An Old Worn Out Boat, Prime Candidate for Cold Molding?

Hi @WhiteRabbet,
5'3" is what I was looking for, 8'3" was an obvious typo.
Okay:
LOA 16.77m
LWL 14.17m
BOA 4.58m
BWL 4.29m
TC 1.60m
Disp 25.4 tonnes

• To get 25.4 tonnes I use a Cm 0f 0.50 (V hull shape) and a Cp of .522 for a Cb 0f 0.26 (low?).
• The hull speed is 9.15 kn.
• Using AS4132.1 I get a mid-section bottom design pressure of 30.2 kPa, and using Edmund's I get 34.1 kPa.
• Based on a frame spacing of 305 mm, this results in a plywood plate thickness of about 10 mm (mid-section).
• Assuming a chine stringer, I get a maximum rib span of 2.6 m. The rib (57mm x 57 mm) is a little light for this span (using AS4132) so I think there is a stringer between the keel and the chine. However, Edmunds would say it is okay without the stringer (he allows a 50% design pressure reduction).

Let me know if this seems right.

Regards AlanX

 

The only thing that doesnt seem right, is that TC 0f 98-1/2” is not a typo. As far as I i understand what we are talking about:

https://photos.app.goo.gl/mNr9NKRGNoyEadV38

Measuring from the blue tape at waterline, to top point of blue tape on keel/rabbet line. It measures 8’2-1/2”.

 

Also - there is a chine stinger

 

Hi @WhiteRabbet,
Not clear if the measurement is vertical or slope, Tc is a vertical measurement.
https://www.schoonerman.com/ship-design/images/1511_8_7-ship-curves-form.jpg

Regards AlanX

 

Yes, can easily paint over top of Loctite roof and flashing black polyurethane using any paint you want, it will stick great. Paint over the Loctite construction adhesive too.
I coated the entire hull wood, so a wooded hull with a mix of black PL and the FG milled fibers of about 30% volume mixed in. By sight and feel, not measured.
But I had prior to that cleaned out all the plank seams, the hull was super dry, and filled all seams with the Loctite construction adhesive and sawdust mix. Hull went many years with just that as a caulk compound in the water. And of course all my framing was in good shape, any bad frames were replaced, and I rescrewed the hull with bronze screws one size up. I just wanted a strong hull, and it is much stronger than new now.

Used a plastic 6" putty knife blade as a spreader. It definitely seals out the water, it stretches and flexes with the wood. Adding the glass toughens the rubber to make it harder and stronger than by itself. Basically giving it a reinforcement fiber, they do similar stuff with concrete and other mixtures, epoxies, etc... Loctite roof and flashing is like 5200 but slightly softer and a lot cheaper. Other thing recoats are easy, it can be sanded too with coarse paper and a RO sander or belt sander if you want a smooth surface. You dont want to put coatings over rotten wood. If you can pressure wash wood and it stays mostly intact it is not rotten or you can not push a screw driver in then it is not rotten. But wood rots in spots. So any spots of wood rot have to be fixed, boat needs to be in relatively seaworthy. Idea simply is keeping out the water using a resilient coating on wood. You could do the same with 3M 5200, but will cost 3 times the price.

Other thing about using Loctite PL premium polyurethane construction adhesive mixed with saw dust, that is like a great way to reinforce planking seams by gluing the planks together in a hard rubber bond that will still be able to yield to the forces working on the hull. Plus it is able to fill large gaps, the sawdust allows it to cure in thick layers and can be sanded smooth/ Both of these are cured products, they wont smear when sanded, they turn into sanding dust. This mix will not escape the plank seams, it stay in place. It expands as it cures. Some people are using it on plywood bottoms. It is a quick good way to seal plywood panels.

I have fixed rotten wood by cutting out rotted sections, treating the wood with white boric acid roach powder dissolved in 90% alcohol, that poisons the wood to rot. Then either glue and screw on new woods, or patch the hole with a mix of the Loctite construction adhesive mixed with sawdust if it is small area. This also works well as a wood filler for gouges and holes in wood, even larger holes. Lay some cereal bag plastic against the mix or use some blue painter tape and you can keep it pressed down as it does expand when curing.

If you want, mix different colored wood dust and you get a good approximation or the surrounding wood, and it takes wood stains very well.

You dont want to use Loctite Black PL in the wood seams simply because wood plank seams on a wood hull are hard caulked for hull stiffness. The Loctite construction adhesive mixed with sawdust has just the right amount of spring tension to give it the correct stiffness.

Here are these 2 adhesives
https://www.homedepot.com/p/Loctite...ive-1390594/202020474?ITC=AUC-150983-23-12140

https://www.homedepot.com/p/Loctite...e-Roof-and-Flashing-Sealant-1675273/203163733

It does take about 60 tubes of the black stuff to coat a 37 foot boat.
And best to also add the FG milled fibers to it. Milled fibers come in different sizes, I used 1/32", but could go longer. I have also thought of using XYNOLE fabric cloth with the Black PL for the resin glue as XYNOLE stretches and it is not too expensive and resistant to abrasion.

Other thing is, no marine worms, gribbles, can eat into the wood anymore. Still need bottom paint though for barnacles.

 

Oh ok, I was measuring curve. Ill get that measured

 

TC: 48”

 

I work mostly in metric these days but can't see too much difference between 98-1/2" and 8'2 1/2".

