Thread: Flexible stayed mast - lug rig?

Hi Ian,

The problem is often one of working out where a particular effect comes from and then trying to quantify it in some way.

When I drew up the Goat I was trying to get some of the easy performance of the NS14 class boats which were and are still my favourite boat to sail. Everything is focussed on reducing drag because they don't have much power - only 100sq ft to push a 14ft 140lb (4.3m 63kg) hull and two people through the water.

I thought about the loss of efficiency of the rig compared to the NS14's highly developed lightweight rotating mast and fully battened sail.

So I decided to add 5 square feet of sail. This had little downside because the GIS can be reefed and the NS14 couldn't. Also I had sailed Beth which has about 85sq ft of sail with a beam of 32 inches and knew how the reefing was effective without slowing down an easily driven boat too much.

I used a similar approach when drawing up the lug rig for the PDRacer. I assumed the lug rig, which theoretically is more disturbed by the mast pressing against more of the cross section of the sail compared to the boom on the spirt rig which only affects the lower section of the sail and only on one tack.

So I bumped up the sail area of the PDR lug rig to overcome that extra "inefficiency". So the lug rig is 87sq ft and the sprit rig is 82 square feet.

I have only sailed directly against a lug rig once where the boat was sailed by a hot sailor (Mike in his sexy black PDR) and he absolutely trounced me in light to moderate winds in terms of upwind speed.

So ... 5 square feet more than makes up the difference of the extended "crease" in the sail. At least in light to moderate winds.

I think part of it too is that the homemade polytarp lug sail ends up being a much nicer shape than the homemade polytarp sprit sail. It really is a stupendously good sail for the time and cost invested.

That represents the problem ... Brian has a highly developed rig .. which as a package performs very well indeed. But what makes it perform? His rig is quite different from most of the other scows and you also have Brian, who obviously is a very talented sailor and hugely experienced in the scows pushing the thing along.

I think that all you can say is that he has found a "package" that works very well. Is the performance from the spar curvature, from the sail shape, from the interaction, because his highly developed controls are effective for his particular rig?

It is really hard to know. I would say it is all that and more.

I would also say the difference between the mast touching and not touching is not a critical difference for most rigs, but Brian was trying to overcome a whole bunch of problems with his stiff rig and the side bend was one of the side effects when he had sorted everything else out as well.

His rig is quite different from the others. If there was a dead similar rig without the mast that side bend, then there would be grounds for a clear comparison.

But at the moment I think that the difference might be in the range that a couple of square feet of sail makes for a mid eighty square foot sail at the most. So my route is to avoid the complication and add the sail.

After all it is possible to reef!

MIK

Oh ... second hand windsurfer masts are nowhere strong enough for a one person dinghy - let alone a two to three person boat like the goat.

Just compare the mast diameters.

Staying would resolve the bending load a bit ... but would add considerable compression load that the windsurf masts are also not particularly well set up to handle.

Windsurf masts are not really a very good place to start for dinghy masts. It is better to choose something with a bigger starting diameter and even diameter up to the hounds in a stayed rig.

MIK

Hi guys, guess I had to drop in here! Just sold my Scow so feeling a bit shocked.

There is one place where windsurfing masts are proven to work on the smaller 65 sq ft sail of the Scow. John Claridge actually bought a big batch of alloy winsurfing masts to use for the yard and boom. They had been made by a yacht spar maker but were no good for windurfing.

John used the top 3m for the yard, hence the tapered spars. When he ran out of them he had a devil of a job making a grp yard that match the same bend exactly. The sail design was fixed by the class by then. John also use these spars to make the booms in the early days. He used the 3m starting from the bottom. So the front of the boom was wider in section than the end of teh boom.

My black super fast Lymington River Scow has these spars and was faster than any other Scow on the planet.

Brian

hi all,

seems to me that the mast with full diameter in the wind on the lee side of the sail (Brians / Hoyt's arrangement) may cause more aerodynamic disturbance than a mast protruding in the sail to the windward side like with the goat's.
Therefore as well as for workability I will stick with the orginal.

My 2ct - Jörn

Originally Posted by Boatmik

Oh ... second hand windsurfer masts are nowhere strong enough for a one person dinghy - let alone a two to three person boat like the goat.

Just compare the mast diameters.

Staying would resolve the bending load a bit ... but would add considerable compression load that the windsurf masts are also not particularly well set up to handle.

Windsurf masts are not really a very good place to start for dinghy masts. It is better to choose something with a bigger starting diameter and even diameter up to the hounds in a stayed rig.

MIK

Thanks for the replys. I wasn't thinking of this as an option for a Goat, more as a possibility for a smaller 50 -60 sq ft PDR style polytarp lugsail for something smaller/narrower. As you say, though, windsurfing masts are designed for quite different loads and staying wouldn't resolve all of that.

Back of my mind was/is Mik's quick canoe plus his outriggers plus a PDR lug rig for a quickly built / versatile water craft that can be easily roofracked for going further afield on holiday. Paddle it down a river as is, put the outriggers and sail on for the lakes. More sail for excitement/speed, reef right down for a sedate cruise with the kids. Sounds like I might have to build a proper mast!

Thanks for the help.

Ian

I think a windsurfer mast would be a good candidate for converting a paddling canoe to a part time sailing canoe - something like my drop in sailing rig. I think it would handle the loads of that OK.

But adding outriggers would mean a huge amount of stablity that will break the windsurfer mast in pretty short order.

MIK

When my tubes arrived from Carbon Fibre Tubes I was very worried at just how thin they were 1.4mm . Very flexible at first until bent and then they were stiff.

I was concerned they might buckle under compression. Luckily I have lots of local high tec boat builders and begged some waste offcuts of structural boat building foam. I cut discs of this foam and made enough for all three tubes to have a disc of foam inside the tube every 1' or so. Like MIK's ladder structure I suppose. Even made different discs all along the yard since it was tapered.

I reckon from memory that my windsurfing masts were stronger, just could not face cutting them up. Not used since 1990! One is a lovely carbon job.

Brian

Originally Posted by keyhavenpotter

Hi guys, guess I had to drop in here! Just sold my Scow so feeling a bit shocked.

Hello Brian,

I thought you loved your scow? What are you planning on sailing next?

Best regards,

Joost

Hi Joost, I do love the Scows, it's just am struggling the balance issues I have. Ducking my head under the boom is a problem and swivelling my head from side to side! Hopeless really.

Anyway, I felt a sailing canoe where I sit more more still and only shuffle a small difference from side to side might work for me.

One turned up so here I am with my very first sail in her in the Solent. The narrow easily driven hull is great, very responsive to sail, and the outriggers give me security if I go a bit wobbly. The outrigger floats hardly touch the water when sailing.

[ame=http://www.youtube.com/watch?v=cy816d_-Fi8]YouTube - Shearwater sailing canoe, first sail in the Solent[/ame]

here she is on the beach



So far so good,

Brian

Hello Brian,

Good to see that that you are back on the water with a boat causing you less balance issues.

Looks like she is moving along quite nicely.

Best regards,

Joost