Chris 249 forum posts in last 60 days

mathew said..

Chris 249 said..
Leaving aside what handicap class that is and whether it's very serious by big-boat standards (most modern F-Ps are full cruisers) Is their foam core 100mmm or so thick and of soft foam, as it is in boards?

I am curious as to why you apply the 100mm (aka some large thickness) to this discussion? I am trying to understand how this applies to the discussion of pushing-tech-forwards - please elaborate.

The thickness of the foam is somewhat immaterial wrt. sandwich construction - beyond a certain thickness vs stiffness ratio. In fact the thicker the foam, the less stiff it becomes because the sheer forces ( of one skin vs the other ) are further apart so the net-stiffness is lower.

I brought up thick foam exactly because as you said it has structural issues - and yet that is what we use a lot in boards. Therefore if we want to push technology forward, why can’t we look at other sailing craft, which often ARE very weight conscious and often use thinner cores or different core material such as Nomex. Why can’t we look at the use of carbon tows or the Bighead fittings?
Why do you get so aggro when someone dares to suggest that we look at other forms of sailing craft? Why is it OK for people to sit here and pour **** on Cobra and other manufacturers, and not OK when someone dares to suggest that perhaps we open our eyes to what is happening elsewhere and consider what can be learned?

Gestalt said..

Chris 249 said..

Gestalt said..

stainless is not the best for marine environments. best is titanium, by a long shot. then brass.. i get stainless is stronger than brass but it's also heavier and it rusts.. if you do a deep dive into stainless in marine environments you will see it has a very hectic cleaning schedule or it rusts, tea stains etc. titanium unfortunately is very expensive..

Titanium was banned for some uses in big boats decades ago because in practise, it fractures easily with no warning. It's been dropped for most uses, AFAIK, because it doesn't do much that isn't better done with carbon or ss.

There's thousands of boats from the '60s and '70s out there with stainless steel bolts holding multi-ton ballast keels with no problems, normally zero cleaning, and years of living in bilge water. I had the keel bolts from one of my yachts pulled when it was 40 years old and most of them were perfectly fine and the other had other issues. I used to work in the industry and never heard of anyone even considering ti bolts for keels, and can't recall them ever being used for critical rigging areas.

I'm no boatbuilder but looking at the areas where people spend vastly much more cash on building lightweight sailing craft (ie $35,000 for the bare hull of a 17 foot singlehander, or $70,000 for a foiling Moth) it's normally a case of using thin cores of Nomex or high density foam with carbon over the top. High-load areas like the rigging attachments are made up very easily and lightly by using carbon tows (strands) epoxied to the carbon skin. I think my brother's 37 foot catamaran has its rigging loads taken by simple carbon tows, which would weigh a few grammes and take far more load than anything any windsurfer ever felt.

I'm not up on windsurfer sailcloth, but I still find it odd that a 5.7m dacron sail from the original Windsurfer is less than 2kg and therefore dramatically lighter than most modern sails. I've noted before here that I've weighed by yacht, dinghy, cat and windsurfer sails and the latter are far heavier for their area and the claims that windsurfer sails are tougher seems to be complete BS - I don't know anyone who both wavesailed and done a tough Sydney-Hobart would claim that. or anyone who would have wound the tension into an F18 cat rig and then stacked it big time in a blow. There may be very good reasons for the extra weight in windsurfer sails but I do wonder whether the board sails are more driven by marketing than boat sails. Certainly windsurfer sail makers keep on claiming that sails have ever-wider ranges but they also keep on writing catalogues that say you need the same number of sails to cover the wind range as they did decades ago, whereas the yachts that have gone to 3DI or modern laminates are showing that using different modern approaches really can increase sail range.

