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#178500 - 05/18/09 04:50 AM Re: Foam strip construction * [Re: Gato]  
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Quote

The funny thing is that some of the people arguing for bigger min weight for the cat (60kg) also wants the boat to be able to carry more weight.



grin Yes, I admit to that being true ! grin

And I thank you as you have still been to kind to me as I also argued for using aluminium components for dolphin strikerless beamsa and an unstayed mast using commerical alu tubing, Not too forget argueing for rotomolded hulls (possibly using twinex). All things that add weight to the design.

So yes, I do think it to be fair that I'm placed in the low-tech and heavier corner. Not argueing about that I'm afraid.



But on a different topic.

Have you weighted the new DS mast section already ?

I know the Pixie mast (timber/glass) you made came out at 8.9 kg. ; for I guess 6.5 mtr length.

The (strongest and stiffest) aluminium unstayed mast from tubing that I'm looking at (if it were to be extended to 6.5 mtr length) would come out at 9.85 kg with about 20% less moment of enertia with respect to forward swing during diving of the platform; so it is not too far off the Pixie mast (timber/glass) at all.

Wouter

Last edited by Wouter; 05/18/09 06:12 AM.

Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
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#178502 - 05/18/09 05:14 AM Re: Foam strip construction [Re: Wouter]  
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The ready mast for the DS12 (Ply/carbon) all fittings(carbon)forestay and shrouds (dyneema) has a total weight of 6kg (not weighted on a precision instrument)for 5.8 m spar.
Total cost under 300.
Work about 8 hours
I am about to start one in Foam/carbon just for fun.

#178503 - 05/18/09 05:22 AM Re: Foam strip construction [Re: Gato]  
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I have nothing against alumasts or unstayed rigs, what I did was the cheapest solution I could find where I live.

#178506 - 05/18/09 05:30 AM Re: Foam strip construction [Re: Gato]  
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Quote

I have nothing against alumasts or unstayed rigs, what I did was the cheapest solution I could find where I live.


Ohh please, don't think I have any objections. I think it is very entlightening what you are doing with the masts and hull construction. No need to develop the unstayed rigs, we already know the data related to those.

You are doing new stuff which is many times more valuable.

And thanks for the new data.

Again, for the other designers out there. The 5.8 mtr equivalent (unstayed alu from plain tubing) would come out at 8.5 kg. So a 2.5 kg loss to the unstayed alu mast in that situation. And it will feel the same when accelerating or decelerating. The unstayed rig just has its weight lower in the mast, thus resulting in equality between the two masts. That is good to know as you already state that the dive recovery of the DS12 and Tabby were acceptable.



Quote

I am about to start one in Foam/carbon just for fun.


Now THAT is very interesting.

Also for the F16's. I'm not expecting the foam to add more then about 1.5 kg to the mast weight (using 5 mm thick strips). And we already know that a viable carbon mast without foam comes in at 10 kg when bare. So 12 kg for the bare F16 mast section should be viable; arriving at sub 15kg for the fully fitted mast. With a tip weight a tad above the class minimum of 6kg (alu F16 mast have about 7.5 kg, that is when the supplier ships the right one). And it is homebuildable !

If you can perfect this building method then you really have something very interesting.

So yes, I'll be keeping a close eye on your webpage.

Wouter

Last edited by Wouter; 05/18/09 06:51 AM.

Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
#178714 - 05/18/09 06:20 PM Re: Foam strip construction [Re: Wouter]  
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That looks good Wouter, and I don't mind the freestanding rig support concept. Not sure about skegs, but appendages are a very personal matter if not one design.

#178771 - 05/19/09 04:11 AM Re: Foam strip construction [Re: ncik]  
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Quote

That looks good Wouter, and I don't mind the freestanding rig support concept. Not sure about skegs, ...



Thanks Ncik,

I'm also a bit conflicted about the skegs.

I know about the various advantages of them especially in the ease of use, low cost and ease of production. Also they are a great feature when gettin in and out through the surf; a thing that is very difficult with a dinghy like the laser and still difficult with a boarded cat. However, I personally would love to squeeze every bit of performance out of the basic concept that I can and of course the kids don't seem to mind having them in the various dinghy classes.

If it is any concellation; the design still allows for both although it will be best for either to have different hull shapes.

Other features of the design are of course that it has not martingale (dolphinstriker) as it simple doesn't need one in the slightest. This is the beauty of the presented mast support arrangement the trampoline (tension) induced forces largely cancel the rig forces when it comes to the beams. This will allow even very low grade alu alloys to be used like the T4 tempers. Only exception is of course the bottom section of the mast.

