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[Martin13]

I am building a 1/16 scale of Brave Borderer approx 1800mm long. I used 8mm ply for the bulkheads and covered with 1.5mm ply with the bow section made of block balsa. I had no end of trouble trying to get the chine line correct at the bow using existing plans, but the model is too heavy so it now lives on a shelf.

Mk2 version using plans supplied by John Lambert. It was suggested that instead of using ply to skin the frame - that I should plank the frame with 3mm balsa then cover with 2 sheets of woven fibreglass not stranded matt. End result should be a much stronger hull and a lot lighter.

Am I on the right track or am I going to the Mk3 version.....at least I have learnt a lot so far

Martin from Down Under  :-\ :-\ :-\

[John W E]

hi there Martin from Down Under 

I see the forward chine is causing you some (shall we say - stress) on the hull.  The way it sort of bends down in an 'S' shape when looked at from the side.

To be honest with you, plank on frame is only one option for you.   There is the method of using carved foam, which has been described on this forum elsewhere I think, where you carve the shape of the hull you want out of the foam, seal it with either an emulsion paint or some other material.  Use a releasant on top of that, lay your matting on top of that & then finish off with car body filler and sand until you reach the desired finish. 

My personal choice would be to go 'plank on frame' and for the bottom of the boat, I would diagonally plank with the thinnest and narrowest strips of wood possible, something in the region of say 4mm wide x 0.5 mm thick Obechi.   For the sides of the hull I would diagonally plank that as well using maybe 10 mm wide x 0.5 thick Obechi wood.

On top of this, I would lay two layers of tissue matting, finished off with a top coat of resin, sanded smoothly.   

Then, when you remove the hull from the building board and turn it over it may be adviseable to add a layer of tissue matting on the inside of the hull as well in between the frames.

I should think you would find the hull will be pretty strong after this.

Hope this is of some help.

aye
John
bluebird

[Martin13]

Thanks John,

I have seen that method on the forum re diagonal planking but I have one problem with it.

Down here in Australia, I have not been able to source Obechi for sale and the thinnest marine ply when and if its available, is 0.75mm which has an extraordinary price tag hence using the 1.5mm ply.

You don't think the 3mm balsa is appropriate ?

Fibreglass matting instead of woven cloth is the way to go ?

I have been to a local supplier re fibreglass - but they have matting and cloth in many different weights - what do you suggest

Thanks again for your expertise

Martin
a long way down under

[HS93 (RIP)]

This may give you an idea of how to cover a hull with light glass cloth.

http://www.rcgroups.com/forums/showthread.php?t=329811

you may be able to get thin ply mail order as you will only need it in small strips have you tried   http://www.pt-boat.com/  he does sheets of lazer cut ply for this purpose and is in AUS

Peter

[Martin13]

Thanks Peter.

All info is good info.
Thanks for the Contact in Aust. have send john an email requestng lazer cut ply

Thanks a heap

Martin
Down Under

[tigertiger]

What weight or grade of cloth is used.

I will be back in UK next year and want to buy some.
Is 'Light Cloth' a grade?

TT

[boatmadman]

Martin,

Can you get Cedar down there? I have used this for planking in several boats, it works well and has a natural oil in it that has a water resistance.

If you can get it, just make sure that the grain in the planks is nice and straight - along the length of the plank, with little or no twists and no knots.

Ian

[Martin13]

I sent off an email to pt-boat.com here in Aust and the reply is as follows:-


Hi Martin,

I can do strips for you in various thicknesses of marine ply but I don't
have 0.5mm in stock, I know I can get 0.6mm and I think 0.4mm but not
sure about 0.5mm.

My laser cutter can only cut sheets up to 12" x 18" but as I cut 1220 x
1220 ply sheets into 4 x 3 smaller panels of 305mm x 406mm strips
shorter than 406mm become the optimal length.

I usually buy Finish Birch GL3 aircraft grade marine ply, there is also
GL1 ply with no knots but it's pretty expensive.

Given that, let me know what you want and I'll get a price for the
timber and work out a price for cutting.

