Mysterious marks on hull

Geoffreykwright · June 01, 2020, 07:16:05 AM

Hi - I m hoping someone can help me identify some odd marks on my hull. I've got a 2000 Cat 34 Mk II (hull 1494). In the winter she sits in a 6-pad cradle. I bought her in 2013. Yesterday I was applying the VC-17 for a delayed season launch (we're all delayed at my club due to Covid 19). I noticed some fine marks above and below the aft port-side cradle pad. I've shown 3 photos. One of the boat in the cradle to show position of the pad (although that photo is a few years old) and the other two showing the fine lines (with the VC-17 on top). This is my seventh season prepping the boat and first time I've ever seen these marks. I am wondering perhaps she wasn't sitting straight in the cradle and there is too much pressure on this one pad causing too much hull flex in this one spot? Could the outer layer of the hull material be stressed enough to cause some small ridges (or cracks - yikes)? could this just be cosmetic or could the integrity of the hull be compromised? Is there any way to check (other than the obvious of launch and see if I float)? Thanks in advance.

Stu Jackson · June 01, 2020, 09:39:47 AM

Looks more like uneven sanding of prior bottom paint layers than anything you've described as worrisome to you. Perhaps a side view shot to see if there is any oil canning.

Geoffreykwright · June 01, 2020, 10:08:41 AM

Stu - thanks. This DOES look like something which could be sanded off - only thing is i've never sanded the bottom before. The hull comes out so clean every year I just put the new VC-17 over the old. I've never seen marks like this before and thought it was suspicious that they were both around the same pad.

Having said that - it was getting close to dark when the boat came out for the winter and cannot guarantee that those marks were not there before...possibly some build up on the hull below waterline. If this were due to too much hull flex (if the boat wasn't perfectly balanced) is it possible this is the top layer of the hull material with some stress cracks? Kind of how gelcoat on the top-deck sometimes 'spider webs'?

Noah · June 01, 2020, 11:00:39 AM

If you are worried, sand off the bottom paint in that area(s) and see what the hull looks likes underneath...?

Ron Hill · June 01, 2020, 04:38:54 PM

Goef : It almost looks like blistering paint to me. Take a pin knife and puncture it for a check and try to sand another.

A thought

Geoffreykwright · June 01, 2020, 07:24:47 PM

Ron - thanks. What would cause the paint to blister? (This would have been the old VC-17 from last season).

Ed Shankle · June 02, 2020, 05:22:19 AM

Geoff,
Was the hull power washed at haul out? Wondering if it was done too exuberantly in that section. Can you try sanding a small area? Was there any hull work being done on a boat next to you?

Regards,
Ed

Jim Hardesty · June 02, 2020, 05:23:35 AM

I believe Shamrock has a similar condition. I also use VC17 live in a similar climate. When pulled in the fall the paint looks good, a light pressure washing makes it look like new, over winter some small areas of the paint will lift off. My theory is the problem lies with the barrier coat, moisture gets in gelcoat then lifts the paint. I don't think the barrier coat was applied correctly, thick enough, at the initial commissioning, I've seen/fixed too many other things that weren't done correctly. I lightly sand with scotch bright and or wipe with acetone then repaint each season. I'm not very concerned with it, not nearly enough to strip and redo the barrier coat. Maybe if I move to salt water and change bottom paint.
Repainting the bottom takes me a short day counting the masking and prep. VC17 is so thin it doesn't build up and it does a very good job where I sail.
Hope that helps,
Jim

Geoffreykwright · June 02, 2020, 05:47:06 AM

all - thanks for your advice. I'll try sanding a bit and see what I can see.

Jim Hardesty · June 02, 2020, 07:05:40 AM

I've seen others just sand/skuff bare areas and touch up. It works for them. I put too many miles on to feel good about doing that. Here's hoping I can do that this year. I've cut back on my plans already.
Jim

sselinger · June 02, 2020, 10:16:54 AM

I have seen these on my 1990 C34. It's just years of VC17 building up. A simple sanding will resolve and you should not see it again in this area for a number of years.

KWKloeber · June 02, 2020, 09:58:24 PM

Geoff I have a slightly different take on this. Yes, it could be VC17 build-up, but I haven't experienced that because VC is so paper-thin/watery that it has never "built up" on me.

I have had the barrier coat (VC Tar) do that when, after completely redoing the bottom, we splashed with the tar (7 sprayed coats) still curing. The travel lift belts kinda squished/"pulled" the barrier coat in one small area. I fixed it the next annual haul out.

But, unless I KNEW the cause - I wouldn't sand it (initially) -- I'd take a rag and acetone and remove a section(s) of the VC (it will come right off) to see what the underlying cause was, rather than sand off the result of it. If it is simply build-up, then no harm done -- the method will remove most the wrinkles (w/o sanding copper into the atmosphere.)

just a different approach...

ken

Jim Hardesty · June 03, 2020, 04:42:02 AM

QuoteBut, unless I KNEW the cause - I wouldn't sand it (initially) -- I'd take a rag and acetone and remove a section(s) of the VC (it will come right off) to see what the underlying cause was, rather than sand off the result of it. If it is simply build-up, then no harm done -- the method will remove most the wrinkles (w/o sanding copper into the atmosphere.)

I agree with Ken. The only abrasive I use is Scotch Bright. Have lots of paper towels and a gallon of acetone. If I ever do strip the VC17 would try an area with acetone and paper towels, think that would be a lot neater/easier and better for environment than sanding.
Jim

Colonel Butler · June 03, 2020, 04:23:57 PM

Sure doesn't look like a build up of VC17 flaking off. My last boat had 25 years of VC17 applied and there is so little left after each year (fresh water) that it does not have a chance to build up plus the new coat dissolves the previous coat. Do you know what sort of previous bottom paint or barrier coat was there before you purchased the boat? Looks like that may have not been bonded properly and the pad in that area may have been overloaded causing it to crack and delaminate

Geoffreykwright · June 04, 2020, 07:52:44 AM

Col. Butler - not sure what the PO used as bottom paint, but this is my 7th launch (7th application of VC-17). When you say 'delaminate' do you think the integrity of the hull has been breeched? I am happy to follow the Forum's advice (Scotch Brite, acetone, etc) before sanding....if there is risk of hull damage due to too much loading on this one pad, should I get a professional in to have a look?