Darker Hull Colors

[sailaway78]

It's about time to pull the boat and do a bottom job. Am seriously considering painting the hull while it's out. I really like the looks of the dark hulls, particularly the very dark blues and black. Does anyone have any first hand experience with how much this heats up the interior, when you live in the warmer climates. Opinions would be welcome too.

 

[RichH]

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 make such hulls look 'very bumpy'. If you plan on painting, etc. your hull 'dark', be sure to contact owners of your specific model and find out what actually happened after long term /years soak in the sun. If you cant find enough valid testimonials, simply walk the boatyards and look at all those old hulls that were painted 'dark' .... as almost always you will see the surface deformation that develops over a few years due to the thermal stress and subsequent curing. **** If the boat has a cored hull ..... you can severely weaken the bond of the substrates (increases delamination potential) if you over-heat the hull by painting it dark. A dark hulled boat is stunningly beautiful IMHO as the 'contrast' to the light deckhouse, etc. usually winds up being a real 'eye-popper' But for myself I had my one and only DARK hulled boat. Unless I relocate to upper New England or Canada I wont ever have a dark hulled boat again ..... they're too damn hot and usually grow 'surface bumps'.

 

[Dan H]

Rich H, I agree with everything you said,

My dark blue painted hull had print through 100%. I do have a question as to why you think painting a cored hull will have the bond seriously weakened if the hull was painted a dark color and overheated? How much heat are we talking about? I know a dark color out in the sun gets very hot. I don't mean to argue at all, but it seems most decks are cored and some have a dark colored non-skid. I would think that with the sun being more overhead, the deck could probably see as much heat as the topsides, but they don't all seem to de-laminate. I am just curious about your statement, I'm not arguing with you.

 

[Don S/V ILLusion]

fiberglass cures very very slowly

DanFiberglass such as the types used in hull construction never fully cure. Add the heat absorbed by a dark topsides color and the heat created by absorbing the UV radiation reflected off the water and it cures at different rates depending upon thickness and core material compared with a white hull which will cure more slowly. The variation in rates can often deform the glass. When you add the additional problems of dark colors showing any minor anomaly in the glass, the normal degradation from UV on colored materials, be them paint or colored gels, and the variabilities in application, colored topsides can show more problems than similar condition white ones.Having said that, print-through is a function of the glass schedule, not the paint application or gelcoat flaw.I'll take Rich's word for it that a dark colored topsides is hot but I have never noticed any difference here in NE although that characteristic could be considered a positive in winter...

 

[Ross]

Dan wrote, "Fiberglass such as the types used in hull construction never fully c

That is absurd! On what do you base that statement? What constitutes a full cure?

 

[r.w.landau]

Polyester resin is the biggest that it will ever be when it is applied.

From there it shrinks. So does concrete, paint, and most other applied items.The roving shows through or reads through because the gelcoat and the first matt layer shrink and then the first woven roving layer shows through. I think you will find this on even white/ offwhite boats. Many production lines this was a continuous process and the resin never cured until it was all layed up. Curing is a function of the catalyst. It is not a structural issue, it is all appearance r.w.landau Nice N Easy, I know this has gone off track....Hope you get your first hand answer soon...

 

[RichH]

Dan ---

Just personal experience and (very small sampling) observations ....I have a large ILYA scow that is super thin skinned and with an airex deck core and balsa hull core ('everything' is cored to keep the boat super-light). Everything was fine until I painted a huge RED 3ft. wide stripe down the middle of the foredeck .... took one season of hot sun and EVERYTHING under the red stripe totally delaminated the skin from the airex core. I added 5-6" wide shear stripes on the hull (balsa core) .... yup, delaminated under the shear stripes too. Dont know how true this is but the Old Niagara 35 (cored hull) with a dark blue hull is subject such delamination due to the heat, not the light colored hulls .... or so a friend of mine who is a surveyor states. I think also there were some hunters with cored rudders that when hauled if painted dark would eventually delaminate ... the 'factory' recommendation was to paint these rudders light/white ... this from a another surveyor friend who owned a H35. Dont know if this small 'sample' can be extrapolated to 'widespread', but Im suspicious of the dark colors over cored laminates .... and I did have to re-skin my scow. I 'think' I remember Don Casey also explains 'print through' as a function of excessive heat further curing the gel and matting in one of his books .... might be "Surveying or Inspection the Ageing Sailboat". I know Casey also mentioned it one of his 'ancient' articles in the dim past .... dont exactly remember which.