Regards
John Drain
[email protected]
...

Can members please advise which product is best for planking including thickness and width of strips to use on the hull - never planked a hull before, only partially in tricky spots.

I have been advised by a fibreglass supplier to use 185gsm woven cloth - does this sound correct ???

Martin     :-\ :-\ :-\
Down Under

[kayem]

"Aircraft grade marine ply" ??????

I think I know what the guy means, but there's no such thing as Birch marine plywood, and there's never been such a thing as "Aircraft grade marine ply" either. Also true BS1088 marine ply, it has that identification stamped all over it, is very hard to find less than 6mm thick, and it isn't even manufactured below 4mm thick. For model boats, stick with good quality WBP (water and boil proof) birch ply, that's all you need. The only modelling use for proper marine ply that I can think of would be a heavy duty boat stand that you wanted to leave out in the rain.

[John W E]

Hi there Malcolm

To be quite honest, you have several options open to you.   Which one you decide on is entirely up to you and which one suits you the best.  You could plank a hull quite successfully using 3mm thick balsa strips.   Planking a hull with balsa has been done by several members of this forum quite successfully.   I have planked with balsa on 2-3 occasions.

The resason I dislike using balsa as a planking material is, I am very heavy handed when it comes to sanding  and I have sanded through on several occasions.

The way I personally overcame the problem of sanding through was, when I had finished planking a hull, before I did anything else, I coated it with a coating of polyester resin with hardener mixed in to allow it to soak into the balsa wood, making the balsa wood slightly harder and better for me to sand.

If you go the plywood way and use plywood as planking, 1mm thick plywood cut into 8mm strips would do the job.   Personally, I would go for 0.5 or 0.6 mm plywood, or whichever is the best option for you.

I would cut the plywood into 8mm thick strips.

I have a friend who sat one night with a stanley knife and a steel straight edge.  He marked off and cut a 4x2 sheet of 1mm thick plywood into strips for to plank with.  This was just to save him the cost of having it cut for him into strips plus he did not want to waste any. 

Now, I have included a little scribble, which may assist you in how to diagonally and double-diagonally plank your hull.    Once you have all the basic framework set in, where you have your keel/chine/stringer/deck edge stringer in place - it pays you to add bottom stringers.   The more you add in, the closer you will get to your bottom hull profile.   The same on the sides, because the hull you are proposing to build has a fair amound of flair at the bow end.

When you eventually come to start to plank, my personal preference is to commence approximately at the centre of the hull - mid-section.  Your first plank should be approximately 45 degrees angle to the keel.

As you plank towards the bow, you will note that the angle of the plank will increase.  This is normal.  My normal method of planking, is, to do 5 planks one side of the hull/5 planks the opposite side of the hull and by that time the 5 planks on the other side are dry (i.e. the glue has dried).

Then, I go 3 planks one side of the 5 and 3 planks the other side of the 5 (in other words 3 planks towards the bow and 3 planks towards the stern).   Once they are, I do exactly the same on the opposite side.

When the hull bottom is complete with one layer of planks, I do the sides in exactly the same method - i.e. 45 degrees from the deck edge at mid-section of the hull.

Once I have the full hull completed with one layer of planking, I lightly rub it down to remove any abnormalities, fill in any hollows with P38 filler and then apply my 2nd top layer of planks in the opposite direction to the bottom layer of planks.

Once this has been done and I have sanded and filled - I then proceed and give it a coat of polyester resin with hardener mixed.  This is where I think you will have to make your own mind up of what fibre glass material you are happy working in.  Some of the very light woven material (similar to what the aircraft lads and lasses use) some people find it easy to work with and some find it difficult because it can be difficult to remove air bubbles out of.

If you have had no experience in working with fibre glass, it may pay you to try and work with a very light chopped strand glass mat thats for Kayem  .

I hope this is of some use to you.

aye
John e
bluebird

[tigertiger]

Who is a good, reasonable price supplier of the folowing in the UK.


