Thread: Is that a 12' GIS I see hull down on your horizon

Not sure which way Rick went in the end, but I think we decided to leave the sides of the bulkhead straight rather than the computer derived curve then measure offsets for the actual curve taken by the plywood.

The stresses are high in the forefoot so the ply tends to torture quite a bit. The computer assumes that it takes a combination of conic and cylindrical sections (ie is untortured). So computer and real practice are not necessarily in agreement in areas like this.

So Rick will give me three offsets for the curve I need to add to the bulkhead ... if it is enough to worry about.

MIK

I tried to send the pics to MIK, but his machine would not download them. So everyone gets to see them at the same time as him!

Rick

Chris Craft-y indeed!

This design is shaping up quite nicely. Seems like the transom could accommodate self draining in some manner, but I realize that there's more build yet to come.

Bravo to Rick L. for the speedy work!


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Howdy ... for those wanting to understand more about the rotating short cord wing mast have a look at these two resources from the Taser class website.

They were like our textbook for the NS14 class as well.

The Tasar Manual

See section on "Sailing to Windward" for info on the wing mast principles

Also the section on basic handling has nice sections on modern boat handling to help everyone.

This resource eventually evolved into an expensive book

Best wishes
Michael

I've just read the entire thread and looked at as many of the snaps of the new boat as I have been able to find. She's looking very svelte; from the stern quarter-views she has a slight look of the Bolger "Sneakeasy", to my own weird eyes at any rate.

I've had the square top to the sail ambling about in my head since seeing the first outline drawings of it, and in the course of reading this thread I started to remember the "winglets" - or end-plates - on modern aircraft, and the end-plates - or "wings" ;) - on relatively recent watercraft. This transferred itself into idly pondering what might happen if a similar lift-loss-preventing device were fitted to the square top of the sail. This is no doubt way off-topic, but has anyone experimented with something like that? Please PM me instead of muddying the clear waters of this thread any further than I have done already!

Howdy Alex,

I can help you quite easily. For wing tips etc there are very many incorrect solutions and a much smaller set of ones that really work.

The things that make it easier for aircraft is that commercial aircraft have a fairly narrow efficient speed range and also don't have to tack (fly upside down) very often.

After Australia 2 won the America's cup there were wings on keels left right and centre - every type of boat was trying to work out how to implement them.

It was quickly found that they offered little or no advantage because they had been sortof stuck on with people missing the whole idea ... there are some really interesting angles in the original that you just can't work out without serious experimental runs on computer or in a test tank.

So that was a practical upshot on the difficulties of getting it right.

Then they found that fitting wings to keels was not so good for offshore racing because the boat would surf down the face of a wave and then just keep going straight.

On rudders they have had more success. Bolger with his shallow rudders made to work using an endplate.

Another rudder use was on the Moths when the hull got down to a foot wide. To prevent nosediving they had a T foil on the rudder which prevented the nose going down in a gust - reducing nosediving. That wasn't for efficiency but for handling and control ... which is another type of efficiency I guess.

This was one step towards foiiling moths as well.

MIK

Thnaks for your informative reply :). That reminds me of the famous video that lurks on the net of the then test pilot at Boeing doing barrel rolls in the 707 prototype ;). But very much of that and both prototype and test-pilot would have rapidly transmigrated "across the rainbow bridge".

Name nomination:

Daughter of Goat

(This coming from the father of a teenage girl who is beautiful and sassy and is turning out more lovely than I could ever hope for but in a way I could not have envisioned...)

Sadly, the acronym would work against it...


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Originally Posted by davlafont

Name nomination:

Daughter of Goat

(This coming from the father of a teenage girl who is beautiful and sassy and is turning out more lovely than I could ever hope for but in a way I could not have envisioned...)

Sadly, the acronym would work against it...


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Naaa, can't have DOG! Bite your tongue Dave. My guess is it will have a name soon, once its curves are fully developed.

