Mish-Mash

This is the place to post your ideas, thoughts, questions and comments as relates to general boatbuilding and reconstruction techniques and procedures (i.e. recoring, epoxy, fiberglass, wood, etc.)
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Idon84
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Mish-Mash

Post by Idon84 »

I was wondering if anyone has any thoughts on the use of Mish Mash for bulkheads etc. I have a few bulkheads that I am NOT going to remove but would like to put the same type of pliable filler between the parts. I've only found a few sources that say to use "Industrial Talc" or "Pulverized Limestone" mixed with epoxy.

All replaced bulkheads will have foam spacers.

Thoughts...?

Bryon & Maria
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Post by Rachel »

When you say "between the parts," are you referring to the fillets between the bulkheads and the hull? Or?

Rachel
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Post by Idon84 »

YES.
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Post by Figment »

ok, I'll bite.

What the hell is "mish mash"?
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Post by Idon84 »

OK... so now I don't feel like such a dork because it doesn't look like everyone has heard of this either. So here's the deal.

I've removed many bulkheads in my cabin the last few months. I'm about to change gears and start to rebuild/tab/install new bulkheads. For these areas I will be using foam spacers between the hull and the bulkhead as is customary for anyone who wants to do it right.

The issue is with the main bulkheads that I did not remove. Behind the tabbings and between the bulkhead and hull is a flexible filling material instead of foam spacers etc. that was installed by the builder. I would describe it as more "material" than polyester resin because it is flexible almost like a ball of beeswax (or like a big yellow booger), tacky and sticks to both the hull and the bulkhead well. I have a few areas that I'm going to need to fill in (came out during grinding) and don't want to make a hard spot so I'm trying to figure out what to put between the hull and bulkhead before I reinstall the tabbings.

I don't have any good pictures of the actual stuff but in my readings and such I've found several references on the subject.

1. Asbestos/polyester mixture was used prior to 1979 at Sam L Morse (BCC Builder) before they switched to Industrial Talc

2. Pulverized limestone

Both references said to use more "material" than polyester/epoxy to make it more flexible. I was just hoping someone else might have a good recipe for the same thing. I was originally thinking of using Windshield Polyurethane for this job because I have access to quantities of the stuff but I'm afraid it would be way to permanent... Not to mention it is quite stiff when cured.

Oh well, I guess I'm going to grab some limestone and run a test batch to see if I can replicate.

Thanks,

Bryon
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Post by Ceasar Choppy »

Is there any reason you are afraid of replacing these boogers with foam?

It sounds like silcone to me, except silicone isn't tacky. (Those of you with early Pearsons will attest to the Pearson yard's love of silicone!). Either way, whether you have a hardspot depends more on how you tab/fillet than anything else.

The thought of using limestone on a boat just doesn't sound right!
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Post by CharlieJ »

Pulverized Limestone makes an excellent, smooth, strong filler for epoxies. As hard as silica and works just about the same, but makes a smoother fillet.

JUST as hard to sand if it's cured for a while.
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Post by feetup »

I would be quite surprised if epoxy and limestone was soft and flexible. However, as has been stated, a soft area between two rigid tabbings would still amount to a hard spot against the hull.
I see no trouble having rigid bulkheads tabbed to the hull provided they fit cleanly and do not force the hull outward or pull it inboard. Having an impermeable substance between bulkhead and hull to keep the ply from absorbing moisture seems like a no brain-er, as does pre-sealing the edges of the ply.
The customary method of injecting a thick mixture of epoxy and filler (cabosil) between bulkhead and hull, and filleting the squeeze out, then tabbing over the green, or washed and sanded cured fillet would work as well as it always has.
To replace the boogers you have ground out you could use polysulfide, or polyurethane. Even 5200, since it is unlikely you will want to remove the bulkhead without some demolition.
Speaking of your boogers, does it smell like uncured polyester? I encountered a situation recently where there was a foam-in-place filling in a rudder and a good portion of it had not cured (since 1982) and was a sticky yellow booger like blob in the center of the foam. Could your boogers be similar?

Feetup
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Post by bcooke »

...polyester/epoxy...
Two entirely different materials that should never be seen bunched together. Nothing mixed with epoxy is going to be flexible in the normal sense of the word.

On my 40 year old boat the bulkheads don't actually touch the hull except by accident. The tabbings are the only connection. My opinion only but I think filling that space would be a waste of time and not contribute anything. Certainly that goo is not providing anything structural or transfering any loads. The tabbings are doing all the work. Maybe they stuck the goo in there to hold the bulkheads in position while the tabbings set up.
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Post by Rachel »

I've always understood that having the large, structural bulkheads touching the hull was a no-no, because it would create a hard spot and also an undesirable bulge that would disturb the fair lines of the hull.

Along those lines, I believe you want a small gap between bulkhead and hull that is filled with something soft, like foam. Then the tabbing is firmly glassed to the bulkhead and the hull, which is what attaches the bulkhead to the hull, while spreading out the stress and load.

