R/C Naval Combat

It's possible for a BB to bounce off rigid armor and come back out through the balsa, but it'll lose energy in the initial impact. I've used rigid armor in narrow bows before (Courageous and Hood) but saw no exit holes from BBs bouncing off it. Holes from rebounds may be relatively rare except in close range firing where the BB hasn't lost much velocity.The aluminum sheet in Ibuki's bow will be mounted in silicone so it will have some give side to side when hit.

It's 0830 and I'm about to fill the balsa molds for the secondary bulge 1/8" stringers with gelcoat. (They're too narrow for a mix of chopped glass and resin, which would be stronger.) Around 1300 I'll remove the balsa from the new stringers, which will form a shelf sticking out 1/8" from the hull sides. The 1/4" ribs are already drawn on the hull. I'll glue 1/4" strips of balsa over them from the new stringers to the lower hull and fill the gaps between the balsa and underlying original ribs with resin and chopped matt. If that's finished today the hull can be sheeted this week. More photos will be posted tomorrow.

Bob

The stringers for the secondary bulges turned out fine and the balsa used to mold them has been removed from the sides of the hull. The stringers extend 1/8" out from the hull side and taper into it at each end. Total stringer thickness including the hull is about 1/4".

The hull windows were cut out yesterday and strips of 1/4" by 1/16" balsa were glued over the ribs from the new stringers to the lower hull. The gaps between the balsa strips and the ribs are up to 3/16" wide. One side of each gap has been blocked so the hull can be stood on end and each pocket so formed can be filled with gelcoat. That'll be done tonight so by tomorrow evening Ibuki will have it's secondary bulges. The brass armour mounting bolts will be installed Wednesday and the hull will be ready to sheet.

Bob 

The secondary bulges turned out fine, with their long curving stringers forming a narrow shelf at the top and their bottom edge blending into the lower hull. Eight ribs per side were thickened to match the bulge contours. While admiring the results this morning I realized I'd made an incredibly stupid mistake.

By concentrating so much on the secondary bulge stringers I forgot to tape the main bulge stringers and cut them off with the hull windows. Dohh!!!

The main bulges were visible on the hull sides for only 3 windows ahead and 2 aft of the secondary bulges, but the Mogami hull's main bulges were made too short. According to the plan from 'Japanese Cruisers of WWII' they should be visible for 5 windows ahead and 3-4 aft .

My original plan was to tape the entire length of the main bulges as shown on the plans and cut the windows out, leaving the main bulge stringers. I was also going to leave the main bulge stringers in the two windows where the secondary bulge stringers are entirely within the 3/8" deck stringer.

Thanks to my stupidity I have to rebuild the main bulge stringers in 10 of the 22 windows on each side of the hull. That'll take 2-3 days so the Ibuki won't be sheeted in time for this weekend's model show. Unfortunately the replacement stringers will not have as strong a connection to the ribs.

I think I'll cut shallow wedges into the sides of each rib so the new stringers can't be forced inward by BB hits. If I just resined the stringers between flat rib edges they'd easily be sheared off by BBs. Fortunately I'd reinforced the hull with more fiberglass after buying it so the ribs are 3/16" thick. For a really quick repair the stringers can be made of 1/8" by 3/16" basswood, reinforced on the inside by a strip of fiberglass that'll cross the stringers and ribs. Alternatively, I can make balsa molds for the stringers and mold them directly to the hull, which will take a day or two longer but give a stronger result. I'll start replacing the stringers tonight and hopefully finish by the weekend.

Bob

The missing main bulge stringers on Ibuki's port side were replaced last night. Using a square file I cut 1/4" wide notches in the sides of each rib at the stringer location. The notches were wedge shaped, 1/16" deep on the outside faces of the ribs and tapering to nothing by the inside faces. (The ribs were 1/4" wide x 3/16" thick.) 

Next, strips of 3/16" x 1/16" balsa were CA glued to the outside of the hull over the stringer positions. Resin and 6 strips of fiberglass were applied on the inside of the balsa between the ribs, making the stringers the same thickness as the ribs. The fiberglass matt was cut in 1/4" wide strips and each was worked into the notches in the ribs. A final strip of fiberglass matt ran along the stringers and intervening ribs on the inside of the hull. The process took an hour, plus 30 minutes this morning to cut and sand off the balsa and trim the stringers to 1/8" width. They seem strong and can't be driven into the hull because of the wedge-shaped notches.

Tonight the process will be repeated on the starboard side. Checking the 'JCoWWII' side plans against the cross-sections showed discrepancies in main bulge length so I went with the cross-section plan, which was a better match to the model hull's shape and had the stringers crossing one less window at the bow and 2 less at the stern. A total of six windows per side will have main bulge stringers restored.

The Ibuki hull will be ready to sheet this weekend.

Bob 

The replacement main bulge stringers turned out fine and are solidly glassed to the ribs. The secondary bulges are finished too. Tonight I'll install 18  x #4  1" brass bolts to hold the internal armour. Usually I put them through ribs (which are at least 3/16" thick at the bolt locations to retain strength). Because this is a carrier the bolts can go through the 3/8" deck stringer. On a regular ship model the deck stringer can't be used because there isn't enough space for the bolts and their nuts with the deck installed.

