Hull reinforcing

[chowdan]

Originally Posted by robwilk37

cant speak to pink lady, but on my project it involved new laminated floors with closer spacing, new MDF ply bulkheads and biax/epoxy tabbing, horiz stringers at the waterline, essentially double-hulled from the WL down, glassed hull/deck joint, collision bulkhead, carbon-fiber keel wrap blah blah blah. you get the idea.

but then i started from a gutted bare hull, so easier to make the improvements...

MDF as your bulkhead?? [emoji52] [emoji52] [emoji52] that I do not believe is the right material to use...

[robwilk37]

MDF = Marine Doug Fir... not my first rodeo.

[Sailmonkey]

Originally Posted by robwilk37

MDF = Marine Doug Fir... not my first rodeo.

MDF is also a more commonly used abbreviation for medium density fiberboard.

[robwilk37]

i think its safe to assume no one on this site is building structural members for a boat out of fiberboard.

[Cheechako]

Originally Posted by Sailmonkey

MDF is also a more commonly used abbreviation for medium density fiberboard.

yep

[Cheechako]

I don't know what Pink Lady used, but stringers glassed to the inside would be the way to reinforce a hull for stiffness anyway. For puncture resistance more glass.
Yes fiberglass does get more brittle over decades. Especially in the sun a lot. I suppose old boats often make up for it by being more heavily laid up in the first place than newer boats.

[CarlF]

If you look at how monohulls of that era fail have hull/deck failures, there's a fairly short list to address:

1. Reinforce rudder post area - (also replace rudder post, bearings and rebuild rudder)
2. Drop keel and replace bolts
3. Replace chainplates and add stronger/longer chainplate reinforcement - especially stem head.
4. Add more tabbing to bulkhead - hull connections
5. Fiberglass tape on the inside of the hull-deck joint
6: Add kevlar fabric in bow area for collision with logs or other floating hazards
7: Reinforce for inward deck compression at mast step by adding post or cable to keep deck from rising and crossbeam reinforcement
8: replace ports or at least acrylic in ports
9: Reinforce all deck and cockpit hatches especially hinges and latches. Reinforce companionway area.

The S&S 34 is pretty robust in all these areas so there may be a limited advantage.

The above assumes there is no rot or delamination in hull, deck, bulkhead, or stringers.

[noelex 77]

Originally Posted by Cheechako

Yes fiberglass does get more brittle over decades. Especially in the sun a lot. I suppose old boats often make up for it by being more heavily laid up in the first place than newer boats.

There have been a number of papers on the long term reduction in strength/stiffness of fibreglass. All materials deteriorate, but when stored in water there is more degradation of polyester fibreglass structures than is commonly thought. See table below.

However, the early fibreglass boats were very overbuilt.

[KC375]

Originally Posted by tkeithlu

Extra layers of FG on the hull would add more weight than strength, but extra plywood frames embedded in FG would. So would horizontal frames. But do you really need it? Is the hull flexing? Reinforcing won't help much when you hit the corner of a shipping container; that's a puncture. You probably can avoid hitting the side of a tanker, unless, of course, you are an officer in the Norwegian Navy.

Or US Navy

[Shanty1]

Thanks for your response guys. No I don’t own one yet. I am looking I am preparing for a solo non stop unassisted circumnavigation of Australia. Then maybe onto the world. I am asking about the hull because I would expect a 35-40 year old boat to have seen better days. If I reckon it’s up to it I will leave it alone.

[Mr B]

I did, I replaced both hulls totally as they had big holes in them,
They were 5 mm thick, now they are 13mm thick,
With bigger stringers all fibreglassed into the hulls as one piece,
The original hulls flexed something chronic when sitting on a beach, Which did concern me,
The new hulls were stiffened up to allow me to park on sandy beaches,

[dfelsent]

Originally Posted by noelex 77

There have been a number of papers on the long term reduction in strength/stiffness of fibreglass. All materials deteriorate, but when stored in water there is more degradation of polyester fibreglass structures than is commonly thought. See table below.



However, the early fibreglass boats were very overbuilt.

Interesting graph. But there is too much context missing there. And it starts at 10 on the y axis emphasizing whatever effect it shows.
Can you link to the source? I don’t disbelieve it, but am curious re test conditions etc...

Thanks

[Fore and Aft]

First I have seen MDF used for furniture in trailer boats. I asked the boat builder why and he said you could get a quick perfect finish when spray painting all the panels.
If you are worried about the hull strength why not peel of the gelcoat below the waterline and 300mm above the waterline then glass with 2 layers of 450gm double bias cloth?
Cheers

[appick]

Originally Posted by robwilk37

i think its safe to assume no one on this site is building structural members for a boat out of fiberboard.

I've seen an Allmand 31 that was built with fiber board for bulkheads! A friend was looking at one. Under the cabinets where some wires passed through a bulkhead it had a big hole drilled out. It'd gotten wet and puffed out. I grabbed a chunk and showed him and the broker. I'd never ever own one of those lol. It was all veneered so most people would think it was plywood, and I've come to learn the year they were built can affect quality greatly. Towards the end getting close the bankruptcy they cut some major corners.

[noelex 77]

Originally Posted by dfelsent

Interesting graph. But there is too much context missing there. And it starts at 10 on the y axis emphasizing whatever effect it shows.
Can you link to the source? I don’t disbelieve it, but am curious re test conditions etc...

Thanks

Yes, the Y axis starts at 10 and the X axis is non linear. However, no matter how you graph the data, it does show a significant deterioration.

It is important to understand that it is for continuous immersion. In many countries boats are routinely lifted out over the winter season. Also epoxy and vinylester resins are very different. Modern boats frequently have at least a token amount of vinylester resin in the layup together with an aftermarket epoxy barrier coat from new. This will slow the water penetration considerably.

The graph was from an article written by Professor Geoffrey Pritchard and published in Practical Boat Owner March 1995.

No material is perfect, but fibreglass (polyester) does lose strength with long term water immersion even if no external signs, such as osmosis, are evident. The idea of reinforcing older fibreglass boats that are considering difficult offshore voyages is worth considering.