Not sure if you noticed but we are talking about windsurfers and not boats. How it makes sense to compare an Lt sail to modern sails I leave to you because that analogy to me makes zero sense.

anyways I'm calling bull **** on your post..
www.samaterials.com/blog/how-is-titanium-used-in-marine.html
www.sail-world.com/news/236027/The-Tech-Inside-AC75-Soft-Wings


some science
www.alekvs.com/stainless-steel-vs-titanium-a-comprehensive-comparison/

The point is that there is absolutely no reason to ignore the lessons learned at vast expense by boat builders. Why would anyone want to ignore what multi-million dollar construction jobs using specialist structural engineers do? Why discuss some new footstrap inserts and then apparently get annoyed by those who bring up the fact that there's potentially ways of fitting footstraps that could, for example, be lighter, structurally more efficient, and basically remove any chance of leakage into the core?

If you are saying you are interested in improvements, why get angry about people who show other avenues of improvement? You say you want light stuff and then reject out of hand the facts that show that minimising battens, for example, could be another avenue of improvement in some respects.

Why call bull**** when not a single thing in your links disagrees with what was said about titanium? I said it was banned from "some" uses and has been dropped for "most" uses. All that was doing was pointing out that it has certain problems and we can learn from that.

jontyh said..
Managed to get a late 80s Mistral comp light for ?20, (surprisingly light compared to my old club version) and have only the board and fin, so will need to make a centreboard, and bodge on a chinook mast base ( should be ok, as the bolts line up with the 2 mast foot holes and can bolt it on with long bolts accessed from below) . So, was thinking that as i will be sailing with a modern rig possibly a 5.5 m ks3, so making the C of E further back. I might make a thinner centreboard and bigger fin, to either fit in the existing swivel mechanism, or glass in a new fin box.
My question is, does anybody know what i'm likely to find construction wise if i rout out the old fin box? and has anyone modified such an old board successfully?

Would the CE be further back? The Superlight sail had a very long boom and that may have compensated for the pinhead shape.

Gestalt said..

stainless is not the best for marine environments. best is titanium, by a long shot. then brass.. i get stainless is stronger than brass but it's also heavier and it rusts.. if you do a deep dive into stainless in marine environments you will see it has a very hectic cleaning schedule or it rusts, tea stains etc. titanium unfortunately is very expensive..

Titanium was banned for some uses in big boats decades ago because in practise, it fractures easily with no warning. It's been dropped for most uses, AFAIK, because it doesn't do much that isn't better done with carbon or ss.

There's thousands of boats from the '60s and '70s out there with stainless steel bolts holding multi-ton ballast keels with no problems, normally zero cleaning, and years of living in bilge water. I had the keel bolts from one of my yachts pulled when it was 40 years old and most of them were perfectly fine and the other had other issues. I used to work in the industry and never heard of anyone even considering ti bolts for keels, and can't recall them ever being used for critical rigging areas.

I'm no boatbuilder but looking at the areas where people spend vastly much more cash on building lightweight sailing craft (ie $35,000 for the bare hull of a 17 foot singlehander, or $70,000 for a foiling Moth) it's normally a case of using thin cores of Nomex or high density foam with carbon over the top. High-load areas like the rigging attachments are made up very easily and lightly by using carbon tows (strands) epoxied to the carbon skin. I think my brother's 37 foot catamaran has its rigging loads taken by simple carbon tows, which would weigh a few grammes and take far more load than anything any windsurfer ever felt.

I'm not up on windsurfer sailcloth, but I still find it odd that a 5.7m dacron sail from the original Windsurfer is less than 2kg and therefore dramatically lighter than most modern sails. I've noted before here that I've weighed by yacht, dinghy, cat and windsurfer sails and the latter are far heavier for their area and the claims that windsurfer sails are tougher seems to be complete BS - I don't know anyone who both wavesailed and done a tough Sydney-Hobart would claim that. or anyone who would have wound the tension into an F18 cat rig and then stacked it big time in a blow. There may be very good reasons for the extra weight in windsurfer sails but I do wonder whether the board sails are more driven by marketing than boat sails. Certainly windsurfer sail makers keep on claiming that sails have ever-wider ranges but they also keep on writing catalogues that say you need the same number of sails to cover the wind range as they did decades ago, whereas the yachts that have gone to 3DI or modern laminates are showing that using different modern approaches really can increase sail range.