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Author Topic: sizing bulkheads/formers to deck advice  (Read 314 times)

Gazzalene

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sizing bulkheads/formers to deck advice
« on: May 16, 2019, 11:03:18 PM »

I am new to boats and building from plans.
I have 2 on the go and neither are going well,i have now turned these into "practice" builds.
I have made many mistakes and learned from them, some areas I am at a loss at .
The issue now I want correct is bulkhead width,twice now they have been to narrow,following the plan.
the second time I made sure they were the exact width of the deck BUT then I realised they need to be narrower so the deck can be sanded back to match the side angle.
is there a method to know how much wider the deck  should be, other wise the next attempt will see me making the deck way to big/wide.
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Nordlys

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Re: sizing bulkheads/formers to deck advice
« Reply #1 on: May 17, 2019, 08:39:05 AM »

The Bulkheads / frames as I call them, are taken directly from the plan. There is no variable size. Once you have assembled all the bulkheads/frames to the keel you then have a measurable size to cut the deck material to fit.
You refer to Bulkhead width? Just use the plan for the size?
Am I missing something here?
N
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John W E

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Re: sizing bulkheads/formers to deck advice
« Reply #2 on: May 17, 2019, 08:53:12 AM »


Hi Gazzalene
have you had a look at the Tug Cervia build in the Masterclasses,

it may help you with you builds
https://www.modelboatmayhem.co.uk/forum/index.php/topic,7947.0.html



john
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Gazzalene

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Re: sizing bulkheads/formers to deck advice
« Reply #3 on: May 17, 2019, 08:55:39 AM »

I have started 2 builds,basic speed boats. I think they are classed as hard chine?
I have copied all parts on the plan exactly to size. I soon found out that the first plan did not even have bulkheads drawn symmetrical!
So I cut new ones going by the center line not the fully drawn buklhead.
When I glued the bulkheads to the hardchine they were the width of the chine and the second build the bulkheads were the exact width of the deck BUT when I got to shaping this left not enough wood at the very top, does that make sense,hard to describe.
it seems to mee the bulkheads need to be narrower than chine/deck to allow for sanding.
I cut the bulkheads and deck to the outside of the lines on the plan.
I see a post that said plans should not be taken as exact,if that's the case what do I measure first OR build to?
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warspite

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Re: sizing bulkheads/formers to deck advice
« Reply #4 on: May 18, 2019, 11:41:09 AM »

The bulk heads are the basic former for the inside of the boat, (usually they are mirror images about the centre line though some ships like those for offshore rigs do have cut outs that do cause the sides to be altered in specific places) the deck is usually the same width as the top of the bulkhead as the deck fits between the sides which protrude above the top edge to the same depth as the deck, i.e. essentially framing the deck, so


if the top edge of the bulkhead is say 100 mm wide, then the deck is 100 mm wide, if the deck is made from 2 mm thick material, then it should follow that if the bulkhead was say for a bulk carrier and the top and keel of the ship were parallel and say 75 mm deep then the sides of the vessel should be 75 mm + 2 mm (for the deck to sit flush with) and if the hull is made from 1 mm material, then the choice is + 1 mm if the sides go below the bulkhead or flush, if the keel protrudes so that the sides sit on the keel material and it therefore transpires that the keel would be wider than the bulkhead to be flush with the outside of the sides.


Then the problem with a double skin, any material added to the outside of the vessel (bar the deck) would have to be flush with outside edges, it could be that the sides are flush with the top of the bulkhead and then the outside skin added to be above the bulkhead height, the deck then would sit over the whole of the bulkhead and over the inside skin, so overall wider in this instance.


Confused - tune in next week when we discuss string theory  %) ok2 {-)
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Gazzalene

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Re: sizing bulkheads/formers to deck advice
« Reply #5 on: May 18, 2019, 02:48:51 PM »

Warspite, I typed a nice long reply and attached a picture ONLY to be told file too big and the entire post/reply disappeared!
So this reply will be shorter.
 "if the top edge of the bulkhead is say 100 mm wide, then the deck is 100 mm wide, if the deck is made from 2 mm thick material, then"

When I read the above comment I thought,Brill the magic formula is add deck thickness to the deck outline OR take the thickness from the bulkhead BUTTTTTTT it all got very complicated very quickly.