 

[Dan]

I saw it with my own eyes Ross,

I know it sounds crazy Ross. Someone painted my hull dark blue. This is a 1977 C25 Catalina. The paint job was flaking off in one area so I sanded the entire boat back to the original gelcoat. While I was sanding I could see the print through the instant the sander touched the paint. If any sanding at all had been done to the primer, the print through would have been gone. So the only thing I could come up with was that the resin continued to cure, either before or after it was painted, I don't know. The paint job was really nice in some areas. The primer even showed print through. I wouldn't have believed it either Ross if I hadn't seen it myself... for hours and hours of sanding.Laying in bed thinking about this all night, as far as delamination of cored hulls, it must have to do with the external skin expanding and shearing off the core relative to the temperature of the core and the inner skin. I can see where a thin skin could do this faster than a thicker one, but the problem still exists. Expanded PVC cores have lots of little air bubbles, essentially good insulation, so heat transfer through the laminate would be minimal, exasperating the situation. The inner skin temp will never equal the outer skin in sunlight, so the shear force will always be there, except at night. I have some pieces of FRP lying around, I’ll have to run some tests and see how hot the surfaces get painted dark colors. I’m curious because I’m ready to re-do my topsides in a dark color. Like Burgundy, with a white cove and boottop. Maybe the dark blue helped me out by getting the print though behind me. Thanks for the info guys,Dan

 

[Tim Donley]

Post cure of the resin

Contrary to uneducated opinion, the polyester and vinylester resins will post cure with the elevated temperatures.A dark color will elevate the resin beyond HDT (heat distortion tempurature) usually around 160 degrees f. depending on resin formulation. When the suface cools the resin rich area in the weave of the reinforcement or mat will shrink a very small amount. With repitition of this, the print thru will become evident. However,it does not need to be a dark color to achieve this process.Cored hulls present their own set of problems depending on materials and process used in manufacturing, possibly resulting in outgasing of core or some other component utilized in the building process creating delam bubbles.Resin achieves the bulk of its cure within hours of catalyzation. From that point on the resin will continue to cure the last few percent over the next millium, it's the nature of the beast.I hope this brings some light to the subject.Tim Donley

 

[sailaway78]

This thread has made up my mind

Not being one who likes to tempt fate, this thread has made up my mind. The boat will remain white. After pulling it, I'll do a little work on the hull, and it it doesn't come out as nice as I want it, will paint, but it will remain white. If the dark colors get hot enough to maybe screw up the glass, I certainly don't want that much heat in the boat. Especially since I plan on some sailing S. of 20N in the future. An interesting thread.

 

[Joseph Shirley]

Another oppinion

I had my boat in Mexico for 6 years and used a number of different colored bottoms while there, and none had any appreciable affect on the inside temp as the water was always much cooler than the air. I had one extremely bad experience with black however; and that was caused by the morning sun beating on the side of the rudder when the boat was out of the water. The rudder got so hot that the glass on one side expanded and completely delaminated with what were huge blisters. I had to strip one side of the rudder and re-glass it. I never used black again, and when the blue was out of the water I kept the rudder shaded.As far as topside hull colors is concerned the color does make a difference, and most of the smart sailors in the tropics use white hulls and if possible light colored decks. Even a teak deck gets to hot you can't walk on it barefoot.Joe

 

[Brian D]

Here is an interesting question...

Is there any way to "dye" the gelcoat? Not paint, but dye.

 

[Rick D]

Hull Split

I painted a wood hulled T-Bird Endeavor Blue which had two layers of glass over the wood. Within two months, the glass had split on the sun side at the bulkhead! All the way from the cap rail to the waterline. I ground it out and reglassed it but kept the boat blue. SoCal is pretty mild, so I had no further problems, but it was obvious the paint had an effect (the boat was white for ten years before in the same slip, oriented the same way). RD

 

[Dan H]

You mean aside from the rust stains?

I don't think so. If you want to change the color of your hull, why don't you think about re-gelcoating it the exact color you want? It's not that hard to do. Like everything, it's all in the prep.

 

[Doug Burton]

Darn!

I've always loved the look of a dark hull but had no idea it can cause so many problems. Ya learn sumptin every day!

 

[Pete]

there is an expression

that goes something like you will have a dark hull twice in your boating life the first time and the last time BOTH at the same time. !! How about it dark hull owners would you have another one or go back to white ??? I do have to admit the dark colors look GOOD ! !

 

[Don S/V ILLusion]

Pete

Don't know about anyone else but having had both white and a dark colored hull, it really makes no difference to me. The only drawback I ever noticed with this boat is that every nick and scratch makes me remember previous docking errors or dinghy mishaps which are more apparent with a dark hull and would be a lot easier to forget if the hull was white...

 

[sailaway78]

Seems to be a north thing

Seems to be a pattern developing here. Most of the reply's that are positive concerning darker hulls are from farther north, and the negatives seem to come from more to the south.

 

[Ross]

I have used several square yards of Airex core and of Corecell

The few times that I have had problems with the glass failing to bond to the core were those time when I was too stingy with the resin. The color of the composite structure had nothing to do with it. When I starved the core the glass didn't bond well and after curing I had voids. When I used enough resin I had no problems. I did have to apply glass to both sides of the core to prevent warping. But in my opinion the delamination is a workmanship problem not a color problem. With 1/2 inch Corecell selling for about 4 dollars per square foot someone with deeper pockets than mine will have to settle this with good repeatable testing.

 

[Chuck Creel]

dark hulls

little late jumping on the band wagon but had to share a point made by a friend of mine.and i quote,, " when you need help from the USCG tell them your the blue boat in the blue water" . should be pretty easy to spot us eh?