Re-core questions

[galleywench]

Hi all,
A few questions came up this weekend when I started cutting the top skin off the cabin top in preparation for my re-core project. With all the knowledge here, I am guessing these are fairly common questions (I did do a search, but didn't find what I needed).

Anyway, here goes (I've posted pictures on http://www.alberg35.com for reference):
1. Using my cordless circular saw, I cut out roughly a 4'x4' section (in 3 pieces) on the upper cabin top just in front of the companionway hatch. The skin came off quite easily but I found that about 1/3 of the core appeared to be in good shape with no water intrusion. I was able to easily dig out the majority of the rotten core with a wide chisel, but the 'good' core held on pretty tenaciously. I decided to leave the good core in place for now until I got some advice as to whether I should just leave it and epoxy in new material around it or if it makes more sense to get rid of all of it and start with a clean slate... Any thoughts on this?
2. I know that the cabin top sides are solid, but I'm not sure if the angled section between the upper and lower cabin top is cored (I believe Triton's have opening ports set into this area). I can drill some test holes to see what lives in there, but does anyone know if this section is cored?

cabintop.jpg (18.77 KiB) Viewed 3215 times

3. I need to shore up the inside skin with a support framework so the new core doesn't sag when I weight down the new core material when laying up, but I was surprised how flexible the whole section was. I am now wondering if I should be cutting off the skin in smaller pieces or should I do it all at once? My initial plan was to do the entire cabin top (both the higher and lower sections) and recore that at once, but given the flimsiness of the remaining bottom skin, should I just do one small area at a time?

[Quetzalsailor]

Yes, shore carefully. You'll be working out on this weak surface. Cut less at a time, unless you shore adequately. Do one area at a time. The deck maintains the shape of the boat. Adjoining areas of deck hold the shape of partly demolished deck.

Drill exploratory holes from the side you're working from to determine whether you've got core. You may be able to see it from below, though. You'd see the inside laminate dip towards the outside laminate.

Removing the balsa is easy with an angle grinder and 36 grit disc. Don't loose concentration and go through the inner lamina.

Not hard to see that cored structures are a great way to save weight and material. They're pretty much the same as I beams where the top and bottom flat parts of the beam are the same as your laminated faces and the vertical part of the I is the same as your balsa. I once made my own I beams. I bought 20' flat stock and carried it home in a too-short Chevy van. The steel drooped so much that it hit the ground, so the shop guy gave me a short section of I beam to prop the steel stock up at the back door. Then the straps only hit the road on bumps. I welded the stock into the well-known I shape and it was, of course, perfectly rigid enough. Here's one of my four beams after welding but before installing.

[Tim]

Once you've opened the area, just remove all the core and start fresh. In other areas, you might try a series of 1/2" test holes to determine the core's condition before you open up a large area, if you don't want to do the entire area. Wide chisels and 5-in-1 tools are good for digging out existing core, which can indeed be incredibly tenacious in its grip even with 1960s adhesion technology.

The semi-vertical transitional area between the two sections of your coachroof is almost certainly not cored, but stranger things have happened. Usually, deck coring exists only in horizontal areas, not vertical, but of course there are plenty of exceptions. I'd be quite surprised if you found core in the doghouse bump, though.

You should build your support structure before you remove top skin and core over large areas, not after. The inner skin tends to be extremely thin and will change shape unless you build the support first. So in other words, build your support structure now, before you continue work at all on the coachroof. The boat's not going to fall apart if you don't, but you're certain to lose the designed shape of the coachroof if you don't build the structure.

[galleywench]

Once you've opened the area, just remove all the core and start fresh. In other areas, you might try a series of 1/2" test holes to determine the core's condition before you open up a large area, if you don't want to do the entire area. Wide chisels and 5-in-1 tools are good for digging out existing core, which can indeed be incredibly tenacious in its grip even with 1960s adhesion technology.

I kind of figured this would be the best approach, but thought I'd ask anyway.

The semi-vertical transitional area between the two sections of your coachroof is almost certainly not cored, but stranger things have happened. Usually, deck coring exists only in horizontal areas, not vertical, but of course there are plenty of exceptions. I'd be quite surprised if you found core in the doghouse bump, though.

I'll try a few test cores to make sure, I hope there isn't any core in there.