0.4mm ply

Fibreglas tissue (and what grade/weight should I use on a hull exterior?)

I will be back in UK in Jan and want to get some stuff to take back to china with me.

TT.

[kayem]

The resason I dislike using balsa as a planking material is, I am very heavy handed when it comes to sanding  and I have sanded through on several occasions.

The way I personally overcame the problem of sanding through was, when I had finished planking a hull, before I did anything else, I coated it with a coating of polyester resin with hardener mixed in to allow it to soak into the balsa wood, making the balsa wood slightly harder and better for me to sand.

If you have had no experience in working with fibre glass, it may pay you to try and work with a very light chopped strand glass mat thats for Kayem  .

aye
John e
bluebird

Ooh, thanks John, I didn't know you cared!

On the rest of Bluebird's post, it's the usual recommendation, use whatever method works best for you, but I much prefer balsa planking to ply for this kind of thing, the planking takes a fraction of the time for one thing, and this is how I do it.

Use fairly firm balsa, not the really soft stuff, and for most hulls I'd use thicker wood, probably 5mm, or what we used to call 'three sixteenths'. This isn't too bendy, which is both a help and a hindrance, it's a little harder to work with, use a razor plane to bevel plank edges, but thicker wood will follow the hull lines better, so you're less likely to get hollows, and it gives you a lot more leeway when it comes to sanding, which is good if you're heavy handed as Bluebird claims to be. After all the glue is hard, a very light going-over with the razor plane, and then the way I sand is to use quite coarse 80 grit paper on a fairly large block, all you want to do is take off any high spots and raised plank edges, don't worry about any hollows, that way you should end up with a minimum of about 3mm of balsa everywhere, even over the bulkheads, and you should have something a lot better than it would be if you'd planked with 3mm wood in the first place. After that, I apply a coat of fibreglass resin to seal everything, but I'd hate to have to try to sand the hull after this, it would just stick to the abrasive paper and clog it, so once the resin has set, add a layer of 450gm glass mat over it. Once that's hard, you have a solid and uniform surface that isn't going to move up and down as you sand it, so apply P38 filler everywhere you can see hollows and imperfections, and sand away on that to your heart's content.

This is just the method that works best for me, but I've planked an awful lot of hulls this way with good results, so you might find it works for you as well.

[Colin Bishop]

I have usually used Kayem's method for my hulls except that, after the main smoothing has taken place, I use sanding sealer to impregnate toughen the wood before final finishing. I agree that medium to hardish grade balsa is good to work with.

[kayem]

And here's one I made earlier.

This is a 36" steam launch hull done in the way I described a couple of posts ago. Slightly different from what most of you would want to achieve, as this is only intended as the pattern for a fibreglass mould, all the bulkheads etc are solid, though with minor changes the same method would be perfectly OK for most types of hull that were to be used for a sailing model, indeed almost all of the internal structure on this one could have been removed to achieve this if I'd wanted that. Underneath are 6mm plywood full size plan and profile shapes, though without the added keel on the profile, it's better to add this later, and about ten 6mm ply formers. The midsection and transom were worked out on my drawing board, and all the others by eye using a flexible lath, a practiced eye and years of experience for a fair curve. Once that all looked OK, the hull was planked with 5mm balsa in short sections, all joined over a former, and a little like Martin's Bismarck. Where you can use this method, it's a far quicker and less fiddly process than planking with longer lengths, which is I suppose most would consider to be the 'proper' way. You might expect to end up with something rather like an old fashioned threepenny bit using this method, but the curves are such that only a bit of fairly gentle work with razor plane and sanding block were needed to end up with the right shape that I could run my hand along without feeling any unwanted corners. If you work accurately with a job like this, you should end up with a minimum thickness of around 3mm of planking in the thinnest areas. As can be seen, the bow was done with balsa block, and as the transom wasn't quite the shape I wanted, I added a second layer of 5mm planking, and planed this away until it blended smoothly into the first layer. Next steps were exactly as described previously, a coat of resin to seal the wood, a layer of 450gm mat to make everything good and solid, infinitely better than glass tissue which has no real strength at all, a couple more coats of resin containing an additive so it sanded better, then filled as needed with P38 and sanded again to a nice smooth finish. After the keel was added, what you see here is ready for the final finishing coats of resin, and I can't imagine any faster way of getting a result like this.

