HMS Repulse 1/96 RC scratch build

[Davidh]

Hi Steve,

Thanks for the heads up with regards to the rear towed sonar housing. I suspected as much. I have had to design this curving bulge around a new set of rear planes as my last ones are swept and inaccurate. Once the front sonar array was done I then turned my attention to gluing down a sail profile. This is simply a piece of pine shaped like the outline of the sail and slightly raised. For the kit it will obviously show the positioning of the sail. It also means that if the bottom edge of the sail is not even then light will not come up from underneath. Will sand this surface down nice and smooth.

There is not a lot of good above photo's showing the stern top hull between the rear of the missile deck and the top rudder. There are some pics near water line that show the subtle rise of the DSRV hatch but most of the pic's are from angles that make distances hard to judge and also you get textures that throw off shapes at lower angles. There seem to be a lot of tiles missing in some photo's, once again it depends on the boat.

I have turned up the rear escape hatch, the one that the DSRV attaches to in emergencies. Turned it up out of a small piece of brass. Drilled a hole in the deck and then glued and filled around it. Once again study of as many rear photo's gives me some idea as to the rest of the hull detail, hatches and all.

As mentioned I have made a start on the stern planes. Resolution didn't have swept planes, a misconception that has perpetuated over the decades. The Jecobin plans that many people have used adhere to this and that may be apart of the problem. The have a straight trailing edge.
I have cut out the profile of these planes using pine and then attacked them with the sander. These planes a quite tapered as the profile narrows towards the tip. The leading edge is straight. As I designed these planes, in the back of my mind I had to think about how these would be integrated into a kit and to make sure that the pivoting axis line ran straight through the hull and parallel with the other plane out the other side. Getting these angles right would be crucial for creating accurate parts of the future kit. A lot of fine sanding involved and trial and error fitting to the sides of the hull. Matching up and aligning small holes where the shafts will be arranged.

David H

[steveuk]

Hi Dave, good progress there. You are right there are not many good pics of the very stern. Your photo "Resolution rear end" sitting very high in the water (with green scum line) in the dock is a good one. If you know that the "scar" (section where the outer hull has been cut away exposing the pressure hull inside ) is roughly at the half way point between the rudder and missile deck, this helps to place where those deck fittings are. You can see most of them in your photo: - 3 pairs of ballast tank vents, stern escape hatch, two stern bullseye fairleads, and 3 stern cleats.

I haven't got as far as drawing out the stern yet, (still busy on my bow), but if you like I will try to make a rough drawing of the stern deck area showing deck fittings and the tile edge route?

In the meantime I have drawn on your latest model stern pic. This is how I imagine the towed array trunking should look running around the stern plane arrangement.

[Davidh]

Thanks Steve,

That would be great, any extra drawings will only help. The adjust pick of my towed array detail looks a little thick. Judging off the photo I sent you of the rear planes from underneath, I did' think that the port plane extended further out front on the leading edge that the strbd side.

Dave

[steveuk]

Yes, I agree a lot smaller than how I have drawn it (my clunky drawing using mouse). What I am trying to convey is the curve in the corner at the root of the plane guard. The cable needs a gentle curve to make it around the corner without snagging. There may even be a pulley wheel fitted inside there to help the cable take the corner easily - well that's how I would design it.

[steveuk]

Ok Dave, I sent you a little drawing I did of the stern deck details. I think your model will be finished very soon.

Not so much good news for my progress, however. Those MOD pics you got have thrown up some things about mine that mean I have to make more adjustments. Spent the last three days pouring over photos and re-drawing! Finally the stern arrangements on my drawing are in, but I need to take 10mm off the front end, then OA length will be in spec and the drawing accurately match profile photos. This explains why I couldn't settle on bow plain location until now.
It will all be worth it in the end!!

[Davidh]

Hello all

Have some more pictures of progress. The wooden frame around the top hull will be the reinforcing of the fibreglass hardback over the silicon mould. Have also put the hinges on the
missile deck doors. These were made from .2mm brass wire snipped and super glued in place.