You should build your support structure before you remove top skin and core over large areas, not after. The inner skin tends to be extremely thin and will change shape unless you build the support first. So in other words, build your support structure now, before you continue work at all on the coachroof. The boat's not going to fall apart if you don't, but you're certain to lose the designed shape of the coachroof if you don't build the structure.

I guess I know what my next task is going to be... I'm glad my cordless saw battery ran out of juice when it did or I might have taken the whole thing off.

How elaborate should I make the bracing structure? Do you typically scribe the curve of the deck onto a board and use that cutout for the support beam, or do you keep it simple?

[Tim]

Keep it simple, cheap, straightforward, etc. Strapping and dimensional lumber, nothing fancy.

[galleywench]

Excellent, I have plenty of strapping and 2x3's.
I am really looking forward to the day when I can start actually building things back up... sometimes it seems like I will never make any progress in the right direction. Just when I think I am about to start rebuilding, I end up adding another thing to add to my list of 'stuff to do before I start making her pretty again'

Anyway, I want to thank everyone on this forum (and especially Tim) for showing me that it can be done. I just have to focus on the little steps so I don't get overwhelmed.

[Zach]

This job is made much easier by a Fein Multimaster or knock off... use the scraper blade held on an angle around the outer surface and it chews out the balsa quickly.

It also takes off the loose bits that don't pull up off the core. My Triton was cored with balsa planks. When you find the planks that are a little soft, pry up on one end and then the other to see which way the grain splits. A lot of them will come up whole if you are lucky and didn't have good adhesion from the start...

Zach

[Hirilondë]

1. .................... I was able to easily dig out the majority of the rotten core with a wide chisel, but the 'good' core held on pretty tenaciously. I decided to leave the good core in place for now until I got some advice as to whether I should just leave it and epoxy in new material around it or if it makes more sense to get rid of all of it and start with a clean slate... Any thoughts on this?

If it is that tenacious and solid it most likely does not need to be removed. I does however really need to be dry. Even though it did not get wet, it may have gotten damp. Make sure it is dry before covering it up. Leaving it open but protected may have already dried it of the little moisture that may have gotten in already. A heat lamp can help if needed. Be careful though using one, you aren't trying to cook things, just warm them up a little to speed drying.

[bigd14]

You can also leave strips of the thicker top skin material as reference marks. It holds its shape much better. I did this when replacing the entire bow core. I left a strip in the middle (the white stripe in the photo) that I could use as a reference and simply excavated core material out of it. I did one side then the other. Took a bit of fairing, but it worked out pretty well.

Doug

[galleywench]

This job is made much easier by a Fein Multimaster or knock off... use the scraper blade held on an angle around the outer surface and it chews out the balsa quickly.

Unfortunately the Fein is not in the budget, but I plan on a dremel multimax or the bosch.

It also takes off the loose bits that don't pull up off the core. My Triton was cored with balsa planks. When you find the planks that are a little soft, pry up on one end and then the other to see which way the grain splits. A lot of them will come up whole if you are lucky and didn't have good adhesion from the start...
Zach

I found planks as well, no end grain found so far.

[Hulukupu]

It probably goes without saying, but be sure to check all deck-mounted hardware for underlying rot. I had substantial rot under cleats that were surrounded by otherwise solid end-grain balsa core.

[Triton 185]

Hello.....Triton 185 also had planked balsa that was revealed when I removed the outer skin.

Before I removed the skin this is what the boat looked like on the inside.

Before removing the outer skins I supported the inside contours with two layer of 3/8" plywood and 2 x 4's. I cut large wedges on my bandsaw to snug the system into place - enough pressure to keep the shape but not to deform it. Note: the wedges can be placed at the top or the bottom of the posts.

This is what the it all looked like prior to removing the outer skins.

