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>> Home > Boat Building Blogs > 36" Thames River Police Launch
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mdlbt.com/47891
36" Thames River Police Launch Print Booklet
Author: robbob   Posts: 17   Photos: 137   Subscribers: 6   Views: 3185   Responses: 84   |   Most recent posts shown first   (Show oldest first)

Showing page 1 of 2   |   Jump to page: 1   2  

mdlbt.com/50439
Building the Cabin. Part 2 - Posted: 16th Feb 2019
Before the front window panels can be added to the cabin structure they need to be shaped to follow the curvature of the front deck as much as possible and then glued together with a reinforcing strip on the back of the joint.

Unfortunately I made an error 😡 when shaping and jointing the parts and had to make some new panels from some thin ply that I had to hand using the old panels as a template, hence the roughly cut window apertures in the ‘photos.

This was unfortunate but I feel better for the confession 🙏.

The new window panel was then glued and pinned to the front of the cabin assembly and left to dry while in the meantime I used my hot air gun to heat and bend the roof panel to the correct curvature.
The roof panel was then pinned and glued in place on the cabin framework and when dry was trimmed with a small plane and the front window panel trimmed down to the roof profile.

I added some additional framing and bracing pieces at the base of the front window panels and a ‘shelf’ which will form part of the dashboard inside the cabin.
I also added some extra framing and an end panel at the rear of the roof and a thin square bead was fitted around the base of the cabin sides and front to improve the appearance where the cabin meets the deck.

Before adding further detail to the cabin I used some Z-Poxy finishing resin on the roof panel to strengthen it and provide a better surface for the paint finish which comprised of one coat of white primer, two coats of gloss ‘Appliance White’ and two coats of gloss lacquer, all with a thorough rub down between.

When all the paint had dried and hardened I gave the exterior of the cabin a first coat of ‘Antique Pine’ stain.

Next I will add some detail to the deck.

Attached Photos - Click To View Large

Response by mturpin013 on the 17th Feb 2019
I'm assuming the antique pine stain was applied to the sides of the cabin not the roof ?
Response by robbob on the 17th Feb 2019
Ha Ha...very perceptive of you Mike 😜

mdlbt.com/50258
Building the Cabin. Part 1 - Posted: 9th Feb 2019
The superstructure of the launch is very simple, and from a practical point it was designed to give the crew a large field of view across the river and fast access in and out to deal with emergency situations. Consequently the construction is quite basic and would be quite straightforward if permanently fixed to the boat but this cabin needs to be removable to give access to the battery location and motor.

Because of this the cabin needs to be a strong and rigid structure of its own and yet fit invisibly to the rest of the model, it’s also only a three sided structure because of the open access at the rear and that alone will be a point of weakness to the structure.

I started by glueing the internal bracing strips to the insides of the deck sides as described in the instruction sheet and some strips that form the base for the sides that sit on the deck, these also needs to be sanded to an angle to sit flush on the deck and also create a vertical face that some further strips are fixed to which meet the inside walls of the deck well.

Although all the parts for the cabin are accurately laser cut I chose to do a dry ‘test fit’ using pins and elastic bands to hold the side panels and roof braces together.
This 'dry fit' was neccessary because I had previously decided to fit false obeche panels over the balsa sides and floor of the well to get a better surface to finish in the way I intend, balsa does not have any pleasing grain and does not look good even when stained, so I pinned all these panels in place to account for their addition to the internal dimensions of the well deck.

When I was happy that the geometry of the side panels and front window panels was correct I glued all the roof braces in place and added some reinforcing fillets to make it more rigid, temporary braces were glued across the front and rear of the assembly to keep the whole thing rigid and square during further assembly. The pins and rubber bands were used to pull in the side panels while the aliphatic glue set.

All of this was done with the cabin on the boat so that the correct ‘dry’ fit converted to a permanent fit.

Part 2 will continue with the addition of the front window panels and roof.

