PDA

View Full Version : stress cracks / gunwale flex



hardcrab
08-26-2006, 01:55 PM
I have an area approx. 8" X 40" just forward of the Donzi decals on my '66 - 18' 2+3 with substantial stress cracks ( most likely pier rash ).
While the deck is off, and I'll be laying up mat in this repair area , I was thinking about reinforceing the gunwales from the seating area and back with a few layers of mat to help prevent the possibility of fracture when playing in heavy seas.
I'm curious if anyone else is doing this , and does it adversely affect the natural hull flex.
I would guess it could only be an improvement ( less the added weight )

:confused:

gcarter
08-26-2006, 03:07 PM
How about some pictures inside and outside of that area?

hardcrab
08-26-2006, 03:31 PM
there is no indication of a problem on the inside;
the cracks are thru the gel coat.

my plan is to lay up mat + cloth inside, then grind out the stressed areas and fill

P.S. sorry I haven't figured out how to post pics

gcarter
08-26-2006, 06:03 PM
Take a look at "A" & "B" below. These are typical stiffeners used for problems like yours. Lay up a couple of these vertically in the area your speeking of. These will stiffen the hull side much more and save quite a bit of weight.
Good luck.

hardcrab
08-26-2006, 07:01 PM
George,

Would you consider using several runs as a precaution to future problems?
These would act like trusses when aligned with the stringer gussets. I like the idea, I just haven't seen it done.
Would they stop short of the chine ?

rustnrot
08-26-2006, 07:39 PM
George, that looks like a book I need to get. What is the title?

gcarter
08-26-2006, 07:44 PM
George,
Would you consider using several runs as a precaution to future problems?
These would act like trusses when aligned with the stringer gussets. I like the idea, I just haven't seen it done.
Would they stop short of the chine ?
I'd run them right to the bottom. Also you can slice the cardboard tube to make it fit the shape of the hull better.
If you feel like it's weak, I'd run several.

gcarter
08-26-2006, 07:50 PM
George, that looks like a book I need to get. What is the title?
Fiberglass boat building for amateurs by Ken Hankenson N.A.
Published by Glen-L in 1982,
Sorry, no ISBN #, but Library of Congress # 82-80253

hardcrab
08-27-2006, 09:08 AM
to take it a step further,
would this method be used as a precaution on restoration projects as insurance, and not just repair work ?

ultimately, I'm not overly concerned with my repair area, I have noticed discussion in other posts where gunwale fractures have happened in rough seas, bad landings, ect.
does the 40 yr old fiberglass need a little help ?

gcarter
08-27-2006, 09:57 AM
It could be just as important as a lot of folks here adding multiple gussets into the stringers/bottom.
The 'glass flexes a lot more than gel does, that's why you get cracks in high stress areas. Since you know there's a problem from the gel cracks, just stiffen it up in that area. Probably one every two feet is more than sufficient.
I doubt if you have weakened 'glass there, it just might have been a little light in the initial lay up.

hardcrab
08-27-2006, 10:20 AM
thanks for the input George,

I guess what I'm hearing is that putting three of these stiffeners at 2' intervals on both sides would be time well spent / no harm done.

:smash:

hardcrab
08-27-2006, 12:09 PM
thanks Root -

yeah, it makes good sense, no use in reinventing the wheel. :superman:

gcarter
08-27-2006, 01:04 PM
This is one of the things that make this forum so great. I completely disagree w/Jamie on the hull deck connection...and that's OK.
Since I put my boat back together, I've already taken one side of the deck loose bow to stern to adjust the cockpit floor support on the stbd side. I couldn't have done that with a glassed in joint, or a semi permanent adhesive. Instead, I through bolted the joint w/200 machine screws. I'd say it's a pretty strong joint.
Going back to Jamie's explanation above, he is correct in everything he said.
The hull side at the chine is probably the strongest stiffiner in the boat. Then depending on the attachment method, the hull/deck joint can be pretty good.
So the "oil canning" can take place in the entervening area.
Are the stress cracks horizontal? If they are, then the vertical stiffeners will help in that the size of the "oil can" is greatly reduced.

hardcrab
08-27-2006, 01:39 PM
yes, horizontal.
with only slight crazing ( forks, "Y's", )

gcarter
08-27-2006, 06:23 PM
Well said about using a sealer Jamie. But since I have a machine screw every 3.5", all I used was some RTV. It's not at all structural but it does keep the water out. In 70 hours, so far, I haven't had any issues.