Barrel Back….

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Barrel Back….

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17 January 2009 at 07:41 #6532
Paul T
Participant
@pault84577
Classic 1940s mahogany speedboat
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17 January 2009 at 07:41 #17964
Paul T
Participant
@pault84577
My current main project is this 1.5m long barrel back, I have wanted to build this model for some time and a recent flurry of postings about the design competition made up my mind to design and build the model.

The design was done on CAD so I can easily change scale or print out the parts that I need to make.

This photo shows the engine placed in its position, I have had to cant the unit at 21deg to get it into the hull below the hatch cover, I am still debating air or water cooling as the liquid option will mean some major engine mods.

The model design allows for either electric or IC power and after much thought I have opted for this 35cc IC unit, I realise that most lakes have banned the use of IC engines so I will have to sail on the local canal or just use the small 600 size electric “get me home” motor ( 2 strokes have a habit of stalling in mid lake) to sail on Runcorn boating lake.

The frame is built from 12mm ply and will eventually be covered with 3 layers of skin: ply, kevlar and mahogany plank.

Paul
17 January 2009 at 10:42 #17965
Bob Abell 2
Participant
@bobabell2
Hello Paul

You could fit a fan on the prop shaft coupling and blow the air backwards?

Make the motor mounting extra strong…………..As these engines are a swine to start at times!……………..My strimmer is a devil to start and hard graft!

It`s looking the biz!

Bob
17 January 2009 at 13:06 #17967
Paul T
Participant
@pault84577
Hi Bob

The engine has a built in fan so to make it work all I have to do is put the cowl back on but I would be using an electric fan to feed air into the engine bay my problem is getting the hot air out of the hull with out spoiling the look of the boat, I have an idea that I am playing with at the moment using a long thin exhaust at the rear of the cockpit.

Paul
20 January 2009 at 15:45 #18046
Paul T
Participant
@pault84577
Some more progress photos

Engine cover 1st fitting cockpit basic fitting with access holes into forward radio / battery compartment. Fuel tank fitted

As I have opted for the engine to be air cooled I have put the cowl back on and now I have to cut some air vents into the rear of the cockpit…………..got to sand all the filler down before skining the hull.

Paul
20 January 2009 at 17:42 #18047
Bob Abell 2
Participant
@bobabell2
Hello Paul

Are your frames really 12mm thick?……..they look about 6mm to me?

Just askin`………Bob
20 January 2009 at 18:20 #18048
Paul T
Participant
@pault84577
Hi Bob

Yes the frames are 12mm it might seem over the top but I needed a strong frame to take the engine.

Paul
20 January 2009 at 18:41 #18050
ashley needham
Participant
@ashleyneedham69188
WOW. Is all I can say. How about using the exhaust system to pull air through the boat??? Ashley

Or fins on the propshaft to pull air thro, or pump it out/ whatever.?
20 January 2009 at 21:11 #18054
Paul T
Participant
@pault84577
Hi Ashley

The engine has a built in fan that will be backed up with a pair of electric fans to shove the hot air out of the boat just behind the rear seats (where a vent can be hidden)

The exhaust will be split into two pipes and water cooled before leaving the transom.

Paul
22 January 2009 at 08:42 #18073
Paul T
Participant
@pault84577
These are the re posted progress photos…..sorry I made a bit of a hash of posting the last lot.
22 January 2009 at 19:04 #18087
ashley needham
Participant
@ashleyneedham69188
EXTRA WOW! what about the driver?? is it action man scale or wot?? Ashley

nb, are you going to use “sustainable” Mahogany?? or perhaps this is not an issue when the boat is belting out greenhouse gasses at an alarming rate….
22 January 2009 at 20:19 #18088
Paul T
Participant
@pault84577
Hi Ashley

Its the wrong scale for action man but I am going to make the steering wheel turn in sync with the rudder just in case I find a suitable figure for a driver.

The mahogany comes from a sustainable source……..the timber yard has tons of the stuff and if I run it on moonshine does that qualify as bio fuel (it is organic after all)

Paul (If I could fit a V8 I would)
22 January 2009 at 20:57 #18090
ashley needham
Participant
@ashleyneedham69188
Paul. What size figure would you need then ?? to my mind, an open top boat like that with no driver would not be complete.

I am thinking you are not quite grasping the correct concept of sustainable…… Ashley
23 January 2009 at 07:17 #18097
Paul T
Participant
@pault84577
Good Morning Ashley

Of course I know what sustainable means…………………it means finding the cheapest price for something which in the case of materials means finding a supplier who has a large stock that he wants to get rid of.

The materials are then delivered for free on a 40ft wagon to my workshop….the workshop is powered by a 3 phase transformer (that hums along with the radio) the heat from which keeps my timber warm so I don’t turn it off.

