Pacemaker Hull split

[leokow]

I have a 1972 28ft pacemaler powered by chrysler 318's. I have been refinishing this boat for the past 9 years. Last year I noticed a crack in the hull about 2 inches up from the bottom on the port side and extending about 24 inches from the bottom of the bow aft. What made me notice it was a black oily substance that seemed to be difused into the bottom paint. Closer inspection revealed a crack and I believed the oily substance to be bilge oil ,water and whatever else that was trapped under the floor in the bow of the boat. After cutting an access hole in the interior deck and cleaning and sanding I saw that the crack did penetrate all the way thru. I drilled a hole about a 1/4 inch at each end of the crack to try to prevent any further lengthening ,then cut out as much material from the inside as I could and re-layered fabric and resin to approx. 1/2 " thickness about 6 inches up each side of the hull .On the out side I did a similar cut out except I couldn't remove all the discolored glass fiber on either side of the crack for fear of opening it up too much and compromising the strength of the boat. I layered the glass and resin , each section about an inch or two larger the the one before it until it was built back up to the original thickness of the rest of the hull. The entire bottom was then given a the proper amount of interprotect sealant and then 3 coats of micron bottom paint. Upon removing the boat from the water to drydock this week I noticed a wet spot near where the old crack was. to my utter dismay I found the crack had returned only now it was about 4 feet long from bow along a line to the stern. Can anyone out there help me to correct this problem once and for all , without junking the the boat ,thank you. I keep having nightmares of traversing the inlet and having the boat split in two !! Thank you ...Leo

[Buckle]

Leokow,

Last time when you repared the cracked laminate, you didnt do anything to elminate the problem from re-occurring again. Thus future laminate failure. Look closely in the insides of the cracked hull area. Are they any stress concentrations. Are the ribs/stringers broken? Look for the source.

Is the engine the original? If not seriously look at how the power of the engine is transferred into the hull. You may need to beef up the engine beds/stringers etc.

But when you repair the laminate next time, grind out the crack totally. Remove the laminate a good 3 or 4 inches from the surrounding area. Micro-cracking may be present which can lead to cracks and laminate failure. Once you have ground out the crack totally, de-grease the area and repair. Feather the edges of the repair both insdie and out. Theres no harm in over repairing the laminating.

How is your boat stored. Does it go aground. Whats on the seabed when your boat goes around? This could be the source?

Read the book, care and repair of polymer composites by armstrong. Its great for GRP repairs.

[gonzo]

The repair technique made the problem worse. The crack is the result of stress somewhere. It may be that a structural member-stringer, frame, etc.- is rotted or broken. A patch over a crack creates a hard spot that produces more stress at the edges. The proper method is to grind off the laminate and make a patch that results in the same thickness as the original.

[leokow]

Thank you for the reply Gonzo...but what you suggest is exactly what I did. I went back to my original post to see if I was unclear about what I had previously tried top do but I think I explained it fairly clearly. However I do agree with you that the crack is from stress .I have only owned the boat for the past 10 years and it's 32 years old. I have never grounded it as long as I have been running it ..the engines are the same only rebuilt. It did sit dry on land for a period of years before I bought it according to the previous owner. I was thinking along the lines of water laying trapped in the bow and freezing on the inside of the boat exerting ice pressure from inside out. There are no stringers or other supports that far up into the bow that I can see and the area I'm speaking of seems to be almost solid from one side to the other. I guess a picture would explain it much better .when I get back to the boat I will clean off the area as best I can and take a photo and attach it to the next post . I think It'll make things a lot clearer. Thank you again

[gonzo]

Ice will do it. However, it may also be inherent in the design or a flaw in the original laminate.

[B. Hamm]

Well first, what materials did you use for this patch?

Bill H.