Attached Photos - Click To View Large

Response by rolfman2000 on the 9th Feb 2019
Now its starting to look like a Thames Police Launch. Keep up the good work Robbob. Cheers, Dave W 😊
Response by mturpin013 on the 9th Feb 2019
Hi rob I have just completed a similar job on a Freeman 22 cabin cruiser, a three sided structure with a couple of additional cross pieces made from bamboo at the deck level and finally glassing the whole structure it finished as a very rigid cabin, however I appreciate you have more window apertures in yours which leaves little area for increasing strength between roof and the sides. having said all that I'm sure you will have produced a superb cabin to match the rest of the boat.
all the best Michael

mdlbt.com/49990
Rubbing fenders, more epoxy & hatch coamings. - Posted: 27th Jan 2019
With all of the deck planking fitted I can now fix the rubbing fenders to the hull where the deck meets the hull sides.
These are made from 6.5mm x 5mm obeche strip steamed and bent to shape and fixed with 30 minute epoxy, unfortunately the strips are not quite long enough to do this in one piece even with the rear rubbing fender in place at the stern so a join has to be made which I hope won’t be too conspicuous. The fender tapers in height from bow to stern and the piece that runs across the stern was made from 5mm x 5mm obeche. All the fenders were ‘pilot drilled’ for the pins that held them in place while the glue set.

The complete hull was then given a further two coats of epoxy resin with a rub down between coats and a final ‘polish’ with 240 grit paper used wet. The resulting finish is perfectly smooth and ready for paint.
The front and rear hatches were fitted with the coamings that will hold the hatches in place.

The rotary disk sander that I bought from Lidl is certainly proving to be very useful in shaping small parts at this stage of the construction. I note that it’s back on sale now (Feb 2019) so if you have the opportunity and £30 ….go buy yourself one!

The next stage will be to assemble the cabin.

Attached Photos - Click To View Large

Response by mturpin013 on the 27th Jan 2019
You cant beat elbow grease, there aren't any shortcuts to achieving a perfect paint finish. I thought it may be useful to other builders to mention something we discussed at AP and that is the fact that it wasn't good practice to use any filler after glassing as this filling however thin or small will over time shrink at a different rate to that of the paint, making it visible as a "shrink line" albeit small. If you do find yourself in the position of requiring some minor filling you should try to use a material that is the same chemical make up as your paint eg if using cellulose then use cellulose putty for minor filling but do allow it to harden for a couple of weeks before final coat.
Also the disc sander from Lidl is brilliant for the price, I did make a small modification by taking out some of the end float by fitting an additional washer/spacer
Response by robbob on the 28th Jan 2019
Mike.
If I have to apply any filler to the hull then it's not ready for glassing, only once the surface is a perfect as I can make it would I apply the glass cloth and resin.

With the sander I had to hot glue the 'captive nut' inside that locks the tilting table as it's not 'captive' by any stretch of the imagination 😲.
And I also removed the angle setting marker and re-applied it after setting a true 90 degree angle as it was a couple of degrees out. So after a little 'fettling', nothing that any competent person couldn't do, it works really well and accurately 👍😁👍

mdlbt.com/49822
The deck planking. - Posted: 22nd Jan 2019
The kit I’m constructing is a pre-production prototype and consequently it does not have the ‘laser etched planking’ feature that has been subsequently introduced in the final production kits on the ‘upper’ deck and the ‘well’ deck.

This is of no concern to me because I think I prefer to do my own planking anyway but I do have to do a bit of preparatory ‘laying out’ of the deck pattern to ensure that it’s symmetrical and laid in a pleasing fashion.

I have chosen to use 1.6 mm x 9.5 mm obeche hardwood strip-wood (from SLEC) for this with a thin black plasticard caulking between the planks. This is what I did when I constructed the VMW Fire Tender and the result was very effective and visually pleasing.
Obeche has a pleasing grain, takes stain very easily and is also considerably cheaper than mahogany which I feel would be far too ‘dark red’ when finally lacquered.

