Balsa cored hull?

I'm new to this forum but I,ve been restoring / rebuilding boats for a while.
My latest project is a 1987 Baja Force 200. Stringers, floor, interior rebuild.

After some exploritory grinding and drilling on the interior of the hull I found that the hull is balsa cored. The 1" by 1" square blocks taped together. I admit I don't know much about cored hulls.

1st question: The core doesn't seem to be rotten but the wood is very soft it can be dug out easily with a screw driver. Is it suppose to be soft?

2nd question: I have heard horror stories about soaked, rotten cored hulls. I only checked one spot, is there any reason to be concerned about the rest of the hull? Even though the floor and stringers were rotten the transome is in great shape whith no rot.

3rd question: Is there anything wrong with buying a boat with a cored hull?

4th question: How do I tell when looking for future projects if the hull is cored?


Sorry for the long post

Thanks in advanced.

 

Anyone there?

 

I am - but I am of no use to you....

 

its balsa wood ,,yes its easy to remove,,this is what the new wave generation has to deal with ,,not like real wooden boats,,,not trying to be smart ,,just the facts.... replace balsa with balsa and around through hulls use epoxie longliner..........answer for #1 answer for #4 get a survey,,,,,there is no more old growth wood ,,most of the new boats are plastic and glass with balsa cores

 

Longliner- thanks for the reply. The core that I'm talking about is the hull itself, not the stringers or floor. How would this be easy to remove? If the balsa core was wet would'nt the boat be unrepairable? The only thing I can think of would be to cut the entire perimeter of the inside of the hull and peel up the fiberglass to get the core out.

 

yes ;the balsa is sandwiched between glass or something else someone else here can help you more then me,,,,,good luck,,,longliner

 

Hey Itchy,
couple of things with the balsa core. The balsa will "wick" water , that is it will transfer water away from the hull breach. About the only way for the balsa to get wet is from a hull injury, inside or outside. If the balsa is wet, it will be next to impossible to dry it out without opening the laminant, that is stripping away the inside or outside layer of glass. If you are talking about a salt water boat, the closer you can get to the injury? the balsa will show up with dark streaks/marks (decomp of microscopic marine animals) if it is a freshwater boat, may not be able to trace the location of the injury other than physical inspection. We hooked a vacuum pump to a crack in a sailboat, sealed the inlet around the crack, drilled a series of 1/8 inch holes around the injury about 16" out. We kinda figured that if the air could be drawn in thru the small holes and be "sucked" towards the pump, the water would be drawn with it. It worked, we sucked almost a gallon of water out of the hull, the boat was only in the water about 4 hours after it was struck (regatta, you know how those guys are). If you are dealing with balsa core that is wet all the way to the gunnels, your boat has a major problem, it was exposed to a lot of water for a long time. Quick check...the manufacturer will be able to give you an idea of the "dry" weight of the boat. You can get pretty close by adding the features, etc of your boat....calculate the difference, that may give you an idea of how much water the balsa core may be holding. Couple of xtra pounds may not matter....so long as the reason for the absorption is cared for...
good luck
mobjack68

 

first things first you need the tools, get your hands on a mositure meter will cost a few hundred dollars, this way u can check the whole hull and with a marker write down the readings on the hull , then take a photo so you will have a record of the hull, you could get one of the local boat repair shops to do this for you just pay them for thier time , too many boat owners try to get a free check up, be honest with them tell them u are doing it your self, most of the guys out there will steer u right and give u some good addvice. yes to your first ?, but it should be dry not wet, only after u have run a meter over the hull will u know, the balsa is soft and is easy cut with a knife u can even chip away with ur thumb nail, the core acts like a I beem , 2 layers of glass sandwiched the balsa very strong and light weight, and a lot cheaper than a soild fiberglass hull , but water may get into the core and u will get rot , nowadays they use foam most of the time, if you do have to remove the core on the hull do this by sections say 1 foot wide from top to bottom this way you will keep the shape when u have the first set of sections done , go to the next set, always have the boat checked out for moisture before u buy, alot of times people will drill holes and try to suck the water out the only proplem is that its imposable to dry will take a lot of time and the balsa will have dry rot after sometime the balsa will turn into dust and u no longer have a cored hull , if u have wet core remove it there is no bandaid sulution , if someone came to my shop and told me drill some holes to dry it out i tell them take there boat away not doing a 1/2 arse job

 

cored hull bottoms

sorry about your luck..cored hull bottoms are a big problem.
1/ You can remove the local balsa, however the water will migrate throughout the structure. The previous responses are good, use a moisture meter to locate the troubled areas and tap with a plactic hammer to find softness.
2/Sounds like your boat had rainwater sitting in it. This situation is typical because the wood at the low positions has absorbed water, the transom is seperate from the bottom core and the stringers, therefore no migration.
3/yes
4/Get information, call the manufacturer & get facts
Generaly speaking you may open the local damaged area then open a second area to allow air flow. Use a shopvac at one end a heater at the inlet. This is the best way to 'dry out' on a small scale. Once dry use a epoxy repair and seal the area as best you can. Remember you must replace the skin in the area inorder to retain the strength as the core system is design for the skin to carry the loads. After this find the inlet for the water and seal it. Many 'sins' are comitted in both production & repair, no protrusion into the core should be in contact with the wood. By this I mean wood screws are not allowed.

 

Thanks for the replies, I don't think I have a problem whith the core in this boat, I just don't want to get burned on the next one.
Do you guys have any links for a good moisture meter?

I've also done some research since this post and it seams that almost all the manufacturers since the early 80s use core laminates in there hulls. Now what do I do, Start building my own boats without cores? or is the balsa core hull an ok design if is properly done?

 

Itchy:

Your research may be only half right. Most reputable manfacturesrs today do not core below the waterline. If they do, it would be for racing applications to lessen weight.

 

Yes, end-grain balsa is one of the best core materials available, provided it is installed correctly.

Yoke.

 

I don't know Yoke....Vacuum bagged Klegecell core gets some awful high marks...AND no rot.
mobjack68

 

Mob,

Yes and no.

Balsa has a much higher compressive strength than klegecell/divinycell, good when you're bolting on loaded hardware. (yes, I'm aware of the irony)

Properly installed balsa has corebond adhesive or resin in all the gaps between blocks, thus ensuring that water won't spread too far if the skin is compromised. Compared to plywood coring, the balsa is much stiffer, lighter and less prone to rot.

But, balsa is also about twice as dense as "regular" foam core. (H-80/K75)

Yoke.

 

Balsa scores the highest in shear strength too!