BIPOLAR

Build logs from members building catamarans, trimarans and other multi-hull variants.
mahnamahna
Posts: 579
Joined: Wed Aug 02, 2006 4:48 pm
Location: Gosford NSW

Re: BIPOLAR

Post by mahnamahna » Wed Feb 12, 2014 11:34 am

Hi Groper,

Perhaps I can answer some of these questions for you as I am building the same boat and rig, as is Mike, (Whimsical). As you probably already know, the masts rotate on posts that are "buried" in the hulls and glassed to the soles, the deck topside and underside as well as to the bulkhead itself. The posts are stepped almost against the inside of each hull side and almost against the chamfer panels but not quite. As a consequence, the 500mm wide doorways through to the sections in front of the mast post bulkhead needed to be moved about 200mm outboard from their original position on the hull centreline in each hull, and fyi, the mast posts are on the first of the full width spanning bulkheads (in a normal rig the mast is stepped on the second spanning bulkhead so our masts are about 2 meters forward of a normal rig.

The mast posts are in each of the forward berths on the front bulkhead of those rooms and an ensuite on the starboard side and a walk in closet on the port side is on the other side of the doorways that were moved to make room for the post and to give the posts solid bulkhead to attach to, which otherwise would have been through and block half the doorway if it was left in its original position and of course that would neither work as a doorway nor give the post adequate bulkhead to attach to. So as mentioned the 500mm wide doorways were moved about 200mm outboard from the centre line of each hull. Here is a pic taken just as I was completing the doorway move, and prior to that the 4 layers of glass on the sole to dissipate the loads that the post will generate:

http://www.mahnamahna.com.au/port%20bh4 ... 20back.htm and

http://www.mahnamahna.com.au/sb%20mast% ... ed%201.htm,

taken from my blog at the time http://www.mahnamahna.com.au/August%202009.html

We have webs under the sole then the actual hull, so the post does not step to the hull itself. This support glass needed to be continuous, not broken by the bulkhead so it needed to be partially removed then replaced once the sole reinforcing was done. As I noted in my blog at the time, once the bulkhead portion was glassed back in (and the doorway moved) you would be hard pressed to tell the work had been done.

As for the cabinetry along the outboard hull sides, I simply curved the cupboards inward toward the hull sides from the 300mm full depth to about 150mm to meet the new doorway edge and this creates a curved companionway from middle of hull to the outboard sides. http://www.mahnamahna.com.au/shaped%20c ... 20robe.htm It all works rather well and in fact the new door position helps with cupboard size and amenity in both the ensuite and wardrobe so it in fact would be a good idea even without the posts. You get much greater depth of bench tops which is especially good in the ensuite. You lose a little cupboard where it needs to curve out to meet the new door position but you gain more than you lose.

I dont yet have my posts which may be a good thing. as with the reduction in mast size, it may also mean a slightly smaller post diameter. Michael has removed 3.7 meters of mast from the top of his masts, as mine are not yet made it occurs to me that I could possibly remove length from the bottom of my masts rather than the top (and of course not build the extra length at all rather than build them full length then cut them back down, that would be a huge waste of money in extra material) and in the process also reduce the overall cord of the wing. The original masts have a cord length of over 700mmm at the base and 380mm at the top, but if you take some 3.5 meters off the bottom rather than the top as Mike had to do, then the cord will be shortened all the way along so that at the base it would be around 600mm (staying 380mm at the top). This will reduce the drive of the wing, which might mean less length need be removed, less material and weight (and cost) per mast, and possibly need and be adequate with a smaller diameter post. This is all yet to be discussed with the engineers. But less weight aloft is a good thing, and of course less material (carbon fibre and resin) would reduce the cost significantly, remember Mike removed almost 25% of mast so it would not be unreasonable to expect that building them shorter in the first place would reduce cost by at least 20%.

As it stands with 200mm diameter posts, with the doors moved outboard the posts do not intrude, in fact I will have one of them inside a hanging closet in the starboard hull so that it will not even be visible inside the boat unless you look inside the cupboard. On the port side the bunk is athwart ships so the post is going to be visible, but I will glass shelves to it or an angled wall to house a wall mounted screen for a tv of about 15 inchs connected to the main screen feed so I can view the plotter/radar multifunction display from the berth as well as entertainment.

