Why the inefficient round masts?

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EarthBM
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Why the inefficient round masts?

Post by EarthBM »

Does anyone know why DF went for a fixed round mast (at least on DF 35 Touring)? I haven't seen other masts, other than the elliptical one on DF 1000. Theoretical power penalty for a fixed round mast vs rotating tear-drop shaped one is ~20-30%. Empirically, for boats with rotating masts (from my first hand experience on beach cats, and second hand on Farriers) not rotating the mast costs ~10% of waterspeed, which kind of adds up (5% for mast shape, 10% for rotating it, the rest is balanced by hadsails which hopefully provide same power).

Do DF 35 Extreme, 920s and 1200s also have fixed mast?

Has anyone tried to upgrade? I was told it may have been an option on 1000s.

I am kind of guessing that on DF 35s it has to do with the process of making a carbon fibre mast being difficult as it is, just thought that for the price they could've made an efficient mast.
Ivan -- DF 35 #29 "Lykke"
Double Horizon
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Post by Double Horizon »

Maybe Quorning got a "deal" on round masts? (just joking) I was told it was because it makes the boat less likely to be blown over while folded, in a cross wind. Yes a rotating mast was on option on the 1000 racing version with aluminum mast, but last 1000 made had the racing rig dimension in CF and it was round.
Last edited by Double Horizon on Fri 03 Jun 11, 12:09, edited 1 time in total.
Larry - Former Owner DF-1200
Mario
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Post by Mario »

Yes, I have got the same answer from JQ: the round mast has smaller side- area and gives smaller lateral-resistance than elliptical one, which is essential at 20 m over the water.
At the end of April we had a bit stormy weather in Cph and one day my fellow phoned me from our marina: Mario come and se your boat. When I came, the boat lifted the windward ama up to 1-1,5 m over the water in gusts :shock: . I have never seen it before. I jumped on the boat and fold just one meter out, which was enough to keep the boat on the water. I don’t remember how strong the wind was, sth like 20 m/s I guess, but the wind was perpendicular precisely. The boat was moored with all 4s, had genua rolled and with cover on stay, and big was with cover on the bom – all give lateral resistance and tilt the boat. I know that Corsairs with elliptical mast flip at gusts when folded (and moored in all 4s in a marina!).
Slowhand
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Post by Slowhand »

I am pretty convinced that Larry is closest to the most reliable explanation, although he present it as a joke. The mast on a 920'er is spun and therefore not very flexible. This means that it must be braced exaggerated and thus becomes very heavy. Basically a strange design for a boat made for speed and performance. A wing mast can be rotated and easily be set reasonable in high wind in harbor- just as on the DF 800.
Double Horizon
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Post by Double Horizon »

Slowhand wrote:I am pretty convinced that Larry is closest to the most reliable explanation, although he present it as a joke. The mast on a 920'er is spun and therefore not very flexible. This means that it must be braced exaggerated and thus becomes very heavy. Basically a strange design for a boat made for speed and performance. A wing mast can be rotated and easily be set reasonable in high wind in harbor- just as on the DF 800.
What you wrote about a wing mast doesn't consider an unattended boat or folded boat. Dragonflies and Farrier trimarans have been known to blow over when folded in a slip or in dry storage. The 1200 is very heavy and is probably the only one stable enough to be left folded in a storm without too much worry, on dry land. Any waves in a slip and the picture changes. When storing my past boats for winter (a 920 and 1000) I always used to use the halyards (one each side) to attach to a very stable or heavy anchor point.
Larry - Former Owner DF-1200
Slowhand
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Post by Slowhand »

I agree - the boat should not be left unattended in heave weather, but then we can go back to the initial question: why then a round fixed mast?
Where I live we are not allowed to store the boat on land in the winter with mast on. We have to demount, and this carbon mast is really heavy - 3 persons to handle it.
My point is, that designing an inefficient and heavy mast like the one on the 920, and even not solve the capsize issue, can only be drawn to a question of economy.
clarivoile
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Post by clarivoile »

obviously!
D920 E
Double Horizon
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Post by Double Horizon »

