How to straighten a Bent keel

[Riotvan88]

Hi again 

 

Sorry for the daft questions but it's my 1st build and I'm wanting to make sure I do everything correctly and not rush any steps. 

 

From the pictures you can see my keel is curved from bow to stern slightly, the photos makes it look worse than it actually is but in any case its not straight. 

 

My question is can I make a jig by gluing wood blocks to a solid base the idea bieng to sandwich the keel between the blocks and keep it straight. Then whilst in this jig glue and pin the bulkheads , false deck and add balsa blocks between the bulkheads. 

 

Or should I soak the keel and clamp flat overnight? I thought best to seek advice from this forum 1st before continuing as its been great so far. Thanks 

Edited April 2, 2020 by Riotvan88

[Clark]

You mean the curve from stern to bow? It may be the best to test the bending proceeder on an extra plywood piece. Usually wood can be bended by applying heat. If the wood is watered, the water helps to spread the heat. I am not sure how plywood reacts.

Clark

[ulrich]

Hello Riotvan88<

I would create a slot to hold the keel to a wood base by gluing 2 square "dowels", as long as the entire keel, wide enough apart to hold the keel tightly. Make sure these square "dowels" a low enough to not interfere with the bottom of the bulkheads. the bow and stern section of the false keel need to be held by square angles up to the top of bow and stern. This should keep the keel straight for now. After you have assembled the bulkheads to the keel you need to glue blocks between each bulkhead to keep it straight. Better would be to fill all the voids between the bulkheads and make it a solid hull. For that, I would use bass wood, no balsa wood. Good luck

Ulrich

[Chuck]

That is a very common problem.  It is to be expected.  You cant blame mfgs for this as a long piece of wood with slots cut tends to want to bend.  The easiest way is to create a slot for the keel as mentioned.   But in addition, use brackets as a way to clamp the whole thing in position.  Once straightened by these and you have planked the wales and above, you can remove the brackets and it will remain straight as an arrow.  All POB models should be built this way regardless.  Three or four should do the trick.

 

[Baker]

You might find advice here

 

Glue (filler)blocks between the frames is perhaps the best idea.
 

[Jaager]

I build POF and am a bit biased on terminology.

As a side note,  what you ( and most everybody) call bulkheads are actually molds.  Subs have bulkheads,  some steel ships have bulkheads, Chinese wooden ships have bulkheads.  Western wooden ships did not have bulkheads.  They certainly are not frames.   What you (and everyone else) call the keel is actually a central support spine.

I have never built POB, so this is theory.  How I would try to rectify this:

1.  This curve is the natural shape that your piece of plywood seeks.  Anything that you do only to it  (bend it back with steam or heat) is likely to be a temporary fix. It will still "want" to bend.  You can clamp it to a baseboard and use the planking applied while clamped to hold the shape.  But when removed an twist force will be on the glue joints of the molds and inside planking - forever.  It may or may not hold. 

2.  If the molds have not been glued,  there is a stronger fix.  Scab a long streamer on each side of the central spine.

Remove the black area on each mold.  Get a couple of long sticks of straight hardwood ( 1/4" x 1/4"  or 1/4" x 1/2" or substantial size ).   Drill holes thru the sticks and central spine all along the length.  Use threaded bolts, washers and nuts to fix the sticks and central spine together.  Make sure this assembly is dead straight.  Remove the assembly.  Glue the molds to the central spine.  Slide the sticks thru the holes along the length and glue the sticks to the spine.  Check to make sure it is still dead straight.  The bolts can be removed and bamboo skewers glued thru the holes.  You just need a drill bit that is the diameter of the skewers.

 

3.  The holes in the molds remove some of the bonding surface between them and the spine.  Short pieces of SQUARE wood can be used to reinforce the bond.  Eight pieces per molds.  Just do not block the path of the straightener sticks.

 

4.  Rather than Balsa, consider using Pine to fill the outer planking edge between the molds.   Assuming that you do not have power tools,  a hand fret saw. planes, knives and sanding block will do.  Select Pine in 1" thickness is easily found. There may also be thinner stock of solid Pine.   Cut out the shapes, glue up the layers to fit between the molds, and do as much shaping as you can before fixing them between the molds.  You are unlikely to be lucky enough that a sum one 1" layers will be a tight fit between the molds.  The outer surface does not need to be continuous.  Cardboard or what ever is to hand can be fitted between a layer to make up the difference.  It does not need to reach the outer shaped surface.  You just want the unit to be a push fit between the molds.

