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Lordwrench · #1 07-10-2014, 12:02 PM

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Bushwacker · #2 07-10-2014, 02:17 PM

Very educational post! That's what would happen to afishin82's Seafari-to-CC "conversion" without a core on the inside of the hull! The Seafari inner liner covers up very little of the inside of the hull because the tall coaming in the cap, which is highest right in the center of the hull where it's most needed, adds so much bending stiffness to the hull. The MA model can also have a more open inner liner because of it's taller and stiffer cap. I'm sure Moesly put a lot of thought into those solid inner liners in the CC's! They add a lot of bending strength to the hull, so if you cut them away to add rod stowage against the hull without restoring the lost stiffness, this is a good example of what to expect! Too bad the PO spent so much on beautiful cosmetics without getting the basic structure right!

Besides the addition of a core on the hull sides, I would assume most of the deck will have to come out so those cracks can be repaired from the inside. A friend that's been doing fiberglass repairs on big yachts for about 25 years says that when you see cracks like that on the outside, the delamination on the inside is usually much worse.

Bushwacker · #3 07-10-2014, 04:26 PM

Quote:

Originally Posted by Lordwrench

. . I also decided to put this up for others as a lesson on modification planning for structural strength retention and rigidity. . .

Thanks for posting Bryce! It's valuable information indeed! Denny

flyingfrizzle · #4 07-10-2014, 04:52 PM

Sorry to hear that Bryce, that was a beautiful boat. I had a mitchcraft that had a bad split in the hull as well. It was a rolled one piece hull with no liner, coring or stiffeners. Like Denny said, once I cut into it, It was much worse on the inside.. Hope yours is not as bad.

Caymanboy · #5 07-12-2014, 05:55 AM

Da-aum, pretty boat to have her hog like that.

Happy pooch though.

Blue_Heron · #6 07-12-2014, 09:37 AM

Bryce,
Thanks for posting. Yours is certainly a cautionary tale for those considering modifications that may alter the structure of the boat, or for those considering purchase of a boat that has been so modified.

I remember this boat from the for sale section a couple or three years ago. I actually saved a couple pictures because I liked the color scheme and was considering it for my 25. But I don't remember if there was a thread in repairs and modifications. Was there one? I don't want to shame the former owner, but I'd like to see if the original stringers were kept, or if they were replaced. Do you know if it had the four stringer system, or the two box stringers? If I remember correctly, they made the transition in '71 or '72.

I agree with Denny that removing the inner liner from the hull sides reduces the stiffness. But the hull bottom, deck, and stringers should act together to create a diaphram type beam that's pretty stiff by itself, so I wonder if there isn't something else going on as well. For the diaphram to bend enough to crack at the keel, I would think the gunwales would have to bow out a LOT. Is that what's happening? Is there any separation at the joint between the deck and the hull sides?

Dave

dave s · #7 07-12-2014, 11:05 AM

That's a beautiful boat; shame you have to open her up again.
Sounds like more wrong than just the liner; I'd examine the substructure carefully, esp. the stringer to hull bond and stringer to sole.
Like Dave says, tying it all together forms an integrated I beam effect.

In my build I plan to add extra layup and bulkheads and core the sides, since I also removed the inner liner and seen how some of the original glass is looking dry.

Bushwacker · #8 07-12-2014, 11:36 AM

Quote:

Originally Posted by Blue_Heron

. . . Do you know if it had the four stringer system, or the two box stringers? If I remember correctly, they made the transition in '71 or '72.

I agree with Denny that removing the inner liner from the hull sides reduces the stiffness. But the hull bottom, deck, and stringers should act together to create a diaphram type beam that's pretty stiff by itself, so I wonder if there isn't something else going on as well. For the diaphram to bend enough to crack at the keel, I would think the gunwales would have to bow out a LOT. Is that what's happening? Is there any separation at the joint between the deck and the hull sides?

Dave

Dave, my '72 is a 4-stringer hull, so I'd guess this boat also had 4-stringers. I think Potter made the switch in '73 or '74. The first 2 stringer hull I have seen was a '73, but there may be some fuzz on the year the boats were actually produced, since the year on the title is when they were sold.

You're right about the deck bonded to the top of the stringers creating one hell of a large stiff I-beam or diaphragm. If the new deck wasn't well bonded to the top of the stringers, that would significantly reduce the stiffness of the "assembly", especially in torsion, so that's something that should be looked at during the "autopsy" of this failure. I also agree that there is probably a lot of distress at the hull/deck joint. Yacht surveyor Dave Pasco mention deck joint distress as being very common on boats with structural hull failures. Rub rails are often attached to that joint with tapping screws, which don't hold well if there is relative motion between mating parts, because the sharp threads act like knives that cut into the glass.

Ryan · #9 07-12-2014, 08:06 PM

You might want to contact Mike at wildfire marine and see what he thinks. Pretty sure he did the restoration for Zach.

Blue_Heron · #10 07-14-2014, 07:42 PM

Quote:

Originally Posted by Lordwrench

"But I don't remember if there was a thread in repairs and modifications. Was there one?"

Yes

I went back and found the thread. Not much there. Only two pictures with the deck off. There are only two stringers showing in the pics, not as wide as the usual two box stringers, not as narrow as the usual four stringer variety. And the fuel tank deck is in place, so you can't tell if the keelson was removed or left in place. Hard to tell what it looked like when they closed it up.

With the level of hull failure you're seeing, I can't help but think you're going to find some stringer issues when you open her up. Either delamination, or the deck not bonded like Denny said, or some modification to the original stringer layout that reduced overall strength. There's some serious flex in the hull bottom for that keel to crack open like it did.

Only time will tell. Good luck.
Dave