Balsa partial cored boat question

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Antihero27

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I have a 18ft 87 ebbtide that has a partial cored hull. It basically has four, four inch strips running the lenght of the boat on both sides of the main stringers. These are rotten, and I plan to replace. What would be the best material besides balsa wood to use for this purpose. I'm trying to get away from wood in the boat. The current coring can't be more than 3/8 thick, though its hard to tell now that its mush. I'm not a engineer, but I just want a similar product that can replace it, not rot, be hand laminated with epoxy, for the cheapest cost.

Also question about transom, the rear of my boat is 82 inches across, 32 which is the transom. The transom was roughly 1 1/2 inches thick, it looked to be a total of two inches with skins and resin. The question I have has to do with the remaining 25 inches on both sides. This area makes a outward curve to the transom, the wood in it look to be 3/8 ply, or balsa, it was mush and I can't really tell. Whats a good material to make this curve thats not wood. I planned to use 3/4 Bluewater 26 coosa for the the transom, but thats not going to bend to make that curve. Any ideas how to do this without using wood?



Here is the curve, this isn't my boat but the same boat and curve.1987-ebbtide-166-campione-series-fish-n-ski-3.jpg
Also
Thank You in advance.
 
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surlyjoe

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Re: Balsa partial cored boat question

do a google for DIAB , they make all kinds of cool foam.
 
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Antihero27

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Re: Balsa partial cored boat question

I appreciate your reply...You mean like DIVINYCELL? I thought it wasn't compatible with epoxy. The kind that is scribed is covered in a poly scrim cloth that is only compatible with poly/vinyl resin. Also, how do I know which one to buy, strength wise?
 
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Antihero27

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Re: Balsa partial cored boat question

Another question and maybe someone will dibble into what type core to use in better depth for me....
Question is there any reason you shouldn't use carbon fiber to tab in stringers transom? Someone gave me 2 50 yards each of 3,4 And 6 inch carbon fiber 5.7 oz plain weave. Just curious if there is a reason.
 
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Antihero27

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Re: Balsa partial cored boat question

Is there a secret to getting questions answered? I read the "How To's" didn't see that in there. Oh well... Another question I am a bit stumped on. Having now gutted my boat. I realize the transom was 2 inches thick in the center. The stern of the boat is 82 inches across 30 which made up the transom. The outside edges were just 1/4 balsa or plywood placed in 4 inch strips side by side, top to bottom. My question is how does that hold a 400 lb motor on? The center was just tabbed to the outside strips that had woven roven across them. If you look in picture above you can get an idea what I mean. Where motor is its thick. Curve area not so much. Hope that makes sense.... Do you think its possible to bend 1/4 ply to make that curve? Seems the way they did it was kinda crappy. The curve area is 30 inches long moving outward 6 inches from corner. To those who might reply,thanks
 
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surlyjoe

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Re: Balsa partial cored boat question

I stole this from the racing dinghy forum, I hope it helps answer some questions. everyone says to use airex in impact areas, and divinycell for everything else just to cut costs, I have never heard of either having a problem with epoxy, where did you hear that from?

I think the lack of replies is probably due to not many people having worked on cored hulls, its used mostly in racing sail boats and large yachts.

Cross-Linked Foam Advantages:

-Lighter than balsa for same laminate stiffness (but total laminate is thicker, taking up interior space).
-Will not absorb water or rot.
-Can use solid sheets rather than kerf-cut sheets for much of the hull, eliminating many potential water pathways in the laminate.
-Cheaper than linear foam core material.

Cross-Linked Foam Disadvantages:

-More expensive than balsa
-Not very resilient. Severe dynamic loading, such as extreme slamming, can cause this core material to fail. It just crumples. This is what happened to a number of the Whitbread 60's that used cross-linked foam core in their bows. The outer skins and core had to be replaced half way through the race.

