Upper Decks

[andyg]

Hi guys not sure I've posted this in the right place,apologies if I haven't. I was wondering how boatyards reinforced the roofs on the the big new hire boat with the big sundeck. I've looked at a few and I don't see a whole load of poles inside supporting the roof and it can't be as simple matter of using stronger glass matting when laying up the mould ? Or is it ?? 

[marshman]

Look inside - they probably have bulkheads holding the roof up!

[ExSurveyor]

My boat has a flat full length roof some 26' x 12'.

It has bulkheads dividing the internal space and just one support pole, offset in the salon that has a clever swivel table attached.

It appears very stable and no distortion after 32 years.

 

[andyg]

8 hours ago, psychicsurveyor said:

My boat has a flat full length roof some 26' x 12'.

It has bulkheads dividing the internal space and just one support pole, offset in the salon that has a clever swivel table attached.

It appears very stable and no distortion after 32 years.

 

I actually hired one of these back in their Oulton broads days. Must be a good 25 years ago. My kids were 10 and 5 back then and they played up top quite happily. I remember checking to see how strong the roof was. 

[TheQ]

11 hours ago, psychicsurveyor said:

My boat has a flat full length roof some 26' x 12'.

It has bulkheads dividing the internal space and just one support pole, offset in the salon that has a clever swivel table attached.

It appears very stable and no distortion after 32 years.

 

That 's pretty good considering that, That is not the original design, they were designed to have a small cabin up front and you trundle your own caravan on the back..

 Though the floor must be pretty solid.

[ExSurveyor]

6 minutes ago, TheQ said:

That 's pretty good considering that, That is not the original design, they were designed to have a small cabin up front and you trundle your own caravan on the back..

 Though the floor must be pretty solid.

This model was the complete redesign after the first three didn't let and the subsequent alterations didn't work. The four poster with the basin in the helm was never going to catch on.

I did look at the original model to see if I could alter it to a twin cabin but it just wasn't practical or economic.

 

 

[Oddfellow]

Rigidity in GRP layup is derived from many things and there are formulas for how strong things will be in flex under convex and concave pressure. 

Consideration has to be given to weight also as Polyester resin is not light stuff. 

A roof structure with large areas designed to take the weight of the crew will be made up of laminated fibreglass and core materials. Typically, end-grain balsa wood is used as it is very light, very strong and will allow impregnation by the resin. There are other materials too that are stronger and lighter. 

The outter layers will be probably 8-10oz of GRP, 1/2 inch or 3/4 inch of core and then sandwiched with 6-10oz of grp on the inside. The Balsa adds a huge amount of rigidity but very little weight. 

Internal bulkheads within the vessel bond the roof section with the floor or hull section to create a very strong shape. 

 

[andyg]

1 hour ago, Oddfellow said:

Rigidity in GRP layup is derived from many things and there are formulas for how strong things will be in flex under convex and concave pressure. 

Consideration has to be given to weight also as Polyester resin is not light stuff. 

A roof structure with large areas designed to take the weight of the crew will be made up of laminated fibreglass and core materials. Typically, end-grain balsa wood is used as it is very light, very strong and will allow impregnation by the resin. There are other materials too that are stronger and lighter. 

The outter layers will be probably 8-10oz of GRP, 1/2 inch or 3/4 inch of core and then sandwiched with 6-10oz of grp on the inside. The Balsa adds a huge amount of rigidity but very little weight. 

Internal bulkheads within the vessel bond the roof section with the floor or hull section to create a very strong shape. 

 

Thanks for that great insight 👍

[Oddfellow]

I ought to clarify my statement a bit. ANY load bearing deck and large expanse area will be created in this way. For large heavy loaded areas, you would generally increase the thickness of lamination to better deal with the stresses of the weight. It's also important to realise that building in shapes into such areas rather than have them just flat. The same physics of rigidity of right angles and so on apply throughout. 

So, for instance, a dual rolling sunroof is likely to have recessed in the roof moulding areas for the runners. These, of course, allow the roof line to look good but also provide additional strength.   

[ExSurveyor]

The topliner roof has a slight convex curve, no doubt for strength and rainwater dispersal.

[Oddfellow]

29 minutes ago, psychicsurveyor said:

The topliner roof has a slight convex curve, no doubt for strength and rainwater dispersal.

I don't think there's much strength in a slight curve like this: It's not an arch and there's no real weight up there, so I doubt that compression strength will play much of a part but I am no expert in structural engineering.

It will likely be mostly for shedding water and you'll see subtle curves on virtually every boat roof for this purpose. The topliner was a unique design. I'm not too sure, but I don't think the roof is structurally part of the boat. Strength is derived from that wide lip all the way around the edge and I see from your photo that there's a drain hole in the corner (I bet that get's clogged) rather than scuppers along the ridge.