The eco people called on me to point out the size of my carbon footprint so I put up a windmill but at night I turn off the motor that makes the blades go round.

I drive a 3 ton truck that eats diesel……..but that has become cheaper so no problem there……and I drive everywhere…even to the corner shop and to help the enviroment I have stuck a sunflower on my filler cap so the eco people think I use bio fuel.

I recently worked out how many building materials I have used in my professional life:

25.000.000 bricks (give or take)

34.000.000 blocks (roughly)

100.000 tons of concrete

80.000 tons of steel

So in my 50 years on this planet I wonder what my contribution to warmer summers has been?

Paul
23 January 2009 at 12:17 #18109
ashley needham
Participant
@ashleyneedham69188
!!!!!!! I see you HAVE grasped the concept correctly!! Ashley
28 January 2009 at 06:43 #18179
Paul T
Participant
@pault84577
Update

I am putting the inner ply skin onto the hull at the moment and having great fun with clamps, rachet straps and nail gun pulling the ply into shape around the barrel transom, even though its only 3mm ply its still very difficult to form short and tight curves.

I have had to change glue from PVA to epoxy as my first fitting of the ply around the transom failed because the PVA was just not strong enough and the ply sprang off (even pulling the nails with it)

I will post some photos later after I have removed the latest set of clamps and straps.

Paul
29 January 2009 at 20:00 #18204
ashley needham
Participant
@ashleyneedham69188
Perhaps you should clinch the nails over at the rear in good old fashioned boat builders fashion ?? Ashley
29 January 2009 at 20:25 #18208
Paul T
Participant
@pault84577
Hi Ashley

Had to use woodscrews to pull the ply into shape but its getting there slowly.

Hope to take some photos soon

Paul
31 January 2009 at 18:23 #18234
Paul T
Participant
@pault84577
Here are some photos of the 1st skin layer of 3mm ply

I wanted to post the photos “warts and all” so that you could see the problem areas.

On this view you can see where the ply split as I pulled it around the transom..still a little filler goes a long way.

This shot shows the hatches.

Close up of thr rear hatch

Side view.

The next stage is to complete the filling and rubbing down before the fitting the kevlar to the hull.

Paul
31 January 2009 at 18:49 #18235
Bob Abell 2
Participant
@bobabell2
It`s coming on quite nicely now…………….Paul

Where does he rudder go?

Bob
31 January 2009 at 19:04 #18236
Paul T
Participant
@pault84577
Hi Bob

Access for the rudder is via the rear hatch.

Paul
1 February 2009 at 07:31 #18240
Paul T
Participant
@pault84577
Dear All

To explain the filler and big crack in the stb side..

One inherent problem of building at this large scale is the choice of materials, when building a smaller model the selection of balsa or ultra thin ply make the creation of compound curves fairly straight forward but with the larger model these materials become to fragile.

So the obvious move is to select a more robust material that is more in keeping with the size of the model and that has the ability to survive the occasional high speed bash into the bank.

Easy enough you might think, a quick walk around any timber yard will provide any amount of bendy 8x 4 sheets of marine ply which whilst perfect for building a full size boat has certain drawbacks.

The bendy & flexible properties of ply diminish in direct proportion to the size of panel that you are cutting and so you eventually encounter the problem of rigidity as commercially available marine ply, whilst perfect for building full size boats, has limitations when being used on a model especially when forming double or compound curves such as the barrel back has.

The result of this rigidity is that great care and lots of steam is required to form the curves and even then when the ply is bent and fixed to the required shape as it cools you run the risk of the material failing, which is what happened to me.

Easy to fix?

Not when you have used wood screws and epoxy glue to pull and stick to ply into position.

Its “catch 22” if I remove the ply I will distroy so much of the farme that the model would be scrap….and yet the panel has failed as such is now prone to further problems.

Paul
1 February 2009 at 07:55 #18242
Bob Abell 2
Participant
@bobabell2
I would glue a doubler behind the crack, to make it rigid, to withstand a good sanding!

You could have planked the frame in the first place……………but what the hell?……………the final top coat of mahogany will hide all the cracks………….once and for all!

So what are these…………………..”further problems then?”

Dr Bob
1 February 2009 at 10:16 #18243
Paul T
Participant
@pault84577
Hi Dr. Bob

I have doubled up the skin at that point so that I could sand it back to shape and the Kevlar and mahogany will cover the problem area.

My only worry for future problems is that the panel is flawed further along its length and that it wont withstand a side impact….silly I know as the Kevlar should resolve that problem but I do like to look for possiable flaws.

Paul
2 February 2009 at 20:03 #18266
ashley needham
Participant
@ashleyneedham69188
Paul. Nice. I thought for some reason that the rear would be rounder than that? might just have literally been expecting a `barrel back`. Ashley
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