I am a complete novice and do not know what I am doing wrong,i am copying the paln sizes exacly.

I have inc a drawing of my issue to make my point clearer
 
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Gazzalene

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Re: sizing bulkheads/formers to deck advice
« Reply #6 on: May 18, 2019, 02:54:49 PM »

Diagram 1 shows I have no deck sand
Diagram 2 shows I could sand to match bulkhead if deck was wider OR bulkheads narrower.

I have 2 plans and both show the bulkheads the same width as deck/hardchine

If I build as plan and diagram 1 when I put the side skin on against the bulkheads I get a gap at the deck,near the front. At the transom it fine.

Perhaps boat building will not be for me,the technic part is my issue,very annoying
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John W E

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Re: sizing bulkheads/formers to deck advice
« Reply #7 on: May 18, 2019, 05:56:22 PM »


ok - hi ya - I think you are being too cautious here.  A bit beyond yourself by too much thinking and not enough making :-)


if you look at your sketch number 1 and you have fitted all your stringers, all your keel and everything and you have skimmed the hull with plywood or whatever; your outer skin should be proud of the top of your frames/bulkheads.  Allowing you to fit a deck in to which you will have to what is known as scribe the deck in.


Doing it this way and not taking the thickness of your deck off the top of the frames; will leave you a model slightly higher - in other words the thickness of your deck.


Now, on your 2nd pic - doing it that way -


what you would do is build your hull, frames and so forth and apply your outer skin of the hull and then sand the top of the skin flush with your bulkheads/frames.  Then apply your deck on top of it.


Then, sand your deck to the shape of the outside of your hull.


This again, if you don't remove the thickness of your deck from the top of the frames you will be left with a slightly higher hull.


If you read either the Spashette build or the Cervia tug build, or RAF 64 FOOT launch in the masterclass builds on this forum, you will see how I use method 2 of your drawings.   I find this one of the easiest ways.


john
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Gazzalene

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Re: sizing bulkheads/formers to deck advice
« Reply #8 on: May 18, 2019, 06:22:24 PM »

Hi John, thanks for taking the time to help.

I can sort of understand your directions BUT on my models ,one is built up on the deck and the other is built up on a hardchine (?)

So from my view point, I have cut the parts exact to plans and when I go to sand the deck on one is to "small" to correct angle and the other as same issue but with the hardchine.

I can understand the 2nd method you say BUT the deck is glued to the bulkheads from the very start.
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RST

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Re: sizing bulkheads/formers to deck advice
« Reply #9 on: May 18, 2019, 06:43:27 PM »

Gazalene, might I ask exactly what boats you're building please? If you're building to plans, some modellers license is usually always required*.  I've fallen into same problems you have, still do it occasionally! I find it easier if I take a section/frame, sketch on the thickness of the wood/plastic I'm using then adjust the outline to suit. Are you wanting 100% to plan to the nearest mm? Usually better to add a few mm, and sand back, just as much sanding / fairing as cutting for me anyway to get close-ish to what's supposed to be. When it doesn't fair out, a sliver of wood cyano'd in place and re-sanded does the trick.   As long as it ends up symmetrical and faired  at the end of the day.




* Every modeller builds slightly different, different wood and thickness etc.
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Gazzalene

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Re: sizing bulkheads/formers to deck advice
« Reply #10 on: May 18, 2019, 06:57:34 PM »

RST, I have done just as you said, on one of the builds I have added a 2mm strip along the deck,not pretty.

The plans I found online, one is called "brave moppie"  project 66 from meccano magazine.
The other is called Viper, no more detail than that.
Both speed boats or hydroplane? very basic,all balsa build.
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