Bow & Stern blocks

[DaveBaxt]

After looking at several different build logs I have come to the conclusion that a few people including my self, have experienced  problems keeping a nice curve with the first layer of planks, not at the bow where you would normally fit blocks, but just aft of the bow and  between two bulk heads and under the water line. This seems to me to be between two bulkheads with the greatest change in shape ans usually before the second layer of planks is fitted this flat area is then built up with filler to get the correct shape. My question is ,does anyone use shaped blocks in this area the same as in the bow and stern to help maintain this nice curve?

              Also I have been using balsa wood for the blocks but find  pins do not hold too well and wonder if there is a better wood which can be used, perhaps mdf can be used for this? Hope I am making sense and people understand where I mean on the hull. Best regards Dave

[Gregory]

I would use bass.  I personally  wouldn't go for a solid fill. 

 

I would add what amounts to several additional bulkheads, using maybe 3/16 -1/4  sheet.

 

Use the plans/existing bulkheads to interpolate the shape..

Edited June 9, 2021 by Gregory

[mtaylor]

I'm using basswood for by current build and plywood for the bulkheads.  There are a few issues to be aware of though with the first one being gluing.... make sure it's well clued.  The other is do to the hardness difference.   Basswood sands a lot easier than the ply and it's easy to take off too much which means either fill it in or rip it out and re-do.  

 

[Roger Pellett]

Here in the US lumberyards and Home Improvement stores sell dimensioned construction lumber described as SPF which stands for Spruce, Pine, Fir.  The store where I shop also has 5 quarter pine (1-1/2 in) that believe it or not comes from New Zeeland.  There are several varieties of pine but the stuff sold by these stores as planed boards works fine for carving hulls so would work for the blocks that you need.  It is easy to carve but harder than basswood.

 

Unfortunately I don’t know what is available in Great Britain.

 

Roger

[DaveBaxt]

8 hours ago, Gregory said:

I would use bass.  I personally  wouldn't go for a solid fill. 

 

I would add what amounts to several additional bulkheads, using maybe 3/16 -1/4  sheet.

 

Use the plans/existing bulkheads to interpolate the shape..

 That sounds like a good way to do this but could be a little tricky as I have already fitted sections for strengthening but definately worth considering for my next build. I could also consider building a model with frames. Thanks once again for your help . Dave

[DaveBaxt]

Thanks guys for your input, so it looks like bass wood is the way to go however this SPF sounds interesting too so may search about here in the uk. Best regards Dave

[Mark P]

Good Morning Dave;

 

A general tip which applies to wood purchased from DIY stores, builders' merchants & non-specialist timber merchants, is to let it season for as long as possible. Most wood from these sources is recently converted from logs, and has a high moisture content. If you intend to do much in the way of filling blocks, buy the wood now and lay it by, ready to use in the future. This will avoid the risk of shrinkage after you have carefully shaped it and covered it with planking. 

 

All the best,

 

Mark P

[DaveBaxt]

1 hour ago, Mark P said:

Good Morning Dave;

 

A general tip which applies to wood purchased from DIY stores, builders' merchants & non-specialist timber merchants, is to let it season for as long as possible. Most wood from these sources is recently converted from logs, and has a high moisture content. If you intend to do much in the way of filling blocks, buy the wood now and lay it by, ready to use in the future. This will avoid the risk of shrinkage after you have carefully shaped it and covered it with planking. 

 

All the best,

 

Mark P

Thanks Mark I hadn,t thought of that but good idea. I have done a quick search and found lots of outlets that sell blocks of basswood for carving etc and thought these would be ideal however I wonder does it make any difference which way the blocks are fitted ie does it matter if the end of the blocks are what will be the surface to glue the planks onto? One well known model shop here in uk sells different thickness basswood ply would and think this wood work well too. Perhaps if purchased from model shop the plywood would be ok to use straight away. Whats your thoughts on this Mark?

Edited June 10, 2021 by DaveBaxt

[Gregory]

7 hours ago, DaveBaxt said:

 That sounds like a good way to do this but could be a little tricky as I have already fitted sections for strengthening

 

When I described extra bulkheads, they don't have to extend to the backbone like the original framing.

 

All you are looking to do is fill out the outer profile to provide a surface for planking. Just add what amounts to shims

to the edges of the existing bulkheads.  Create as many layers as you feel necessary.  It is a lot like adding blocks, but laminated so

you can reduce the amount of shaping needed.

