Dear Mr. Sidecar

Sidecar

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3,121
1,490
Tasmania
^^^^ In a mile, at a glide ratio of ~ 40:1, he should have dropped ~ 132 ft. Optimum airspeed /descent ratio would be at ~ 60 knots. He could have kept going until he hit stall speed, ~40 knots, so he could have kept going for roughly 4 miles without touching and normally would have lost ~ 540 ft of altitude.
 

Rasputin22

Rasputin22
13,895
3,454
^^^^ In a mile, at a glide ratio of ~ 40:1, he should have dropped ~ 132 ft. Optimum airspeed /descent ratio would be at ~ 60 knots. He could have kept going until he hit stall speed, ~40 knots, so he could have kept going for roughly 4 miles without touching and normally would have lost ~ 540 ft of altitude.
I liked the height above ground to percentage of ground effect graph shown here. It doesn't hurt that the sailplane probably has a 60' wingspan so at 10' alt he was getting nearly the max advantage. In soaring circles a really low run along a ridge is called a 'wormburner'!
 
That's a very impressive demonstration of just how efficient aircraft flying in ground effect can be.

In other news, I have a Fusion mockup of the canting daggerboard.

SwingDaggerPerspectiveDown.png


SwingDaggerPerspectiveUp.png


SwingDaggerElevationDown.png


SwingDaggerElevationUp.png
 

Sidecar

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3,121
1,490
Tasmania
I liked the height above ground to percentage of ground effect graph shown here. It doesn't hurt that the sailplane probably has a 60' wingspan so at 10' alt he was getting nearly the max advantage. In soaring circles a really low run along a ridge is called a 'wormburner'!
So ~ 40% reduction of induced drag…..
2FCDBACF-824A-490A-B794-8B0E9BD431B1.jpeg
 

Sidecar

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3,121
1,490
Tasmania
In other news, I have a Fusion mockup of the canting daggerboard.

View attachment 543776
Some constructive comments:

The daggerboard case will take up some of the interior, so make sure you have enough “pod“ to have a decent berth inside. It is not just the thickness of the case, but also the curvature of the hull which will eat into it.

The pivot attachment points of your balanced sails will have to take a lot of load. Better to shift (or at least enlarge) your vertical posts to align some mass directly under the pivot points to minimise local loading. The bottom end of the posts will also give you more strength for mounting the strut vangs which you will need to stop the luffs from skying and boom clew from drooping.

The profile would look cleaner if the reverse bow knuckle aligned with the splay chine.
 
Some constructive comments:

The pivot attachment points of your balanced sails will have to take a lot of load. Better to shift (or at least enlarge) your vertical posts to align some mass directly under the pivot points to minimise local loading. The bottom end of the posts will also give you more strength for mounting the strut vangs which you will need to stop the luffs from skying and boom clew from drooping.

The profile would look cleaner if the reverse bow knuckle aligned with the splay chine.
Both of these things I've noticed myself. The vertical posts were put there before I'd decided on the rig and figured out where it was meant to go, and now it's a huge PITA to change it. Of course they would be lined up for support on the real thing.
The bow knuckle is the same situation. I altered the chamfer on the "pod" which moved the chine down, but I made some shortcuts on the deck and trunks and now there's way too many things that are referencing that reversed knuckle that when I try to change it everything breaks.
 

ProaSailor

dreaming my life away...
6,106
793
Oregon
The entire premise behind my first proa design with the crab claw rig in my profile pic
How do you reef a crab claw ("Oceanic lateen") sail? Other than brails or "spilling lines", apparently you don't, which is far from ideal. They look so simple but that's a serious flaw, especially on bigger boats.
reto1a.jpg

Source:
 
I'm a long way from knowing all that I should know about balanced club sails but I suspect that your balance point would work better moved forward a bit. Phil Bolger in 100 Small Boat rigs talks about balanced club jibs twice and said that "The pivot point shouldn't be more than one fifth of the length of the foot from the tack and less is safer".
 

Sidecar

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3,121
1,490
Tasmania
@SkipJ

We had this same conversation years ago, when Sidecar was still on the drawing board/under construction.

If you are talking about pin headed mainsails, you are maybe correct. But Sidecar has a big square head mainsail, which allows the pivot to be further aft. The aim being to maximise sail area for a given mast height and especially the area in front of the mast to keep the CE forward because the mast position is fixed. And is also why Sidecar’s mainsail leech is vertical. Full mainsail pivot on Sidecar is at 38% foot length. It also has to work when reefed, which naturally shifts the balance point further aft on the sail. With 2 reefs in, the balance point is just over 50%. In all cases, the CE of the sail is always aft of the balance point. The big square head, especially when reefed, has a catenary effect on the luff stay, like drawing a bow string, so whilst the sail CE does shift forward, the head of the sail shifts aft, which shifts CE back a little, giving a little more safety margin.