[mtaylor]

A additional thought on this.  Were the bulkheads a tight fit or an easy fit?  Being a tight fit can warp a keel.   The other advice is all good so test until you find one that works for you.

[Riotvan88]

18 hours ago, mtaylor said:

A additional thought on this.  Were the bulkheads a tight fit or an easy fit?  Being a tight fit can warp a keel.   The other advice is all good so test until you find one that works for you.

The bulkheads are quite an easy fit nothing is glued yet 

[Riotvan88]

Thanks for all the advice, I went and built a basic jig to clamp the keel straight using wood blocks

On 4/2/2020 at 3:13 PM, SpyGlass said:

Humm may i respectfully disagree with Chuck on this.

The manufacturer is responsible-I dont know which kit  this is but it is fairly small one and it would be reasonable to expect  a straight keel. Scratch build is different.

The correct answer is - ask for a replacement-a reputable manufacturer would supply one.

It should not be necessary with a kit to start correcting such faults.

Over the years I suppose about 1 in 5 l kits I have had had  a marked keel curve - . They have always been replaced without query.

 

I have tried many methods out of interest to correct the curve  - one example here  keel curve

 

Only one had some success - involved soaking, clamping between glass and keeping damp inside a plastic bag for several days and it still wasnt perfect and it was a huge fiddle.

Contact the maker !

 

 

Thanks for all the advice from everyone. I considered contacting the kit maker the kit is a caldercraft Sherborne 1:64. However looking at the build logs I feel this is common issue so I need to learn to deal with it early on. 

 

So I made a basic jig using a base board and square wooden blocks I arranged this to clamp the keel tightly.  This seems to have worked its difficult to tell how straight because of the sheer bit I definitely think it's an improvement. I then fitted the false deck to the false keel with pins, nothing is glued yet. 

 

I'm thinking if I glue this up and then fit basswood blocks to every space between the molds/bulkheads as someone suggested hopefully it'll then stay straight. 

Edited April 3, 2020 by Riotvan88

[JeffT]

Problem solved 🙂

[Ryland Craze]

Good solution for the warped keel.  It really straightened it out.  I had the same problem with my Sherborne kit.

[Riotvan88]

7 hours ago, Ryland Craze said:

Good solution for the warped keel.  It really straightened it out.  I had the same problem with my Sherborne kit.

Thanks, How did you solve it on your kit? What I'm hoping is that I can fill the spaces between the bulkheads with wood and it'll hold it straight. 

[Ryland Craze]

7 hours ago, Riotvan88 said:

Thanks, How did you solve it on your kit?

I made vertical cuts using a razor saw on the first layer of the plywood false keel to make it more flexible.  I then put it in a jig to hold the false keel straight.  After I installed the bulkheads, I placed wooden fillers between the bulkheads to make the assembly rigid.  Once the false deck and the gunport patterns were installed, I had no problems with warpage.  I have attached a picture showing what I did to the false keel.

[Riotvan88]

15 minutes ago, Ryland Craze said:

I made vertical cuts using a razor saw on the first layer of the plywood false keel to make it more flexible.  I then put it in a jig to hold the false keel straight.  After I installed the bulkheads, I placed wooden fillers between the bulkheads to make the assembly rigid.  Once the false deck and the gunport patterns were installed, I had no problems with warpage.  I have attached a picture showing what I did to the false keel.

OK thanks, I've not made any cuts in the keel but I plan to use blocks like you did. Are those the blocks in the picture or did you completely fill the spaces? 

 

Also did you paint the interior structure with varnish prior to sealing it behind planking? Just the colour of yours in the photo looks darker than mine. 

[Ryland Craze]

I did not completely fill in the space between the bulkheads, I planked over what you see in the picture.  I did not varnish any of the wood.  I believe it is the lighting that makes it darker.  Here is another picture where I used more lighting:

Notice that I used a black felt tip marker on the outer edges of the bulkheads.  This let me know that when I faired the bulkheads, as long as I had some black remaining on the edge of the bulkhead, I knew that I had not over faired them.

[Riotvan88]

Recently picked this model up again after being shelved for a couple of years. Progress as of today. 

[Riotvan88]

Made a start on the deck. 3D printed jig for deck pattern

[mtaylor]

Looks good.   I suggest you open a build log to continue with posting progress photss.   This area is just for questions and since the questions have been answered, make a build log to continue.