Kelsall - KSS Build Method

[BigCat]

I don't see much difference between Kelsall's technique and cold molding with thin strips of plywood, and I think any concerns about "stresses" being placed in the laminate, has no demonstrated basis in fact, and seems very unlikely to this observer.

Basically, the Kelsall technique of making a boat bottom uses the bent part only to make a form, and much of the bottom laminate is wet laid using that rather thin form. The laminate laid after the bottom is formed is under no tension at all, and the part of the laminate that was laid before bending and subsequently bent is under very little tension.

I don't see much point to claiming deficiencies in Kelsall's knowledge of infusion without specifics. As far as I can see, he gets the job done, as he has for the last 50 years. Many boats have been built to his plans in the last 50 years, and he sailed one of his own in the single handed trans-Atlantic race. I think he knows what good fiberglass laminate looks like.

I don't use Kelsall's bottom-forming method myself. I laminate the turn of the bilge wet, either by vacuum infusing or hand layup. If you use vinylester resin, hand layup is just as strong as vacuum infusion, but heavier, so it's the builder's choice. Like Kelsall, and lately, Kurt Hughes, I am making flat panels for the topsides on a laminating table with vacuum infusion, but the post-lamination bending is very slight-about 1/3 inch of bend for each foot of length. This is, after all, how wooden boats have always been made, by bending a straight material over a framework to give it some curve.

Kelsall's bottom-forming techniques are at their best in smaller boats, boats small enough to use just one panel for a whole boat half, topsides and bottom all at once. Large boats, like my BigCat 65, need two panels for each side, and have less to gain from his technique, IMHO.

Kelsall has some new technique that I haven't gotten into, that has to do with squashing foam. See his site for details at Catamarans - Kelsall Catamarans - Boat Designs.

He also has some nice formulas posted, for catamaran stability, predicted speed under power, and predicted speed under sail. You can use the stability formula to tell you when to reef, as it predicts the wind speed that can overturn a boat. Throw in a safety factor, and there you are. See: http://www.kelsall.com/images/articl...ormulas_KC.pdf

[geekclothing]

I am happy to see that there are places like this that one can gain an insight from others knowledge/experience.
Regarding the easy catamarans... at the moment they are our second option. I would think the resale of a kelsall using GRP would be higher than that of an easy?? While resale is not everything, we are quite young and are currently uninterested in the property market in Australia (interest rates etc) and so are considering building a cat for a couple of years, go sail it for a few more then reconsider the property market. So we need good money for our boat.
Regarding designsz comments about structural analysis. This appeals to me as an engineer. I would expect that any boat designer (cat or mono) should be able to demonstrate a fair amount of structural analysis knowledge. Is this not the case?? Surely someone cant just draw a nice cat shape, and wack up a mast and bobs your aunty??
Regarding the fairness.. i think if you bend the hulls around correctly aligned frames the hulls should be fair enough?? I can also see benefits in the bending of the flat panels for areas other than the hulls... ie curved cockpit seating etc etc.. Anyway thanks for the input, i hope the discussion goes on...
Have fun

[Designz]

Originally Posted by geekclothing

I am happy to see that there are places like this that one can gain an insight from others knowledge/experience.
Regarding the easy catamarans... at the moment they are our second option. I would think the resale of a kelsall using GRP would be higher than that of an easy?? While resale is not everything, we are quite young and are currently uninterested in the property market in Australia (interest rates etc) and so are considering building a cat for a couple of years, go sail it for a few more then reconsider the property market. So we need good money for our boat.
Regarding designsz comments about structural analysis. This appeals to me as an engineer. I would expect that any boat designer (cat or mono) should be able to demonstrate a fair amount of structural analysis knowledge. Is this not the case?? Surely someone cant just draw a nice cat shape, and wack up a mast and bobs your aunty??
Regarding the fairness.. i think if you bend the hulls around correctly aligned frames the hulls should be fair enough?? I can also see benefits in the bending of the flat panels for areas other than the hulls... ie curved cockpit seating etc etc.. Anyway thanks for the input, i hope the discussion goes on...
Have fun

Dear geekclothing,

Yes I am an engineer and you are quite right there is a lot more to boat design than just drawing some pretty pictures. Structural analysis is not a trivial subject (especially when it comes to composite construction). My initial comments regarding the KSS method were made because I attended a workshop and I have some concerns about what I saw (as outlined in my initial post). My sole intention was to make others aware of these issues for their benefit. Bending laminated composite panels into a shape (even if they have had cuts and darts made in them) locks considerable stresses into the structure. This weakens the completed structure, - ask any composite engineer.