Because I wanted an outer curved plank around the hull edge I had to cut this from 1.6mm obeche sheet to the correct shape and width as it would be impossible to bend a strip to this extreme curve. These also needed a section trimmed out to allow the bow gunwales to be positioned correctly.

Once both sides were cut and shaped I could then form the ply gunwales to the correct curve by my heating and bending process and glued them down to the deck. I understand that on the production kits these gunwales are now incorporated into the side skins which will make the construction a bit easier.

The remaining outer planks on the hull edges were made from straight lengths of obeche but required some easing cuts so that they could be bent to the curve of the hull. Hopefully these cuts will not be too noticeable in the finished deck.

When all the edge planks were glued in place I temporarily laid out the obeche planking strips with a thin strip of black plasticard as caulking and all held in place with masking tape. The centre plank was arranged to lie over the centre line from bow to stern. The setting out of the planks in this manner confirmed that the layout worked as intended and so I began fixing down the planking from the centre plank of the hull outwards with a fast bonding superglue and the process proved to be quite quick to complete. The side deck planks were equally straightforward but did require some to be carefully shaped in a tapered fashion at each end to fill the remaining gaps.

The rear deck was also planked by working out from the centre plank and thankfully the planking layout matched and followed the bow deck planking perfectly.

The surplus plasticard ‘caulking’ was then trimmed flush to the planks with a very sharp chisel and the entire deck rubbed down with my sanding plate until it was all perfectly smooth.

For those building this model that don’t feel confident enough to do ‘real planking’ will probably want to make use of the laser etched planking on the ply deck panels to achieve a similar result with very minimal effort, but I quite like the challenge of doing it the hard way and the benefit of a slightly better finish.

Attached Photos - Click To View Large

Response by robbob on the 23rd Jan 2019
At that scale it could work if you have a small enough tip on the pen.
I have one that is .1mm 🤓
Response by mturpin013 on the 23rd Jan 2019
Rob likewise it was good to meet up, and the boat/s lived up to expectations.
Response by Joburg-sailor on the 24th Jan 2019
Thanks Rob
I will try to seek out a 0.1mm pen!

mdlbt.com/49641
Motor, mount & prop-shaft. - Posted: 15th Jan 2019
The prop-shaft, coupling and motor mount that I ordered from ModelBoatBits has arrived so it seems a good a good time to make up a supporting wedge for the mount to fix to.

I do have a rigid brass motor alignment aid that I used when building the Crash Tender but do you think I can find it in the workshop?....nope! 😡

I expect it will turn up when I need it least! 🤞

Not wanting to waste time I used a length of heat shrink tubing over the motor coupling to make it as rigid as possible, a trick I had seen done elsewhere, and this enabled me to position the motor on its mount in the desired position and measure the angle that the mounting wedge needs to be made to.

I used an offcut of beech that I had in the workshop which I cut to size and then shaped it on the rotary sander that I bought in Lidl, fantastic piece of kit !!.

The wedge was then drilled to take the nylon motor mount and also the fixing screws that pass through the beech block, through the balsa base of the box and into the ply reinforcing plate that I put in during early construction of the hull.

After cleaning up the hole through the keel the prop-shaft was keyed with some abrasive, smeared with some epoxy and then pushed through to mate with the motor coupling. I used the excess epoxy resin around the shaft inside the hull and used some packing tape to stop it running out when I inverted the hull to seal the lower end.

A quick spin on the motor confirmed that the alignment was spot-on and the hull set aside while the epoxy set.

The next step will be to plank the deck.

Attached Photos - Click To View Large

Response by robbob on the 19th Jan 2019
That's a really good question that I really can't answer right now as I've yet to run the boat !.
The motor enclosure does have quite large ventilation panels on either side which are covered in a mesh and I'm hoping that the motor will be able to 'breathe' as a result.

The brushless in my Fire Boat doesn't even get warm after a long hard run and that's enclosed in the hull but has admittedly got a lot more free air around it in the motor
compartment.

