A shelter deck trawler - plans ref MAGM 2040
|Gareth Jones||28/11/2010 18:38:14|
796 forum posts
| For the past few months I have been debating what to build next. The choice came down to two possibilties, Shemara II (plans bought for me as a Christmas present by my wife last year) or the Spurn lightship (original builders drawings supplied by the Hull Maritime Museum).|
I like to work in 1:24 scale and both would be big models but they would fit in the back of my car (a Honda Jazz with magic seats!), although I will probably need a hand to lift either of them in and out.
I have only built one previous plank on frame model (a TID tug) and in the end the decision was made on the basis that the Shemarah plans have all the hull sections so it will be easier to make all the frames accurately and quickly. The plans are in 1:25 scale which will make the model approximately 1045 mm long but its very deep and wide so it will certainly be heavy when complete.
I have been inspired by Paul Godfrey's excellent built sequence of a Mountfleet Sir Launcelot, so hopefully this is the start of the Shemarah II story. My personal target is to have the model on the Goole MBC stand at the CADMA show in 2012. However my project manageress has just reminded me that I have a narrow boat model to finish, a porch to build, a GMBC newsletter to write and probably lots of other jobs as well so I may not meet the programme.
First thoughts are that the motor will be a Graupner Speed 900BB torque driving an 80 mm 4 bladed prop via an MFA 2.1:1 belt drive reduction gearbox. If anyone has any experience of this combination (or of building Shemara II from these plans) I would be interested to hear their views.
Over the last few days I have traced all the hull frame half sections on to greaseproof paper, reversed the paper and repeated the exercise so that I have a full frame outline for each section. I have 19 frames to cut out, the majority in 3mm ply but a couple will be in 6 mm. These two thicker ones will be either side of the main hull opening to provide hand holds to lift the hull in and out of the water.
The centre section under the main superstructure and centre trawl winch will be removable to provide access to the inside of the hull. Although its not a very long, its wide and deep so there should be plenty of room for the systems and the ballast. The hull section for most of its length is around 13 inches wide and deep so I cannot cut the frames from the normal model shop pieces of 4 ft x 1ft ply sheets and will have to order some 4 ft x 2 ft from SLEC. I made up a dummy 4 x 2 sheet from newspaper, laid it on the desk and then played around overlaying the traced frames to work out the best layout with the minimum waste.
I have now ordered 3 sheets of 3 mm ply for the majority of the frames, 2 sheets of 1.5 mm for the skinning and 1 sheet of 6 mm for the thick frames which should give me plenty of spare stock to cover any mistakes.
Not much is likely to happen for the next few weeks until Father Christmas will hopefully bring me a scroll saw and I will start cutting the frames - if he doesnt it could be a long job with my coping saw.
|Gareth Jones||05/02/2011 20:28:46|
796 forum posts
Although I try not to start a new model before I have finished building the one before, I have had a bit of a Shemarah moment today. Having spent the last few days building a toilet and washbasin for my 1:12 narrow boat I decided I would do something different and start cutting out the frames for Shemarah. The tracings were laid out on the 4' x 2' sheets of ply and interlocked to get the maximum number of frames from each sheet.
The sheet is then cut down to a size which is manageable on my scroll saw, in this case two frames, and the frame tracing stuck on with Scotch repositionable spray mount. I have found by trial and error that spraying the tracing rather than the ply means there is less glue left on the ply and its easier to sand afterwards as its not so sticky. Using repositionable adhesive makes it easy to peel off the tracing paper.
Here are the first three frames cut out but I manged seven in total today so there are only another 12 to go.
|Gareth Jones||12/02/2011 21:09:06|
796 forum posts
After sitting in the bath to consider the motor problem I have come up with a neat solution which looks as though it will work, but only just. I have a Graupner 900BB torque motor in my TID tug which is vastly overpowered. Consequently I plan to use that motor in Shemarah with an MFA 2.1:1 reduction belt drive to a 75 mm prop. I plan to buy a Graupner 720BB torque to refit in the TID driving its 55 mm prop directly. This has the added benefit of giving me another motor/prop combination to add to my data base (and also Colin Bishop's). After ringing around suppliers I found 720BB torques are also in short supply but I have managed to find one and its in the post.
All the frames are now cut out thanks to my daughter who decided she wanted to strip the wall paper in the dining room which gave me a bonus few hours in the workshop. The next job was to line them all up in packs of about 5 at a time and cut the slot for the keel.
I had marked out the building board which is made from a piece of 18 mm MDF and the first frame, which is the transom was attached. At this point I realise I made a mistake in cutting the board a bit too narrow. Tightening the screws which hold the wooden frame supports to the board is a bit awkward, I should have made the whole thing a couple of inches wider.
