Kasala latest news: crutches’ corner

Including submissions to John Hogg Prize, Howard Fund, and Catalyst
AlexQ23
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Kasala latest news: crutches’ corner

Postby AlexQ23 » Sun Nov 26, 2017 8:03 pm

Effective design appears when you can dedicate different purpose on a single element. For example, the support tube of crutches has a multifunction task:
- It hold a step
- It support the telescopic mast holder
- It receive the strap holder
- The rudder control system is bolted on
- And for sure, it received the crutches mechanism
Mast holder will support the mast when on trailer, but it will also be a convenient place for future solar panels.
There is one single 5 inches wide strap on each side, surrounding the cockpit. If you want to sail for long period of time, you need to be comfortably installed. To make an ergonomic seat, the angle formed between your back and the seat itself should be 110°. To obtain this angle, the length of the strap is precisely measured, allowing the crew to control with efficiency and ease, the boat stability. Feet rest are also well placed, forming a small bench inside the cockpit, for children eventually. There is a bungee cord placed between the two strap holders at the rear, which avoid excessive slack into the strap when on rest.
Each crutch is design to take a load of 100 kgf (200 lbs) and this is more than enough to keep the boat well balanced when she is lying on the strand.
[img][IMG]http://i65.tinypic.com/20gnww.jpg[/IMGIMG]http://i68.tinypic.com/j7cjzl.jpg[/IMG[IMG]http://i66.tinypic.com/2638pww.jpg[/img]]][/img]

AlexQ23
Quiet member
Posts: 22
Joined: Thu Feb 09, 2017 8:21 pm

Re: Kasala latest news: crutches’ corner

Postby AlexQ23 » Sun Dec 03, 2017 7:57 pm

Sorry guys, it seems that the pictures don't go through. So lets try it...
ImageImageImage

John Perry
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Joined: Tue Nov 08, 2016 6:39 pm

Re: Kasala latest news: crutches’ corner

Postby John Perry » Wed Apr 25, 2018 11:57 am

Hi Alex

I read your article about the 'Kasala' project in the current AYRS newsletter. It does look to be a very nicely built boat and I look forward to hearing about a successful launch - it seems that you have done nearly all the work and just need to buy some sails and bolt on a few off the shelf items to get the boat sailing. If it were me I would forget about electronics at this stage and just go sailing, but not everyone would agree. I rather think that nearly all the electronics you could want on a small cruising boat is now available in a mobile phone, the only exception being a depth sounder, although with your swing back keel perhaps you would not even need that. I would admit that we do use the lead ballasted swing keel on our own boat in lieu of a depth sounder. I would say that the 'sitting out' position with a foot rest and broard strap to lean against does look very comfortable!

One area that I would be interested to read more about is your performance prediction made in advance of sailing the boat. In your article you present polar diagrams for performance. Looking closely at these small diagrams, I don't see any units or numerical scales so it's not clear what boat speeds you are predicting in what wind strengths, or even whether these are diagrams showing boat speed or showing some other parameter such as rig forces. Also, in comparing the 'roto-duplex' rig with alternative rigs it would be useful to include dimensions and other details of the alternative rigs that you have considered. I dont mean this critically, my thinking is that there may actually be a huge amount of study and theoretical work behind those deceptively simple looking little graphs, so it would be good to be able to read more about it.

With best wishes

AlexQ23
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Re: Kasala latest news: crutches’ corner

Postby AlexQ23 » Sat Apr 28, 2018 2:00 pm

Thank you for your comments. I agree with you that electronics are not essentials in this stage. Later, I planned to install a bi-data so I can get the speed/log and a dept sounder. From the GPS you can only record the ground speed and sometimes it’s not enough.
The comparison between the different sails polar diagrams are just there as an indicator and they are , as you notice, not of a real value. But it’s a target. I hope that with the roto-duplex rig, we will be able to point higher toward the wind, due, mainly to the thin rotating mast profile but also to the sail configuration. A front sail on the leeward side is more efficient as demonstrated by the use of bloopers, tall boy etc.... The ratio of mast diameter and sail cord (foot) is less than 2% and the mast will be able to rotate to windward giving to the extrados of the sail the maximum efficiency.
I hope also that before the wind we will be able to increase the performance of the sails due to a “jet pipe” effect between the two sails. In fact a 4.1 m dinghy hull (120kg) with two crew member on board was able to reach planning speed before the wind with just two main sails of 5 m² each and with a wind of 3 to 4 bfs!
The hull of Kasala is design to reach rapidly the maximum hull speed, around 6 knots. This is due to a large Cp of 0.60 and a well balanced immerses hull volume. At this stage, the hull has to get over her bow wave and that does require an extra boost of energy. It could be bring by the lateral chine panel. When the boat is heeling at about 20° ( 3 to 4 bfs), this panel lay flat on the water and at this speed, a dynamic lift pressure of nearly 170 kgf is generated. So, if the boat is not fully loaded and if the crew move back at the rear of the cockpit, I’m quite confident that we will be able to exceed the hull speed. But that has still to be proving on the water!
My intention is to keep you inform with all the data collected during the trials and to bring you some real polar diagrams.