Seems like hard, solid material between bulkhead and hull would run counter to this.

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Post by feetup »

Ultimately, tabbing, while generally thin enough to provide some flexibility, will constitute a hard spot. The trouble with hard spots is not in their inherent nature, but in the execution. If a poorly fitting bulkhead is wedged into the hull and tabbed in it will flex the hull enough to show a ridge or bulge in the fairness of the hull. If the bulkheads are placed into the hull, while the hull is still green, and not fully cured the tabbing will pull slightly as it cures and the result will be similar.
Obviously the object of tabbing bulkheads and stringers to a hull is to form multiple box sections to make the hull stuffer so it will maintain it's shape under the loads encountered both in the water and on the hard. The largest of these loads comes from the rig, and from the forces the rig transfers to the keel, which is why the areas around the chain plates and below the mast on a deck stepped mast are as close to full transverse bulkheads as possible while still allowing normal folks to move about. Ideally, these bulkheads should form a homogeneous structure with the hull and deck so all the loads from mast and standing rigging are carried by the entire circumference of the hull and deck at this point. The way these loads are transferred to the hull is the key to not deforming the fair structure of the hull layup.
Gluing the bulkhead to the hull is not possible or practical with the materials available today, but if it were, it would be the classic example of what is called "point loading" where all of the force is transferred over a very small area. This would be the worst method but I use it as a negative example. We are trying to achieve the opposite. The best method for that is to attempt to spread the load out over as large an area as practical. The loads on the bulkhead are pretty much planar, or in line with the flat of the plate. They transfer their loads to the hull at close to 90 degrees to the plane of the hull, which is the plane in which the hull is least stiff, and most prone to flex. There is no way to avoid this, but we can spread the loading out over a larger area of the hull, whereby the fiberglass is able to withstand the loads without deformation.
The way to do this is to be sure that the bulkhead fits freely, without any pressure points, and to prepare the hull bulkhead joint for tabbing with a fillet so the fiberglass of the tabbing rolls cleanly onto the hull at a tangent, not at an abrupt angle. To spread the load outward from the bulkhead we can use multiple layers of tabbing, progressively wider on the hull side. There is no structural advantage in having the tabbing layered progressively on the bulkhead since the bulkhead/tabbing interface is almost purely in shear, but the further we can taper the layers of glass tabbing out onto the hull the less likelihood we will create a stress riser and subsequent deformation of the hull. To get as much of the hull carrying the load as possible we simply try to tab the entire length of the joint between bulkhead and hull, and ideally between bulkhead and deck, although there are cases where the latter is not practical.
If the bulkheads are to do their job they must, by necessity be joined rigidly to the hull. The key is in tapering the joint out over a large area so the joint changes from rigid to flexible as smoothly as possible. A flexible joint on something loaded as heavily as a main bulkhead is destined to fail, most likely by the separating of the tabbing from the plywood, or by the delamination of the tabbing.
Bulges, and hollows in the hull corresponding to the bulkheads and stringers are not a result of a rigid joint, but a result of a poorly executed flexible joint.

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Post by Idon84 »

Makes sense. The Boogers probably are uncured polyester as Feetup states. I think the idea of injecting 5200 in between the bulkhead and hull would be the best bet. The bulkheads are still firmly in place because I left the tabbings at the top alone. The bottoms wiggle a bit. They do NOT fit snugly to the hull and have about 1/4 to 1/2 inch (at most) between the hull and ply. I've already started sealing the bulkheads with epoxy to protect them. Building a good fillet before tabbing and making sure the ply doesn't sit right on the hull shouldn't be a problem.

Thanks for the discussion. Definitely helps!

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Post by Rachel »

By the way, I looked at your linked photo album, and let me say that your boat is officially Drool-worthy. Is she a Hess BCC? Please don't be shy about adding photos to your posts!

Rachel

PS: I looked more. Wow, you have her nice and ... gutted. Looks like it was the right thing to do, although it must have been a bit hard to take the plunge, given how good she looked before you started. Was she built from a kit? (she must know more!)
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Post by Hirilondë »

By the time I got to this thread the following comment had already been made:
Idon84 wrote:For these areas I will be using foam spacers between the hull and the bulkhead as is customary for anyone who wants to do it right.
Maybe I read more into a sentence than there is, but it seems he says "I don't want to do it right"? (I never use foam)

I work on fiberglass boats every day. I work on Hinckleys, Little Harbors, Morris's, J Boats and many others. I have seen many methods of tabbing bulkheads that work well. I have found that care and precision in the work is what matters most. There is no definitive best, customary or right way. Foam and other soft fillers are used to support the tabbing as it is laid out and avoid causing a hard spot by not being hard. A well done filet yields the same result by forming to the hull the entire length of the joint, thus making a hard spot that helps the tabbing distribute the strains.

