Mainship Stringers

[LongJohn]

A surveyor told me that in later years, MS hull stringers were 'built up' from several thin balsa core layers. He said that it was the reason that MS stringers always tested positive for moisture. I'd rather not drill one to verify. Can anybody verify that?

 

[Lepke]

Properly sealed, they should stay dry. If they're epoxy bonded into a single piece, they, like a glulam, should be as strong as steel and stronger than solid wood beams. I've bonded many keels, ribs, bulkheads, etc., with epoxy and never had a moisture issue. In theory there is a micro porosity in resin, but items I've cut open, laminated wood, even plywood, bonded and sealed in epoxy, never have shown any sign of moisture or recorded a higher moisture content that kiln dried wood.
Although in some fiberglass boats, Bayliner especially, I have found shoddy workmanship in interior fiberglass work even though the hull was well done. It looked like 2 different crews worked on different aspects of the boats. One professional and one amateurish.

 

[Art]

Some boat builders use rigid closed cell foam as interior mold for building very thick fiberglass overlay into the thick hull itself. Never need worry about moisture touching the inside of stringer; nothing to rot.

 

[Dougcole]

Interesting.


About two years ago on my '05 400 there were some discolored stains on the stb side center line stringer running down from the through bolts for the motor mounts. It scared the heck out of me, so I carefully pulled each bolt. The inside of the bolt hole felt dry and no liquid or anything ran out for 24 hours with the bolt out.


I was still nervous though, so a surveyor buddy of mine came over with his moisture meter and tested the stringer, it tested dry. I put it back together and moved on. The stains have never shown back up, but I still worry sometimes.


Sorry for the thread creep. Periphery info at best, I guess.

 

[boan400]

A surveyor told me that in later years, MS hull stringers were 'built up' from several thin balsa core layers. He said that it was the reason that MS stringers always tested positive for moisture. I'd rather not drill one to verify. Can anybody verify that?

Long John
I visited the factory in 2005 when I ordered my boat. I saw the way the stringers was built. They was made of plywood glued together. I have pics.
boan

 

[Riverguy]

A surveyor told me that in later years, MS hull stringers were 'built up' from several thin balsa core layers. He said that it was the reason that MS stringers always tested positive for moisture. I'd rather not drill one to verify. Can anybody verify that?

I strongly suspect this surveyor's opinion is misinformed, on two levels.


1) For many years and right up to the end, Mainship always advertised the use of 'pre-encapsulated' marine plywood-cored stringers. That, along with the solid (non-cored) bottom were hallmarks of their design. The idea that ANY boat manufacturer (except possibly for ultra-light/fast planing hulls) would use balsa as a core material in stringers is just plain goofy. Balsa is actually MORE expensive than marine plywood, and the only reason to use it is to save weight. The weight savings would have been miniscule and the cost increase substantial. I have never seen any evidence that Mainship used anything but marine plywood coring in their stringers -- at any time.



BTW...pre-encapsulated means they were fully wrapped in glass before they ever went into the hull. This is far superior to the "glassed in place" stringers you find in Carver, Sea-Ray and many other mass-market boats. There are any number of articles and reports on Mainship's use of this process as recently as 2008.


Dozens of references can be found by using this 'explicit' google search:


https://www.google.com/search?q="mainship"+"encapsulated"

2) All mositure meters are notoriously inaccurate for reliably determining the 'wettness' of thickly encapsulated stringers. Moreover, "wetness" does not (in and of itself) indicate a problem.


Two essential articles on this topic are:


Don Robertson's Marine Marketplace - The Use & Misuse of Moisture Meters


and



https://www.seaworthysurvey.com/wet-stringers-may-may-want-know/


Note especially here in this latter article, the surveyor's observation that "90% of wood stringer boats older than 5 years have elevated moisture in the stringers."


Perhaps you can show this to your surveyor and invite him to respond. If what he says is true, he should be able to tell us the source of his information.

 

[Art]

R G


In quality older boats [10 to 40+ years old] of good construction practices: Wood cored stringers can or can not be in good condition. I have removed and replaced entire stringers in production method ski boats that were wood core rotted in marine plywood and have also found considerable rot in wood cored stringers of Chris Craft and other full sized production boats.


That said - Plenty of older boat stringers have wood core in good condition. Basically it comes down to how wet and for how long the stringer material was let to stay soaked as well as how many holes in the fiberglass surround were available for both water and air to gain access to the wood core.


Some builders did not use wood in their stringers; but rather used closed cell foam as a mold for the stringer's thick fiberglass surround to be intricately/fully embedded into the hull of the boat. These foam cored stringers will never "give up the ghost" as long as the builders fiberglass stringer weave into the hull was sufficient.


Rule of thumb: Don't leave drilled holes open in stringers, and, it is great if no holes are drilled into stringers at all. In other words... keep stringers sealed off from water and air intrusion. Oh, and as a practical matter... don't let water stand in bilge against stringers. Best to always keep bilge dry!

 

[ghost]

Nothing better than a drill bit to know exactly what is or is not going on. Takes less than a minute, less time than your post and avoids all opinions. Nothing better than empirical evidence over good or bad intentioned opinions any day. This is a good use for an epoxy putty stick, the kind where there is an inner and outer core, you just squish it around in your hand for a couple minutes and the kneading mixes the epoxy, you only need about an eighth of teaspoon wiped in with your finger to ensure the hole is permanently sealed. You can evaluate a whole stringer top to bottom and fill the test holes in ten minutes.

I’d have at it. Mark the bit with tape so you control your depth. Gold standard.

 

[Art]

Nothing better than a drill bit to know exactly what is or is not going on. Takes less than a minute, less time than your post and avoids all opinions. Nothing better than empirical evidence over good or bad intentioned opinions any day. This is a good use for an epoxy putty stick, the kind where there is an inner and outer core, you just squish it around in your hand for a couple minutes and the kneading mixes the epoxy, you only need about an eighth of teaspoon wiped in with your finger to ensure the hole is permanently sealed. You can evaluate a whole stringer top to bottom and fill the test holes in ten minutes.

I’d have at it. Mark the bit with tape so you control your depth. Gold standard.

YUP!!!

 

[Mrwesson]

My older mainship was layed up with thick woven cloth on the stringers and I suspect even without a core would be sufficiently strong to withstand anything i'd throw at it.

Haven't tested them and they show no sign of failure after 40 years. Tap around with a brass hammer and if you hear something funny then i'd test..

If it failed it would be because moisture got in from screwing into them and would weep brown water from that hole(an obvious indication). Don't sweat it and if anything your time would be best served unscrewing anything into the glass, fill hole with 5200 and screw back in.

Also when he says "mainships always test positive for moisture" keep in mind they started making them in the late 70's and his opinion is probably skewed from seeing so many classic mainships.

 

[Art]

My older mainship was layed up with thick woven cloth on the stringers and I suspect even without a core would be sufficiently strong to withstand anything i'd throw at it.

Haven't tested them and they show no sign of failure after 40 years. Tap around with a brass hammer and if you hear something funny then i'd test..

If it failed it would be because moisture got in from screwing into them and would weep brown water from that hole(an obvious indication). Don't sweat it and if anything your time would be best served unscrewing anything into the glass, fill hole with 5200 and screw back in.

Also when he says "mainships always test positive for moisture" keep in mind they started making them in the late 70's and his opinion is probably skewed from seeing so many classic mainships.

Another YUP!!

 

[bayview]

Any surveyor who said that is just dumb. He hasn't tested all models of every year of that manufacturer. makers change things all the time.