This is not a racing boat remember, so I'll not be using the motor to it's full ability, scale speed is all I really want and expect.
I'll report back when it's had some sea trials 😁
Robbob.
Response by BOATSHED on the 20th Jan 2019
Thanks for your reply. I am more of a speed freak. I love the Vosper /MTB's style hulls as you can really push them to there limits, as I can also with the deep V huntsman style hulls. My Proboat Miss Geico catamaran I can run flat out even on turns. But am unsure about fitting an out runner, I have scaled down the Crash Tender to 28" and have just put in a small outrunner but very apprehensive of running her. This is because i'm unsure of overheating and catching fire. Silly rally as she is a fireboat. But as you have one in your Crash Tender with no problems, then I will finish her off and give her a run. Thanks for your help. I am watching this build as eagerly as I did your wonderful Crash Tender. I cannot wait to see the en result and some video of her on water. I'm sad I wasn't able to get along to the show this weekend.
Response by Sifi70 on the 20th Jan 2019
That’s great, thanks for the link. I will go on there now and have a read. My Father will be looking to add a decent motor to his Crash tender from Slec. We purchased it for him for Christmas.

Good luck with the rest of the build.

Simon

mdlbt.com/49558
Fitting the rubbing strakes. - Posted: 11th Jan 2019
Before I can apply the final coats of epoxy on the hull I need to fit the two rubbing strakes.
I started with the bottom rubbing strake which runs along the chine where the side skins and bottom skins meet. The strakes meet the external keel at the bow and also extend across the stern.
I used a length of square section of obeche which needed a gentle curve towards the bow, rather than steam the wood I soaked it in water for a few minutes to soften it and then used a heat gun while bending the strip gently to the required curve.

When the wood had cooled and dried the bend was set I did a test fit and drilled very fine holes through the strip so that the modelling pins I use to hold the piece in place would not split the wood.
A 30 minute epoxy was used to fit the strakes on both sides of the hull and stern.

Above this bottom strake is a second rubbing strake and this also meets the keel at the bow and runs across the stern, I used a broader and thinner obeche strip for this and it was prepared and fixed in the same way.

The final pieces to fit will be the gunwales which run around the hull where the sides meet the deck but I will not fit them until I have planked the deck.

Attached Photos - Click To View Large

Response by mturpin013 on the 13th Jan 2019
Rob, don't forget to bring the Crash Tender, star of the show me thinks!
Response by robbob on the 13th Jan 2019
Hi Boatshed.
Yes, I am installing full r/c and running gear and it's all cleverly hidden away in various places which is a bit tricky on an open deck boat.
Fortunately I do get to keep the model, and when it's finished, if it's up to scratch, VMW want to use 'photos of the model for their website and publicity.
Robbob.
Response by BOATSHED on the 14th Jan 2019
With the couple of pictures you posted the other day, they looked so great I think it would be an insult if they declined the use of what you have built. Surely after seeing your Crash Tender that you built then they would know the type of finish you would add to the build. I'm looking forward to seeing the end product. Keep up the good work.

mdlbt.com/49516
Glassfibre cloth & epoxy resin - Posted: 9th Jan 2019
I used glassfibre cloth and epoxy resin successfully when building my 46” RAF Crash Tender and I chose to do the same with the Police Boat.
See: https://model-boats.com/builds/view/23951 for the Crash Tender blog.
The application of the cloth and resin serves to strengthen the hull enormously and produces a completely watertight hull, and after additional coats of resin are applied and sanded between coats
resulting in a surface that is absolutely smooth and the perfect substrate for the subsequent paint process.

With the benefit of my previous experience and greater confidence working with these materials I used a ‘fast’ hardener with the resin which gives a working time of 30 minutes and a much shorter curing time where previously I had used a 90 minute ‘slow’ hardener.

