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jules ferry · 20-07-2017, 17:06

Quote:

Originally Posted by longjonsilver

The weak link in english.

que Dieu vous benisse
jon

Merci

honey badger · 20-07-2017, 19:00

Quote:

Originally Posted by PhiSig1071

I don't know a ton about Wharrams, but weren't they designed specifically to have wooden crossbeams for flex? Is the additional stiffness of the metal crossbeams going to cause issues? What about stress on the crossbeams themselves from the hulls flexing? Doesn't metal weaken more than wood when it's subjected to that kind of repeated stress?

Hey mate.Having built wharram beams I can quite honestly say that if the beams ever flexed it was unknown to me. The flex comes from the rope lashings imho.

On the Narai the beams are a solid laminate almost 30cm high x 100cm ? They are thru bolted to the beam troughs. Under the beams are situated rubber pads that may amount to some flex.

Cavalier MK2 · 20-07-2017, 19:56

Quote:

Originally Posted by honey badger

Hey mate.Having built wharram beams I can quite honestly say that if the beams ever flexed it was unknown to me. The flex comes from the rope lashings imho.

On the Narai the beams are a solid laminate almost 30cm high x 100cm ? They are thru bolted to the beam troughs. Under the beams are situated rubber pads that may amount to some flex.

Yep, the flex is supplied by the mountings, either rubber and pivot bolts ala classic or lashings.

I know of a builder who used steel beams with the classic method without structural issues. Flotation was another matter as when the boat broke loose and swamped in a storm there was enough weight with the steel beams to sink it.

Snowpetrel · 20-07-2017, 21:35

Welding those extruded alloy scafolds might significantly weaken them due to the loss of temper and HAZ. It might be that bolting them together is a stronger option and it would allow you to unbolt and inspect the inside faces for corrosion or cracks.

I really like those warrams. Very good sea boats.

I've played around with ethylene glycol as a rot treatment on ply. It seems to do a good job of drying out wet wood and killing fungus, without effecting gluing strength.

honey badger · 20-07-2017, 23:50

Quote:

Originally Posted by Cavalier MK2

Yep, the flex is supplied by the mountings, either rubber and pivot bolts ala classic or lashings.

I know of a builder who used steel beams with the classic method without structural issues. Flotation was another matter as when the boat broke loose and swamped in a storm there was enough weight with the steel beams to sink it.

Cav. The weight issue sure is one reason I like the aluminium option. I tried to lift one end of those original beams and I am sure I nearly cracked me back.They are heavy A.F.[emoji12]

honey badger · 20-07-2017, 23:58

Quote:

Originally Posted by Snowpetrel

Welding those extruded alloy scafolds might significantly weaken them due to the loss of temper and HAZ. It might be that bolting them together is a stronger option and it would allow you to unbolt and inspect the inside faces for corrosion or cracks.

I really like those warrams. Very good sea boats.

I've played around with ethylene glycol as a rot treatment on ply. It seems to do a good job of drying out wet wood and killing fungus, without effecting gluing strength.

Thanks for the heads up mate.Yes I like the idea of bolting them too.I would probably use 10mm stainless threaded rod in this case. The idea of being able to inspect them is ace.

You are right about the welding issues.A friend of mine is a boilie. I was going to make 10cm welds at interval.

jules ferry · 21-07-2017, 05:51

Hello there,
I saw a MK IV for sale, made out of aluminium, maybe in New Zeland.
The bad thing about these old cutters is that you have a big genoa, that will not pass, because of the stay(sorry for the terms) So I took it off to have it as a flying one(?)
Also, living in the Caribbean, having a roof, a cockpit and a bimini changes your life at the anchorage. Solar panels, water recuperation, shield...
A thing to bear in mind when you mod these boat is that they where not glued with epoxy, back in the seventies. Nails and resorcine/uree formol glues.
So, you will have many nails that are going to show on the hulls and rust. And if you don't fix that, rot...

**boatman61** · 21-07-2017, 06:56

Why dont you construct Tiki style H beams instead of metal or solid wood.. the Narai was designed in days pre epoxy and the modern H beams are just as strong but lighter.

mikereed100 · 21-07-2017, 07:24

Quote:

Originally Posted by honey badger

Hey mate.Having built wharram beams I can quite honestly say that if the beams ever flexed it was unknown to me. The flex comes from the rope lashings imho.

On the Narai the beams are a solid laminate almost 30cm high x 100cm ? They are thru bolted to the beam troughs. Under the beams are situated rubber pads that may amount to some flex.

Ahh, but even though the beams may not visibly flex, they are still being subjected to fatigue cycles. When it comes to loss of strength over time due to fatigue, wood is one of the best materials, while aluminum is one of the worst. Your aluminum beams may be fine for the life of your boat, especially since the lashings and rubber pads absorb a lot of the flexing, but, given how cheap and easy it would be to do them in wood, is it worth the risk? Just saying it might be worth some investigation before you commit.

honey badger · 21-07-2017, 10:10

Yes we have spoken to the engineer at the company who makes these planks. He said the combination of 3 beams on their side will have a S.W.L of 10 tonnes. I will have four of these beams.
So to break it down some more it will be 12 individual planks @ 250 kg S.W.L.

honey badger · 21-07-2017, 12:42

Quote:

Originally Posted by boatman61

Why dont you construct Tiki style H beams instead of metal or solid wood.. the Narai was designed in days pre epoxy and the modern H beams are just as strong but lighter.

Boatie those aluminium planks are essentially engineered beams. The alu will still be lighter than an H beam imho.

boatsmith · 22-07-2017, 02:07

Paul i don't have a GOOD reason but I don't like the aluminum crossbeams. The wooden beams do flex, not much but the do. Not diggin' the aluminum planks. Look at Little Cat's aluminum beams. They seem more like it.