Too late now though I will have to carry on as is. Here are the next few frames together with the rough cut keel which is going to be a sandwich of two pieces of 3 mm ply since I have not got a big enough piece of 6 mm ply left.
Just to give an inpression of how big and beamy this thing is going to be, here are most of the rest of the frames slotted in to their approximate position.
The next job is to glue the keel sandwich together and then cut holes in two of the main frames for a handle, details of which will appear in a forthcoming episode. There is also quite a lot of titivating to do on the frames to tidy them up and sand them. I am not sure yet whether to have stringers in the tops of the frames at deck level. in which case I will have to cut slots for them, as I did for the keel.
|DONALD MOODIE||18/02/2011 23:30:01|
|2 forum posts|
My name is Donald Moodie and I am the skipper/owner of Shemarah II. I was pleasantly surprised when I came across your blog about building a model of my vessel. I am eager to follow the progress of your project and hear of any further 'Shemarah moments!'
Look forward to hearing from you
|Gareth Jones||19/02/2011 20:36:11|
796 forum posts
Its great to hear from you and I am delighted that you are planning to follow the progress of my Shemarah build. I have been considering building the model since I first saw the article in Model Boats magazine about 18 months ago. I have had a look around at quite a few model boat shows since then, to see if anyone else has built a model of Shemarah II but so far I have not seen one. I have seen some photos of a model on one of the trawler photo galleries but it looked as though it was a bit smaller than the one I am building.
The plans are very detailed so I don't really have any excuses for getting anything wrong. However when I reach the stage of doing the wheelhouse and deck fittings, some photos of the real vessel would be very usefull. If you have any, or would be able to take some in the future I would be very grateful. Jim Pottinger's photos in the original article will be a big help but they are pretty small and it is often difficult to understand the detail of the equipment. However I do not usually build my models very quickly so it will be at least six months before I get near that stage.
I hope you find the story interesting and the finished model does justice to the original. Having the real vessel's skipper following the progress of the build will give me an added incentive to get on with the job,
Edited By Gareth Jones on 19/02/2011 20:37:24
|John W E||20/02/2011 17:59:26|
264 forum posts
hi there Gareth
This looks a very nice build. I believe you are building from a James Pottinger plan?
Some of his plans are very easy to work from. I hope you are finding this build easy.
Looking at your build, may I please make 1-2 comments?
It may pay you to add several stringers down each side of the hull, preferably one either side of the keel. One in the area where the bilge keels are located and one at deck level. The reason for the 3 stringers: The first stringers which are located next to the keel will give a greater area for glue, for your plank and give a stronger joint. The second one, in the area of the bilge keels will give added strength and thickness to locate the bilge keels too. Bilge keels are vulnerable and tend to be knocked / snapped off quite easily but using brass pins through the bilge keels into the stringer adds strength. The third one at deck level, gives you an area for your deck to the glued too.
The other option I can think of, but requires far more stringers, roughly between 8-10 per side of the hull, would be to diagonally plank this hull - in 0.8 mm thick plywood, possibly covered with tissue matt and resin to give an extremely strong hull.
Of the several hulls which I have built (plus I am busy building one of James Pottingers plans now/The Sea Lady beam trawler) I have diagonally planks 2 of them and found this method to be stronger type of build. My model of the Sea Lady I have planked longitudinally.
Hope this helps.
The choice is yours
|Gareth Jones||21/02/2011 21:26:57|
796 forum posts
Thanks for the advice John, I am still pondering which will be the best way to plank the hull. There are some very large flat areas and my first thoughts are to cover those with 1.5 mm ply sheet. The rest I am not sure about yet but my original plan, based on a quick survey of the web, was to use 1.5 mm lime planking. Either way I will be adding a number of stringers as you suggest. I was also planning to cover the exterior with resin and glass cloth or tissue to waterproof and strengthen it. I will also coat the inside with resin. When you diagonally planked your hull with 0.8 mm ply did you use a single layer or two?
The plans are by James Pottinger, redrawn by Dave Metcalf. They are very comprehensive and easy to follow in showing the details of the original vessel and the lines of the hull. There is no model construction information so I guess it would not be a project for a complete novice.
I have reverted to my original profession today and done a bit of systems engineering. I have robbed the Graupner Speed 900 BB torque from my TID tug and mated it to the MFA belt drive reduction gearbox that I got for my birthday on Saturday (62 if you really need to know). This exercise was not without its problems, one expected, the other unexpected.
The first picture below shows the motor and gearbox fitted roughly in the proposed position in the hull to get the line of the propshaft and the second is a close up of the motor.