The bows take no rig loads so it should be possible to build these light.

The basic design is ready although I need some way of perfecting the hullshape. I fear only building it will do that. Anyway we'll see about that.

Wouter


Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
#178994 - 05/20/09 08:12 AM Re: Foam strip construction [Re: Wouter]  
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Originally Posted by Wouter

Quote

That looks good Wouter, and I don't mind the freestanding rig support concept. Not sure about skegs, ...

I'm also a bit conflicted about the skegs.

I know about the various advantages of them especially in the ease of use, low cost and ease of production. Also they are a great feature when gettin in and out through the surf; a thing that is very difficult with a dinghy like the laser and still difficult with a boarded cat. However, I personally would love to squeeze every bit of performance out of the basic concept that I can and of course the kids don't seem to mind having them in the various dinghy classes.

If it is any consolation; the design still allows for both although it will be best for either to have different hull shapes.


That's a tough decision to make. A few cruising cats use only one daggerboard and John Shuttleworth says that the loss is 1% upwind.
I can think of other alternatives as well: one board in the middle (under the mast base), external pivoting boards (like old Dutch boats), external daggerboards, pivoting daggerboards...


Luiz
#179032 - 05/20/09 11:30 AM Re: Foam strip construction [Re: Luiz]  
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Well that is true but I believe that it is better to go all the way into one direction in stead of doing something half. So for me it is either 2 daggerboards or a pair of skegs. pivoting centre boards have no advantage what so ever, so they are out anyway.

In my design their are two options that I serious consider

-1- Two skegs and a hull shape that is much like the Taipan 4.9 or the Nacra F18 (not inter 18 or infusion or newer F16's / F18's)

-2- Two daggerboards with aspect ratio of 3 (no need to go overboard here, this is efficient enough).


Option 2 basically means a wetted length of 0.45 mtr and board width of 0.15 meter. This should give the craft a draft of at max 0.60 mtr with the boards fully down. The rudders will stick almost as deep so there is not much to be gained in shallow water ability anyway. 0.6 mtr deep water is just above the knee and that is something whole different from a F18 doing a draft of 1.20 mtr (ribcage height) Or even the Laser dinghy at 0.75+ mtr draft with the board down. Note that the Laser dinghy (in my view the main competition) has a board with aspect ratio of only 2.

The overall length of the daggerboards will then be 0.95 mtr and it will have of course a 10% board thickness.

The difference in performance around the course between a good skeg design and a normal daggerboard design is about 2 to 3%. This may be a bit more when comparing the newest high aspect board that also gybe to the skegs, but nevertheless the difference is small. I'm more concerned about the image the design will present. And if the dinghies have boards then I don't want the catamaran alternative to have "training wheels"

Wouter



Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
#179117 - 05/20/09 08:50 PM Re: Foam strip construction [Re: Wouter]  
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Originally Posted by Wouter


I'm more concerned about the image the design will present. And if the dinghies have boards then I don't want the catamaran alternative to have "training wheels"



Makes sense to me.
Note that a pivoting daggerboard should not be confused with a centreboard. It is a hybrid between a daggerboard and centreboard that has been used in fun boards (windsurfers) for years.

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Luiz
#179128 - 05/21/09 03:10 AM Re: Foam strip construction [Re: Luiz]  
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The Arrow's and Arafura cadets have pivoting centreboards, the big advantage is that its easy to pull down or up and cleat, with a bit of shockcord in the system its fool proof for breakage. The downside is the frame thats needed to handle the board, it makes it awkward to move around within 2ft of the mast.
regards


Jeff Southall
Nacra 5.8 1667 Ram Raider
Nacra 18 Square
Taipan 5.7 134
Mosquito 404
Arrow 1576
#179165 - 05/21/09 08:15 AM Re: Foam strip construction [Re: JeffS]  
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One centreboard in the middle or one in each hull?


Luiz
#179285 - 05/21/09 05:33 PM Re: Foam strip construction [Re: Wouter]  
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Just playing a bit here; was thinking of Gato's pictures during the trip when he was sailing downwind. Seemed like things went a bit too slow.

The size of the depicted asymmetric is 8.9 sq. mtr. but I think 8.5 sq.mtr will be a more realistic size. The depicted pole length is 2.0 mtr and quite short for the given hull length.

Wouter

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Last edited by Wouter; 05/21/09 05:46 PM.

Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
#179299 - 05/21/09 07:09 PM Re: Foam strip construction [Re: Wouter]  
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How big will the mast need to be?

#179323 - 05/21/09 11:18 PM Re: Foam strip construction [Re: ncik]  
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The Arrow (14ft) and Arafura (11ft) have a single central centreboard. It works quite well but it is a pain in light winds when you want to sit in and forward near the mast, the frames for the board get in the way.

Do you think the stayless mast will be able to handle the kite? What about trapeze? That would be cool if it could.


Simon
BLADE F16 AUS405
#179324 - 05/21/09 11:39 PM Re: Foam strip construction [Re: Wouter]  
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Think you said the kids would already go too fast and get too far from the beach with 15knots, and you are still thinking of more power?

#179329 - 05/22/09 01:50 AM Re: Foam strip construction [Re: Gato]  
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Quote

Think you said the kids would already go too fast and get too far from the beach with 15knots, and you are still thinking of more power?



Weren't you also they guy that said that I wanted a boat for myself that I could sit on ? I thought that if I get plastered with that accusation anyway, that I might as well go all the way ! grin (A little joke here)

But seriously, I never intended the boat to be for kids (<12 years) as you remember, but rather for teenagers (>12). And, if the young on the Hobie Dragoon can handle spi then the teenagers on F12 can surely do so too. Although, it must be said that these Dragoon youth are doublehanding. Ohh, it just occured to me that they can double hand on my F12 as well with the weight specs I have on paper. Additionally, the reach will remain the fastest leg, so if any kid can do 15 knots there (and the others are okay with that) then why put on the breaks for the (slower) downwind legs ?


Anyway, I'm looking at the spi only as an option (again for the parents etc), I'm not intending it as a a racing component for youths (10-14 years) if the class picks up in that target group.

I have been thinking about the Water Tribe type events and your own trip in the archipelago. In those situations a spinnaker will surely be a welcome addition. It also acts to keep the design interesting when the owners get older and allows for more market for the builders. The latter is important to improve on their economic viability.

That is basically the idea behind it.

Wouter


Last edited by Wouter; 05/22/09 03:15 AM.

Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
#179330 - 05/22/09 02:09 AM Re: Foam strip construction [Re: ncik]  
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Quote

How big will the mast need to be?



The same size it is now.


Quote

Do you think the stayless mast will be able to handle the kite? What about trapeze? That would be cool if it could.



Yes and yes.


Uhhmm, may I point out something here ?

I have a feeling that many of us here are evaluating the different design features with their gut rather the contents of their sculls. I mean that if the sheeting system can put the leech under 150 kg of tension and do so on a 2 mtr long boom then why does anyone think that a spinnaker luff tension or a trapeze wire are a problem for the same mast design ?

To give everybody an idea of what a commericially bought 250 Euro unstayed aluminium mast can handle I present the following example. On a class 5 landyacht (5.5 sq. mtr. sail on a 5.5 mtr mast), the lower mast section is 50 mm in outer diameter and it handles a 5:1 sheet system fitted to boom about 1 mtr away from the mast. When combined with the heeling loads this means the unstayed mast can handle about 250 kgm bending loads. The sleeved sail design handles in this case a max luff tension of 110 kg and a max leach tension of about 140 kg and is as flat as a board.

My F12, even with a 3:1 sheet system at the leech and a 75 kg skipper, will only put the mast under 294 kgm bending loads. An increase of only 18% and still well within the safety margin for the mast.


The luff tension on a 8.5 sq. mtr spi will not get anyway near 150 kg and neither will a man on the wire. But more importantly the spi luff tension and mainsail leech tension will largely cancel on another and the sideways loading that the spi+mainsail can put on the mast on the downwind is always less then the load the mainsail can generate when sailing close hauled. That is why we don't double trapeze downwind on normal cats. This means that a mast design that works upwind can always handle a spinnaker. The same cancellation principle applies to a trapeze (here the trapeze load and sail force load largely cancel one another)

One reason I opposed trapeze wires is that the proposed platform and rig don't really need it. It is already a wide boat for the rig. It compares to a 2.90 mtr wide F18 (which are now only 2.60 mtr wide). When taking the lower heeling moments of the smaller rig into account then 185 kgm (or a 67 kg skipper on a 50 kg F12) will already achieve parity with that design when hiking. A skipper of 45 kg would do so when on the trapeze, but I personally focus more an having such light crews team up for the F12 rather then solo sailing them. The other reason is that I want to avoid the cost of the trapeze gear (like harnasses that kids quickly grow out of) as well as the hassle associated with it, like puncturing the hulls with the hook. The reasons for not supporting a trapeze were however never technical in nature, the unstayed mast can take the loads associated with it. More of problem will be how the sail will respond under mast flexing. It may become hard to control properly, but only just giving it a try may give the answer there. The estimates however, suggest it may still be acceptable.