My comments about the infusion process taught by Derek are easily verifiable, - just do some research.

I think there are some good points about the KSS method, but I also think that it should be used with prudence and modified to address some of the aforementioned issues. I know there has been some strong opposition to some of my comments, but one needs to ask - what is their level of experience/knowledge, - are they engineers with considerable experience? (do they really understand the technical issues?).

Designz
P.S. I have no intension of answering any further attacks on these comments, however constructive, intelligent comments are very welcome.

[Leduard]

Originally Posted by Designz

Nathan,

I am a professional naval architect and I have attended one of these workshops. While I fully understand why this method appeals to so many people, I have the following concerns about this construction method;
This is my view.
1) During the building of the hulls considerable stresses and loads are inherently locked into the structure (the sandwich laminate). This does the following;

• Reduces the reserve strength of the laminate (because some of it has been taken up in resisting the loads imposed during construction).
• Make the structure less flexible, i.e. it will not be so forgiving of a "bump" or collision of some kind during use.

2) Many of the infusion practices presented at the Kelsell need to be revisited and improved. After my workshop I spent a considerable amount of time researching resin infusion techniques and I was horrified at the lack of in depth understanding that was displayed during the workshop. As a qualified boat builder (with many years experience in a wide range of techniques) I was not impressed with some of the answers that I received to questions, nor some of the practices I saw him demonstrate.

Many people (and probably Dereck himself) will say that they have had few failures during construction, but that is no excuse for poor practices. One of the issues with sandwich construction is that it is hard to be absolutely sure of the final product (without doing extensive destructive testing), so every caution should be taken to minimize the risks.

By all means attend a workshop (if you feel that it will assist you), but I think there are plenty of other ways to learn about infusion techniques and depending on the final design you choose the designer can also assist you with the build process. Also be aware that Dereck has a vast amount of practical experience, but poor technical experience (by his own admission to me during the workshop), thus he sounds very convincing and many people love him for that, but the technical aspects of catamaran design (and especially structural analysis) are ignored at your peril.

Regards,

designz

Hi designz,

I am a mechanical engineer by trade (with several good years experience in designing structures) and I am working with Derek as a designer.

From structural point of view, I cannot see any problems with Derek's approach towards hull structure compared with any other methods. In my opinion there are **no** "considerable stresses and loads that are inherently locked into the structure" as you put it. If you would like to detail with me this matter, you can write me privately at liviu at kelsall dot com (as we might be off topic here), or explain here what you mean in more detail (if the moderator will allow us). I am happy to hear your opinion.

Derek has got a very Socratic way of instructing people (as you find it at the workshop) and I remind you that he designed, built and sailed some of biggest and quickest cats in the world .....

Regards,
Liviu

[Robertcateran]

Originally Posted by geekclothing

I am happy to see that there are places like this that one can gain an insight from others knowledge/experience.
Regarding the easy catamarans... at the moment they are our second option. I would think the resale of a kelsall using GRP would be higher than that of an easy?? While resale is not everything, we are quite young and are currently uninterested in the property market in Australia (interest rates etc) and so are considering building a cat for a couple of years, go sail it for a few more then reconsider the property market. So we need good money for our boat.
Regarding designsz comments about structural analysis. This appeals to me as an engineer. I would expect that any boat designer (cat or mono) should be able to demonstrate a fair amount of structural analysis knowledge. Is this not the case?? Surely someone cant just draw a nice cat shape, and wack up a mast and bobs your aunty??
Regarding the fairness.. i think if you bend the hulls around correctly aligned frames the hulls should be fair enough?? I can also see benefits in the bending of the flat panels for areas other than the hulls... ie curved cockpit seating etc etc.. Anyway thanks for the input, i hope the discussion goes on...
Have fun

Have you considered Pacific Multihulls for a kit, or prelaminated polypropylene instead of plywood. It is very similar in price , may even be cheaper than good quality ply by the time you epoxy saturate it and give it some external glassing to prevent surface checking.

