.

Pete

[KevinMC]

Hi Pete,

Well, there's a story

Hi Pete,

Well, there's a story to be told there... Before the thread began I spent several weeks collecting all the photographic and drawing references I could find. As posted, I ultimately settled on the PBP drawings as being the closest (but far from perfect) match to all the photos I had. After purchasing the PBP drawings I still spent quite a bit of time "tweaking" them to bring them closer to my understanding of reality, again based on all the photos that I had. I found the outline of the PBP drawing largely good, but many of the internal details were mis-sized or mis-located. (As an example, the prominent red and white hatch on the top of the hull most of the way down to the stern was oversized and located too far aft on the original drawings.) By using relative measurements from multiple photos I worked to correct the many minor details such as this, but again I accepted the outline as being basically correct.

When the "second" drawing showed up I had just fininshed priming my hull and was getting ready to put panel line tape on it. To ensure that my lines went down straight, I had drawn many "reference lines" on the hull. As I was looking at these I began to find small details that were not lining up. Most notable was the alignment of the missile doors- when I drew the lines to demark the outside edges of the doors at the right height (from the side-view drawing) they appeard to be too close to the centerline of the hull when viewed from the top (compared to the top-view drawing). The only way this can occur is if the hull's cross section has too rounded a shape.

Return now to the "new drawings". For kicks and giggles I brought them into AutoCAD and dropped down my corrected PBP drawings overtop. I found they matched my corrected drawings very well, again which I'd corrected based on photographs. Next I had a peek at the included cross sections, and coincidentally found that there was a much more prominent "corner" where the missile doors ended. That would certainly correct the inconsistancy I was seeing on my hull, and agreed very well with some photos I'd gathered of the Kursk with the front end cut off. Finally, my attention was caught by an oddity in the drawing just under the missile doors where I noticed that there was a little concave area just under the lip. When I went back to my photos (where the light is right) sure enough I found a hint of a shadow just under the lip of the missile doors that could only be explained by a little recess. This was the clicher- I don't know who did these drawings or where they originated, but someone put a great deal of care into inking them and from all the comparisons I've done I'm convinced there's as authentic as I'm ever going to get my hands on. (The only thing I've found about them that disagrees with photos I have is the location and shape of the horizontal stern planes.) With that realization, I finished converting the new drawings to CAD format and began the work to correct what I had built.

Was it wise to switch reference material mid-way through my build? Absolutely not. I've easily lost a month on my completion date, and (silly as this will sound) I feel like this thread has taken a turn in the direction of "how not to" instead of "how to". But the flip side to that argument is that by the time I get it done all the open water will be stiff anyways (have I mentionned I'm in Canada) and I know from all the model aircraft I've built if I ignored this I'll never be happy with it. Even if no one else noticed, I'd know it's wrong and I don't want to put this much effort into a project to have that hanging over me...

From this point forward there will be no more cheese, I promise! Back to the build...

[PaulC]

Kevin,

Thanks for the explanation. I

Kevin,

Thanks for the explanation. I was wondering the same thing. Your reasoning makes perfect sense to me. And I understand completely the fear of the inaccuracy hanging over your head for the life of the boat. You made the right decision IMO.

[steveuk]

Was it wise to switch

Was it wise to switch reference material mid-way through my build? Absolutely not. I've easily lost a month on my completion date, and (silly as this will sound) I feel like this thread has taken a turn in the direction of "how not to" instead of "how to". But the flip side to that argument is that by the time I get it done all the open water will be stiff anyways (have I mentionned I'm in Canada) and I know from all the model aircraft I've built if I ignored this I'll never be happy with it. Even if no one else noticed, I'd know it's wrong and I don't want to put this much effort into a project to have that hanging over me...

I like the honesty of this thread. It not only shows everything coming together well but it also shows the problems you encounter and how you overcome them. This is more like reality for most of us. ..I am reminded of a quote from another model builder, who said "Rule one is - NEVER trust another persons plan drawing!" I have found this to be true myself, even with kits. eg Having bent a section of hand rails over a plan I then discovered it was way too short - the model plans were way out to the fibreglass hull. This caused quite a bit of cussing as I had to bend the Aluminium rod back and rebend it correctly by best guesswork. I have no idea why they provided plans that do not match the exact dimensions of the hull. As they are they next to useless!

I also usually end up with my own set of working drawings based on lots of sources of info which all agree.

[KevinMC]

Thanks for the support guys,

Thanks for the support guys, it's much appreciated! When all is said and done, I'd sooner take a bit longer to have a hull that is as right as I can get it rather than to have a hull tomorrow that's just "pretty close".

Here's a set of templates I made that match the new hull contours. The templates are printed off and glued to bristol board for stiffness. What I've been doing (and should have been photographing as I was going) is to slide these over my hull to the correct "station" and I get an immediate idea of how much material I have to add or remove to bring the hull into shape.




And here's a template in use... Notice the large gaps on the "bottom" side of the photo (top side of the hull) and to a lesser extent the gaps on the top that need to be filled. These will get built up with drywall compound in two or three passes.

[KevinMC]

Last night's main task was

Last night's main task was to get the curvature of the bow "into spec" with the drawing. What's not show here is that the hull must be perfectly aligned with the drawings and propped up to sit exactly on it's side. Once done, I use a small square to check to see where the hull really is with respect to my drawing. (As shown photos 1 and 2) and I've gone so far as to mark down on the drawing how much I need to build up. (Photo 3.)










To build up the difference, I cut some 1/4" strips of 1/16" balsa (cross grain) and glued them down to the upper cuvature of the bow. Once sanded to shape, this balsa spine will serve as an indicator when I sand down the DW compound that will be used to build up the rest of the bow.




Here's the result, ready for "coarse filling". Notice I've also got the new bow cap in place, sanded to the correct contour using the same process.

[KevinMC]

Last set for today- Since

Last set for today- Since it takes a while for the DW compound to dry (for the thickness I'm laying it down in places) it's worth my while to always finish up a night with some mud. This looks really rough, but remember that I have to build it up over 2 or 3 coats.







Finally, Mylo had asked a while back if I would photograph the hull with a ruler to put it into perspective. The upper end of this ruler is 50" up from the floor.

[anonymous]

@KevinMc

very good work http://www.subcommittee.com/forum/icon_smile.gif

Gantu

@KevinMc

very good work

Gantu