Glassfibre construction, help me learn.

[leep]

Hi guys,

Just trying to get a better understanding of glass fibre building.

Juist to put you in the picture I work for a naval architects in Scotland designing 90metre +++ offshore vessels all steel construction and have no idea about smaller boats.

A few weeks ago my girlfriend and I went on a british boating holiday on the Caledonian Canal and onto Loch Ness (Didn't find the monster) in a 30foot inland waterway cabin cruiser and we really enjoyed ourselves.

A few weeks prior to that my neighbour bought a 14foot glass fibre fishing boat and I couldn't help but notice that the exterior finishes were very different.

Now, I understand that there would be a little more in terms of stiffening in the 30 footer when compared to the 14 footer but the 30 footer was not like a glass fibre finish. Clearly when I opened the engine room hatch you could see the glass fibre clearly.

What I'm saying is I'm aware of gel coats. But even this did not seem like a gel coat finish on the 30 footer. So my question is:-

Is there some sort of filler that they put on some glass fibre constructions that will later be sanded back to help fair the hull cause that was what this was like.

Also,

What sort of thickness of glass fibre can you expect to find in a 30footer @ the bow, sides, stern and keel areas? I'm just curious as it's a material I know nothing about.

Thanks in advance,

Lee.

[apex1]

Originally Posted by leep

Hi guys,

Is there some sort of filler that they put on some glass fibre constructions that will later be sanded back to help fair the hull cause that was what this was like.


Lee.

Yes, you´re right on that.
"Narrow boats" do not stand the test of time in a harsh environment, and they must not. So, building is easier to hammer them together and fair the shape as required.
A seagoing (or coastal) vessel is another issue.

Figures for a layup are not serious without many more information given. But if you need to have a clue what is the average scantling for "narrow boats" have a look at "selway fisher".

Kindest regards
Richard

[Rick Willoughby]

Originally Posted by leep

....
Also,

What sort of thickness of glass fibre can you expect to find in a 30footer @ the bow, sides, stern and keel areas? I'm just curious as it's a material I know nothing about.

Thanks in advance,

Lee.

Lee
The more modern building technique for one-off boats use a reinforcing material like glass or carbon fibre epoxied in sandwich mode to lightweight core such as Corecell or end grain balsa.

The formed panels are very stiff in their own right and do not need much internal support. Just a couple of bulkheads rather than full framing.

One of the forum regulars is making a comprehensive report on his current build here:
My little piece of peace
This one uses glass on balsa. He notes the layup on the pre-cut panels somewhere in the thread.

There is another blog here that gives very good detail on the total build including home made panel construction:
http://www.adventuresofgreg.com/HPB/HPBmain.html
This one is much lighter being carbon over corecell. It is an 8m (28ft) boat that should have a total hull weight of 52kg excluding any fittings.

You can build even lighter using carbon over honeycomb as used in aircraft bulkheads and floors.

The amount of glass used in the skin is more often constrained by local impact/wear resistance than the strength required to take the gross loads on the hull - even in slamming conditions. Rubbing against a dock or a mooring buoy can inflict more damage than slamming into waves at 40kts.

Obviously the gross strength has to take into account the type of boat and intended use. A planing hull will have higher hull pressure than a displacement hull for example.

Hulls made with this flat panel method will be faired with some light weight compound that is usually easy to sand. There are specific fairing compounds or many mix their own using resin and microbubbles of glass.

Rick W