Sorry for the essay, I hope this answers your questions.

Very exited by those light wind (to Windward!) numbers. Mike in Perth once said to me if you can achieve 80% of windspeed in light air you are doing well and Michael got to 85% in the lighter air. Very confident now the rig is the way to go.

Cheers,

Paul

groper
Posts: 239
Joined: Sun Nov 18, 2012 11:23 am
Location: cairns

Re: BIPOLAR

Post by groper » Wed Feb 12, 2014 9:48 pm

Thankyou very much for that MM - i for some reason did not click that you were also going down the biplane rig path...? Must have missed that amongst everything else on the forums..

This location you described for the mast posts, was the only location i could possibly figure in my boat... although i wish i had the hull volume you guys do with your bigger boats - my hulls are quite a bit narrower and i really dont know if i could fit a mast post and a doorway in that location - even if it was shifted off to one side... ill have to do some measuring and double check that...

I was also concerned that this location was too far forward in my boat and therefore the CE of the sails too far forward. This bulkhead on my boat is located at 71% of the LWL... If i convert the hull to a sailing boat and complete the transom extensions with rudders, it will be 73% of the LWL... how does that compare with yours?

Who was the designer of this wing masted biplane rig?

Your right on the cost and weight of the smaller masts... by my calculation, the mast cost in materials and weight should get exponentially less with decreasing mast height. This is because the cantilever bending equations show an exponential stress relationship with increasing length. So a 25% shorter mast should equal something like a 50% lighter mast. 50% less carbon and resin is alot of money. The labour cost in making it will be about the same tho i figure...

I might just be able to jump on this band wagon yet...

rexd666
Site Admin
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Location: Melbourne, Vic

Re: BIPOLAR

Post by rexd666 » Wed Feb 12, 2014 10:22 pm

Good to see it's working out for you Michael. Someone has to be first to find out the issues, but sounds like you got them sorted quickly and back on the water to enjoy the hard work. I do wonder if the cost savings will be lost in having to design the mast again for the new length and loads if others go that way.

Paul I see you are posting on yikes.com.au again, give me some reading to catch up on tonight. Hopefully things are back on track. Heading over to your own build thread to see if I have forgotten any updates.

Groper I could have sworn you were an Engineer especially when you pull out the cantilever bending equations.
Steve

mahnamahna
Posts: 579
Joined: Wed Aug 02, 2006 4:48 pm
Location: Gosford NSW

Re: BIPOLAR

Post by mahnamahna » Thu Feb 13, 2014 12:33 am

Interesting story Groper on the rig design and engineering.

Of course Schionning initially used the rig idea on their Radical Bay 8mt but they did not invent the idea AFAIK. There have been some notable BiRig racers such as Team Phillips for example. On the RB8's the rig is stepped on the inboard side of each hull. Initially Schionning had the rig for the 1230 bi on the outboard side of the hulls, but well after a number of plans/kits were sold for it the engineering for the rig was still not forthcoming, for various reasons including family upheaval vis a vis Spirited.

Trying to tread carefully with my words as I dont posess all the facts, I just know a number of us started to lose patience with the lack of rig information. Anyway, after a while some rig details finally emerged and Schionning had decided to move the rig to the inboard hull sides as it helped with getting the sheeting points closer to directly below the booms that was not possible with the outboard rig placement.

However, when the rig was placed outboard the distance between the masts was 6.5 meters and the booms were 6 meters allowing for clearance so that the boat could be depowered rapidly by releasing the sheets and allowing the masts to rotate with the wind and spill the power. When the rig was moved to the inboard side the distance between the masts shortened to 5.5 meters, but Schionning wanted the booms to remain at 6 meters to maintain their original sail plan.