[Circlip]

      Just to throw more fuel on your fire Martin 13, the last skinning I did ( All be it on a PSS SR71 ) was by using
      Epoxy Resin and Silk.  Silk used to be easily obtainable in lightweight grades when we used to have at least two
      model shops in EVERY town over here. I had to go to the local Asian material importers, (Dress Material) for mine.

[John W E]

Hi all

As we can see, we have two versions now, of how to produce a hull and YES there are many other ways of producing a hull which we have to bear in mind.

What we have to take into account is that everyone has their own preferred method of producing - I know one way of making Kayem and I run 100 miles  :) and that is, if you were to give us sheets of Plasticard, and, then tell us to make a hull out of that.   No doubt we would have a good go, but, I do know what we would prefer to use instead of Plasticard.

Anyway, the only thing I can comment on about Kayem's method is, when you produce a hull using double diagonal out of either balsa wood/obechi/plywood you are building in an added strength by having the grains of the materials running at 90 degrees to each other.  That has far more impact strength than the grain running in one direction only.   When I build a lot of my hulls of double diagonal, I only use the tissue mat, as Kayem has said - it gives no added strength to the hull, its only there to seal it.   As the strength comes from the double diagonal build.

I have attached a couple of photographs of a hull which I built not so long ago, for the Fairmile B, and, as you can see, the inner planking is Obechi and the outerplanking is 4mm x 0.5mm thickness mahogany and this was coated with an Epoxy system SP, no matting was used whatsoever.  This will also show you the type of finish you can obtain by using Epoxies.

Epoxies tend to be a bit more expensive than polyesters - but be careful, some epoxies are not very user friendly.   I know one or two people who are very allergic to the substance.  When they use it they have to be dressed up like a NASA astronaut.

Aye
john e
bluebird

[Circlip]

     Never thought about allergies John, cheers, you've just explained why I've got six digits on one hand and eight
     ont other!
     Kayem, is that chopped strand matt (sorry - mat) on your hull build?

          Ian

[HS93 (RIP)]

This will give you an idea of the cloth used in the link I posted. It is very light in weight, I think the method that  kayem was using was for a mould where weight is not a factor, if you use ply have a look at the PT boat site and he gives info on what he uses for a hull of similar size to your's, and then it's just down to waterproofing with the fiberglass.

Peter

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXAU14&P=ML

[HS93 (RIP)]

tigertiger
 The best ply I have had of late was from    http://www.jperkinsdistribution.co.uk/   But I tend to buy a few sheets at a time and keep it on stock so they don't mind sending it to me , send them an e-mail and tell them your situation and they may be able to tell you who stocks it in the are you will be in , and you can then Pre order, most shops stock ply of that size but jperkins tend over the years to be the most consistand in quality.

Peter

[tigertiger]

This has been a really usefull thread with lots of great info.

Kayem, I would never have thought of doing things your way, with short thick strips. This makes life really easy.

Bluebird, I understand your point about weight. as I want to build scale sail, where keeping the weight below te waterline is important due to heeling forces.

HS 93 thanks for the links, I will contact them.


Now I would like some advice please

On my next planned build (Arab Dhow) the planking will show and I want it to be a bit rough. I was thinking of 3mm balsa plank, coated in resin afterwards with F/glass tissue or matt internally between frames for added strength. The hull is about 600mm overall length.
Will this work.

In the future I will be building larger hulls between 1m and 2m. These will be for scale sail and the planking will not be showing.
Do you think 3mm will be strong enough in this instance?
Would 5mm to too difficult for some of the curves?
would using matting externally be too heavy?

I look forward to opposing views at the debate here so far has been very informative.
Thanks again.
TT

[kayem]

Here are a few comments on a few of the comments that followed my last post.