[BigCat]

"Yes I am an engineer" If you read his bio, you will find that Derek Kelsall is also an engineer. He has been doing some things for so long that he has forgotten just why he does them, though. A USCG engineer e-mailed him to ask the derivation of his stability formula, and he couldn't quite remember where he had gotten part of it. If you want, you can get Kelsall or any other firm to design to any commonly accepted standard you like. My BigCat 65 is designed to the ABS rules for offshore yachts.

I don't think anyone can analyze a structure in contact with the ocean and tell you what the maximum stresses the ocean can give it are, however, so you will find that at bottom, all rules are rules of thumb. I think you can prove that scantling "A" is equivalent to scantling "B," but I don't think you can prove that either is the maximum that the ocean can throw at the boat.

[Alan Wheeler]

Designz is quite right. I am not sure quite why you can not understand that. If you stress a structure and lock that stress in. The stress doesn't make the structure stronger. It can make a structure stiffer, less flex. This means when further stress is applied in direction, the structure fails to flex and will break. I have no idea if the Kelsall design has that issue when it is built, I don't know the design. But if Designz suggests that is the way he see's it, why does he have to be shot down over his opinion.

A USCG engineer e-mailed him to ask the derivation of his stability formula, and he couldn't quite remember where he had gotten part of it.

I find that a very strange comment. If you are a boat design engineer, you don't just forget those things. That does kinda ring strange to me. It sounds more like the guy is a good boat builder has found a great method of building the boat in good speed and ease, but it seems strange that some very important aspects of boat design are "forgotten" due to length of time. Stability indexing is no small issue and you don't forget how you come up with it.

[Robertcateran]

It goes to show that Derek has forgotten more on boat building than most people will ever learn. I don't find it strange at all. I am mathematically trained and I know I have derived many formulas that I have confidence in but could not recall how I went about it. Even if I went over my notes it would take a while to come up with the same processes. The formula made plenty of sense to me when I went over it from first principles, but it would probably take me a lot longer to redo it as I am a bit slower.

My objection to the post is that there is clearly little stress locked into the glass fibre.
The Kelsall boats have an excellent record without any problems that this person suggested.
Robert

[BigCat]

Mr. Kelsall is in his 70s, as you might expect from the fact that he is the designer of the first foam core multihull. He has younger folks working for him, though. I'd point out that wood is quite similar to fiberglass in that it is fibers held together with a kind of natural glue, and say that if bending such a material is a problem, why is it that you can make the lightest boats of cold moulded wood, for a given strength?

[Alan Wheeler]

why is it that you can make the lightest boats of cold moulded wood, for a given strength?

Arrh, good question of which there is also a very good answer.
Firstly, let me qualify myself. I am not a boat designer. Nor do I have any experience with the Kelsall design nor have I even seen one, at least that I know of. So I am not comenting on the Kelsall design.
With all designs and construction, it is not about making a material simply strong enough to resist an impact, it is about sending stress along the structure to be dissipated within the structure. Some materials can do this easier than others. In is the sole reason why FC is as strong as it is. The materials on their own are very week. The materials together are much stronger. That materials in the finished product, able to dispate the stress is incredibly strong. Cold molded timber is similar. The structure itself is designed to take the stress of impact and dissipate it in and along the internal structure. It makes for a very strong timber hull with tremendous strength bow on to impact. But take pounding the wrong way and timber breaks apart very quickly.
Am am sure the Kelsall design is very strong. I am not disputing that and I am not really sure that Designz has said the design is unseaworthy. But he has raised some interesting points worthy of discussion in any and all high speed vessel designs, cold molded from ply. Ply dose indeed make for a very easy and quick to put together form of boat building. And for many types of vessels, may well be sufficiently strong enough for their intended use. But is this true for the Kelsall??? The first question I would ask is, what is the intended design for. Fast Open Ocean passage making? or coastal fair weather work? or?? Then the second question is, does the design meet those requirements. Then finally, especially for you designers, if you were drawing up a design for an open ocean fast passage maker, what would you do to make it strong enough for your intended purpose? Then you view that with what has been done and I think in Design point of view, he see's something lacking. Sorry. I am putting words i the mouths of posters and it may well be not what Designz is intending to communicate, so please don't assume such.

