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Old 01-08-2012, 21:07   #1
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Help - Advice With Radius Chine Plating

Hi all,
My husband and I are building a Roberts 37 radius chine in steel. We are up to plating the radius section and having awful trouble pulling the plate around to fit the compound curves. We have looked at some web sites that show other Roberts being built, and tried to use the same techniques suggested ie we have split the plate along its length, used come alongs, clamps, etc but we still have ended up with awful bulges or flat spots by forcing the plate to curve against its will. We know that we can fair it all up afterwards but wonder if there is any secret techniques to getting the plates to fit better in the first place when they go on? It all sounds so easy but we are struggling and feel we are spending too much time on each plate. Any ideas would be greatly appreciated.
Cath and Gaz
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Old 02-08-2012, 02:06   #2
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Re: Help - advice with radius chine plating

See if you can rent a bending brake large enough to roll your plate. Failing that buy one and then sell it when your build is complete, or find a local machine shop that can bend your plate for you.
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Old 02-08-2012, 02:19   #3
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Re: Help - advice with radius chine plating

Boracay is multi chine and I brought her as a complete hull, so do take my suggestions with a pinch of salt.

I have built several boats, but not steel or radius chine.

If you have not already discussed this with the designer then this should be your first step.

Building any round bilge boat in steel is going to more an art than a science with the old amateur boat builder's problem of knowing how to do it after you've done it.

From my ancient observations it is possible to "stretch" steel plate (by hammering, but there are other techniques...) and to "shrink" it by heating an area to red hot and then cooling it rapidly (with a damp cloth?). Don't try these at home!

Your other alternatives include splitting the rolled plates lengthways or cutting it into shorter lengths. The heat of cutting may help (or hinder!) the formation of the desired compound curves.

Using very thin ply or even cardboard to template the curve may give you some idea of how much compound curve is needed.

If your boat has similar lines to mine (Roberts Offshore 44) then you may care to take particular care with the chine that runs from amidship just above the waterline to the stern and the same chine at the bow as this catches the eye.

During my 5 year insurance survey the surveyor noted that corrosion in the round bilge area is a particular problem with steel boats so paying particular attention to good drainage in this area (and all others of course) could pay dividends in the future.

It may be a good idea to start sussing out a surveyor now to save anxiety when the boat is near launching. The major marine insurance companies should have recommendations.
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Old 02-08-2012, 02:43   #4
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Re: Help - advice with radius chine plating

For a radius chine, if you're going to get away with pre-rolled plates, you'll have to cut them into pretty short sections, certainly less than the radius I would guess, even if you do slit them in from each end.
Have you looked at any websites from similar builds? The only ones I look at are for aluminium radius chine hulls because I'm working towards such a project, but I can recommend Brian's building blog at Odyssey Yachts

Building Odyssey

and the following page describe how he dealt with this exact issue (apart from the material, but in some ways steel is perhaps more forgiving, certainly it is said to be much more amenable to heat shrinking... but this is not easy to do without lots of practice.)
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Old 02-08-2012, 04:17   #5
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Re: Help - advice with radius chine plating

The "development of compound surfaces" is the science you need to read up on.
The finish you acquire is the "art", making the plate the right shape is the science.
The way it was demonstated in tech college to my class was by taking a 1/4 section out of an orange, north to south pole, and cutting the skin lengthwise to the minimum cuts to make it lie flat.
Enjoy the orange
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Old 05-08-2012, 00:50   #6
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Re: Help - advice with radius chine plating

Thanks for the replies.
I agree Boracay, that we will know how to do it after we have done it!! Thank goodness for this forum where we have access to a wealth of knowledge and experience.
Thanks for the link Andrew, he has done a great job on the Odyssey. I have seen that method of leaving the whole radius plate and cutting small sections on another website, but we decided to stick to the method on the other Roberts builds we have seen ie cutting the plate lengthways where the compound curve is at its worst. I wonder which method is easier, because we are still having to be brutal with the plate to get it to fit doing it this way.
It was helpful to read that it is more art than science, we are thinking about 'sculpting' each plate now instead of thinking there is a rigid method that will work for every plate. Each plate wants to act differently it seems.
It is frustratingly slow and it is testing every bit of our patience but we are slowly progressing........
i will post some pictures on my profile when i get the chance.
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Old 05-08-2012, 01:22   #7
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Re: Help - advice with radius chine plating

Compound curves are difficult without the correct presses and rollers. When I built Nekeyah I had an engineering firm form the one compound curve needed.
Threaded steel rod welded to the plate and then through heavy angle braced against frames can be a good way of applying force. You may be able to heat and cool the edges of the plate to cause shrinkage whilst doing this.
Have you thought of cutting your sections out of a large steel pipe?
Regards,
Richard.
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Old 05-08-2012, 04:11   #8
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Re: Help - advice with radius chine plating

Milly

My guess is that, doing it the way you have chosen, you will need to trim your long edges so all the longitudinal seams have progressively bigger gaps as you move towards the (bow and stern) ends of each length of curved plate, in comparison with the ideal (small) gap at the midsection.