Slowhand wrote:I agree - the boat should not be left unattended in heave weather, but then we can go back to the initial question: why then a round fixed mast?
Where I live we are not allowed to store the boat on land in the winter with mast on. We have to demount, and this carbon mast is really heavy - 3 persons to handle it.
My point is, that designing an inefficient and heavy mast like the one on the 920, and even not solve the capsize issue, can only be drawn to a question of economy.
It is heavy because of all the steel. The collars near the spreaders are very substantial stainless and certainly not cheap to make. The mast cap and rigging are also very heavy. I don't know enough about mast design to say how it should be done, but clearly more CF along with synthetic rigging would help allot. I just replaced my backstays with Dyneema rope, and replaced about 36 pounds with about 7 pounds (including thimbles and quicklinks) for just those two wires combined. I increased windage slightly though.

The jumper stays alone on the 1200 must total around 100 pounds, and two people can carry the mast without the stays and spreaders, but once it's all assembled that's no longer possible.
Larry - Former Owner DF-1200
EarthBM
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Post by EarthBM »

On Friday I spoke with the guy who helped design the tear-shaped rotating rig on some F-tris. He Said that i was off with 20-30% power penalty estimate for a fixed round mast. More like 10%. When my Hobie 16 mast was getting stuck after a gybe the penalty was worse than having a fixed round mast because its efficient teardrop shape was perpendicular to where it should've been. So he said that for a cruising boat, with reduced windage, it made sense. He did say that he was a bit surprised by how complex DF's spreader-shroud set up was.

Larry, do you trust the splices on your new backstays?
Ivan -- DF 35 #29 "Lykke"
Double Horizon
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Post by Double Horizon »

EarthBM wrote:
Larry, do you trust the splices on your new backstays?
Absolutely! I used a modified Brummel splice (see instructions at the Colligo Marine site http://www.colligomarine.com/docs/misc/ ... ev_1_2.pdf ). I have become very proficient with this splice and have done it more than 25 times, so I have become pretty fast (but still careful) and no longer need the directions. I used the 72-times-diameter minimum bury and tapered the ends gradually as directed. I showed my rigger some of my work and he said he couldn't do better splices in his shop.

The rigger says the splices have at least 90% of the rope strength which is rated at 34,000 pounds break strength.

A locked Brummel splice has each side of the loop interlocked in the weave, and then the tail is buried so the weave and tail can't pull out. The buried tail is squeezed when the line is loaded, the same way a straw toy finger-trap grips your finger. The stronger the pull, the stronger the grip.

The weakest part is now the quick links, or perhaps the chain plates. The quicklinks Quorning uses are rated 2200 kilos SWL so even if they use a 5:1 safety margin for that rating, that would mean 24,250 pounds. The rated break strength for the original 8mm dyform wire is less than that.

I used Dyneema on my DF-1000 about 6 years ago and the current owner says they still look to be in good shape. The Dyneema I used then was supplied by Precourt in Canada but they are no longer in business. they did the splices then, and used the same modified Brummel splice.

Picture link http://www.nstsystems.com/multihulls/Pa ... igging.jpg
Larry - Former Owner DF-1200
EarthBM
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Post by EarthBM »

Nice! I once posted a question about what spares one would need if he were to go on a 10yr voyage. What I really meant was "are there DF-specific items that would become a problem if Quorning closes shop because of the economy, so better get them now?". Waterstays that are to be replaced every 5 years (I still can't believe this is reasonable) were on my mind. Now It looks like we are very close to lightweight Dyneema waterstay replacements!
Ivan -- DF 35 #29 "Lykke"
Double Horizon
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Post by Double Horizon »

I also replaced the stays that connect the tip of the bowsprit with the ama bows with Dyneema, and have plans to replace the bow stays that prevent folding. Those will be replaced with under-net stays by replacing one of the forward hinge bolts with a strong (load rated) eye, and connecting to the outer end of the aft cross beams. I plan to use lashings to be able to adjust that.
Larry - Former Owner DF-1200
gminkovsky
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Post by gminkovsky »

Larry,

I am very interested in your approach to anti-folding.

