MartinRF
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Posts posted by MartinRF
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Thanks, I enjoyed it despite my French being less than minimal.
/Martin
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Photos of T9 interiors make me believe the main beam is for supporting the mast only as it does not penetrate the hulls fully. If this is the case and you have a 'floating' dolphin striker there are no bending loads on the main beam, only compression. The attachemnt points of the dolphin striker strap would be the only high-load spots. As you may have seen on my web we re-engineered this on our Spyders.
The mid beam may be for secondary loads only, like carrying the aft end of the motor pod. It depends on how it is attached to the hulls. If so it will only see low loads.
This leaves with the front and aft beams for keeping the hulls together. There are three main sources of loads on these beams:
- Wracking as the hulls are moving out of sync crossing waves at an angle.
- Rigg loads. Shrouds are attached to the outside of the hulls which will induce some rotation of the hulls. The main sheet loads the middle of the aft beam -- added bending.
- Daggerboards will also try to rotate the hulls.
I have done no T9 number crunching. I don't have enough information for that and it would have been nice with data on the beams as specified in the drawings. I have enclosed a summary of some modeling I did for a Belgian Spyder owner many moons ago after he had broken his front beam.
/Martin
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Epoxy only for laminating or also for sealing the wood surfaces?
Clear finish or painted?
Dagger boards and rudder blades are built how?
Aluminium cross beams? Sleeved?
How old?
Background to my questions:
* A complete seal -- inside and out -- is best. Epoxy is pretty good moisture barrier in my experience.
* Epoxy does not offer much protection from UV and it is vulnerabel itself. In my experience the wood below the epoxy degrades quicker than the epoxy and eventually mini-cracks deveop in the epoxy barrier when the wood-epoxy bond is gon. Hence painted on all exposed surface is recommended -- a recommendation I have not followed myself and the clear finished areas are the ones that have generated most maintenace work.
Clear finish on the inside is a good idea as it makes it possible to keep an eye on things.
* I don't think I have run the numbers for solid wood boards so I don't know if they are strong enough. It is very common to underestimate how big the loads on the boards can be. I know Ian Farrier lists solid wood as an alternative -- still with a substantial reinforcement running down each side.
* Tennant's aluminium cross beams are under-engineered in my experience. We had problems right away and I have come across a score of other owners with more or less severe problems to report.
* Age: General interest.
/Martin
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Unless the Isomat NG-37 is strong enough on its own.
Do you have the construction drawings or can someone else inform us on the dimensions of original front beam?
/Martin
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Epoxy only for laminating or also for sealing the wood surfaces?
Clear finish or painted?
Dagger boards and rudder blades are built how?
Aluminium cross beams? Sleeved?
How old?
Smaller sister: http://hem.bredband.net/b262106/
/Martin
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How thick is this board?
How far out will you stand?
/Martin
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Added question: How do I know it is replacement time?
/Martin
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I vote for PE or Nylon fishing nets.
http://hem.bredband.net/b262106/pages/trampolines/index.html
/Martin
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Martin- what a great site you have lots of info. i'm very interested in your composite beams, does this let you do away with the dolphin striker?
The composite beams started out with a composite dolphin striker. We designed and built them because the alu beams were not up to the job -- wracking while sailng in waves bent the fore beam. It happened twice despite beafing up that beam after the first time. Later I came in contact with a Belgian Spyder owner who broke his fore beam and an American whose dolphin striker ripped out of the main beam. Not fun but it was this we feared would happen when we saw the drawings. Hence, the change in dolphin striker design.
The the job market made me move from my native Gothenburg to Stockholm and the boat ended up on a mooring rather than in a marina berth. I found the dolphin striker sometimes 'interacted' with the mooring in an unfavourable way and it had always been a bit of an occupier of much needed space on the trailer. Eventually I removed it and added a fair ammount of unidirectional carbon to the mast beam -- a net weight gain of about 1 kg if memory serves.
So, yes, no dolpin striker but not from the outset.
Added bonus: you actually feel a bit protected from the elements by the mast beam despite it only being 35 cm deep.
/Martin
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80 days? How long would it take a log in the Gulf Stream? (The log would be swept north of the UK, I think)
/Martin
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Rotating mast solution:
http://hem.bredband.net/b262106/pages/launching/index.html
(scroll down to mid-page)
Dolphin striker for alu tube:
http://hem.bredband.net/b262106/images/old_dolphin_striker.png
I don't think rotating/non-rotating is important for mast base loads. Sail-mastbend interaction is another cup of tea though.
/Martin
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8:1 and no winches sounds way too little to me.
http://hem.bredband.net/b262106/pages/controls/index.html
I see no running backstays so the main sheet is what tensions the fore stay.
Are your sails of stout enough material? My first set of sails were underbuilt dacron things (1986) and de-formed badly as the wind picked up. Reefing the main was more about controling shape to be able to point rather than avoiding capsize.