This was unacceptable to Mike, Michael, Sean and me. I in particular was sold on the whole idea of building a cat on the rig being able to be depowered fast by releasing or cutting the sheets as I have little to no sailing experience and having what amounts to brakes holds some attraction to me! To no longer be able to do that, 3 years into my build was totally unacceptable. And Schionning was very adamant we could not shorten the booms and would not engineer it to our design requests. Fair enough, its their design and if they dont want to put their name to that so be it. But it didnt make sense to me but I am completely ignorant in design and sailing knowledge. So I spoke with another designer that had successfully designed a bi rig cruising cat and he confirmed to me that not being able to release the sheets and have one boom clear the other mast was not a good idea. Even if I was willing to learn not to rely on being able to release the sheets, should a sheet ever break and a boom crash into the other mast, something every catastrophic is going to break, probably the other mast! SO, we commissioned probably Australia's if not one of the world's leading carbon unstayed mast experts in Rob Denney to consult and he recommended an engineer/fabrication company that we that are having wings made are all using. Those that dont know of Rob, google Harry Proa. Rob advocates for unstayed masts in many forums and believes they are the way to go on any boat.

I have been somewhat concerned that the rig we have had since is also not what I was sold on when I first signed on. Schionning wanted the rig to be shorter (which may explain why they didnt want shorter booms) because another design element they were keen on was to lower the centre of effort of a cat so as to counter one of the flaws inherent in the form, that being the possibility of flipping a cat if caught with too much sail, of course the rig cannot help with pitchpoling but a shorter rig does make it virtually if not actually impossible to fly a hull and tip over sideways with short masts and unstayed carbon masts will bend and self spill some of the power before the tipping moment, (engineers and sailing experts excuse my laymans view and explanation) and I also assume that having a mast on each side also spreads the load to both hulls so that both are being pushed down somewhat also resisting the ability for the windward hull to fly.

But the masts ended up much taller than I had initially been told by Schionning they would be. So now that Michael has cut his down and found that they work better at the shorter height I am now very very happy with the rig, it now has every element I was sold on in the first place.

Rexd, I should have a reasonable update the end of the week. Transom steps have taken me a while longer than I would have liked because I am making them up as I go along now. very happy with what I have come up with though.

A tip for new players though, the moment you move off standard and go bespoke the time factor goes up considerably.

groper
Posts: 239
Joined: Sun Nov 18, 2012 11:23 am
Location: cairns

Re: BIPOLAR

Post by groper » Thu Feb 13, 2014 6:56 pm

Yes Paul, im aware the biplane rig concept has been around for a long time, i was referring to the 'specific' rig design for you guys as it seems a little bit of a departure (for the better) from the radical bay type rigs ive seen using wishbone booms etc.

I like the idea of the articulation control at the mast boom intersection, and its very important to have control there. If i do something similar, i may end up using a hydraulic ram with push button control to achieve the same end rather than the winch in the boom...

The required boom length is what gets me with this mast location on the forward main bulkhead. It has to be quite long in order to get the CoE back far enough and give a longitudinally balanced sail plan. Could probably balance this out by shifting the centerboard location, but this will probably clash with other design considerations - such as the location of the 2nd full span bulkhead. So i can understand why schionning was reluctant to reduce the boom length. At the same time - i also think that 6m booms is way overkill in terms of sail size when you have an efficient rotating wing rig with squarish top sails.

My idea of the ideal sail plan would be to step the masts on the 2nd full span bulkhead, keep the reasonably tall masts, but reduce the boom length for the same sail area or even slightly less area. This way you have a higher aspect ratio sail plan which is more efficient for its size. I cant do this on my current boat tho as the stub masts would have to go through the cabin pillars and it would ruin the looks of everything, not to mention the huge complexity reinforcing the top bearing area with the cabin already mostly finished and the windows glued in.

mahnamahna
Posts: 579
Joined: Wed Aug 02, 2006 4:48 pm
Location: Gosford NSW

Re: BIPOLAR

Post by mahnamahna » Thu Feb 13, 2014 11:53 pm

groper wrote:
I like the idea of the articulation control at the mast boom intersection, and its very important to have control there. If i do something similar, i may end up using a hydraulic ram with push button control to achieve the same end rather than the winch in the boom.
I am not sure we are at cross purposes here. The wing rotate freely on the posts, if not for the sheets they could rotate 360 degrees, but 180 degrees is all that you require for depowering of course. My complaint was that with the other mast blocking its path, the inboard tacked boom, if ever released (deliberate or accidental) would smash into the other mast and something would break, most likely the other mast. After we commissioned our own engineering with shorter booms we reinstated the ability to release the sheets to depower.