Is the eyebolt to be custom made?
Do you plan to replace the actual pin in the forward hinge or one of the bolts that attach the hinge to the main hull?
What will be the attachment point on the outer end of aka?
How much work will it be fold/unfold?

George
Double Horizon
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Post by Double Horizon »

gminkovsky wrote:Larry,

I am very interested in your approach to anti-folding.

Is the eyebolt to be custom made?
Do you plan to replace the actual pin in the forward hinge or one of the bolts that attach the hinge to the main hull?
What will be the attachment point on the outer end of aka?
How much work will it be fold/unfold?

George
George, in this case also, I looked up the breaking strength of the wire Quorning used for the bow stays, and all of my components ratings will exceed that. (The geometry of the bow stays is such that the load on the under-net stay will be less, because the angle of pull is much less.) I replaced one hinge bolt with a Wichard eye nut, 1/2" and 316 stainless hex bolt. (I had to enlarge the 12mm hole slightly with a 1/2" drill). The rated breaking load of that eye bolt is 15,550 and the nut is also calculated to be similar to the original wire (Tensile strength of 316 stainless is 35,000 psi).

For the rear attachment, I plan to use a Wichard folding pad eye model 6505 with backing plate, similar to the type used to attach the end of the ama fold-in lines on the 1000. The size I chose has a 3000 kg SWL. It would be attached to the bottom of the aft lower flange of the rear cross beam, as far outboard as possible and still low enough to let the Dyneema clear the nets without interference. I haven't started this project yet, so can't give exact placement.

The longer section of Dyneema would be 3/8" diameter spliced with thimbles at each end. A quick link would attach the forward end to the eye, and the aft end would attach to a snap shackle on the release side. The lashings would be at least 5 turns of 1/4" Dyneema used between the aft folding pad eye and a Wichard Trigger Snap Shackle model 2655 at the aft end. This is a very strong shackle that will not release accidentally (and even though they are expensive I was able to find two of them on eBay for about half normal price). The snap shackle would be situated below the gap between the net and aft beam, for accessibility. When released for folding, the longer section of Dyneema would be stowed at the aft lifting eye and attached with a shock cord or some other quick method. The snap shackle on the short section of lashings could be allowed to dangle, or could also be secured with shock cord.
Larry - Former Owner DF-1200
Double Horizon
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Post by Double Horizon »

One other note about working with 12-strand single braid Dyneema. There is some looseness in the weave that doesn't come out until the rope is under high load. This causes "constructional stretch" which is about 2% (my estimate) using Amsteel or Endura 12. I had to re-splice my upper backstay sections a foot shorter because of this after a few weeks (not an issue). The Dynex Dux eliminates this, at extra cost, but even using Dux you can expect some constructional stretch in the splices, because they are long with 72-times-diameter bury. The buried portion of the splice also increases the diameter of the line which reduces the line length by about 8 times the diameter (2" with 1/4" line or 4" with 1/2" line). The constructional stretch in these splices will also be a factor, so my advice would be to ignore the length reduction in the splices because most of it will work back out in constructional stretch.

Once the rope has been used and constructional stretch has worked out, the situation will become stable and you will not see any significant amount of additional stretch unless the line is under CONTINUOUS VERY high load (like around 10% or more of rated strength). So for any application where length is critical, like bow stay replacement, I would recommend the use of the Dynex Dux and lashings to allow fine adjustment.
Larry - Former Owner DF-1200
Double Horizon
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Post by Double Horizon »

Follow-up note: I have replaced my Dyneema backstays again with the stainless stays Quorning provides. I had made the mistake of sizing the Dyneema for strength rather than stretch, and the Dyneema was not large enough in diameter to control stretch under the loads in high winds. I would not try this again unless it is Dynex Dux (pre-stretched) or another material of larger diameter that limits stretch and creep.

Also - after just 2 months of use I found significant chafe where the battens rub the stay -- this would likely become a problem after several years, or even sooner for someone who makes a long downwind run (e.g. crossing an ocean in the trade winds).
Larry - Former Owner DF-1200
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