Personally, I like the unstayed mast setup idea with a spinnaker. Note that there are no side stays or forestay and the spi can gybe very easily in front of the mast. It can be a very clean set up altogether. The very small spi area may also allow using cheap non-ratcheting blocks. The spi pole is just the same section as the boom (same length etc) with three lines to support it. That leaves only the spi sail itself as the major cost, but with what a performance gain !

Wouter

Last edited by Wouter; 05/22/09 03:29 AM.

Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
#179407 - 05/22/09 02:37 PM Re: Foam strip construction [Re: Wouter]  
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Wouter,

If you want a spinaker halyard and two trapeze lines to work with a sleeved main, it will be necessary to attach the three of them to the mast after it is already inside the mainsail sleeve. It can be done if the main is like the Laser, without halyard.

In this case one alternative would be a furled spi or screacher without halyard, with its top swivel attached directly to the mast. The spi/screacher would be furled for upwind sailing. Maybe its foot could be attached to a forward bridle instead of more complex pole?


Luiz
#179453 - 05/23/09 06:41 AM Re: Foam strip construction [Re: Luiz]  
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Considering the tensions the leech of an unstayed rig will see anyway I think we can simply attach the turning block for the spi halyard directly the sleeve itself. It will need to have a local reinforcement there and probably a strap inside the sleeve.

An alternative is to just have an opening in the front part of the sleeve and have an eye strap protrude through it on which the turning block is mounted.

A third alternative is to go for a mast top spinnaker and that is not a problem for a mast that is unstayed already. If we do that then this F12 will be monster downwind boat because that will increase the sail area by 2.5 sq. mtr. to a total of 11 sq. mtr. You'll be beating F18's on the downwind legs !

Personally, I like the block-stitched-sleeve and internal trap the best. Simple, cheap and doesn't affect the capabilities of the unstayed rig in any when the spin is not fitted (as in complete 360 weather vaning)

Wouter


Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
#179454 - 05/23/09 06:47 AM Re: Foam strip construction [Re: Luiz]  
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Wouter Offline
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Quote

If you want a spinaker halyard and two trapeze lines to work with a sleeved main,


I'm personally not thinking about any trapeze lines on this design. If we need more righting moment then I rather choose to make the boat wider. However, I don't think we need to go beyond 2.0 mtr width anyway.


Quote

It can be done if the main is like the Laser, without halyard.



While it is possible to make the sleeved sail "hoistable" by giving it a zippered sleeve, I don't favor that solution. I don't think it is needed as the sail can weathervane 360 around the mast as it is anyway. So there is no safety issue involved. Additionally, zippers are expensive and wear down quicker over time then the sail itself.

If ever the rig needs to come off during a waterborn rescue then one can simply pull the sail off from the top. Hell, demasting the unstayed rig in the same manner will be viable as well. Unhook the support tubes and have the sail fall forward in the water between the bows. Unhook the mast foot and then slide the bottom section out of the sleeve and work your way up the mast that way while pulling it more and more on the boat and rolling the sail around the boom. The top mast section will then be slid out from the top. Rigging the boat up on the water will be the same procedure in reverse. I don't think any of the stayed rigs can mimic something like this. And ohh, the support tubes slide up and down when the mast moves forward or backwards and thus guide the mast in the sideways direction during any of this. It will also be possible to have the mast fall back onto the boat after unhooking the boom. Again the support tubes will double act as a back rest to the mast (while rotating around their supports on the hull. Hell the sleeved rig can even be folded up like that. Just slide the upper section out of the bottom section and fold it along side the lower section. This package will then only protrude some 0.75 mtr past the sterns and about 0.5 mtr in front of the mainbeam while the lower section stays attached to the mainbeam.

We can even use the spi halyard as a support line during lowering or raising of the rig. The option is many and I'm really beginning to appreciated this unstayed rig solution.


We don't use halyards on the unstayed rig on landyachts and I don't see any reason to do so on the F12 when using the same setup.

Wouter

Last edited by Wouter; 05/23/09 07:05 AM.

Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
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