Originally Posted by Boatmik

Howdy ... for those wanting to understand more about the rotating short cord wing mast have a look at these two resources from the Taser class website.

They were like our textbook for the NS14 class as well.

Michael

FWIW,

Attached is my rendering of beginning thoughts of a homebuilt 28' freestanding rotating wing based on Bethwaites research and the resulting Taser mast.

I was planning on building the main structure same as any hollow wooden stick and using a carbon fiber 'sock' to add strength - so as to keep the mast section as small as possible ( a la Taser) The section shown may be much stronger than needed. I planned to build a test section to better figure the bending characteristics - especially for the top half of the mast.

Wicked22_rotating_unstayed_mast.jpg

Love the new boat MIK... thanks to Rick for doing the dirty work.

Cheers,
He who wants a 22' version

Howdy Tommyboy,

Development of the rotating masts for the NS14 class didn't stop with Bethwaite's Aluminium spars. Even at the time they were heavy compared to other alternatives - I had one on my second NS14.

He had developed them from his wooden masts for the NS14 and Nova for the TASER dinghy.

They were reasonable for the time, but heavy because of the two piece construction necessary to get the taper that Bethwaite thought was necessary.

Bethwaite's idea and NS14 experience until that point supported that the taper was necessary.

Time doesn't stand still and now the Taser with its 118sq ft of sail is slower around a racecourse than the 100 square foot sailed NS14. Same weight, similar foils, but years of incremental improvement. This is now about 1.5% to 3% faster according to
NS14 The Development Class :: View topic - Yardsticks and the Portsmouth yardsticks.

But when I started thinking of a rotating mast in wood I went back to the ones I knew best, which were Bethwaite's tapered wooden masts on the NS14.

There is no data for them anywhere on the net except for some measurements of a Cherub rotating timber mast - which has more sail and a spinnaker to deal with.

So I do what I do and started collecting data.

The masts went from tapered timber to constant aluminium drawn sections with really thin walls. The round drawn sections were then rolled to make them much more elliptical.

They then went to carbon tops (because you can't make any materials choices that increase the cost of an item by more than 20% - which restricted from being a full cerbon mast. Then gradually the carbon moved down, keeping in line with the 20% rule so the entire spar could be carbon.

But the important thing with the Alloy and carbon masts is that they are constant section. There is no taper. The masts are designed to have the right sideways bend for the NS14 and the fore and aft measurement is so large (100mm) that not much bend is expected fore and aft (relative to the mast - which is usually never fore and aft in the boat).



So that is the way I am going. Similar fore and aft chord and right width to get about the same side bend. side bend of the constant section controlled below the hounds by one of three methods.

For people overseas a clip ... now a little old but not too old showing the speed of these boats with quite small sail area and the wingmasts in action



MIK

I may have missed it but it appears we are talking, here, about unstayed-rotating wing masts, right?

The videos of the NS14s running around the course suggest they are truly unstayed, but the apparent small size of the masts leaves me amazed....and wondering.

HI Archie,

They are stayed. Simple three wire rig going to a single shackle on the front of the mast.

MIK

Interestingly, the older boats in the video had spreaders, and even diamond stays, but the modern boat in the pic does not. This suggests that there is no sideways control of bend at all these days as the masts are so VERY stiff. Will you need spreaders on your wooden version do you think?

Edit: I saw that in MG14 mode, the boats do have spreaders and diamonds, but then in MG14 mode they carry a crew on a wire and a spinnaker. For those outside of Oz who don't know these boats, the MG 14 (Manly Graduate 14) is a separate class buts uses the same hull and sail plan, except that the MG14 carries a spinnaker and the crew is allowed a trapeze wire. When you see the tiny size of the 2 sail rig (100sq ft as MIK mentioned above), it seems incredible that you could get a crew out on a wire, but the rig is very powerful for its size. Amazing boats. Well worth taking note of the NS14 development and I understand Mik's enthusiasm for copying some of that technology.