 

Same thing far as I know

 

Hi @WhiteRabbet,

A Tc of 4ft is perfect with regard to typical hull coefficients.
The mid-section hull bottom design pressures are now:

26.4 kPa using AS4132.1
34.1 kPa using Edmunds
27.0 kPa using P BMD BASE from ISO 12215-5
​

My calcs (AS4132) suggest a maximum span between stringers of 1.4 m, and I would expect a chine stringer.
This is for the mid-section bottom panel which is the worst case. As you move away the design pressure can be reduced.
As there are stringers, we know that there has to be structural bulkheads to support these stringers.
To design a set of external stringers we would need to know either:

• The spacing between structural bulkheads around the mid-section, or
• The dimensions and span of the bottom stringer(s).

With this we can design the external stringers.
---
Lets look at replacing the support provided by the ribs with an external plywood shell:

Ribs:

• 57 mm x 57 mm
• Oak with a median UFS 96 MPa (Sw)

Plywood:

• Grade F14 (a middle of the road good marine plywood):
• Median UFS 40 MPa (Sp)

Moment for a wooded rib is then:

Mt=50%*(80%*Sw)*bw*tw^2/6
=50%*80%*96*57*57^2/6000
=1,190 Nm
​

Equivalent plywood thickness is then:

tp=sqrt(Mt*6000/50%/80%/40/305)
=38 mm​

If we went FRG (30% v/v with an UFS 207 MPa) then:

tf=sqrt(Mt*6000/34%/207/305)
=18 mm
​

If we went FRG sandwich with a 12 mm plywood core then ... here is a table comparing the options:


So one solution then is a 4 mm layer of FRG then 12 mm of plywood core (say 3 x 4 mm strips) and then another 4 mm layer of FRG on the hull.
This solution assume all the other structural members are good.

Regards AlanX

​

 

Im thinking this could be an excellent solution for leaky topsides, would you agree?

 

Alan, thanks for the in depth analysis. I’m thinking that I ought to put together an in-depth survey of all of what elements are compromised and where, and provide some diagrams so the calculations can be as case specific as possible.. Do you agree?

 

Hi @WhiteRabbet,

When it comes to the time that you commit to spending your dollars, I think it would be a very good idea to confirm the assumptions.

I can only make suggestions or provide ideas/concepts for a possible solution, based on what I have been told.
At least I can back my suggestions and ideas with the underlying mathematics and demonstrate they may be viable.

I think having a sound understanding how the proposed solution works is essential.
Especially when you intend to spend lots of dollars.

Regards AlanX

Post Script: Here is a thought experiment

Subject of repair of the stem, if you put 2 1/4" x 2 1/4" oak ribs on the outside of the hull where the existing internal ribs are located, would you be satisfied that the hull strength is as good as new?

A key assumption here is that the planking and the ribs can still transfer the bearing loads (but not the bending loads) to the longitudinal structural members (i.e. keel, sheer, chine, stringers etc).
If the ribs and the longitudinal structural members are damaged then there is no realistic solution without repair of those longitudinal structural members.

If you now plank the external ribs do we have a complete solution (with some buoyancy adjustments)?

Structurally the following table are equivalents to external Oak Ribs and planking:


Regards AlanX

 

I have been doing tests using what I though may be a superior product for 5 years on my 40ft Pacemaker Aft Cabin with perfect results. I say "similar material" but recently realized that the Black PL Roofing Caulk is actually rebranded, retail version of BASF NP1. I have used NP1 exclusively as a "caulk" and sealant for over 10 years since it was sold by "Sonolastic". NP1 is incredible as it remails "soft" adheres seemingly forever to unprimed versions of Mahogany and White Oak without any drawbacks that I have noticed above and below the water line. I have found that "priming" with System Three S1 sealer seems to make the NP1 nearly impossible to sand off or filet. NP1 comes in a variety of colors while the Loctite version is only offered in black.

My test areas were forward near the bow covering the garboard and keel, midships over an area at the extreme bend of the steambent White Oak frames and at the extreme bottom of the keel and the very aft section of the bottom planking. All areas have remained in perfect condition and the unepoxy bottom paint has adhered better than anywhere else on the bottom. This boat has been 100% sealed above with all decks being covered in a 2 part flexible membrain material. Further, I installed covering boards and "scuppers" so that zero water runs down the hull sides or transom ends. There is zero water intrusion from above. Also, I completely rebuilt the transom using the 5200 method using Okume, 5200, Smiths and African Mahogany and it is as solid and perfect as the day I finished it.

So... This year we are applying the NP1 / Loctite to the entire hull after these years of testing after following SDowney's postings here and on WBF years ago. The NP1 is being put on over a single not yet fully cured layer of S1 sealant. I am quite confident in a successful result and will see what everything looks like at haul-out in late October here in Bay City, MI.

 

They are working on an old grand banks woodie in our boat yard; been working on it about a year; removing a small section at a time and repairing the floors; they section in 12mm okume patches cut to fit as the 1st bottom layer, all bedded in 5200...there is so much metal in the planking for years of reattaching; they are not staggering the butts even; the outside planking is all conventional. They basically need to make sisters for attachment points..

I asked them about their opinion on West System bottoms and they virulently dislike them. They told me they have repaired quite a few WS hulls where the frames move, but the bottom doesn't and the framing essentially pulls itself apart. I suppose a WS properly done would include framing somehow, but gives me a headache to consider.

They also told me the GB they were working on, maybe a 42'er, costed about 80k to do the repairs done, but they said the boat needs 500k to be brought to bristol. They said the old woodies are scaring people as they continue to age out.

Epoxy and fiberglass are not great solutions.

The millwright told me they stopped work in November for the cold and during the 6 months on the hard; some of the repaired transverse floors had decayed and settled past the points of his November repairs. My hunch is the keel top is a bit soft; it has rotten wood atop! All sistered framing. They leave the rotten ones in place; which I find disturbing (personally).

Anyhow, they told me that there are a LOT of great old boats getting to be in pretty tough shape, and they can be bought for cheap, but the work on them is not.