The basic process is to cut the cloth roughly to shape with a good margin of overlap and then use masking tape along one edge so that after the resin has been brushed onto the hull the cloth can just be lifted over onto the resin. I then lightly brush the cloth into the resin and push the cloth into any tight angles, without any further resin on the brush, until the weave of the cloth is filled and there are no air pockets and the cloth is completely flat. At this point DO NO MORE as the resin will start to harden and any more fiddling with it will cause the cloth to lift and bubble, less is definitely more in this instance.
The resin should cure completely overnight and can be trimmed with a sharp blade.

I tend to cover a hull in five stages, as there are five ‘faces’ to the hull and thus it’s a five day process for me, this may be time consuming but I think the results are worth the effort.
I will brush on two further coats of resin when the rubbing strakes and gunwales have been added, this will completely fill the weave of the cloth to create a nice flat surface but it’s essential to rub down each coat after curing.

All the materials were bought from ‘Easy Composites’
https://www.easycomposites.co.uk

Attached Photos - Click To View Large

Response by mturpin013 on the 9th Jan 2019
To those intending to glass a hull, take Robs advise I did and it works fine, it's tempting to load more resin on at the brushing in stage but DON'T
Response by ChrisR on the 19th Jan 2019
I have also coated my 46" RAF Crash Tender with fiber glass matting and used West Systems two part epoxy. i coated the entire hull in one piece apart from the transom. I left it for two days to harden off. it worked very well. I am fitting the rubbing strakes over the top of the fiberglass using modelling pins and 5 minute epoxy.

mdlbt.com/49397
The bow blocks & outer keel - Posted: 6th Jan 2019
The bow of the boat has a compound curve and to create the shape a single block of hard balsa is supplied in the kit, although in my pre-production prototype this had to be formed by laminating some pieces of thick balsa together to the required size.

Rather than laminating up a single block separately I did the laminating and glueing in situ on the hull to ensure a solid tight block, and after the glue had cured I set about shaping it.
Initially I used a razor saw to roughly remove the surplus at the sides and bottom and then began the process of shaping it to the final form. My sanding plate proved invaluable for the final stages of making the block flush with the hull sides.
The underside of the blocks were very carefully shaped with a combination of the sanding plate and abrasive paper around a series large round formers.

I was careful not to just use abrasive paper over fingers as this can create grooves and unevenness in the soft balsa. I had already created a concave shape in the bulkhead former F1 and with the ply bottom skins in place it was relatively easy to extend the contour into the bow blocks being very careful to ensure symmetry on both sides.
A line was drawn on the blocks that extended the curve of the hull strakes to define the shape.
I also used the outer keel as a template throughout the shaping process to make sure that I was not removing too much material. It would be very easy to remove too much material so it pays to do this slowly and carefully, checking all the time for symmetry.

Finally when I was happy with the shape I formed a slight flat on the blocks for the outer keel to sit on, using a back light helped greatly with this, and the whole hull was given a light sanding with a detail sander.

The prototype kit was supplied with keel components made from thick balsa which would easily be damaged in use so I recreated this in thick ply laminations to the required thickness and shaped it so that it was completely flat and square on the inner edges and with a curved profile on its outer edges.
The keel was checked for fit on the hull throughout so that only a minimum amount of filler would be required to blend it to the hull.
It was fixed in place with epoxy adhesive and firmly pinned until it fully set and very little filler used to finish it.
The kit, which is available now from VMW, includes a single piece bow block and ply keel parts as standard, which makes construction much quicker and easier.

I’m glad that bit is over and I’m very pleased with the result.
Next stage will be glass fibre cloth and epoxy resin….

