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  1. #1
    Petty Officer 2nd Class John the landlubber's Avatar
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    Default Hairline cracks! Are they gel-coat or stress cracks???

    I have recently purchase a project hull. it is the double skinned dory type. I have just removed the old antifoul paint so I could get a better overall view of the hull condition, and I have found an area of about 300mm X 900mm where there are lots of hairline cracks going in all directions. Can anyone tell me how I identify the difference between cracks in the gel-coat and stress cracks in the hull. If they do turn out to be the latter do I have to cut this section out and replace it or can I just apply new gel-coat?

  2. #2
    Rear Admiral JasonJ's Avatar
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    Default Re: Hairline cracks! Are they gel-coat or stress cracks???

    Most likely it is crazing or gelcoat cracks. To repair it you would need to grind down to the fiberglass, feathering outward. Then you can apply new gelcoat and be done with it. Odds are the crazing is from a mild impact with something that didn't necessarily do any significant damage other than cracking the gel. Gelcoat loses its flexibility as it ages, and the end result is crazing. I have it in various places on my hull and have not bothered doing anything about it.

  3. #3
    Petty Officer 2nd Class John the landlubber's Avatar
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    Default Re: Hairline cracks! Are they gel-coat or stress cracks???

    Thanks mate, was convinced it was going to be something more sinister. You being a veteran, may be familiar with this hull. I have an RTK rigid raider (5.2m) It is very similar to a 17ft dell quay dory which was for a time the leisure part of RTK marine. This company is based in the U.K and since 1972 have produced landing and assault craft for our military. This hull was built to carry 1 metric ton in weight and with 140hp engine would cruise at over 20 knots loaded. Apparently with 2x 140hp's it could achieve 45-50 knots when travelling light. I will never need this sort of carrying capacity as the most the boat will be carrying will be 4 or 5 persons or 3 persons and some fishing tackle. I intend to put a single 115hp motor on which I reckon will give me a cruising speed of around 23-24 knots, a bit more if pushed. But first I need to find and solve any problems with the hull. It has had many repairs and I know water has gotten into the foam in places in the past. I am hoping to avoid further problems with this by spending some extra time and attention on making the hull completely watertight. I have no experience working with fibreglass, and I haven't yet grasped the basics of which materials I need to use for which job. But I learn quick and am stubborn as a mule, so i'll get there in the end. Will post pic's soon, might be of interest to someone.

  4. #4
    Petty Officer 2nd Class John the landlubber's Avatar
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    Default Re: Hairline cracks! Are they gel-coat or stress cracks???

    In the meantime, coud anyone answer me some basic newbie questions? In some places the hull has what can only be descriped as "pitting". There is not much of this but I would like to know what it is and the best way to deal with it. Can I just rough it up and use some sort of marine grade filler for it? Also, there are a number of deep chips and gouges in the hull where a small amount of matting is showing through. What should I do about them? How long would it take me to remove the gel-coat and replace, it and what sort of costs would be involved? What exactly is meant by the terms "feather outwards" and "grind to a taper"?

  5. #5
    Petty Officer 2nd Class John the landlubber's Avatar
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    Default Re: Hairline cracks! Are they gel-coat or stress cracks???

    P.s, enjoyed your project info JasonJ. Nice boat. Hull looks very similar to mine, except the deck on mine slopes right up to the bow. Reckon i'll be doing the foam, etc with mine but thought since mine is designed to carry so much weight i could make sealed buoyancy cells from twinwall poly drainage pipe instead of stringers. They should give the rigidity I need but also a degree of flexibility and with the advantage of waterproofing most of the foam so I won't have to dig it all out again.Then I could cut the bracing to sit between the ridges in the pipes outer skin, glass it in and foam the gaps under and between the pipes. This would add a little extra weight, especially up front and would allow me to keep the helm right at the back giving more deck space for fishing and give a better ride at speed in our not always user friendly north sea. What do you think?

  6. #6
    Admiral
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    Default Re: Hairline cracks! Are they gel-coat or stress cracks???

    Could you post some pictures?Use Marine Tex for chips, scrapes and gouges.

  7. #7
    Rear Admiral JasonJ's Avatar
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    Default Re: Hairline cracks! Are they gel-coat or stress cracks???

    Yeah, pics would be cool, I am not familiar with your boat. As far as fiberglassing, you may want to invest in some books that can at least give you an idea. One thing I did was go to a shop that repairs and rebuilds boats, and spent some time talking with their repairmen. I learned more in that couple of hours than anywhere else, as they showed me what to do and how to do it, and they gave me a good deal on the fiberglass materials. If you could find a place like that of find someone who can show you face-to-face, that will be very helpful. Interesting idea on the stringers, would be interesting to kick that one around and work all the pros/cons to the concept. Good luck...

  8. #8
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    Default Re: Hairline cracks! Are they gel-coat or stress cracks???

    Must be the one he has, often used as a resque boat and boat for firefighters etc. http://www.boatsandoutboards.co.uk/view/F89216/ http://fishingboats.apolloduck.ie/li....phtml?cid=312 Very similar to your whalers

  9. #9
    Petty Officer 2nd Class John the landlubber's Avatar
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    Default Re: Hairline cracks! Are they gel-coat or stress cracks???

    You are very close with that boat, G dane. Although not quite the same mould, the underside of hull is the same. I have registered with shareaproject and am gonna put some pictures up as soon as I take some, but RTK Marine have a website which shows this boat as well as the 6.3m model. I just typed rigid raider into web browser and came up with pages of info, but never any for sale. Took me ages to get one.

  10. #10
    Petty Officer 2nd Class John the landlubber's Avatar
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    Default Re: Hairline cracks! Are they gel-coat or stress cracks???

    Have a picture on shareaproject now, not mine but same.(well, not condition wise or you'd be asking me the questions, lol)

  11. #11

    Default Re: Hairline cracks! Are they gel-coat or stress cracks???

    I am looking at a 2003 Glastron GX and it has stress cracks under the windshield and a grab bar is it serious?

  12. #12
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    Default Re: Hairline cracks! Are they gel-coat or stress cracks???

    Quote Originally Posted by rpstrickland View Post
    I am looking at a 2003 Glastron GX and it has stress cracks under the windshield and a grab bar is it serious?
    You really should start your own thread, it is considered impolite to high jack someone else's

    Also, pics would really help.
    16' Calglass rebuild underway.

    See my thread here on iBoats for many pics, details, and questions.

  13. #13
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    Default Re: Hairline cracks! Are they gel-coat or stress cracks???

    John, that's a pretty cool looking boat you have there, and you can put twin 140's on it :o wow

    Personally, I'd leave it in the military colours (with the motor to match). heh


    May I ask what something like that sells for there?
    16' Calglass rebuild underway.

    See my thread here on iBoats for many pics, details, and questions.

  14. #14
    Commander scipper77's Avatar
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    Default Re: Hairline cracks! Are they gel-coat or stress cracks???

    This is a 2 year old thread and john hasn't been on sinse jan 1'st 2008.
    Most people are going to do whatever they want. What I find entertaining is how people justify what they do!!

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