I have also been working on the stern planes. I am looking at modifying the interface between the towed array housing that runs down to the plane. It needs to be wider as it curves along the leading edge of the stern plane. I will be moulding this into the port plane and so need to make sure that the design fits when it comes time to moulding. I have decided to go further with the detailing than most people go with deck detail. I have created a section of anechoic tiles that runs along underneath the demarcation line that runs underneath the foreplanes and runs to the bowplanes. I know ,some of you are rolling your eyes and mentioning that if you can't see the detail from 20 ft on the real thing, don't put it on the model.

I go a response from the MOD. Flat refusal, they mentioned that they have no more images. But no suggestions as to who to try, Maybe I will email BAE Systems as the company that took over from Vickers? May be worth a try?

dave h

[steveuk]

Hi Dave, Good work! On the question of adding detail I personally think the more the better. The only limitation is my modelling ability to make stuff that small. As a rule if I can see it in a picture I want to stick it on my model!

I have been busy editing my working drawings again, using the information off those excellent side on pics you sent me. Conveniently the sub has had white lines painted on it at specific locations, and one of these lines is along its center line. I therefore produced some tracings of the actual bow and stern profiles and the hull details, did some maths to re-scale, and then transferred the info over onto my drawings. Refit bow is now drawn up and also the stern plane and rudder positions are properly placed. Also marked is the propeller bearing position (end of the boat), and correct hull taper which flows nicely along the propeller cone shape. Hence I can now measure accurately bow to stern. I do have some good news here on my bow - I don't need to hack 10mm off it after all, it can stay where it is. I was measuring wrong the last time (duhh). OA length comes in correct. So that means I just have to re-make my replacement deck piece with everything moved along a tad. (phew!) Hope to get some progress over the weekend.

[steveuk]

Dave, have you moved the position of your tower back from where you originally had it? It looks a lot further back than I remember.

[Davidh]

Hello all,

I haven't moved the sail any further back. The sail is just slightly ahead of the start of the missile deck slot. I have built a raised deck profile that makes it easier for the builder to simply place the sail over the top and glue it down. It is also designed so that if the bottom edge of the sail is not exactly flush up against the hull then light from the other side will not come through.

I emailed Babcock whom I believe are responsible for overseeing the R class boats in Rosyth. I also emailed BAE systems. They haven't even bothered answering. How hard can it be?..

I have done a little more modification to the stern towed sonar array as it curves around the front of the port side stern plane. I have angled up the leading edge of this plane to meet the housing as it snakes up the side of the hull and then meets the missile deck rear section. I think its looking OK. I have also re-modelled the Vertical fin. My original fin was too thick and wide as well as too big. I have also reduced the height at which the fixed fin sits. I will be putting some light detail on the rudder surface. The rudder now sits on the raised profile that will act as a locator for kit builders. It also gives some clearance for the swing of the rudder.

As I am near the end of the work on the masters I have been looking at the set up for the mast moulds. As mentioned this build will be different to how I originally did the top hull moulds. I will be creating another silicon glove hardback mould. The Silicon is reinforced by a fibreglass shell and then will have further reinforcement with a pine box structure that will stop any warping. I have created a low wood wall around the hull as it sits inside the bottom fibreglass mould. This wall also features small little blocks inside. This is a registration feature to make sure that the silicon mould will align with the fibreglass shell. It will also act as a dam wall for the runny silicon that will well at the bottom before I use the silicon mixed with thixo to cling to the sides of the hull further up.

[steveuk]

Great progress Dave. I esp like your towed array to stern plane shape, flows really well.

I don't understand how those silicone glove hardback moulds work, so I am looking forward to seeing progress pics as you go through that process.

[Davidh]

Hello all,

OK Steve this is how I do it.

