Curving Steel Rubbing Strake Around Stern

[Lee Crook]

Hi All,

 

I will soon be replacing the rubbing strake around my narrowboat stern (at the waterline) and will also adding another strake between this and the upper strake.

 

The strake is 40x12mm square edge convex bar.

 

What is the best process for curving the strake? It is in 6.1m lengths and already very bendy/flexible. I am hoping with the help of an extra pair of hands or two, it's just going to be a case of tacking and physically curving it to follow the curvature of the stern.

 

If anybody has prior experience of this, your advice would be greatly appreciated. I've searched far and wide for a video of this for weeks but haven't found anything.

 

I did find this image (on this forum) which seems to suggest this is how it was done but am seeking advice/confirmation before I proceed.

 

 

Thanks in advance.

Edited October 31, 2023 by Lee Crook
typo

[BEngo]

Mark the line of either the top or the bottom of the new guard.  Tack the end of the guard iron to the hull  then just bend and tack frequently, top and bottom as you go, keeping the edge on your line.  Beware of a tendency to droop!   Be very careful about the line if you have to join the new strip.  You will probably need a forcing jack (like  the screw end half of a G clamp, knocked up out of big nuts, scrap plate and big studding) tacked to the hull,  for the end, or weld an extra bit on  to the guard iron to provide leverage then grind off after use.

 

When it is all tacked up continuously weld top and bottom.

  

Have a look at harrybsmith's thread about Josephine in the build blogs sub forum.

N

Edited October 31, 2023 by BEngo

[Lee Crook]

Ok, many thanks. I'll get some photos taken and upload them when I do the work.

[David Mack]

I would be minded to start in the middle. Place the guard iron across the back of the boat, with both ends supported and weld it to the middle of the back of the boat. Then pull one side round a bit and tack top and bottom, then do the same the other side, and keep on alternating sides. That way you stand a better chance of getting the whole thing symmetrical, and you have a long length either side to give the leverage to push the curve round the tightest bit.

[ditchcrawler]

6 minutes ago, David Mack said:

I would be minded to start in the middle. Place the guard iron across the back of the boat, with both ends supported and weld it to the middle of the back of the boat. Then pull one side round a bit and tack top and bottom, then do the same the other side, and keep on alternating sides. That way you stand a better chance of getting the whole thing symmetrical, and you have a long length either side to give the leverage to push the curve round the tightest bit.

That was my thoughts as well

 

[dave moore]

Tony Bate who built at Norton Canes used to use a roll of masking tape to position the D section before starting to weld. I think he started at one end with tacks but I can’t be sure.

[BEngo]

The shape of the stern has an effect.

If the guard has to rise as well as bend round the stern then life is not as easy as a horizontal run.  Elliptical sterns call for tighter bending than semi- circular.  

 

The key thing is to know where the iron has to be.  The major  skill lies in knowing where that right place is.  The second skill is being able to put the steel there.  That is helped if you have the kit to push it into place and hold it there whilst it is tacked.  

 

N

[Tracy D'arth]

I always start on one side where the hull is not so sharply curved. Starting in the middle on the most severe part of the curve it is difficult to get it level and straight. The full length adds to the leverage and welding a scrap on when you get near the other end to assist with leverage makes it easier too.

A stirrup welded onto the hull over the bar enables a wedge to be knocked in to hold the bar flat against the hull,  moving it along as you weld.

Easy to knock off and grind back fair afterwards.  

[blackrose]

21 hours ago, ditchcrawler said:

That was my thoughts as well

 

 

Me too, but only after he said it...

[Martin Kedian]

On 31/10/2023 at 17:03, BEngo said:

Mark the line of either the top or the bottom of the new guard.  Tack the end of the guard iron to the hull  then just bend and tack frequently, top and bottom as you go, keeping the edge on your line.  Beware of a tendency to droop!   Be very careful about the line if you have to join the new strip.  You will probably need a forcing jack (like  the screw end half of a G clamp, knocked up out of big nuts, scrap plate and big studding) tacked to the hull,  for the end, or weld an extra bit on  to the guard iron to provide leverage then grind off after use.

 

When it is all tacked up continuously weld top and bottom.

  

Have a look at harrybsmith's thread about Josephine in the build blogs sub forum.

N

Perfect description of how to do it having built over 200 hulls and many meters of rubbing strips 

only one extra tool would make life easier a big pair of Stilsons to twist the strips and close any gaps between the hull and the rubbing strips 

[stagedamager]

i'm a fan of marking out the position the guard needs to be, then tacking some flat bar on to the line for the convex to sit on, depending on the sweep, it may be necessary to tack some horseshoes on to wedge into position, and as others have said, regular tacks helps to reduce the risk of the guard kinking.

 

Kind regards

 

Dan

[Lee Crook]

On 01/11/2023 at 12:35, Tracy D'arth said:

I always start on one side where the hull is not so sharply curved. Starting in the middle on the most severe part of the curve it is difficult to get it level and straight. The full length adds to the leverage and welding a scrap on when you get near the other end to assist with leverage makes it easier too.

A stirrup welded onto the hull over the bar enables a wedge to be knocked in to hold the bar flat against the hull,  moving it along as you weld.

Easy to knock off and grind back fair afterwards.  

 

Thanks for the top tip Tracy!

 

Not started on the stern yet but I'm now extremely confident I'll be able to do a pretty decent job.

 

As suggested I used stirrups and wedges (log splitters) to manipulate the strake to the curve. In many respects I think the stern will be easier than the bow as you are fighting two curves at the bow i.e. horizontal and vertical.

 

I still need to fully weld the underside of the top strake which is original but just thought I'd slap some primer on the clean bits before it's grit blasted in a few weeks.

 

Edited January 25 by Lee Crook

[Tracy D'arth]

14 hours ago, Lee Crook said:

 

Thanks for the top tip Tracy!

 

Not started on the stern yet but I'm now extremely confident I'll be able to do a pretty decent job.

 

As suggested I used stirrups and wedges (log splitters) to manipulate the strake to the curve. In many respects I think the stern will be easier than the bow as you are fighting two curves at the bow i.e. horizontal and vertical.

 

I still need to fully weld the underside of the top strake which is original but just thought I'd slap some primer on the clean bits before it's grit blasted in a few weeks.

 

Very well executed, glad I could help.

There seems to be no wear edge protruding from the base plate?  Unusual. 

[Lee Crook]

7 hours ago, Tracy D'arth said:

Very well executed, glad I could help.

There seems to be no wear edge protruding from the base plate?  Unusual. 

 

Thanks Tracy.

 

I have a new baseplate coming in a few weeks. I've managed to get it as a single sheet 10 metres long.

 

 

The original baseplate is badly pitted in areas and the chine was virtually non-existent, so I welded it up completely and ground it back flush ready for the new plate.

Edited January 26 by Lee Crook

[Tracy D'arth]

47 minutes ago, Lee Crook said:

 

Thanks Tracy.

 

I have a new baseplate coming in a few weeks. I've managed to get it as a single sheet 10 metres long.

 

 

The original baseplate is badly pitted in areas and the chine was virtually non-existent, so I welded it up completely and ground it back flush ready for the new plate.

Ah, good idea. Plug welds down the middle to prevent it sagging?

[Lee Crook]

Just now, Tracy D'arth said:

Ah, good idea. Plug welds down the middle to prevent it sagging?

 

Yes, already drilled - mag drill 22mm diameter holes.

[Tracy D'arth]

13 minutes ago, Lee Crook said:

 

Yes, already drilled - mag drill 22mm diameter holes.

👌