Attached Photos - Click To View Large

Response by mturpin013 on the 7th Jan 2019
Missed this one yesterday! what a credit to your workmanship a brilliant job. Your decision to replace the keel with ply I think was a good one, balsa although it would be glassed would still not be as strong.
Not seeing the boat in real life can I ask the question why they decided to use a block rather than curving the ply skins round as the crash tender is. Although skinning may be more difficult, the end profile is a given, but having to profile a balsa block I would suggest is more difficult. Any thoughts? not having done a balsa bow myself
Response by robbob on the 7th Jan 2019
Michael.
I think the reason for the balsa block method is that you can really only bend ply in one plane effectively, to produce the bow shape of this boat would entail the ply being contorted in two planes, one concave and one convex, to form the compound curve and even with thin 1.5mm ply you just can't do that easily.
The crash tender bow is just a convex bend. Thus the balsa block method becomes the only way to achieve the shape and to be honest it's not that difficult to do with care and patience.
Response by cenbeth on the 8th Jan 2019
I read somewhere that if you diagonally plank a hull that can give you concave hulls. I have never done this but would be interested to hear from people who have.

mdlbt.com/49353
Decks & hatches. - Posted: 4th Jan 2019
Because I need access to the wiring at both ends of the boat I formed the framework of an opening at the bow to make the dummy hatch into a real hatch.

In a similar way a hatch was formed in the rear deck which will give me access to the wiring, rudder servo and the ESC cooling.

It’s going to be quite tight to get all that into the cavity under the rear deck but I’ve done a test fit and it will all go in but will involve some ‘keyhole surgery’ through the rear hatch opening when I get to the stage of installing all of the running gear…🤓.

Both of these decks were glued and pinned in place and some packing tape used to pull the decks firmly onto the frames.
The side decks were also trimmed for best fit and secured in the same way and when all was dry and set a small hand plane was used to trim them flush to the hull sides.

The next stage will be to fit the balsawood blocks at the bow and shape them to the hull…..it’s the tricky bit I’ve not been looking forward to…😟

Attached Photos - Click To View Large

Response by mturpin013 on the 4th Jan 2019
Forward thinking, that's a must for this hobby as you can always guarantee that the designers don't always think of everything. (I suppose that's why VM have asked you to trial it)
Its looking good, I always like seeing the build details as hidden construction is not always appreciated when the boat is complete.
Response by robbob on the 5th Jan 2019
Forward planning is essential to me and that's probably why it takes me so long to build stuff, about 75% thinking about it and 25% doing it!

Ever heard of the 6 P's ?

Propper
Planning
Prevents
P***
Poor
Performance

Or..'Failing to plan is planning to fail'

I still make mastakes though...lots 😜

Edit: Just seen my typo above...oops.

mdlbt.com/49209
Plumbing the water-cooling for the ESC - Posted: 29th Dec 2018
The HobbyKing ESC I’m using has the facility for water cooling and as it will be in an enclosed location without any free ventilation it seems sensible to utilise this feature.

To keep the water circuit as short as possible I will put the pickup just behind the propeller and the exhaust on the stern but as the boat has a bulkhead just in front of the stern skin I need to make an access hole through it to allow me to secure the nut on the stern skin.

I made a hole through the bulkhead large enough to get a socket on the nut and reinforced the hole with a ply plate, similarly I reinforced the inside of the stern skin where the outlet passes through it.

When I was happy that the arrangement worked and I could attach the hoses and securing clips easily I glued and pinned the stern skin to the hull.

The water pickup is a standard one that is readily available but it’s supplied with overly large and ugly fixing nuts, the inside one is of no consequence but I thought that the outer one needed smartening up so I put it on a threaded rod and locked it in place with another nut and put that into the chuck of a drill and used a file to re-shape the nut to a pleasing taper….who needs a lathe......😜

I had to reduce the height of the inner keel former as the pickup tube is not long enough to get a good fixing with the internal nut, as the inner keel is balsa I fitted a ply reinforcing plate to spread the load.

The last ‘photo shows the location of the ESC, main battery fuse and receiver. The hoses will be secured to the ESC with spring clips throughout.

I found that the silicone tube I use tends to kink rather easily if the radius of a bend is too small and I found it necessary to form a tight spring coil around the piece that loops the water back through the ESC to prevent this happening.

Attached Photos - Click To View Large


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