I clamped down the wooden wall around the outside of the master. Clamping the structure to the bottom hull mould flange and making sure that it is level and flush so that no silicon will seep under the wooden structure. It's not hugely critical as the silicon is quite thick and doesn't run far. This mould will most likely use up about a litre of silicon so it is a fair investment, it's not cheap so you do want to get it right. It's important to make sure that you have the right amount of catalyst to harden the silicon. I use a silicon called 'Silastic 3481 Base' by Dow Corning. It is a condensation hardener. Usually sets in about 10 hours depending on temp and humidity.

The great thing about silicon is that you don't really need to use a release agent so that to apply silicon to the master and the flange of the lower mould will not need PVA or wax. I mixed up a large batch of silicon and than started to pour about 40% onto the side of the mould around the channel made by the gap between the wooden wall and the side of the upper master. This will make a nice thick rim around the side of the mould. Then I added a small amount of 'Thixotropic-M' which is a thickener for the same silicon and allow the material to cling to walls and slope and not run down. Literally all I needed was a couple of drops to do the job. I then pasted it onto the sides and top of the mould.

This mould would need at minimum, two layers of silicon. It is important that the mould is at least 4=5mm thick. Once you put the first layer on you need to survey the thickness all over because if there is a big difference in thickness between different sections of the one mould you really need to rectify it before you go any further and add the hard back. If this happens then when you finally pull the silicon mould from the hardback the worst that could happen would be a tear and that really really sucks. If not then the lay is so thin that it weeps and will not sit in the hardback without sagging, SO MAKE SURE THAT ITS THICK ENOUGH! You lay up the fibreglass and once pulled form the mould sections of your work will mould the saggy wavy pattern where there should be smooth flat missile deck for example... Make the silicon rough. Paste it on and make it uneven so that the material that you back it with will key with it effectively.

Once you silicon layer is thick and consistent enough then I removed the wooden wall around the outside, being careful not to lift the silicon mould at the rim off the flange of the lower mould. Once done I add a PVA release agent to the rim of the bottom hull mould flange which is f'glass. Then I can start laying up the resin. First I lay up a gel coat that is nice and thick. I use an orange pigment. For years I have used orange as my 'tooling colour'. I have just recently bought an orange pigment for silicon so the turning to the dark side is complete! Once the initial gel coat is down you can then layer it up with an obscene amount of glass cloth.

David H

[steveuk]

wow that looks..scary, covering the whole model over in gloop! How come the silicone doesn't stick? I've only done fibreglass before and that sticks even after wax and release agents.

[Davidh]

Hi all,

Steve, the silicon will not stick to anything except itself. You don't need a release agent when laying up resin and cloth on a silicon mould. However in saying this I do use a release agent as it does extend the life of the silicon as over time the resins can slowly effect the surface of the silicon and damage it. A release agent also just makes it a bit smoother on release. I use a urethane spray release agent called 'Stoner E236'. This is the release agent that I also use when I'm creating urethane castings from a silicon mould.

The whole point of using a silicon mould such as this is that every little detail is captured and it peels off the part. A hard f'glass mould would damage the fragile detail, these silicon moulds are so wobbly they are virtually indestructible.

So after the last layer of silicon has cured I applied a thick coat of resin. As can be seen from the previous photo my tooling is almost always in orange. that's just what I do. Once I have done this and allowed the resin gel coat to set, I'll start laying up layers of glass. mainly chopped strand and weave. I put down a resin coat first in order to stick to the weave and glass above it. You have to use a fair bit of cloth/ strand. This shell needs to be rigid and sturdy. you do not want any flex or warp in this hardback as it will hold the silicon mould in the shape needed. I have found in the past particularly here in Australia that if a mould is not rigid enough and left out in the December heat it will warp, sometimes badly. I've had to chuck moulds away.

I put about 3-4 layers of cloth and then start building the wooden 'egg crate. This is a cheap way of using wide pieces of timber to reinforce the mould and save some money and resin. Two strips down the side and 3 bulkheads across the hardback. Make sure they are glassed down along the length of the mould. This wooden frame will resist the buckling and warping that may occur.

Once this has all been done and given a couple of days to dry then you can think about pulling the master plug from the silicon mould. Firstly I release the lower hull shell. On resolution it is a split mould. Two side pieces held together with wing nuts. Once that is pulled off you have the underside of the master sticking up and ready to be pulled from the silicon and hardback.