[Quetzalsailor]

It's helpful when the designer and builder forms his deck moulds out of shapes that can be bent out of plywood! The 'mine shoring' looks great, just the thing, quick and dirty and obviously strong enough. I'd suggest to someone (who hasn't started) to install the shoring first so that you don't distort things. For the person who has started, be very careful to not distort the single lamina that you have remaining. Perhaps use multiple thicknesses of thinner plywood, rather than the two pictured; they'll bend more readily. Bandsawn wedges are dandy, but a bundle of wood shingles is easier and faster. Buy a whole bundle of 'utility grade' or whatever the cheapest stuff is; you don't need 24" Royals. Bandsaw a bunch of them to 1 1/2" wide, and a handy length long, say half; stack 'em up if you've cut the stud too short. Beware that a row of posts topped with wedges can exert plenty of force ( I jack house parts with two adjacent utility posts if one won't do it; alternately crank on one, then the other). The mechanical advantage of the shallower pitch of shingles is much greater for the force of the taps used to drive them snug. Note that the pictures show that the wedges and posts are drywall screwed in place, important; if you've got the shoring 'just tight enough' to form the shape, a little walking around or working on deck can dislodge 'em. Also useful when you've installed one post and turned away to install the next one...

It's nice to be reminded that I am still young, I'd never seen balsa planks used for coring. The end grain block system is far stronger, and easier to use.

[galleywench]

It probably goes without saying, but be sure to check all deck-mounted hardware for underlying rot. I had substantial rot under cleats that were surrounded by otherwise solid end-grain balsa core.

Definitely, I have every piece of hardware stripped from the decks and the whole deck is coming up. Areas where hardware will be bolted will be replaced with solid glass, no core.

[galleywench]

Holy cow Triton185, that is some serious bracing... I guess I will be making an extra trip to home dopey this afternoon.
I had planned on getting a sheet of plywood, ripping it into 1 foot by roughly 4 foot strips and kerfing it slightly so it will bend to shape of deck underside. Then bracing it up with 2 x 3's. I think I'll still go with that plan, but adding a bunch more 2 x 3's for better support.

On a side note, in the photos, it looks like you have removed your headliner (or maybe Tritons do not have one). I don't believe there is much space between the bottom skin and the headliner, and I am hoping that bracing against the headliner will suffice, I really don't have any desire to add 'Rip out the headliner' to my list of to-do's.

[Triton 185]

On a side note, in the photos, it looks like you have removed your headliner (or maybe Tritons do not have one).

My Triton never had a head liner. I am going to have to do some filling and sanding to get it to look decent.

[Triton 185]

Quetzal, you are correct about using shingles. Much quicker than making your own wedges. For me, I just used some scrap ply and 2 x 4's that I had in the shop. 2 x 3's would also work well.

By the way, before any shoring I covered any holes on the inside with tape and a small piece of plastic so the epoxy would not leak onto the plywood when applying the core. This was also necessary in my case because I used a vacuum bag sytem and did not want any air leaks.

[galleywench]

For the person who has started, be very careful to not distort the single lamina that you have remaining.

Yep, that bottom skin is mighty thin, I wish I had waited until I had shored up that area. Fortunately, the section is relatively small and I can mirror the curve from the other side to create a solid brace across the entire cabintop.

Perhaps use multiple thicknesses of thinner plywood, rather than the two pictured; they'll bend more readily. Bandsawn wedges are dandy, but a bundle of wood shingles is easier and faster. Buy a whole bundle of 'utility grade' or whatever the cheapest stuff is; you don't need 24" Royals. Bandsaw a bunch of them to 1 1/2" wide, and a handy length long, say half; stack 'em up if you've cut the stud too short.

I hadn't thought of that, nice idea... I have a case of window/door shim from a house renovation that ought to work nicely for this sort of thing.

I hope to get it done this weekend, I'll post some photos when I'm finished.

[Hulukupu]

Regarding headliners, I gather you have one. My first Triton had one and, after 40+ years, it was prone to forming hairline cracks from various kinds of blunt trauma. In a warmer moist clime, the cracks reveal themselves because this is the first place that mildew appears.

Be gentle with your interior bracing and consider padding against the headliner. Also bear in mind that the headliner is held in place at seemingly random locations with globs of construction-adhesive-mastic-type stuff, so the pressure of your bracing will not be evenly transmitted from the headliner to the inner skin. In most areas of mine, there was a 1/4 - 1/2" gap.

David

[galleywench]

Despite the nasty cold this weekend, I managed to get the support structure built and in place. Now I can stand on the area where I pulled the core out with only minor deflection (from gap between headliner and bottom skin). I also added some padding (thanks for the suggestion) so I didn't crack the headliner.

Here's a bad picture:

[Zach]

Cool bracing going on in this thread.

I'll have to snag some of these ideas when it warms up!