Explain this concept to a Cujun!

[David Bienvenu]

I have my 66 Seacraft bow rider at a fiberglass shop for a new transom. The top cap was taken off and I pointed out that the front-top of the cap was soft when I stood on it while cleaning my new purchase last month. The cap was turned upside down and cut the inner fiberglass liner out. I expected to find rotted plywood between the fiberglass. Instead there is 100's of 3" x 3" x 7/16" thick pieces of wood layed out end to end. Why is this like this? What should I go back with? I didn't have my camera with me this morning and will go back and take pictures.

Also while the cap is upside down- the copper fuel line that is fiberglassed under the port side of the cap from the stern to the dry storage area needs to be changed. Should I go back with copper, 90/10 CuproNickel,stainless or rubber hose? I'm in the heat exchanger retube business and have all the above in 3/8" OD.

[Capt Chuck]

Balsa wood I presume. Water/wood rot cant't spread because the wood grain changes directions. It was probably soft because the glass delamimated from the balsa [img]images/icons/confused.gif[/img]

[PipeDreamsMarine]

Steele is right..3x3 Balsa matt, it easier to mold into place and form the crown to the deck. If you go back with ply make sure you back score it so it bends nice and easy if not you may pull some of the crown out of the for deck

[Scott]

In theory that’s how its suppose to work ….i.e. no water creep

Looks like that theory didn’t apply here !!!





And I think Capt Chuck has something about the delamination ..I too had areas like this .. maybe it "flexed" one to many times or wasn’t lay-up right to begin with and the bond broke between the glass cap and the end grain…

For me all soft spots were recored with ply wood ...although some of the composite materials would have been good to use in this case ....just gets expensive

The end grain balsa has good strength to weight ratio and can be formed to some degree...so that’s probably why it was used here …and you can still buy it .. as far as the squares go ….I know my hatches had squares cut out of PLYWOOD and laminated together to form the core ….. but that was to help keep such a large are “true” and eliminated cupping that can be seen with sheets of plywood …. There is a thread where Hermco informs us of that …. I would presume that the squares were used to laminated the cap as such and made for an easy lay-up

[Capt Chuck]

Scott
Your probaby right but I wonder if (in your photo)the whole piece delaminated and water was able to get across all the wood and soak down vs spread from piece to piece [img]images/icons/confused.gif[/img]

[abl1111]

Guys,

My experience has proven that balsa is worse than plywood for water rot. I re-did a sailboat that had a balsa deck and the stuff, no matter how it is laid, is like cotton to water. And even worse, it is much harder to get out for a re-do, unless it is complete mush.

If the balsa is not wet or rotted, and the deck is spongy - delam or, just no structure under the deck.

Balsa is used as sandwich material for one reason - weight to strength ratio - and the balsa w/ the cloth/scrim backing is used because it can be curved easily.

I re-did all my 'screwed down ' and sealed Seacraft hatches w/ ply wood. The one hatch that will be hinged, will be made w/ a synthetic core ( for weight and water proof ). I haven't done it yet because I have not figured out exactly howI am going to use the well underneath i.e partially a fishbox and storage or all storage

[Scott]

Originally posted by capt chuck steele:
Scott
Your probaby right but I wonder if (in your photo)the whole piece delaminated and water was able to get across all the wood and soak down vs spread from piece to piece [img]images/icons/confused.gif[/img]

<font size="2" face="Verdana, Helvetica, sans-serif">Good Point ..I'm sure that’s how the Fuel deck rotted out.. In addition what happen here was during many winters it would freeze and ended up cracking the cap ..There were lots of holes in that cap from bow dodgers to cleats to outriggers that I guess allowed water in…..what a mess ....but its all better now !!! [img]images/icons/smile.gif[/img] [img]images/icons/smile.gif[/img] That stuff does soak water up like a sponge .... I was able to wring water out of that core material

[Ed]

It is definitely 3x3 sections of balsa. It is cut that way for two reasons....one is to help with the adhesion of the balsa to the glass and the other as Don mentioned is to provide flex when molding up surfaces with a camber to them.

You can replace the rotten core with balsa again or marine plywood or one of the composite products like divincell, airex or nida core. I would go with one of the composites

[David Bienvenu]

Now I can put a picture of what I had back then. See www.theboatzone.com/gallery/1966-Seacraft-B-Rider/

[strick]

The big hatch over the fuel tank on my 23CC had a core that was made of multiple squares of plywood glued together. It was a PIA to get them all out but I had to as the hatch had a bow in it. At the time I too wondered why they did it this way and now some of the explinations given by the members of the board help to provide an answer. I guess they used the same concept with both plywood and balsa.




Strick