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Author Topic: Advice on working from hull lines  (Read 4534 times)

Thelegos

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Advice on working from hull lines
« on: May 07, 2012, 08:08:55 PM »

This might be a daft question but I've had a look through some books, magazines and builds on Mayhem and not found the answer.

I'm going to try and build a hull from a set of hull lines, are the cross sections drawn to represent the inside of the hull or the outside? put another way do I need to make them slightly smaller to take account of the thickness of the covering? - I hope that makes sense! {:-{

The hull is the 'Clutha'

Roger

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John W E

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Re: Advice on working from hull lines
« Reply #1 on: May 07, 2012, 08:15:08 PM »

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Thelegos

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Re: Advice on working from hull lines
« Reply #2 on: May 07, 2012, 09:32:09 PM »

Thank you John, that's excellent information. I confess I did look though your build but too quickly and missed it :embarrassed:

I've read through more thoroughly and there is a great deal of information I need to know. Back to my drawing board now!!

Roger
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Tug-Kenny

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Re: Advice on working from hull lines
« Reply #3 on: May 09, 2012, 11:45:48 AM »

Hi Thelegos
this may help you

http://www.modelboatmayhem.co.uk/forum/index.php?topic=7947.msg77343#msg77343

aye
john


Hi John,

I've just re-read your great description on Hull building and learnt a few more things about this great little hobby.  Thank you for posting this. There's details I missed the first time around.

I am also building a hull from frames, so I now have a better grasp of it's structure. I have a question that, hopefully, will not deviate from Roger's thread, but be helpful in the future.

Is there a recommended thickness for the frames related to the scale of the boat ?

I saw your build used the 'old' quarter inch size frames. I have bought 4 mm plywood and started cutting, but feel this is a bit thin for a 1:24 scale boat.

Can you enlighten us all please. 

regards


ken
 
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rmaddock

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Re: Advice on working from hull lines
« Reply #4 on: May 09, 2012, 12:18:19 PM »

When I've had plans, they've stated it the shadows are internal or external. I'd guess by default external.
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John W E

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Re: Advice on working from hull lines
« Reply #5 on: May 09, 2012, 06:12:13 PM »

hi ya

Yes and no is the real answer Kenny; the thickness of the frames on the Cervia build were made deliberately 6mm to give the first time/newby builder a fighting chance - whereas when you are pinning planks to the frames with the brass pins, you have the better chance of hitting the centre of the frame without splitting it.   Also, a tug needs to be fairly robust in build to take all of the knocks and also the weight helps with the ballasting.  I have a sneaky feeling that you are building a Dogboat - the Fairmile D ?   in which case I would recommend a 4mm ply for lightness.  But, I wouldnt plank the Fairmile boat with longitudinal planks (running from bow to stern) I would double diagonally plank it - have a look at the Whaleback build; this is the type of planking procedure I would use on the Fairmile.    Keeping the hull light and if built correctly it will be as strong as a fibre glass hull.


Hope this is of some help Ken.

aye
john
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Tug-Kenny

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Re: Advice on working from hull lines
« Reply #6 on: May 09, 2012, 09:47:57 PM »


Got it in one, that man.     %)    Cheers John.

As there are 26 frames in the Fairmile,  I was trying to keep the weight down.  I was ( as you deduced), worried about the planking so I like your suggestion about diagonal planking as an alternative way. I'll start a Blog when there's enough to photograph.

Roger, It's great fun doing it from scratch and also very satisfying.  Any pictures yet ?

ken

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Thelegos

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Re: Advice on working from hull lines
« Reply #7 on: May 09, 2012, 10:37:02 PM »

Hi Ken,

As you say this is a great hobby, and I, like you am very impressed with John's description. So far I've had the plan copied to AO and drawn up the sections. I was planning to cut it initially in thick card to 'test' its accuracy as I've noticed there is a difference in the overall length of the boat shown in the top view and plan when compared to the plan of the hull lines; 58cm vs 55.5cm. I can't see any reason why there should be! I might try to redraw the section for the keel from the hull lines - all new to me but I really want to try it!!

The purpose of this is to try and build a model of the old Thames Police supervision launch 'Watch' and this hull is the nearest thing I've been able to find based on a few old pictures of the real thing. I want it to compliment my recently restored original Veron Thames police launch - a very sad shell rescued from ebay.

Roger




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Tug-Kenny

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Re: Advice on working from hull lines
« Reply #8 on: May 10, 2012, 12:10:07 PM »


I also have the plan versus the frames discrepancy.  This can due to various factors but if you're scaling them yourself then it's easy to widen or shorten them to match.

