Dark colours on GRP boats

[Trident]

For purely cosmetic reasons I am planning to paint a black stripe on the white hull off my 1980's Prout - it will be around a foot wide and go up from the black rubbing strake.

The boat will be used in the Med and tropics so get lots of sun. This of course suggest that the black bit will get hotter and thus may warp the glass as it heats more than the white and when discussing this with friends they agree... BUT

I keep seeing lots of boats with similar stripes in black or dark blue so perhaps its not a problem?

Does anyone have experience of this or the maths to work out if its a real issue or not?

thanks

 

[KellysEye]

>The boat will be used in the Med and tropics so get lots of sun. This of course suggest that the black bit will get hotter and thus may warp the glass as it heats more than the white and when discussing this with friends they agree... BUT

I've seen dark blue boats in the Med and Caribbean and never seen them warp, their hulls are as normal but hotter inside. I can't see why a small black stripe should affect the hull.

 

[Trident]

Its more about the difference between the white and black - a completely dark hull would be uniform in expansion

 

[macd]

I've never heard of any issues with such differential expansion, Trident, and certainly not of warping. That's not to say they don't exist, but plenty of boats have contrasting stripes. I do know (from a former Oz navy fitter), that aligning prop shafts in the tropics on metal boats was an interesting task, since the entire boat was inclined to bend, depending on which side the sun was on.

 

[lw395]

I have seen dark paint bubble in the sunlight.
Possible more of a problem on thin sandwich construction, the paint can get very hot, potentially enough to boil moisture out of the gel coat.

 

[Yngmar]

Our J&J Bavaria has a blue stripe (not even that dark) on the topsides and one on the coachroof, the standard look for more than a decade. There's ten-thousands of these around and none report any issues with deformation in the sun. This is a fictional problem.

The real problem (and often reported) is that the darker gelcoat is however absorbing UV like crazy and while a polish+wax job on the white bits lasts a year, the blue stuff is fading rapidly and needs one every two months, or like most people, you just give up and leave it faded until the rest gets polished. Repairs to it require pigment matching of the gelcoat filler and are much harder to get to blend in than on the white gelcoat.

 

[geem]

We have a dark blue stripe just below deck level. The rest of the hull is white. The blue part of the hull gets incredibly hot. This radiates heat into the boat even though the hull is lined. It corresponds with some lockers in our galley they get very warm because of it. The blue paint is cracked in places due to the heat I suspect. Hard to keep it looking good

 

[LittleSister]

For purely cosmetic reasons I am planning to paint a black stripe on the white hull

Purely cosmetic? Surely it'd be good for at least an extra knot?

 

[coopec]

I hope your yacht is not Airex cored?
"One other disadvantage is that foam core materials can deform at elevated temperatures, and this has become more of an issue as epoxy resin based laminates become more common."
http://blog.dankim.com/2010/01/15/grp-materials/

"Oct 2, 2007 - Has anyone heard of a delamination problem with Airex-cored hulls that are dark colors (black and navy). Apparently the heat generated can cause this. ... The foams and the epoxy resins tend to soften with elevated temperatures... which is one reason I prefer decks cored with end-grain balsa."(Sail net)

 

[Momac]

I would be concerned about the darks paint fading and looking horrible.
Could the stripe be done using vinyl - which may then be more easily removed when it fades or becomes damaged?

 

[savageseadog]

Vinyl is a better option than painting

 

[Malish]

But with a vinyl stripe might the concern be slippage and a nautical wavy effect to the line..

 

[Trident]

I think vinyl is out as I want to run it from the black rubbing strake upwards on a Prout Quasar and this means going around 4 port lights (oval) on each side which to do neatly is beyond my skills I think.

 

[pvb]

For purely cosmetic reasons I am planning to paint a black stripe on the white hull off my 1980's Prout - it will be around a foot wide and go up from the black rubbing strake.

I've just looked at a few pics of Quasars, and many seem to have stripes which look quite attractive so I can understand your reasoning. However, I think black would look very stark and wonder whether you might be better going for a deep blue colour (think HR stripes) like this one...

 

[Trident]

Yes, she currently has the blue stripe as in the picture but the boat is called Penguin so there is a black and white theme to be had on her refit

 

[coopec]

Trident here is an opinion that could be helpful.

"Two possible problems ......

My experiences1. A dark hull is a HOT hull ... and the hull sides don't have to be directly in the sun. 2. Unless the boat already has an extra thick 'matting layer' of fiberglass between the gelcoat and the structural roving you may experience the growth of the 'bumps' .... surface blemishes that are 'raised' due to the constant thermal cycling stress. Most boats built with dark topsides usually have extra thickness of matting layer applied to compensate for the probability of later-on getting the 'bumps'. White or light hulls usually dont have the extra thickness matting layer. Polyester takes forever to totally cure, long term thermal cycling will accelerate the final 'cure' process and if the matting layer is thinner as would be laid up for a 'white' / light hull you will eventually get whats known as 'print-through' (subsequent curing and permanent surface deformation) of the structural (roving, etc.) layers showing through at the surface. The deformation thats gained isnt much but just a few 'wavelengths' of deformation will m...........

https://forums.sailboatowners.com/index.php?threads/darker-hull-colors.95703/

 

[William_H]

My little boat has a dark blue strip about 16cms wide down each side. (view my profile for piccy) It has been in the oz sun for near 40 years and I have never thought of it as being a hot spot and certainly no damage to the solid polyester GRP. olewill

 

[coopec]

hot spot and certainly no damage to the solid polyester GRP. olewill

Yes, I wouldn't expect any damage to solid polyester but a cored construction....?. I think the consensus from guys in my previous post is that they are against dark colors.

 

[Trident]

Mine is a Prout Quasar with solid polyester hulls so I think from what's been said here it should be ok. I guess I'll just have to try it and see... Thanks for the info from everyone