Now is the moment of truth. you want to take your time with this. It always makes me nervous as I need to gently pry them apart. I do not want to create or provoke tears. This is why it's important to make the silicon mould THICK. Once you have pried the master out of the silicon you will see if all that effort has translated into a straight aligned, detailed silicon negative image. So far so good, I don't have any tears..


David H

[steveuk]

Hi Dave,
Does the silicon part of the mould stay joined to the fiberglass outer shell - how does it 'stick' to the hard part? Then..if the silicone part does manage to peel away from the hard outer shell can it be put back in exactly where it needs to be?
This is the part about glove moulds I never quite understand.

[Davidh]

Hi Steve,

These are good questions so I'll try and go through them methodically and as clearly as possible. The silicon mould can easily come out of the fibreglass shell. The F'glass shell purely being there to give the reinforcement needed to keep the silicon in place. So you have a very rigid hard shell supporting a totally flexible and floppy inner mould piece. These two extremes mean that there is middle ground that you have to carefully control. When I first started doing this I was simply going off the instruction of Dave Merriman over at Subdrivers. I had been working with Silicon moulds for small parts like rear planes and the like and am totally sold on this. It IS the way to mould small pieces bar none. So I was confident in the detail translation from the master to the finished part, but with my understanding of the way this silicon behaves it did raise questions of potential problems I could see arising , mainly to do with the scale of the mould undertaken.

For small surfaces it is great however when you are creating a silicon mould where there is a long section of consistent diameter or a long flat section the biggest concern that I had was, would the silicon sag, bulge or undulate along the length of these surfaces? I was told by Dave and followed his advice to make sure that the silicon mould was thick. The thicker the better and evenly thick. If there is big inconsistencies in thickness with abrupt change this will certainly encourage weeping especially if a thicker section was 'above' a thinner section and the weight of the adjoining thicker section started weighing down.

I have undulations in both the Mike silicon mould and the Resolution, they are subtle, you have to look closely. This is a source of frustration. The mould for the mike suffers I think, less from this undulation along the length of the hull because It is a constant radius along the hull. The silicon material along the side of the hull is evenly distributed and the straightness of the hull is helped by this radius. However with Resolution I have found that because the sides of the missile deck are flat as they angle down towards the centreline of the hull there is no inherent curvature in the hull to help reinforce the silicon and so there is undulation and with gravity the possibility of gravitational creep towards the bottom of the hull. It is a bit like the fact that when you roll up a piece of paper into a roll the sides are inherently dead straight. whereease if you created four folds in a piece of paper and then tried to make a rectangular box out of it, it is very easily for the sides not to be straight or dead flat . I have found that as the sides along resolutions missile deck proceed then there is the possibility at the top edge of the mould may slightly pull away from the hardback. All I can say is make the silicon mould as thick as you can and make the surface as rough as you can so the hardshell shape has something to grip onto. I moulded little square blocks in the side of the silicon profile along the top to register the rim in the right place. On my next mould I will mould wedge shaped profiles that will effectively 'lock' the silicon around the rim of the fibreglass shell/ hardback and stop any lateral pull away and any suspected gravitational pull/sag. I am also thinking about cutting a V shaped ridge along the underside of the silicon mould that will then be filled with resin to make the hardback. This fibreglass ridge will then on the finished mould stick upward and run around the whole perimeter of the mould. The V channel in the thick rim of the top of the silicon mould will then be pressed into the fibreglass ridge and this would be another mechanism to hold the silicon mould from any potential sag.

Generally however the silicon mould does sit exactly where it needs to sit inside the hardback/ shell and once you have a good thick gelcoat down it will not move.

These undulations are the cause of a couple of extra hours after the part has popped from the mould hitting the part with generous loads of filler. Sometimes I think this is a sign of defeat. I would love for my parts to come out pristine. they don't however I love doing this so I soldier one. No two parts come out the same. But I will say they don't miss detail!

Dave