This is assuming they were drawn correctly in the first place.  I always match the frames tops with the ships deck width, then any discrepancy will be in the length which does not show as much.  The drawings are everything, so must be accurate.   I hate to see the words  "Not to scale"  as this will involve more than double the work.  %)



ken
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nemesis

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Re: Advice on working from hull lines
« Reply #9 on: May 10, 2012, 12:58:51 PM »

Hi, A thing to look out for is when you get a plan blown up the paper stretches, well that is what I have found. Nemesis
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Perkasaman2

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Re: Advice on working from hull lines
« Reply #10 on: May 10, 2012, 01:14:44 PM »

The opposite is also true, especially, older plans copied using wet copying systems - these plans could also shrink. Modern copiers heat the paper and this can also cause shrinkage.
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John W E

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Re: Advice on working from hull lines
« Reply #11 on: May 10, 2012, 06:38:53 PM »

hi there

I think the main problem with distortion in plans is nothing to do with the paper that they are printed on - but the method of printing.  If you look at some of Model Boats' free plans which come with Magazines there are 1 or 2 of them where the frame drawings dont match up with the side elevation or the plan view.  Even though, when drawn by the draftsman they are correct on his original copy, by the time they go to the printers to be prepared and mass printed, the printer shuffles segments of the plan around to fit a set size of paper.  The programme/method the printer uses may distort the drawings.

The process of enlarging on some these printing machines - can and do stretch at wrong ratios sometimes,.   In other words, the height doesnt correspond with the length of the item being drawn.   To overcome this, we should know what scale the plan has been drawn at.   We should know the correct length of the model we are building and adjust lengths on the plan accordingly,.

aye
john
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Thelegos

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Re: Advice on working from hull lines
« Reply #12 on: May 22, 2012, 09:46:18 PM »

Hi Jon & Ken (and everybody else of course!),


It's been a while since I posted on this thread but I've been wrestling with hull lines, plans and profiles etc. trying to make what I need using the Clutha No.11 plan.

Sadly it's been an uphill struggle and despited coming up with what appeared to be a reasonable set of profiles to work with they now look out of proportion and the height (therefore the draught) looks to small to me compared with the width. I have read that in scaling down the ratios sometimes need to be adjusted to achieve a functional and more 'correct' looking hull - would this be the case here?

The bulwarks will need to be added but they are only 13mm at the widest/deepest point in the centre where the keel to hull is only 43mm.
I've learned a lot, not least of all that the published plan has it's share of inaccuracies which would make a straight from paper build challenging to say the least! I think if I'd been able to buy a hull it would be sailing in a week or two!

Roger %%
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Thelegos

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Re: Advice on working from hull lines
« Reply #13 on: May 22, 2012, 09:53:05 PM »

I intended to add these images to the post above!





Doh! :embarrassed:
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Colin Bishop

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Re: Advice on working from hull lines
« Reply #14 on: May 22, 2012, 09:53:14 PM »

I am currently preparing a Special issue of Model Boats for publication at the end of the Summer. Essentially it will be a compedium of plans features from the extensive archives but will include an article on working with hull lines which I hope people will find helpful. Once you understand the principles it's not very difficult and a knowledge of what lines are really helps when making your own hulls.

Colin
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Thelegos

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Re: Advice on working from hull lines
« Reply #15 on: May 22, 2012, 09:57:52 PM »

Hi Colin,

I'll look forward to that, it's great fun when you get your head into '3D' mode and the structure starts to come together. Perhaps it will look right when built but at the moment I'm unsure - it's a lot of work to do only to find it's completely wrong!!

Roger
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Tug-Kenny

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Re: Advice on working from hull lines
« Reply #16 on: May 22, 2012, 10:38:09 PM »


I have taken the liberty of copying the Frames from your drawing above.  I've marked the two vital measurements that I would need to alter, to change the scale.  All the other frames line fall into place.

These two readings MUST match the drawing below (which shows the side view of the boat) as they can be different, as you've found out.

Regarding proportions then you need to stretch either sideways of vertical until you get a match. Then print out for a final check of size.

In my case you do this 20 times until it prints out the correct shape.     :}    I told you it was fun, but what an achievement when you succeed.

ken
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Thelegos

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Re: Advice on working from hull lines
« Reply #17 on: May 23, 2012, 02:23:48 PM »

Hi Ken,

Thanks for your input, it hadn't crossed my mind to stretch the profiles and using the computer saves hours of redrawing! I don't really want to make the boat longer so can't increase the scale in the true sense but by keeping the widths the same and increasing the height by around 15mm it looks far more in proportion (to me anyway) The acid test will be transferring it to the side view and plan which sadly I won't have time to do today.

Scanning and printing has highlighted the changes in scale that occur with each operation! A couple of mm can be lost each time plus it's important to keep the screen image as close to the paper size as possible; A4 in this case. Compensating for the hull skin thickness can be achieved by the copying process alone. More pitfalls to keep an eye open for!

The hull was always going to be a bit of a compromise which included changing from twin to single screw, you can still just see the old lines on the profile! The deeper hull will make the installation of running gear very much easier.
I'm looking forward to the next try :-)


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Tug-Kenny

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Re: Advice on working from hull lines
« Reply #18 on: May 23, 2012, 08:11:32 PM »


Glad to be of service.     :-))

I found that to save printing ink, it's best to take slice of the width or height in question on your drawing  (about 10mm wide) and make the trial print of it. This can be measured with a ruler and the drawing adjusted to match, if necessary.  To save paper, it can be re-used with the new image 30mm lower.  (mean or what !!)   {-)

    The side plan is great for heights but I didn't see a plan of the deck. This would be needed to get the widths of the Frames.   I do feel you are worrying needlessly about the skin being added to the frames. This will increase the overall size of the ship in proportion anyway so it will look Ok. The scale to the purists would be One notch bigger.   1:32.5  ?

Keep at it

ken
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