Linear Foam (Airex, Corecell, etc.) Advantages:

-Lighter than balsa for same laminate stiffness (but total laminate is thicker, taking up interior space).
-Will not absorb water or rot.
-Can use solid sheets rather than kerf-cut sheets for much of the hull, eliminating many potential water pathways in the laminate.
-Foam sheets can be heat-formed for making shaped laminates.
-Extremely resilient material. When used with resilient resins like epoxies and vinylesters, linear foam-cored laminates can withstand severe dynamic loading much better than balsa- and cross-linked foam-cored laminates. This is why many of the extremely fast offshore-racing multihulls use this type of core; survivability from slamming and impacts at 20+ knots.

Linear Foam Disadvantages:

-More expensive than either balsa or cross-linked foam, particularly when used with epoxy and vinylester resins.
-Can be susceptible to damage from styrene migration during manufacturing. The builder needs to have good control of the lay-up and curing processes.
-Low heat deflection temperature. This means that these foams will deflect and even permanently deform if loaded and exposed to more than 140 deg. Fahrenheit for any extended period of time. Probably not a good core material for a dark-colored deck, and maybe even dark topsides. The manufacturers of linear foams are making some improvements in this area.

Honeycomb Core Advantages:

- Very high stiffness to weight, the highest of all cored laminates.

Honeycomb Core Disadvantages:

- The core material itself is expensive.
- The production process must be extremely well controlled to achieve satisfactory bond between the core and the skins - a high quality and thus expensive process.
- If good bond is not achieved throughout the laminate, or if the bond is lost in a localized area due to an impact or something, the stress between nearby remaining attached core and skin can go up quickly because the contact/bonding area between core and skin is so small, which can then result in progressive delamination.
- Like balsa, can be too stiff for severe dynamic loading, which can result in delamination.
- If even minimal delamination exists and water can somehow get into the laminate, the relatively large (as compared to foam) cells provide lots of space for holding water - won’t rot but can sure get heavy.
Click to expand...
 
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jbcurt00

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Re: Balsa partial cored boat question

Just like rolling a bead onto a piece of sheet metal, complex curves add structural rigidity to fiberglass when it's laid up & cures.

Having multiple complex curves, the fiberglass is certainly strong enough when a 2" plywood core is captive between the lower hull & the cap.

Some bass boats have structural ribs running across the transom &/or knee braces tying the transom to the longitudinal stringers.

You were asking about specialized materials (carbon fiber) that often require even more specialized resins. All of which are more expensive & harder to source then typical resto polyester resin & CSM/1708 fiberglass. Not surprising that there were no responses.

Add the thread title: Balsa cored boat, which is also a more indepth resto task (maybe more complicated too, IDK, never dealt w/ one), and you are again talking about a hull & repair type that has been done by significantly fewer iboaters then a typical poly resin & 'glass hull.

I'd give Yacht Dr & ondrvr (& possibly others) a day or 2 more to find your thread, and if they haven't replied, PM them & ask them to stop by your boat shed here in dry dock & give you their thoughts/opinions. No need to get into specifics in the PM, they'll likely prefer to keep the discussion in the open forum where it will benefit the members the most. Just ask them to stop by & include a link to your thread.

You can likely get a 1/4" ply, balsa or similar material to conform to the curve at rear corners at the transom. But it may require vacuum bagging, and although I know it's likely possible, I don't really have the details about how to vac bag it. YD does, and has discussed it @ a balsa core hull thread before.


The iboats server posts threads that it finds similar at the bottom of every thread. These may be of interest to you:
[h=4]Similar Threads[/h]

You can also do an advanced search from the resto forum homepage, for both balsa core & carbon fiber.

I'd also suggest reading thru GT1000000's thread on his Glasstream, LOTS of great bass boat resto stuff going on at his boat house.

Best of luck w/ your project,
 
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surlyjoe

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Re: Balsa partial cored boat question

OH! and 1/4" Airex should be able to be formed into the transom quarters, it bends pretty well and you wont have to cut it up to get it to fit like they did the balsa.

You'd be amazed how strong a cored section of fiberglass is. if that's how they designed it, it should be plenty strong.
 
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