Steel hull and GRP sides and roof

[scb61]

Once again i impinge on the good nature and knowledge of the members here!!

 

My first offer on a NB has been declined and so i move onwards

Another boat has caught my eye and it would seem to be priced lower than i would have expected as it has a grp sides and roof - should this be something to avoid? is it as easy to keep warm? is it harder to maintain?

 

I have attempted to do as much research as i can over the past few years in readiness for the time when i can purchase a narrowboat and the time is coming - a cheaper second hand narrowboat is preferable as I have little practical experience

 

Many thanks if you are able to offer any advice regarding this

Steve

[craftycarper]

If you use the search facility on here I,m pretty sure there was a long debate on the pros and cons of this design recently sorry I can't be more helpful but I have a all plastic boat

[Southern Star]

I believe from previous posts that because steel and grp expand and contract at different rates, boats are prone to leakage where the materials meet.

[bottle]

Yes have search, see you in about three months.

 

Some will say there is not a problem but from what I have gleaned there is always a problem at the joint between the metal and the GRP, they expand at different rates so causing movement between them and the possibility of leaks.

 

If you go for such a boat check it out very thoroughly for water ingress.

[kevinl]

They're not universally popular and the price reflects that, you will get a lot more boat for your money. My neighbour was a 5 year liveaboard on an uninsulated GRP roofed boat and she never had a problem even in some of the recent winters we've had just using a fire with a back boiler and 2 rads. The only issue I have with them is the grp can look a bit manky when it gets old. Would I buy one, yes if the price was right.

K

[b0atman]

Price & condition are minor compared to are you going to love it and look after it no matter what, doing all jobs yourself where possible ?

Biggest concern is water ingress below waterline,

[scb61]

Thank you for the advice - I have now bought a boat and I am very pleased with it although it has been a little neglected and some work is required

I will have to spend a lot more time using the search feature on here, although it is a little vague for me

[Athy]

Thank you for the advice - I have now bought a boat and I am very pleased with it

Well done, that's good news!

[Arthur Brown]

When a boat has a GRP hut on top I'd always be interested in the history of the hull, especially if it seems older than the top. I wonder whether any historic craft made a second life as a canal cruiser

[Peter X]

I'm coming at this from the theoretical angle, as I know a bit about physics and carpentry but my actual experience of narrowboats is all on one all-steel boat, so can I ask what may seem a daft question?

Given that a particular problem of having a wooden or GRP top on a metal hull is that they have different expansion rates due to temperature, and that over the 55 foot length of a typical go-anywhere narrowboat that will mean a lot of movement, why fight it?

People mention the use of mastic, but I doubt if that or any other sealant or adhesive would cope with the force involved; I'd expect it to break apart one particularly hot or cold day.

 

It seems to me the answer, apart from the standard approach of all-steel of course, is to allow for the top to slide along a little where it meets the hull, probably by attaching it with bolts in slots. This doesn't mean there have to be leaks, because the top can overlap outside the hull for water to run off. Sideways across a boat I would expect there to be much less of a problem, because wood, and I think GRP too, has a certain flexibility that way.

 

Personally I think I would consider a wooden top boat if it was cheaper than an equivalent steel one, but only because I'd be willing and able to do a spot of carpentry and the necessary routine maintenance. I'm currently building my own garden shed entirely out of wood and windows people have discarded, and I'm sure that knowledge could be applied to a boat superstructure. Certainly wood does tend to get damp then rot and collapse if it isn't looked after, but a properly built roof with the felt correctly applied will last many years, maybe even longer than the paint on a metal roof.

[John V]

First off I must state I have NO experience with GRP topped steel boats but quite a lot of experience with GRP,Steel and wood boats (and even a nodding acquaintance with ferrocrete.)

 

The fact that there are such things as GRP topped steel boats has always puzzled me,

 

I would have thought that the economics of GRP work would mean that a production "run" would be required in order to pay for the cost of moulds and formers. Surely this is how GRP fabrication works ....economies of scale! If you are going to all the cost of producing moulds why not mould the hull as well?

 

Anyway GRP cabin only, would mean a source of identical hulls were needed, which would suggest they would have to be made to order, in which case why not build the whole thing in steel? (If putting a GRP cabin on a custom built steel hull it would be quite easy to design a hull to cabin joint that would remain watertight)

 

If it is a case of one off or very limited production utilising ex working boats or I cannot see how they made a profit, as each hull would vary slightly (which would be a source of leaks!!)

 

Wooden cabins IMO are perfectly reasonable and providing they are correctly designed and built with correct materials they will last for many, many years and are a perfectly reasonable thing for a decent DIY woodworker to build.

Re-sale would probably hit snags as being "non standard" would scare many people off.