[Robertcateran]

'WHat would you do to make it strong enough fro your purpose.' end quote from Wheels


Id start by analysing the forces on a boat and consider the spreading and dissipation of stresses . Hard corners around hatches or abrupt changes in thickness of materials can produce point loadings and crack formations. Look at the jet liners that fell apart in the 60s because of hard cornered windows and the Liberty ships needing welders as part of the crew to keep the things a float. Adding material unnecessarily can lead to unseaworthines due to inopportune stress concentrations and a heavier boat which can create extra sailing loads. Good finite element analysis to show where things need to be reinforced can make a huge difference. I'd also consider a balance between stiffness, resilience, cost and weight for the materials and technique. Sometimes a boat can be made more seaworthy with cheaper materials and/or simpler techniques by simply making it bigger.e.g. Bob Oram or Kelsall multihulls or Harryproas or ferro boats,
Robert

[DerekKelsall]

Originally Posted by Designz

Nathan,

I am a professional naval architect and I have attended one of these workshops. While I fully understand why this method appeals to so many people, I have the following concerns about this construction method;
This is my view.
1) During the building of the hulls considerable stresses and loads are inherently locked into the structure (the sandwich laminate). This does the following;

• Reduces the reserve strength of the laminate (because some of it has been taken up in resisting the loads imposed during construction).
• Make the structure less flexible, i.e. it will not be so forgiving of a "bump" or collision of some kind during use.

2) Many of the infusion practices presented at the Kelsell need to be revisited and improved. After my workshop I spent a considerable amount of time researching resin infusion techniques and I was horrified at the lack of in depth understanding that was displayed during the workshop. As a qualified boat builder (with many years experience in a wide range of techniques) I was not impressed with some of the answers that I received to questions, nor some of the practices I saw him demonstrate.

Many people (and probably Dereck himself) will say that they have had few failures during construction, but that is no excuse for poor practices. One of the issues with sandwich construction is that it is hard to be absolutely sure of the final product (without doing extensive destructive testing), so every caution should be taken to minimize the risks.

By all means attend a workshop (if you feel that it will assist you), but I think there are plenty of other ways to learn about infusion techniques and depending on the final design you choose the designer can also assist you with the build process. Also be aware that Dereck has a vast amount of practical experience, but poor technical experience (by his own admission to me during the workshop), thus he sounds very convincing and many people love him for that, but the technical aspects of catamaran design (and especially structural analysis) are ignored at your peril.

Regards,

designz

As a first visit and post - having check through a few topics, there is obviously lots of interesting discussions underway, relevant to my interests - boats and boat building methods and materials, where I have spent some 40+ years designing, building and sailing.

The post by DesignZ could not go unanswered by me.


To attempt to undermine a competitor, while claiming both expertise and anonymity is, I suggest, quite unacceptable. DesignZ – this is my invitation. Put your name to your views and let’s debate the topics openly.
I was exhibiting at the Sanctuary Cove boat show when this thread started. A great show, with one of the widest ranges of catamarans in one location that you could find anywhere, with almost all of the boats, however number of hulls, being of foam and fiberglass. A few resin infusion models can be traced back to KSS workshops.
It was not always this way. The sailing world would be a duller place without foam and multihulls. To make the changes it needed a group of individuals prepared to discount the views of the ‘professionals’ and the ‘experts’ of the time and to put their own theories to the ultimate test.
A look back as a reminder. Two major offshore races played a major role in establishing multihulls and foam construction on the sailing scene. The Solo Atlantic and the Round Britain Races. I sailed the first multihul (without ballast), in the 1964 Atlantic and I won the first Round Britain as the first multi to win a major open race. "Toria" was my first own design, own build, the first foam sandwich and she set the style for future racers. Our influence went on – building foam monos, both largest of type at the time, to win the next solo Atlantic and the first Whitbread around the World, plus a couple of largest racing multis – amongst lots of others.
Ongoing innovation, keeps us ahead of the field, with KSS as our build technology. There has never been a shortage of ‘experts’ telling me how wrong I am at every step. The accusations here are just as erroneous as the all the others prove to be. There is one difference. At least the others put their names to their views.
I welcome the opportunity to explain KSS (and correct a few points) from the topics raised.

1. "KSS is only for the hulls" is a regular from competitors. If this was the case, why were almost all other designers in this field telling the world, for decades, that narrow strips of cedar or strips of foam was very quick and simple. Since 1973, all our clients have used kits of panels made on the mold table. Lots of things are done on each panel, which are unique to ourselves, all adding efficiency to the complete KSS build system.