The gearbox instructions said mount the two bearing blocks loosely on the mounting plate and slide the output shaft through them. This proved impossible as the shaft was a hard drive fit in the inner race of the bearings. I measured the shaft and it was only about 0.001 inches bigger than a 6.0 mm drill (strange mixture of units I know but I have an imperial standard vernier calliper). The 6.0 mm drill fitted easily into the bearings so I put the output shaft in my pillar drill and polished it down with some fine wet and dry paper until it was a push fit the bearings. I then fastened the bearing blocks to the mounting plate. First unexpected problem solved.
The expected problem was that the Graupner motor has a 6.0 mm output shaft but the pulley supplied with the gearbox is drilled 0.25 inches to suit an MFA motor. My original plan was to fit a length of 0.25 inch OD brass tube in the pulley as a sleeve and then drill it out to 6 mm ID. After three goes at this in my pillar drill I gave up - it was too difficult to align the drill and pully and I ended up drilling into the side of the tube each time. Really its a job for a lathe but I have not got one so I may eventually try and sweet-talk one of my club comrades to do the job. However as a temporary solution, which might actually be the permanent one, I tried an alternative method (i.e. bodge). I experimented with wrappping the motor output shaft in thick aluminium foil (Tesco extra thick kitchen foil) and found that a piece approximately 13 cm long gave a nice snug fit in the pully.
To hold the foil in place as it is rolled on the shaft I first gave it a thin coat of spray mount. I then fitted the pully, tightened the grub screw and voila, a pefect fit. I then tried to fit the motor to the mounting plate and discovered the pully would not fit through the hole. Oh bugger, start again. Cut the foil, spray the foil, wrap it round the shaft, feed the shaft through the mounting plate hole and fit the motor mount screws, THEN fit the pulley. I then tested the entire assembly with the mounting plate clamped in a vice and it was fine, a bit noisier than a direct drive motor but not as noisy as a gearbox.
The next decision to make is where to mount the motor, obviously on the end of the prop shaft you say but the photo below shows the problem area. The line of the propshaft is very shallow and gets closer to the keel the further forward it runs so the shaft has to be kept short to get the maximum clearance from the keel. However while the belt drive lets the output shaft be lower than it would be with a direct drive, the large pulley becomes the critical area. The picture below shows that either I need to change the line of the propshaft or cut away the keel and frame to get the motor lower down. The cross marked on the frame is where the line of the prop shaft should run. At this stage either is relatively straight forward and I will probably go for the latter approach when my propshaft arrives to finalise the motor longitudinal position.
Edited By Gareth Jones on 21/02/2011 21:33:27
|John W E||22/02/2011 18:32:48|
264 forum posts
hi there Gareth
I have been searching through my model books to see if I could find the plan feature - it is somewhere - I will keep looking. What I did find though was the Magazine which contains the plans for the Boston Blenheim which is the diagonally planked vessel which I used 0.8mm thickness ply for planking the outside - this isnt a James Pottinger plan.
The other vessel I planked was the Frederique Spashett - using lime wood for the exterior.
You are considering using large sheets of ply to cover the side of the hull; where this is a good idea, the only downfall is ensuring that the resin doesnt crack off the exterior. So it is always well adviseable to 'rough up' the surface with some heavy grade sand paper. The only disadvantage of using plywood as a planking material is that when you come to cover it with epoxy/polyester the resins will not penetrate any further than the first veneer of plywood because of the bonding glue makeup to the plywood.
The next tip I could give, unless you already know - the next time you assemble the motor gear box -stick the gear box shaft into the freezer for an hour to actually shrink the shaft and gently warm the bearings in a tin of warm oil. (NOT BOILING OIL) for approx 10 mins. This will allow the bearings to slide onto the shaft.
Looking forward to seeing your build.
|DONALD MOODIE||22/02/2011 19:48:17|
|2 forum posts||Hi Gareth,|
Hope you are getting on well with the Shemarah model, it will be no problem to help in any way I can when you need photos of inside the wheelhouse or close up deck fittings as the build progresses, please do not hesitate to contact me to help in any way I can. My email is email@example.com
Best Regards Donald.
Sent from my iPad
Edited By DONALD MOODIE on 22/02/2011 19:50:06
|Gareth Jones||22/02/2011 21:14:33|
796 forum posts
Thanks very much for that John. I did try putting the shaft in the freezer but didnt warm the bearings up.
Also thanks very much for the offer of photos Donald, I will let you know which areas I would like in a few months time I hope.
Shemarah will have to take second place to our model narrowboat over the next few weeks as my wife has now finished all the soft furnishings and I am going to make a concerted effort to get it finished in time for a couple of exhibitions coming up soon. I will post some photos when it is complete.
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