 

 

[Mark P]

Good Afternoon Dave;

 

Plywood is a very dimensionally stable material; at the scale sizes at which you would be likely to use it, movement would be so small as to be not worth worrying about. That said, though, the veneers of which it is made would probably absorb moisture from a very damp atmosphere, and would expand if this happened. Depends to some extent on the number of veneers and the quality of the glue used. The greater the number of veneers the better quality the ply, generally; but also the greater expense. However, if you can obtain off-cuts of decent quality, thick ply from a local joinery shop, these would probably make good filler blocks. Avoid shuttering ply: this warps like a live thing!

 

If using sections of timber of any size, remember it shrinks across the grain; ie a plank 6 feet long x 6" x 1" will reduce across the 6" by up to a quarter of an inch if newly sawn; and across the 1" by a small amount; but the length will remain at 6 feet. The other factor is that the end-grain of softwoods will show a pattern of curved lines, depending upon where exactly it was cut from the log. These curves always try to straighten out. 

 

Fixing into end-grain is generally considered to be the weaker fastening method; and most modellers seem to avoid it. The best advice is to be sure to use wood which has lain around for as long as you can manage to leave it.

 

All the best,

 

Mark 

[DaveBaxt]

4 minutes ago, Gregory said:

 

When I described extra bulkheads, they don't have to extend to the backbone like the original framing.

 

All you are looking to do is fill out the outer profile to provide a surface for planking. Just add what amounts to shims

to the edges of the existing bulkheads.  Create as many layers as you feel necessary.  It is a lot like adding blocks, but laminated so

you can reduce the amount of shaping needed.

 

 

Thank you Gregory and I see what you mean and that would work. Best regards Dave

[DaveBaxt]

2 hours ago, Mark P said:

Good Afternoon Dave;

 

Plywood is a very dimensionally stable material; at the scale sizes at which you would be likely to use it, movement would be so small as to be not worth worrying about. That said, though, the veneers of which it is made would probably absorb moisture from a very damp atmosphere, and would expand if this happened. Depends to some extent on the number of veneers and the quality of the glue used. The greater the number of veneers the better quality the ply, generally; but also the greater expense. However, if you can obtain off-cuts of decent quality, thick ply from a local joinery shop, these would probably make good filler blocks. Avoid shuttering ply: this warps like a live thing!

 

If using sections of timber of any size, remember it shrinks across the grain; ie a plank 6 feet long x 6" x 1" will reduce across the 6" by up to a quarter of an inch if newly sawn; and across the 1" by a small amount; but the length will remain at 6 feet. The other factor is that the end-grain of softwoods will show a pattern of curved lines, depending upon where exactly it was cut from the log. These curves always try to straighten out. 

 

Fixing into end-grain is generally considered to be the weaker fastening method; and most modellers seem to avoid it. The best advice is to be sure to use wood which has lain around for as long as you can manage to leave it.

 

All the best,

 

Mark 

Thank you mark for explaining the shrinkage of wood and fascinated at how it does this. As for plywood I have just spent a lot of time straightening out a plywood keel on my HM Bark Endeavour but eventually I got there with building a jig and fitting extra support pieces see my blog if you have I am therefore a bit reluctant to use ply for this purpose and could it cause problems later down the line or is it ok as it would not be allowed to move if used for blocks.Best regards Dave

 

 

[Mark P]

Good Evening Dave;

 

I would see no problem with using blocks of fairly thick ply between the bulkheads at bow or stern. If you use too many, the model will become quite heavy, but thick ply will give you enough material for creating some compound curves, and avoid the risk of leaving it too thin at the edges.

 

If you use normal timber, especially softwoods, you run the risk that it will shrink unless thoroughly seasoned before use. So if using softwood, keep that in mind, and choose the oldest stock you have. 

 

Re your troubles with the keel, all ply will warp if allowed to/forced to. As you have become aware the hard way, it is best to restrain it in the desired shape, as well as you can. But that is good practice with whatever material one is using. 

 

All the best,

 

Mark P

[DaveBaxt]

8 hours ago, Mark P said:

Good Evening Dave;

 

I would see no problem with using blocks of fairly thick ply between the bulkheads at bow or stern. If you use too many, the model will become quite heavy, but thick ply will give you enough material for creating some compound curves, and avoid the risk of leaving it too thin at the edges.

 

If you use normal timber, especially softwoods, you run the risk that it will shrink unless thoroughly seasoned before use. So if using softwood, keep that in mind, and choose the oldest stock you have. 

 

Re your troubles with the keel, all ply will warp if allowed to/forced to. As you have become aware the hard way, it is best to restrain it in the desired shape, as well as you can. But that is good practice with whatever material one is using. 

 

All the best,

 

Mark P

Thank you mark for all your input and for helping me with what is the bestway forward and in some way undestanding why and how is the best mateials to use. I think understanding which is the best woods to use in a subject in its own right and needs careful study. I am still learnig stuff about this hobby on a daily basis . Best regards Dave