Hull sheeting will start this week. I plan to have the hull sheeted and painted by the Martime Museum Model Show in 2 weeks. The upperworks will still be under construction but should be finished by the end of April.

Bob

The original plan was for dual stern mounts mounted beside each other. I realized last week that the aft pair of pillars supporting the flight deck are too close together at deck level for more than one cannon to shoot between them.

The options are to put the 1.5 unit gun in the stern and the 1.0 unit gun in the bow or put both in the stern, angled out to either side to clear the two sets of flight deck support pillars. To clear the pillars they'll have to be at least 10 degrees out from the centerline.

The third option would be to curve the upfeed tubes of both cannons inward allowing one barrel to fire over the other, both shooting straight aft.

Bob

Here's the Ibuki hull after completion ot the secondary bulge stringers and restoration of the main bulge stringers I'd mistakenly cut off. Four sections of the latter can be seen here, along with the aluminum bow armour.

Note the two brass bolts screwed into the deck stringer and the third one to the left with its head cut off. These are the mounting bolts for the internal armour and will also carry clips to secure the wiring harness and CO2 lines.

These are #4 bolts screwed into 7/64" holes with CA glue on the last section of thread to go into the hull. After the glue has set I use the tool shown to cut off the bolt heads; any remnants of the bolt shafts are filed flush with the hull.

Here's the aft end with the curving secondary bulge stringer and two windows with the aft end of the main bulge stringer. The shiny circles in the deck stringer are the filed ends of several armour mounting bolts.

This shows the entire starboard secondary bulge stringer, curving up almost to deck level. Its vertical ends extend halfway onto 1/4" ribs and are about 1/16" higher than the rib surface, so the ends of the secondary bulges will be visible when the hull is sheeted. Those bulges were a prominent feature on the real Ibuki.

Bow view showing aluminum amour plate set in self-leveling concrete sealer, which takes a few days to completely solidify. Note the furthest forward of the 9 armour mounting bolts on each side of the hull.  

Inside the front end of the hangar: the forward 2 pairs of armour mounting bolts are shown, along with the rear end of the aluminum armour in the bow and the curing concrete sealer that'll be trimmed to the end of the aluminum sheet.. 

The Ibuki's hull is ready for sheeting. Hopefully that'll be done by Sunday.

Bob

April 20, 2009 Ibuki Photos:

View inside the bow showing the first two 1/16" balsa 'dams' used to hold self-leveling concrete crack filler until it sets. These will step down in height from bow and stern toward amidships, directing water to a channel that will be made along the keel leading to the bilge pump. The 'dams' have been trimmed down, having been higher with arms going out each window and ca glued against the ribs.

View of the first level of concrete filler in the stern. This stuff cures to a solid rubber compound over about a week, though the upper surface is dry within a day. It isn't very dense - about the same as latex.

Note that I used 2mm styrene as centerline armour aft instead of 1/16" aluminum. The reason was that I was in a hurry and the styrene was easier to shape to match the hull bottom than aluminum. I may add another 1mm of styrene on either side, giving a total thickness over 1/8". The cut-out section along the top is to allow the rudder ams and their linkages to clear the armour.

The rudder stuffing tubes will be protected by two layers of heavy vinyl tubing of different sizes (one inside the other). I found that worked well in other models.

Sheeting the port side. It was fiddly work cutting the small pieces of balsa that fit above the secondary bulge stringer. The bulges will be sheeted after the main hull sides.

Closer view of the bow during sheeting. I always sheet right up to the ends of the hull over the solid bow and stern areas, then sand the balsa, feathering it into the hull, before silk-spanning over it. It looks better than stopping the balsa short of bow and stern. I'll add more balsa below that used to sheet the windows, taking it down onto the bottom of the hull so the lower edge isn't as easy to see.

Bob

Except for the last 10" aft , the hull will be sheeted by the weekend. The bow turned out very nicely, with the balsa smoothly feathered into the extreme end.

The stern can't be sheeted until I decide whether or not to shorten the hangar and lengthen the quarterdeck. The hangar length matches the end bulkhead locations shown on the Ibuki cross-section plan and the bow and stern frame drawings  in 'Japanese Cruisers of WWII', but those drawings seem wrong based on the one side view photo of the stern found. I think the hangar's at least 3/4" too long but to shorten it and reglass the rear of the hangar would delay construction several days and I'm already a few weeks behind schedule. That's something I could do next winter.

The quarterdeck will be complicated to make with wing-like overhangs to port and starboard, 4 support pillars for the flight deck and the need for an access hatch to the rudders. The forward pair of pillars sits exactly over the rudder stuffing tubes so the entire aft section of the flight deck has to be removable to get at the rudders.

Bob

Hi Bryan,

The link didn't work but I know what you're talking about. John Coffill built an IRCWCC Mogami with the aft flight deck and 2 BB cannons underneath it. It was sold a few years ago to someone who never used it and rejoined the NATCF/NABS fleet at the Shearwater Museum show in April. I think it's under refit to Treaty stats. It'll be nice to see it and the Ibuki running together.

Bob

here let me try it this way

It would allow you to build a carrier and still put teeth in its front end,

3 guns forward and a half unit pump sounds like fun....