Videos like that are why sane people wait for a good weather window before starting an offshore passage, and why people who are not only sane but smart use a satphone or SSB modem to download grib files daily while at sea even though the forecast when they set sail predicted smooth sailing all the way.

I object to your vilification of carbon and foam, but you’re right about the ultra light bit.  A boat needs to be built according to the conditions it will be used in, and a boat built for high latitude cruising isn’t going to be ultra light no matter what its hull is made from.

I still stand by my earlier point that your tests are giving you inaccurate results.  Fatigue life is inversely related to stress, if you subject a piece of aluminum to massive alternating stresses (which is what you were doing) it will have a massively short fatigue life (which is what you’re seeing).  But an aluminum sailboat does not get crumpled up like a soda can every time it hits a wave, it is built sufficiently stiff and strong that the stresses are actually quite low which leads to a very long fatigue life.  Why else would there be so many serious high latitude aluminum cruising yachts?

As for steel, I still think it’s a bad idea for a ~25ft boat, but for a ~60ft boat it makes much more sense.  Like I said earlier steel doesn’t scale down very well, but the corollary to that is that the bigger a boat gets the better suited it becomes to steel construction.

I object to your vilification of carbon and foam

I don´t mean to say anything negative about CF/foam core in itself, but I don´t think it is well suited to cruising. I think it is too brittle.
I would love to have a carbon-fiber mast and spars though. I love the low weight and stiffness of CF.

Cheers,
Johannes

On the positive side….Your ultra deep V continuous rocker design built in steel will be the best looking icebreaker ever…....

What do you think about the rig? It looks to me like your model consistently shows a tendency to round up into the wind. I like the idea of having a short mast too, but it seems a lot of traditional proas, like the Marshall Islands and Kiribati ones, have a longer mast that attaches further up the yard. I think this is a way of getting the yard as vertical as possible without it lifting way off the deck when shunting. Would you go with this rig on a full sized boat?
-Thomas

Johannes,

Even using steel, you may not be able to escape epoxy completely. If you are intending to use a thin steel shell you will need good corrosion protection, and this usually means an epoxy based coating.

On the plus side, one good thing about steel is that if you carry a welder on board, repairs are easy (as long as you can get a power supply) and plate steel is readily available.

Here’s a link to some info about ship corrosion and coatings:

https://exchange.dnv.com/publishing/cn/GL_20.pdf

Mal Smith - 29 September 2013 07:07 PM

On the plus side, one good thing about steel is that if you carry a welder on board, repairs are easy (as long as you can get a power supply) and plate steel is readily available.

Heck, if you don’t care how pretty the bead is, all you need is the house batteries, some jumper cables and a welding stick.

Also, there is COR-TEN steel, which might work for a steel hulled boat.

Weathering steel, best-known under the trademark COR-TEN steel and sometimes written without the hyphen as “Corten steel”, is a group of steel alloys which were developed to eliminate the need for painting, and form a stable rust-like appearance if exposed to the weather for several years.

Granted, the “rust bucket” appearance might put off the yachtsman, but heck, that might not be such a bad thing.  😊

I think there might be a difference in “weathering” as opposed to “immersing is sea water” 😊

Videos like that are why sane people wait for a good weather window before starting an offshore passage

When sailing the north Atlantic one must be prepared for this kind of weather. I don´t believe anyone wants to sail through something like that, but things can change very fast out there. As they say: Luck favors the prepared.

[quote ]best looking icebreaker ever

I have not thought about that, but I suppose this hullshape could break through some thinner ice without problems.  😊

Would you go with this rig on a full sized boat?

I don´t think I would use one simple very large crab claw on a big proa. I tested the crab claw this spring I and I really like it. It is very powerful and easy to use. On a 50 - 60 foot proa I would probably use something similar to a Wharram gaff soft wing-sail since it seems to be a very good rig with a low CoE and high lift. I really like the wide slot between the mainsail and the jib on Russells proas, and I think that could be something good to combine with the soft wingsail.

Even using steel, you may not be able to escape epoxy completely. If you are intending to use a thin steel shell you will need good corrosion protection, and this usually means an epoxy based coating.

I am aware of this, but I hope my kids and wife can help me with the painting. It is much less exposure to epxoy then to build it out of epoxy FG and plywood, when I have to mix a small batch for almost any part of the build.
Epoxy based paint is often medium sized epoxy molecules and it is not as allergenic as the very small epoxy molecules of laminating epoxy.

Here’s a link to some info about ship corrosion and coatings:

Thanks! I will read it right after breakfast!

Domex 355 and 550 “W” is weathering steel/Corten steel, but it is important to sandblast and paint it if it used in an marine environment
There is a better corrosion resistance if the paint is chipped off, but it does not like saltwater and galvanic corrosion.
The main reason to use it is due to its toughness and greater stiffness. It will resist welding distortion better then mild steel, and it does not become as brittle in cold temperatures as mild steel.

Cheers,
Johannes

Deep V proa in waves- Slowmotion

I made a short video of my Deep V proa going through waves. I restrain the proa from sailing away to get a better view of the hull working in the waves. I can´t see any excessive pitching. I really like the soft well controlled motion.