2. Resin infusion was brought to my attention by a client in Florida, seven years ago. For me RI was immediately the perfect partner to KSS. Spreading resin by hand is no fun. RI on the table, as I always explain, is very different to what is needed in molds. We set about devising the Resin infusion set-up to suit us. We tried different resin media, different grooving and perforations and different plumbing set ups till we got what we wanted. Now, it is totally reliable for any size of panel, simple to set out and to understand. No one after experiencing KSS, would ever tolerate the sticky mess of conventional hand laminating on boat shapes and full long board finishing etc.

1. At KSS workshops, we do not set out to give a perfect demonstration of boat building. KSS allows and invites ongoing refinement. We take every opportunity to try new ideas, which have to be on full size projects. The workshops have made a huge contribution to where we are, adding and testing refinements. In trials, the task would be much simpler if the only objective was to prove an idea. In seeking efficiency, we need to establish limits, which is a very different matter. For example, how much shape control do we need? We do not have dozens of hulls or parts on which to practice and then pull the perfect cake out of the oven. When we need to tweak the technique to make it work, we have the best outcome. We could fill many pages with the compliments we have received on our workshops, going back over 20+ years. Ref. the negatives, this is only the second to come to my notice.
2. Composite engineering expertise was not available to me in 1965. I applied basic structural analysis and common sense. It has never let me down. The proof in the pudding is indisputable. We work with composite engineers and classification societies regularly now, where clients ask for independent confirmation. In one case, we were asked for independent tests of a sample of our shaping process by a classification surveyor. The tests were conclusive, as I expected. KSS has no similarity to tortured ply. There are no built in stresses in the final structure – with the exception of where we, just occasionally, do bend a full foam sandwich panel in a non critical area.
3. I have three good reasons not to use plumb stems on cruising designs. One of three potentially disastrous incidents – I was in second place in the 1964 Atlantic race, 7 days out, on nice fast reach when my tri ran over some submerged object. I heard the load bang from below. Both rudder and board were broken off below the main hull. A plumb stem would more likely have caved in the bow.

Technical qualifications and innovation do not go hand in hand. Training tells you what to do. Innovation means finding out what works for the boat. KSS is to forget the traditions of boat building. It is to know the properties of the materials and the final requirements of the vessel and apply common sense to the building technique from boat yard experience. I know what it is like on a small multihull, in force ten, in the middle of an ocean, etc., etc. I never forget that any of my offshore designs could face the same.
We have a lot of interest in the KSS workshops. We are hoping to arrange one in Australia in the near future – any suggestions for location or project would be appreciated.
Anyone wishing to know more on any KSS or catamaran topic, please put your questions. We know these subject better than anyone and will happily debate these topics with anyone – on forums or individually.
Re-reading this – I cannot help but think how much simpler my career would have been had I followed the fashion and did what everyone else did or just stayed with my very first foam sandwich method. However, it would not have been nearly as interesting or challenging and a lot of clients would have spent thousands more hours on unnecessary long boarding etc., etc.

Derek.

[knottybuoyz]

Welcome aboard Derek. Nice to see you've joined us and entered the discussions on your building method. I've watched (from afar via the Internet) your building methods. I hope you'll come back often.

[Talbot]

I have often looked at the kelsall designs, but have worried about the problems of water ingress following a stress crack - a problem admitedly for an older boat, but has ruined a number of boats especially those with balsa cores. For that reason, and for their additional strength when the skipper misreads a rock as a smudge on the chart, I have only looked at boats that have solid hulls below the waterline.

What does happen to the kelsall panels?

[DerekKelsall]

The core of PVC does not absorb water. Any break in the outside skin (anywhere) will not allow water to travel within the core unless there are some unusual circumstances, such as a join between foam sheets which has not filled with resin. Unlike balsa, the foam continues to do it's job as a core.
The impact energy that can be absorbed is greater with the foam core than for solid. Try the sledge hammer test. The high point load is where foam core is more vulnerable - tends to tear like cloth, but I have yet to see this go through both skins.
Again, there are misunderstandings. A few US surveyors condemn foam core below the water line. The classification societies have no problem with PVC foam below the waterline. This has stood the 40yr +test. Toria dragged her anchor in Barra during the round Britain. When dragged off the rocks, there was a cut through the outside skin, close to the keel about 6 feet in length. It was repaired about five months later.

Derek.