It seems though that engineers want to over power the boat, either with too much mast or too much boom!

The engineering does not specify controlling the wing to boom angles.

Speak to Michael about this, you may find that on a rotating rig with wing mast such control is redundant. He (Michael) built electric winches into his booms to control the boom to mast angle, but found that once he had sufficiently lubricated the mast bearings so that it was able to more freely rotate, I believe (and I am sure he will give you more detail on this when he gets a chance) he found that the wing to boom angle was not so important and that just control over the sail/wing angles with the sheets and letting the rig decide its own mast boom angle was just fine and one less thing to worry about.

The boat/rig as Michael has described is plenty fast and that it was originally designed with too much power.

You may be over thinking it a little bit for a cruising boat. Part of the attraction (besides the built in safety aspects) is the simplicity of the rig, in both its structures and in the sailing itself. No constant tweaking of strings to try to wring out fractions of knots of speed.

groper
Posts: 239
Joined: Sun Nov 18, 2012 11:23 am
Location: cairns

Re: BIPOLAR

Post by groper » Fri Feb 14, 2014 8:11 am

Yes I fully understand the depowering point you made earlier. There's also another useful ability of letting the booms out past the masts and that's down wind sailing with no chance of accidental gybe... Well if you do gybe the booms swing over the bows rather than the places people are more likely to be standing. Downwind performance should be better too with the rig still generating lift as opposed to simply drag.

Regarding the mast boom articulation- rotating wing masts themselves need to be trimmed for ideal performance. You can do this a couple of ways but the traditional way is with a mast spanner and ropes, so that you can control the trim. My idea was to get rid of the ropes and simply use the sheet in combination with a mast to boom hydraulic ram. It sounds more complicated but I don't think it is, I think it's more elegant than the in boom setup Michael has chosen , but I could be proven wrong if I ever get to doing it. Either way, you can't just let the mast sit in whatever rotation it wants to, unless you don't care about performance that is- which means building a wing mast in the first place was a waste of time and money- should have just built a round pole that doesn't need trimming. It won't naturally assume the correct trim by itself from the boom sheet alone. Ideally you should have a wind vane on the leading edge of the mast so that you can see the incoming flow stagnation point which allows you to trim the mast into ideal angle of attack.

Anyways, how far aft from the bows are you masts?

Was anything like tanks etc moved aft to compensate for the extra weight forward with this rig?

mahnamahna
Posts: 579
Joined: Wed Aug 02, 2006 4:48 pm
Location: Gosford NSW

Re: BIPOLAR

Post by mahnamahna » Fri Feb 14, 2014 10:29 am

Groper,

Yes downwind there should be no chance of gybing, the sheets should prevent them swinging any further and over the bows, only way for the booms to swing past dead aft to the other tack would be to completely back wind them, and that would mean a 180 degree wind shift would it not?

The winches visible on Michael's mast are not for boom control, they are his halyard winches. Michael had electric reversing winches inside his booms to control boom angle. I think he now feels these redundant as he does find that the wing feathers to the best angle on its own independent of where the sheets dictate the boom angle to be (initially this was not the case but it turned out to be insufficiently lubricated bottom mast bearings). But I will let him confirm this to you himself should he choose, certainly Mike (Whimsical) is of the same opinion, that this control will not be necessary and automatic, I just follow their lead, not having any sailing skills of my own to rely on.