These days I don't have this problem thanks to the wonders of modern materials. My lee shroud goes real floppy but as long as I haul in my main sheet the fore stay is OK.
Back to the mast base: Is there any play, anything to alow the mast to lean over? It doesn't look like it but... If not there will be some interesting loads on the mast base. Any signs of stress cracks?
/Martin
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Never heard of Tefgel before. I have used the black, thick stuff used in Scandinavia to protect car under-sides against corrosion. It is cheap and has worked just fine for me. A car safety inspection guy told me the other year lindseed oil does the job. I have not tried it.
Then something like Molykote P-40 might be worth investigating.
https://www.lubricantspecialty.com/product/molykote-p-40-paste
In the assembly manual for the M32 cat, Aston Harald recommends Molykote 1000 for the beam bolts. This is a different application though: stainless steel bolts in all cabon beams and hulls.
/Martin
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Not 15 minutes. He has been doing these media stunts since the 1970s. Mostly not even putting to sea at all.
/Martin
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"Catamarans Offshore" by Rudy Choy is a good read about all this if you can get your hands on a copy.
/Martin
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Judging mast bend from that photo may be tricky. There is a 100 mm pre-bend set-up by help of swept spreaders and diamond tension and the mast is rotated beach-cat style.
Here is another photo in similar wind but as we were sailing two-up I could sit on the windward bow while shooting this. Still not a great photo but I think the mast-top bending windward-and-aft can be seen.
This what it does when the mast is fully rotated and the main sheet is fully in. If I reduce mast rotation the top will start to fall off to leeward and the pre-bend lines up with the sail 'cloth'. Both these and reduction of the mast's contribution to sail depth de-powers the rig quite a bit. Flattening and opening up the jib slot completes the de-powering.
/Martin
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Not boatbuilding either but very definitely carbon fibre layup automated:
/Martin
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Some racing multis, mostly French ones, cant their rig to windward but the rest of us don't bother with that as complication and cost goes through the roof.
As things (shrouds, crossbeams...) have limited stiffness our rigs lean over to leeward instead and the lee shroud goes limp. In my case it is very limp:
I have not thought much about this untill last weekend. This morning I tried to find photos I could use for measurement but only found a couple and all with me singlehandling (= low stability). The one above is the best since I am just about to fly a hull (in a guestimated 10 knots of wind).
Questions:
* How much rig leaning do you see?
* Efficiency takes a hit but only a small one I guess. What about handling, like gust respons? (This comes from old Tornado hands who have told me how much easier to controll super stiff Martström Tornados were compared to the cheaper/softer boats they usually started out in.)
Edit:
* A 'back-of-the-envelope' calculation I just did indicate that the 'measured' rig leaning angle above is in rough harmony with what I should get when taking wire stiffness and beam stiffness into account. Disclaimer: It is getting close to midnight here.
* The photo was shot by a friend sailing a Marström A-cat.
/Martin
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I have met this guy. Being an oddball is what he likes to do. It is his trade mark. He even changed his name to reflect this.
Back in the 1970s he actually did som serious sailing in a 20' boat he had built in his mother's basement.
Just found his web: http://46.28.145.175/?page_id=4593
This nice cold-molded little thing with poor stability took him to the south atlantic and to fame. (His web claims Bris was his first boat but there was a small steel ship convterted to sailboat called Duga before that. I guess he is not keen on reminding the world about that boat as it sank -- to get insurance money I have been told by someone who was there.)
Then followed the usual talk tour of boat clubs, well publicised boat and sailing projects most of which were not executed yet he was known as the long-distance sailer of Sweden. (I had a friend back then who built several boats and sailed them across the atlantic with them without making a media fuss about it.)
While I was building my boat in the mid-80s, Sven was in the middle of one of his projects. He worried a lot about being hit by a mechant wessel so he wanted to design a 5-ish m long sailboat that could survive this. Trying to convince him that even if the boat would survive he wouldn't was a waste of your time.
Anyway, this guy is harmless.
(Disclaimer: I have not had time to read all post above so my contribution may be out of tune with the thread...)
/Martin
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Is this the tri I think it is, the green one that got two new hulls some years ago?
/Martin
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I don't know about crazy, colourful maybe.
Yes, I have met him, he lives (lived maybe because it has been a while) nearby. No, I don't know for sure what speeds he has achieved but it is faster than 'normal' ice yachts -- superior aerodynamics.
He also develope compasses designed to help racers -- for classes not allowing electronics.
These guys also live nearby (and the Trampofoils were developed in a workshop I use for tinkering with parts of my boat).
https://www.youtube.com/watch?v=QQvYogFP9mw
/Martin
/Martin
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Some can't wait:
/Martin
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New?
/Martin
Tornado Worlds
in RaceTalk
Posted
Interesting, Brett Burvill's older brother Hayden won a regatta I helped arrange in Sweden in 1990. I believe Brett was one of the very first people to experiment with foils on Moths.
Who is building Tornados these days?
/Martin