You should start by tacking each of these semi-cylindrical plate runs to the frames only near their mid-length, then start welding the seams from the middle towards the larger gaps at each end, rather than the usual skip welding. I would still keep the beads short, and alternate between welding towards the bow and towards the stern.

My theory is that this will induce a compound curve in each piece, by shrinking the weld zones differentially. You will certainly find that the more open seams at the end will close as you weld towards them. As (say) the one nearest the keel closes significantly, switch to the other side of the same plate and run some weld along the seam nearest the gunwhale. Try to keep the gaps even, IOW.

The key would be not to do ANY welding near the ends until the plate has pulled down (at the ends) to where you want it: ie kissing the stringers and/or frames.
However if you judge that it's pulling down TOO rapidly when you're still some distance from the ends, leave some gaps, and come back to them later.

The reason welding will induce a compound curve is that the edges of the semi-cylinder will shorten due to the weld metal bonding when hot, then shrinking as it cools. If you were to lie your semi-cylinder on the bench, so it can rock about, then run weld beads along the uppermost edges, they will be shortened in comparison with the 'silhouette edge' touching the bench. Consequently both ends of that silhouette edge will lift off the bench, at which point you have your compound curve.

Getting back to your boat: If you do any welds whatsoever to adjacent plates or to framing near the ends before the desired shrinkage has taken place, you'll have 'locked in' the cylindrical shape, and you'll have a fight you won't be able to win.

This method would not be a good idea with aluminium (for the benefit of others reading this) because it's important to prep alu butt welds with the optimum gap. I'm guessing this is why alu radius chine amateur builds tend to use shorter, full width pieces, rather than longer, half-width pieces, as (if I understand correctly) you are doing.

Steel OTOH is extremely forgiving when it comes to filling large gaps: the trouble amateurs most often seemed to encounter (certainly in the 'bad old days' before the www) was not providing enough gap, so that when they ground off the weld, there was nothing left holding the edges together, and they'd get that lovely 'ping' sound, and slivers of daylight. Luckily, in these days of flexible, 1mm thin cutting disks, that situation is easily recovered from.

If you find you didn't provide enough gap towards the ends, just slit the weld you've just laid back a bit with the thin disc , then use it in both directions al gusto; this will let you have another crack without having to start all over again. And it will enable you to err on the conservative side in how much gap increase to allow towards the ends, at least until you find out if the method will work for you.

Ideally I would also recommend staggering the ends of these half-width radius chine sections, but that would make the advice above harder to follow. Welds in steel are so strong that it's probably a counsel of perfection: better on balance to do it in such a way that the welds are not excessively tortured, whatever that takes.

(ON EDIT) Apologies if this is what you were already doing, and I'm probably just stating the bleeding obvious, but someone else might benefit from considering this proposal...
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Old 05-08-2012, 06:54   #9
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Re: Help - advice with radius chine plating

G'day Milly......you might find something useful in this series of posts on the boatdesign forum...Wynand, OP, has a great site and a wealth of experience that might be of use to you, it has to me.

The good, the bad and the ugly - Steel building methods that is.... - Boat Design Forums
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Old 29-08-2012, 22:28   #10
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Re: Help - advice with radius chine plating

Hi all,
Thanks Andrew for your detailed information, and sorry forthe tardy response, the plating, full time work and kids has kept us hopping......
We basically have ended up puting the remaining plates on similar to your suggestions, but have found that every plate wants to act differently so each has been a beast with its own personality!! There has been lots of cutting, tacking, grinding off, cutting, more tacking, lots of swear words and some prayers......I am please to say we are nearly finished, with only the front plating to go now. It has taken us much longer than we anticpated, but I expect this lesson in patience will be handy for the coming months/ years of this project. There will be a lot of fairing to do of the curves later but I dare say this will be easier than getting the plates on...
I have posted a few more pictures on my profile page and will keep updating it as we go.
The weather is starting to warm up here now, we will be heading into our "build up" and then the wet season soon, we are really trying to get the hull finished and sandblasted and painted before the big rain starts.
Wish us luck!!!!
Cheers and thanks again!
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