Regarding moving tanks etc, no there was no instruction from designers/engineers to compensate for weight. Funny you should say that though, there have been 4 1230's launched now and they all seem to be a little nose down in their attitude (I have seen pictures of all 4 in the water). One of them has standard rig, one of them had no rig but still displayed the nose down. Michael compensated with water tanks aft. The nose down must be a design flaw for all 4 of them to end up this way. Further evidence to me, a layperson relying just on common sense, that whilst engineers now use computer modelling to instruct them as to loads etc, they can still get it wrong in the real world, and whilst both the designer and our independent engineers wanted bigger rig/sail area, I as a cruiser (with very limited knowledge and skills) am far more comfortable with a more modest rig.

I wont be worrying about tweaking out an extra half a knot regardless of how expensive the wing masts cost. I am sure you will agree that from Michaels reports, videos and pictures, there isnt any need to concern myself with lack of performance of the design in any conditions.

I will measure the distance aft from the bow the masts will be and report back later.

michaelo
Posts: 51
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Location: Melbourne

Re: BIPOLAR

Post by michaelo » Fri Feb 14, 2014 7:36 pm

You are correct Groper, the mast to boom angle needs to be controllable. The sail exerts a lot of pressure on the trailing edge of the mast and unless the mast rotation is restrained the mast would tend to rotate until it's up against the boom. I have what might be called a spanner from the mast trailing edge just above the boom with the end connected by a line to a winch inside the boom. When tacking the mast flops from one side to the other to the extent the line allows. Sometimes if the wind is too light to push the mast over when tacking I winch the mast to straight ahead to give it a help.
Being able to adjust the mast angle is a necessity. The ideal mast/boom angle changes with point of sail and it is useful to be able to lessen the rotation to depower the rig in strong winds, or when on anchor or mooring we tie the masts off at a large angle maybe 40deg or more in opposite directions.
With regards to sail plan and balance I suspect, though with only limited experience, that cats are fairly insensitive to where the CE and Centre of resistance are. With my boat it seems to make little difference, lot of sail up, little or no sail up, boards up or boards down which affects the CE location, the boat feels balanced and tracks well. Obviously a cat with 2 long narrow hulls is quite different from a monohull as far as balance is concerned.

Paul I don't think the bi rig is actually simpler to sail than a normal rig. Sure,just tacking up the bay I can do from the helm seat with no other input than turning the wheel but for most other situations having the extra sail/boom to handle creates more work or potential problems than with normal rig and roller furling headsail. Gybing is trickier with two booms. You may be able to release the sheets to allow the booms forward but you have to get the booms back the way they came and not wind the sheets around the masts. Raising, lowering, stowing the sail on a boom all takes longer than having a roller furler. I'm not saying that overall the advantages of the bi rig don't outweigh the disadvantages, just that handling the bi rig is not simpler

groper
Posts: 239
Joined: Sun Nov 18, 2012 11:23 am
Location: cairns

Re: BIPOLAR

Post by groper » Fri Feb 14, 2014 8:46 pm

haha, how about 2 roller furling booms for your sails! :idea: i know i know, where do you draw the line, the $$$ has to determine the line in the sand at some point :lol:

Ok so it seems this bi rig may be doable on my boat afterall... this opens up alot more thinking on my part. If i do this, im gonna do it myself... from engineering right through to infusing the carbon masts in a female split mold.

Im thinking of a slightly different approach, so as to avoid a stub mast/ wingmast 2 peice arrangement. This would add complexity to the build. Im thinking more along the lines of a single 1 peice mast construction (wing and stub would be 1 homogenous peice) with the bearings mounted in the boat very similar to the way Rob Denny has done his proas. I dont see why an overhanging flange on the mast in conjunction with a combing on the deck to prevent water ingress should not suffice in all but the worst case scenario of sheets of water flowing all over the deck.

The plan would be to get the profile CNC hot wire cut in foam, then lightly glass over it and fair it to make a plug. Take a 2 peice female split mold off the plug. Infuse the laminate in 1 shot with a tube bag through the inside of the mast sealed to an envelope bag around the outside of the mold. Id have to get some info from you guys about the bearings and get these machined up...

What hardware are you running to control the sheets? Do you use a track along the cabin top or a fixed point directly from your winches? Any pics of the cabin top showing all this Michael?

Sorry about all the questions :)

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