 

ETA....adding a GRP skin to a wooden cabin of course is a totally different thing and can often be found on boats around the coast

Edited September 15, 2014 by John V

[Keeping Up]

In the 1970's Harborough Marine (in Market Harborough) built a great many boats with identical steel hulls (apart from the length) and tops made from GRP sections. There were certainly enough of them to gain the economies of scale that you mention, as they supplied them to the majority of hire fleets as well as the private market. They even sent them out in kit form if you wanted to assemble your own.

 

Here are my experiences of owning one. Summarising, yes she always leaked when it rained but we loved her dearly.

[John V]

Thanks for that information Keeping up, that was interesting.

I am puzzled that there was such a problem with the gunnel joint. That smacks to me of a major design fault, off hand I can think of a couple of techniques that would have fixed the cabin to the hull allowing full flexibility but without allowing water ingress. Some of the other places you describe leaks sound like there were shortcomings in the construction techniques as well.

[Keeping Up]

Thanks for that information Keeping up, that was interesting.

I am puzzled that there was such a problem with the gunnel joint. That smacks to me of a major design fault, off hand I can think of a couple of techniques that would have fixed the cabin to the hull allowing full flexibility but without allowing water ingress. Some of the other places you describe leaks sound like there were shortcomings in the construction techniques as well.

 

Well, she was already 18 years when we got her, and the steel lip at the top of the gunwales was already quite rusty. I didn't fancy removing the top and sorting the rust properly, instead I opted for just trying to keep everything covered in mastic. The construction techniques were certainly not perfect - but she's still being lived on, at 45 years old, and still leaking in the same places according to an email I got just a few months ago from her latest owner.

[John V]

Didn't mean to sound disparaging, sorry if it came out a bit that way.

What I meant was, apart from deterioration of material, GRP tops do not have to leak and if they do, it has to be because of something in the design or construction.

My GRP cruiser is 40 years old and a leak appeared round one of he windows, this proved to be the mastic having deteriorated and re-bedding cured the problem.There is some evidence of a similar historic leak and some evidence of the window having been re-bedded as well (Agreed though, the gunnel joint is GRP to GRP and not GRP to steel) but there are no leaks anywhere else.

[David Mack]

In the 1970's Harborough Marine (in Market Harborough) built a great many boats with identical steel hulls (apart from the length) and tops made from GRP sections.

As did others including Teddesley Boat Centre and Shropshire Union Cruisers.

 

There's an article about a Shroppie grp topped boat in the latest Waterways World.

[ukdiggerboy]

i have a teddesly boat 1974 the top looks as if its leaked since birth lol at the joints of the sections we are at the point of removing it and re settting

water drips on the timber and runs into the buckets now lol

the windows are surprisingly dry

[John V]

Do you have any pictures of the joints themselves?

as far as I can see from that photo it looks as if they are just flanges that bolt together....(with mastic?)

are they solid joints or do they have expansion joints built in?

 

sorry can't help it...just love knowing how things go together!

[Naughty Cal]

I'm coming at this from the theoretical angle, as I know a bit about physics and carpentry but my actual experience of narrowboats is all on one all-steel boat, so can I ask what may seem a daft question?

Given that a particular problem of having a wooden or GRP top on a metal hull is that they have different expansion rates due to temperature, and that over the 55 foot length of a typical go-anywhere narrowboat that will mean a lot of movement, why fight it?

People mention the use of mastic, but I doubt if that or any other sealant or adhesive would cope with the force involved; I'd expect it to break apart one particularly hot or cold day.

 

It seems to me the answer, apart from the standard approach of all-steel of course, is to allow for the top to slide along a little where it meets the hull, probably by attaching it with bolts in slots. This doesn't mean there have to be leaks, because the top can overlap outside the hull for water to run off. Sideways across a boat I would expect there to be much less of a problem, because wood, and I think GRP too, has a certain flexibility that way.

 

Personally I think I would consider a wooden top boat if it was cheaper than an equivalent steel one, but only because I'd be willing and able to do a spot of carpentry and the necessary routine maintenance. I'm currently building my own garden shed entirely out of wood and windows people have discarded, and I'm sure that knowledge could be applied to a boat superstructure. Certainly wood does tend to get damp then rot and collapse if it isn't looked after, but a properly built roof with the felt correctly applied will last many years, maybe even longer than the paint on a metal roof.

Gladly thats not true as the way our boat is constructed relies on a bonding material to hold the inner structural liners of the boat and the outer skin of the hull together!!

[ukdiggerboy]

i am going to cut them open in the next week or so but they look like there two flanges bolted together and then have fibre glass wrapped over the lot ,

 

there is nothing to stop the water, if theres a leak falling straight into the interior so im going to see to that and im thinking of making it a expansion joint at the same time