Aero rigs have similar characteristics, in that when the mainsail is sufficiently reefed, without reducing the jib, there comes a point where the rig can become overbalanced. Perhaps @he b gb could comment?

Certainly, the less balance you have, the less the boom will “thrash” when luffed, but it also increases sheet loads, reduces SA gain and shifts CE aft.

As a point of comparison, the mast on Jester 2 (same Displ and LWL) is 1.5 metres taller for 1m2 less mainsail and its CE is a little higher and ~ 880mm further aft than Sidecar. Refer to diagrams and tables upthread.

Pay your money and make your choice.

068E3A24-2F4C-42D3-97CB-7EFEB8481214.jpeg
 
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You are correct on several fronts ;-) Main one being Sidecar is out sailing and working quite nicely. My experimenting with cambered panel staysails was sidelined for a while after discovering Peter Worsley's circular cam winfgsail control. The circular cam controlled wingsail worked surprisingly well but unfortunately did not scale up reasonably to single handed camp cruiser size. I might build a refined version of the Broomstick if conditions warrant (time, body and mind), it was a fun craft to sail.

But first I need (?) a proa friendly sail system for a small camp cruiser.
 
I'm taking a break from the little boats for a while and applying some of the design to a bigger boat, so here's a 55-foot thought experiment. I don't quite like the way the windward side turned out aesthetically but it's sufficent to allow me to play around with proa concepts on a bigger platform. Offshore the boat would be fitted with a sizable semi-rigid dodger and cockpit enclosure that would guard against water intrusion through the doors, protect the helm (with its dual wheels) and make the boat more aerodynamic. This design will have a balanced schooner and another version will have a biplane rig, which I am looking forward to finally playing around with.

CP55EarlyWWPerspective.png
CP55EarlyLWPerspective.png
 

Sidecar

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3,121
1,490
Tasmania
It was the middle of winter when you came, and it is windage if you aren’t using it ….

I will send you details. It was all done with bits of string and can be done more eloquently than the photos, it was a trial run to see if it was worth the bother. Often down here, it is uncomfortably cool under it with a breeze blowing.

Next time perhaps?
 
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@SkipJ

We had this same conversation years ago, when Sidecar was still on the drawing board/under construction.

If you are talking about pin headed mainsails, you are maybe correct. But Sidecar has a big square head mainsail, which allows the pivot to be further aft. The aim being to maximise sail area for a given mast height and especially the area in front of the mast to keep the CE forward because the mast position is fixed. And is also why Sidecar’s mainsail leech is vertical. Full mainsail pivot on Sidecar is at 38% foot length. It also has to work when reefed, which naturally shifts the balance point further aft on the sail. With 2 reefs in, the balance point is just over 50%. In all cases, the CE of the sail is always aft of the balance point. The big square head, especially when reefed, has a catenary effect on the luff stay, like drawing a bow string, so whilst the sail CE does shift forward, the head of the sail shifts aft, which shifts CE back a little, giving a little more safety margin.

Aero rigs have similar characteristics, in that when the mainsail is sufficiently reefed, without reducing the jib, there comes a point where the rig can become overbalanced. Perhaps @he b gb could comment?

Certainly, the less balance you have, the less the boom will “thrash” when luffed, but it also increases sheet loads, reduces SA gain and shifts CE aft.

As a point of comparison, the mast on Jester 2 (same Displ and LWL) is 1.5 metres taller for 1m2 less mainsail and its CE is a little higher and ~ 880mm further aft than Sidecar. Refer to diagrams and tables upthread.

Pay your money and make your choice.

View attachment 544348
On Cactus I’ve got plenty of gears to change whenever the wind comes up. If the wind Is on the nose or beam the first reef is usually rolling up one of the jibs at around 15 to20, if the wind starts to climb above 20 we start to get a bit of weather helm so it’s time to take a tuck in both the mains. With a single reef in both mains I can have both the jibs back out and sail quite comfortably in 25 kts and the boat feels nicely balanced. I have sailed to windward a few times in 30+ with each main single reefed and just one jib out which it handles ok, but then sailing to weather in 30+ is not what I call fun and only do if I really have to, and then I will try to pinch it up to relieve pressure on the rigs. Ive never had double reefed mains and the jibs out at the same time, if I do try it one day I’m guessing we would probably be overbalanced as you describe in your post.
 
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Sidecar

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3,121
1,490
Tasmania
Seacart 30 to get to its Base Speed needs 60% more sail area on a 60% taller and heavier mast than for Sidecar to get to its Base Speeds. You know where most of the money is in a sail boat? Spend the cash difference to make Sidecar bigger again with a little more sail? What Base Speed would you like?

So for ~ 88% of Seacart speed (arguably more, because Base Speed doesn’t account for the additional windage and pitching) and a small fraction of the cost, a more easily handled boat with a more liveable/usable interior, which one offers the better value for money? Proas aren’t “faster”, just potentially more efficient for a given amount of resources than other boats.
I have posted this elsewhere on SA, but thought it might be useful:
 

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