Firstly, this is only one way of doing the job of producing a fibreglass skinned wood hull, and if some other method suits you better that's fine. I've tried most of the alternatives, all have good and bad points, and this is just the way that suits me best. It's relatively expensive on materials, but I find it by far the fastest method, and when you're doing this kind of thing for a living, time is money. To succeed, you do have to be able to make joints really accurately, never rely on adhesives to fill gaps, both edge to edge joints and end to end, but it's much easier sanding and planing slivers from a 4" length of 5mm thick wood than trying to get a perfect fit with a thin plank that runs from bow to stern, twisting along the way. Bluebird was right about one thing, ask me to build a hull with styrene sheet or Plasticard, and I'd run miles, probably something like double the hundred he suggested.

Peter suggested that this was a heavy method, but I don't think it is. My hull in the pic is heavy, but much of the weight is in the 6mm ply internal structure, which wouldn't be there in the case of a sailing model, and wanting to end up with something fairly robust, I was fairly generous with the glass and resin. If you think about it, my hull is one layer of 450gm glass mat, much the same as any bought hull, the fairly thick balsa planking weights very little, and the internal structure need be no more than any other model with a built-up hull, 3mm ply would have been quite adequate for all the formers etc. There isn't a lot of P38 filler used, and it's mainly at the rear end where I decided to modify the original shape. This method works well for hulls with tighter curves, but you'd have to space the formers closer together, though possibly this would only be needed at the bows, and then you'd use shorter planks between them of course.

A couple of tips I've just thought of, It is important to seal the balsa completely with resin before applying the glass, you'll probably need a couple of coats. Covering curved shapes neatly with fibreglass is a skill that comes with practice, once you develop a feel for working with the stuff, you can both shrink and stretch glass mat with deft use of a brush and a suitable roller. There was no external keel on my hull when I added the glass mat & resin layer, so I was able to cover the entire hull with a single piece, it only needed two or three smallish vertical cuts and overlaps along the deck edge on each side and at the bows. The small double thickness areas that result are easy to sand away once the structure has hardened, but just about the best advice I can give to any modeller is to only ever use abrasive paper on a suitable shaped sanding block, that's the only way you'll ever achieve good results.

[John W E]

hi there TT

The only problem I could foresee with planking the hull of The Dhow with balsa wood, if you do not coat the outside with either dope or a resin, it is going to leave it vulnerable to knocks and scratches which, once the water penetrates, the balsa wood would swell rapidly.

I can understand your problem of sourcing materials where you are living - however, since the model is going to be in the region of 24 inches long, how's about building the hull from balsa wood as Kayem has suggested.   Have a smooth hull and then covering it with a tissue or a light mat.  Then assimilating the planking with either Plasticard or a thin veneer/even thick card, which you could seal with either paint or a varnish.

This would give you adequate protection.

aye
john e
bluebird

[tigertiger]

Thanks Kayem
points noted.

Thanks Bluebird.

Am I right in thinking that a layer of tissue soaked in resin would still be largley opaque?

TT

[John W E]

Hi ya there TT

have a look at this photo it may give you some idea.   The hull has 3 coats of resin with tissue mat on.

As you can see, you can still see the planking underneath.

However, and this is the big however, polyester resin is not waterproof.  After a prolonged period in water. it will start to absorb water.  This is why, on full sized hulls, you use a gelcoat on the surface that is going to be in contact with the water.

So, when we use it on our models, we must coat it with either a varnish or a paint.

Hope this is of some help.

Aye
John e
bluebird

[kayem]

Am I right in thinking that a layer of tissue soaked in resin would still be largley opaque?

TT

That hull in my pic has a layer of 450gm mat, 'ounce and a half' measured the old way, and you can see all the wood grain through it. You can't get much more transparent than that, and glass tissue of course is very much thinner. Always wear rubber gloves, something like those yellow Marigolds, whatever type of resin you're using, they don't feel clumsy once you get used to them, and as Bluebird mentioned, be very careful with epoxy resins, this seems to be a very common and quite serious allergy.