Do what ever you do well, that will make a difference.
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Post by Tim »

Hirilondë wrote:I have found that care and precision in the work is what matters most. There is no definitive best, customary or right way...Do what ever you do well, that will make a difference.
Well said and highly accurate.
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Idon84
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Post by Idon84 »

There are many ways to skin a cat, cook spaghetti, drive a car, and build boats. Where I'm from, www.ssssclub.com the sailors whom I chat with most often prefer using foam spacers to make sure you bulkheads are not touching the hull. So saying it is the RIGHT way to do it is where I'm from. I'm sure everyone does what they want differently so I apologize if I seem presumptuous. It's just the way that make sense to me, even if the foam disintegrates over time. And I can't agree more to the need to be a perfectionist in the building of the new bulkheads or anything for that matter. Fortunately I do not intend on changing much of the way the interior was set up so I have the original bulkheads to use as templates during the build.

Rachel,

Yes it is a Hess Bristol Channel Cutter although it was built in Canada not at the Sam L Morse yard in 1980. There were some issues between Sam L Morse and the Canadian builder so they stopped building them in Canada after a few years. There are several differences between the two boats in the lay up of the hull. The interior of the SLM boats is smooth while in the Canadian boats you can see the roving. Also the core material in the SLM boats is Ply while it is Balsa in the Canadians. Canadian's predominately use Bronze parts while most SLM boats use stainless.

Most of the interiors were custom built from Canada and although I hear the couple whom were well known in the 80's were very good at what they did (as evident by the beautiful interior), they did not leave any place for regular maintenance. Just to get to a Stanchion bases that I thought might be leaking I had to tear apart a large area of Ship Lap (pine wood slats) that was all glued, not screwed to the hull. I'm from the school of who cares how beautiful it is if it isn't functional and easy to take care of. So I'm in the process of removing everything and starting fresh in homage to my racing skipper whom schooled me on that train of though.

The actual story(history) of the boat is long and drawn out but interesting, and explains more of why I have to start fresh. If you would like me to send you that (my fiance has it written up in a word document) I would be glad to send to you. Won't fit here besides I the kind of guy that shies away from vanity and likes to be under the radar so to speak.

Off to Port Townsend to spend some boat money at Cape George Cutters (the new BCC and FC mold owners). Buying a prefabricated engine mount set up with drip pan, some Gel Coated veneering, a new fuel tank, and some bronze parts. JOY!

Bryon

PS Thanks to all again for the ideas/help on this one!
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Post by Rachel »

Idon84 wrote: I'm from the school of who cares how beautiful it is if it isn't functional and easy to take care of.
Sounds like you'll fit right in here - I hope you stick around :)
Idon84 wrote: Buying a... and some bronze parts. JOY!
Mmmm, bronze. Feel free to report back, especially on the bronze "haul." Seems the world is going stainless these days (much to my disappointment), and it's always nice to see/hear abotu some good bronze.

Thanks for the extra info about your boat - interesting.

Rachel
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Post by Triton106 »

Hi Bryon,

Thanks for sharing the photo album of Cosmic Dancer. What a pretty boat! It's comforting to know someone will be taking good care of it. I had the fortune of visiting SLM factory in Costa Mesa, California before they closed the door a couple of years ago and saw first hand one BCC being built. It's truly a labor of love. Almost every piece of joinery is made by hand. No wonder it is hard to make a profit and stay in business. I wish I had the money to invest in one. Instead I have one ("Calypso") on my laptop as screen saver.

Image

Best of luck with your rebuilding process. I respect your wish to stay "under the radar" but if you would not mind, and I believe I speak for a lof of this forum members, a periodic posting of your progress will be most appreciated.
Ray D. Chang
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Idon84
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Post by Idon84 »

Ray,

YES the types of custom things aboard are a little bit daunting, but I try not to worry about that too much. Just keep moving forward and getting things done. I never had a chance to meet anyone at Sam L Morse when I was down in that area a year ago but I have been able to meet some of the guys in Canada who built a few BCC's in their time. I also am working with Todd Uecker of Cape George Cutters. www.CapeGeorgeCutters.com in Port Townsend WA, the new owners of the BCC and FC hull molds... Todd's a good guy and has been sharing sections of the SLM workbook notes for reference with me. Currently I have all the dimentions for the internal water tanks so I can decide if they will fit my "custom" BCC or redraw to fit our boat. It is quite a good thing to have them close to me and such friendly people all at the same time. In the boating world it just seems like most companies could care less if I gave them my business, never phone or write back after I inquire etc.

Anyway I will be sure to keep everyone in the loop on the progress. I love this forum out of all forums out there because it seems as if the people on this site do ALL of their work themselves. I may own a boat that is typically quite expensive & labor intensive but I am by no means anywhere near rich guy in the case of $$ (friends & family are another thing). Buying a fixer and doing all the work myself (with my Fiance Maria, her brother/carpenter Mike, and numerous friends) is the only option in my case.

PS I love that picture of Calypso. That was the picture that made up my mind that having a wood mast wasn't such a bad thing.

Bryon
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