Fiberglass or metal top for Narrowboat?

[Noviceboata]

Hi Guys,

Just wondering what is better regarding the material for the cabin of the narrowboat?  Is a metal cabin more preferable or fiberglass? which boat should cost more?

[LadyG]

4 minutes ago, Noviceboata said:

Hi Guys,

Just wondering what is better regarding the material for the cabin of the narrowboat?  Is a metal cabin more preferable or fiberglass? which boat should cost more?

If you want to buy a boat you can post a link on here to get a strom of critical opinions. If you want to buy a narrowboat, all steel is normal.

 

 

Edited October 25, 2022 by LadyG

[Tracy D'arth]

GRP tops went out of favour long ago. Maintaining a good seal with the steel hull is difficult due to vibration and the differing expansion coefficients.

 

Steel every time.

[Noviceboata]

1 hour ago, Tracy D'arth said:

 Maintaining a good seal with the steel hull is difficult due to vibration and the differing expansion coefficients.

 

Steel every time.

If it's difficult why not the GRP top?

[LadyG]

1 minute ago, Noviceboata said:

If it's difficult why not the GRP top?

As explained the preferred construction is steel hull steel cabin.

[Noviceboata]

Ok. So is there a rule how much more a steel cabin should cost compared to a GRP cabin? 10%, 20% more?

[Jen-in-Wellies]

Impossible to say. The significant thing is that the combination of steel hull and GRP roof went out of fashion well over forty years ago, so you are trying to compare very old boats against each other. All sorts of factors affect value at that age.

[BEngo]

A steel cabin is welded at the joints between the steel sheets and  to the hull so, given a decent welder,  it will be watertight even if badly maintained.  A fibreglass top has joins between the sections and a join to the hull.  These joins  depend on sealants to keep them watertight and sealants do not last forever  especially since the fibreglass expands differently to the steel, canal boats get bashed about and many canal boat engines vibrate the boat.

 

As to cost differential,  it depends on the rest of the boat really.  Be aware though that GRP tops are now, generally, over 40 years old and mostly  found on "project"  boats.

 

N

[Tony Brooks]

26 minutes ago, Noviceboata said:

If it's difficult why not the GRP top?

 

A GRP top normally requires the handrail fixings to go right through the top and thus provide multiple potential leak points.

 

As Tracy explained, keeping the GRP to steel hull seal is difficult, even in the medium term. Steel expands more than GRP, so the joint is constantly under strain. Back it the day a good steel hull designed to accept a GRP top had a substantial up-stand all the way round which the top fitted over so even if the joint seal failed water would leak out under the hull rather than into the accommodation. Lesser hull had much smaller up-stands. Unfortunately by now the up-stands are very likely to be rusted away or perforated rendering them useless leak wise.

 

There is only one thing worse than a GRP top on a steel hull and that is a wooden top on a steel hull.

 

 

[Ronaldo47]

In the late 1970's we hired a GRP-roofed boat (one of Harborough Marine's models I think) that had just had its Elsan loos replaced by pump-outs.  A section of the roof had been removed to facilitate this. Evidently the re-sealing when the roof section had been replaced was defective as water dripped over one of the bunks when it rained. The roll of gaffer tape I always carry in my tool kit came in very useful. 

Edited October 25, 2022 by Ronaldo47
typo

[Noviceboata]

"The roll of gaffer tape I always carry in my tool kit came in very useful )"

 

Thanks for that, so it seems like the general consensus here is that GRP leaks more than metal

 

[Alan de Enfield]

2 minutes ago, Noviceboata said:

"The roll of gaffer tape I always carry in my tool kit came in very useful )"

 

Thanks for that, so it seems like the general consensus here is that GRP leaks more than metal

 

 

Only when it is used in conjunction with other materials (eg Concrete, Wood or Steel). but a 100% GRP boat will leak less and not suffer from the corrosion that steel suffers from.

[blackrose]

I think developments in modern sealants mean that if a GRP top was put onto a steel hull these days it might stand a chance of being leak free for many years. Back in the 1970s the available sealants were crap.

[Tony Brooks]

9 minutes ago, blackrose said:

I think developments in modern sealants mean that if a GRP top was put onto a steel hull these days it might stand a chance of being leak free for many years. Back in the 1970s the available sealants were crap.

 

True, but to do the job properly the whole top will need lifting clear of the hull, the exposed metal work repaired, de-rusted and protected before applying sealat and dropping the top back on. Not a DIY job I think.

[David Mack]

1 hour ago, Tony Brooks said:

 

True, but to do the job properly the whole top will need lifting clear of the hull, the exposed metal work repaired, de-rusted and protected before applying sealat and dropping the top back on. Not a DIY job I think.

I seem to recall posts on here a while ago of someone who had done just that. But only practical if you are doing a complete strip out and refit anyway.

[Tracy D'arth]

1 hour ago, David Mack said:

I seem to recall posts on here a while ago of someone who had done just that. But only practical if you are doing a complete strip out and refit anyway.

Better to weld a steel top over the original and not have to refit it inside. Seen a few done this way.

[Ronaldo47]

In all fairness, we had regularly hired other Harborough Marine-built boats from Black Prince and Anglo-Welsh in the 1970's, and had had no problems with leaky roofs, despite always having had our fair share of rain. We were the first hirers of the leaky roof boat after its refit. The sealant at the joints was still slightly tacky.

Edited October 25, 2022 by Ronaldo47
typos

[blackrose]

4 hours ago, Tony Brooks said:

 

True, but to do the job properly the whole top will need lifting clear of the hull, the exposed metal work repaired, de-rusted and protected before applying sealat and dropping the top back on. Not a DIY job I think.

 

I wasn't talking about repairing an old boat, I said "if a GRP top was put onto a steel hull these days."

 

There's no reason for anyone to build a boat like that these days of course, it was just a scenario to illustrate that if they were still building boats like that these days they wouldn't have the same issues.

 

58 minutes ago, Tracy D'arth said:

Better to weld a steel top over the original and not have to refit it inside. Seen a few done this way.

 

I'd go with sheet aluminium myself. I've seen a couple done like that. No need for paint and doesn't affect the stability as much as steel.

Edited October 25, 2022 by blackrose

[magpie patrick]

13 hours ago, Noviceboata said:

"The roll of gaffer tape I always carry in my tool kit came in very useful )"

 

Thanks for that, so it seems like the general consensus here is that GRP leaks more than metal

 

GRP cabin on a steel Hull certainly does. I've had three boats, one all steel narrow boat, one all-GRP cruiser and one steel hull narrow boat with a GRP cabin. I would never have the last one again.

 

The GRP cruiser is sound but not really suitable for living on - too small and no insulation. There are bigger and better insulated cruisers.

 

Whatever you go for, avoid sliding roofs too - they also leak. 

 

 

[Jen-in-Wellies]

1 hour ago, magpie patrick said:

Whatever you go for, avoid sliding roofs too - they also leak. 

This sort of thing.

[Tony Brooks]

That sort of thing is often horribly draughty, especially in winter.