Cheers,
Johannes

Hi Johannes,

I don’t wanted to post in your thread again, but I have to, for my piece of mind.

Sorry, but you are permanently drawing wrong conclusions.

You estimated 1660kg for a 6mm plating to be 1/2 the displacement of a 60 foot hull. (or 830kg with a 3mm plating) This is absolutly nonsens because this would mean you want go cruising with a 3,2 tonnes displacement. No Way!

But you forgot Frames, bulkheads, stringers, isulation, paint, engine, rig, beams, accomodation, crew, payload and so on and on and on and on.

Do your calculation included a deck?

Even if you double this to 6.4 tonnes you are in the range for a high end 60 foot racing tri. So,. you can never achieve this targetted wheight or displacement.with a steel hull ... or you get a proa submarine.

You have a chance doing it with aluminium, but also there you made some mistakes. You quoted the price to be two times as high as a steel build, and I think you counted that on the price for the wheight of the different materials. In a steel hull you have to calculate the cost for corrosion paint and -treatment after you build the hull. This includes sandblasting and the all the sheating and painting, which is really expensive these days because of the high standards of eviromental protection. A aluminuim hull can be as it is, without paint, not nice, but doable.

I think I said it before in one of my older posts ... think first, calculate as exact as you can and choose the ballast accordingly to your calculations. Boatdesign is nothing else as putting wheight into a hydrodynamicly efficient form. There is no chance doing it the other way. (Hull first and wheight later).

Choosing a 6mm plating just to save a few stringers and frames is the same thing. With that thick and heavy plates you will definetly not save work. Instead you will have to order a crane to bring the big steel plates in place. Of course a 6mm plating is far too heavy for a good performing boat and your point of “pain and gain” is definetly not in the region where you estimate it.

Sorry, for this hard words, but for my own piece of mind I had to say this. I think you are a smart guy and I don’t want to let you run into desaster.

For your 24footer ... why do you not continue with not toxic glues???? There have been plywood boats without epoxy decades ago and these where not as bad as we think today.

Best Regards, Michel

Hi Johannes,

I don’t wanted to post in your thread again, but I have to, for my piece of mind.

I am very sorry you feel this way. I dont understand why, but I know I can write very short and to the point, which can come across as confrontational or rude. This has never been my intent, and I am very sorry if I have ever offended you in any way. We might not see things the same way, and we probably have very different expreiences, but that is why we are here. We all want to learn more.

Thank you for taking some time and posting your views and ideas here in my thread. I is greatly appreciated.

I will try to post some of my calculations here tomorrow. I am way to tired today.

Cheers,
Johannes

Hi Johannes,

you never offended me in any way! Personally all is in the best order.

I just wanted to warn you that your experiments lend you in a direction that cannot work in a real world boat. For my taste its better to make some inconvinient posts which seem to be unfair or unfriendly than to sit back on my armchair and wait for your disaster on the water. You are a nice guy, your enthusiasm and way of develloping ideas are great, even if I do not share your preferences. You simply deserve that your concepts work to get a good sailing boat!

For sure we have different backgrounds, but mine are based on my profession as a boatbuilder. I know how much material, manhours and money go into only a 42 foot sailing boat and have a realistic idea what this means for a 60footer, even with a lot of simplification of a v-hull. This is more than one man can handle!

Best Regards, Michel

The reason I trust 5 mm HSLA steel more than 12 -24 mm plywood or almost any thickness of foam-core CF/GF laminates:

Bring it on! SSAB Hardox - Youtube

This is the kind of toughness that makes me feel secure when sailing in an rocky archipilago or among icebergs in the far north or far south. I do think there is a logical reason most boats that sail to Antartica is made of steel.
I don’t think any amount of plywood could survive this kind of abuse.
Steel might be quite heavy, but nothing beats the toughness and impact resistance of it.

Cheers,
Johannes

I promised to post my very crude and simple weight calculations for my 18 m (59 foot) deep V steel vaka.

Hull sides: 36 m2 5 mm steel plate 1430 kg
Deck: 9 m2 3 mm steel plate 220 kg
Frames: 50 m 8X80 mm 260 kg
Deck stringers: 36 m 5X40 mm 60 kg
Deck frames: 20 m 5X60 mm 50 kg

All togther 2020 kg.

This is actually more steel than needed for this design. It is a large canoe and there will not be standing headroom anywhere except on deck. I plan on building the leepod and deckhouse in plywood to keep the CoG low.
The interior will be simple thin plywood with rope hinges and as basic as possible.

The vaka has a designed displacement of about 3500 kg, so there is 1300 kg left for paint, insulation, interior, leepod, food, water, rig and all other stuff needed for cruising. Since we are used to kayaking I believe we will not bring much stuff.
This is an important part. I view a proa as a sailing canoe and we are used to kayaking and mountain hiking. We don’t want a fancy yacht. We want a lean and fast canoe that can take us anywhere we want to go in the world. If full standing headroom and a “yachty interior” were important I would never consider a proa in the first place.

Cheers,
Johannes