John Perry
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Re: Kasala latest news: crutches’ corner

Postby John Perry » Mon May 28, 2018 12:30 pm

OK, fair enough, the polar diagrams included in your article are just an idea of the performance you would like to achieve and (with tongue in cheek), since you don't have any units on the graphs I am sure the boat will achieve the performance you are looking for!

But seriously, it looks as though you have a beautifully built boat and I hope that Catalyst readers will hear more about it in due course. And if you get a chance to race it against comparable boats with more conventional rigs that would also be interesting.

I would think that the main advantage of multiple sails over a single sail (i.e. una-rig) is that it is possible to have a greater aerodynamic lift force for a given heeling moment (I use the term 'lift' in the fluid dynamics context, meaning a force perpendicular to the free stream velocity - which is not necessarily an upwards force, indeed for sails it is a mainly horizontal force). I dont think that multiple sails are likely to be more efficient than a una-rig (taking efficiency to mean lift to drag ration).

Considering boats that have multiple sails rather than being una rigged, the vast majority afloat have the two sails fore and aft on one mast, e.g. bermudian rig, or on on multiple masts mounted fore and aft on the boat's centreline, but there are now just a few boats that have the masts side by side (biplane rigs). Good performance has been claimed for some biplane rigged boats but perhaps there are not enough of them afloat to make it clear whether they are generally superior to conventional boats. The chances are that neither of these mast configurations are ideal, and I can see that your arrangement where you can move the masts around in a circle gives scope for optimization and so is likely to give some improvement, albeit at the cost of mechanical complexity. Indeed, I would think that this feature of your boat makes it a potentially useful research tool, allowing comparison of performance with the masts in any relative position ranging from fore and aft to side by side.

One statements in your Catalyst article left me wondering - you write "it is a well known fact that a mast profile that is 33% more thick increases drag by 23% and decreases lift by 30%". I wondered how that result had been measured or computed, and also more thick than what?

Fascinating project you have anyway, your construction works looks good and I am sure your boat will attract a lot of interest once its afloat.

AlexQ23
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Re: Kasala latest news: crutches’ corner

Postby AlexQ23 » Tue May 29, 2018 10:12 pm

Hi John!
Yes this is a good summary of what the Kasala project is! Nice done!
The “well known fact” comes from the famous experiments carried out by Croseck and that you can found in different books like “the Sailing Yacht” of Juan Baader or “Architecture du Voilier- tome 1” of Pierre Gutelle. They compare four main sail and mast configuration. The first one, the reference, is the main only without mast. Then, we found a main with a mast profile of 7,5% of the sail cord, then with a 10%. Finaly, the same one but rotate to windward. When you make the calculation of drag increasing and lift decreasing between profile 2 and 3 you find the statement I do insert in my description. Kasala have a rotating mast and have a profile of only 2% of the sail cord. It’s common to found a mast profile of about 6% of C. Let me know if you do not found that study, I will be more than happy to send it to you.
Also, I will continue to let you inform to the further development of the project. For example, this year, I plan to launch the boat and to test the hull resistance at various speeds and see if we can match the calculated resistance curve. Then I will see how the scull operates and if it will reach the predictions.

John Perry
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Re: Kasala latest news: crutches’ corner

Postby John Perry » Wed May 30, 2018 10:19 am

hi Alex - yes I would be interested to read about Croseck's experiments. The books you mention are available second hand from various websites but it would be convenient for me if you could email the study to me as you sugest. j_perry@btinternet.com. Thanks. Regarding your proposal to tow your boat to measure the hull resistance, some of us tried such an experiment the day before one the AYRS Thorpe meeting last Autumn. I can only say that we did not find it as straightforward as we hoped it might be. We were measuring the resistance of a fairly narrow beam 4.5m long hull by towing it at below walking speed on a canal using a small dinghy powered by an electric outboard motor. There was no discernable current or wind. We tried two ways to measure the drag - a sensitive electronic balance and a less sensitive mechanical device, I think meant for weighing luggage of maybe fish. Towing at a steady speed we found that the force readings were very variable making it pretty well impossible to get meaningful results. Possibly the towed boat was weaving about slightly and moving in and out of the propeller wash from the tug. Perhaps a longer tow line and better steering would help. Perhaps data logging a large number of readings and averaging would help. We did average and plot the readings and found them to indicate about twice the drag that had been predicted for that hull using the Michlet software, but because of the uncertainties in the measurements I would not like to say that it was neceaaarily the Michlet results that were wrong. I am not saying that this kind of experiment is not possible, or that it is not worth trying, I would only say that our first attempt at it was not very convincing. So good luck!

John Perry
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Re: Kasala latest news: crutches’ corner

Postby John Perry » Thu May 31, 2018 7:19 am

Alex - Here is another one that also has twin masts rotating in a circle! - http://www.mathisruhl.com/P-WM70T.html

AlexQ23
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Re: Kasala latest news: crutches’ corner

Postby AlexQ23 » Sat Jun 02, 2018 10:37 am

So, this concept boat is not so far from my rig! Thank's for the info.
For the hull drag test, do you thing that pushing the boat could be better than to tow it? We will not have the problem with wake disturbance and my dynamometer can be use in both direction.

John Perry
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Re: Kasala latest news: crutches’ corner

Postby John Perry » Tue Jun 19, 2018 2:54 pm

Hi Alex
A delayed reply since Josephine and I have been sailing along the coast of croatia in our sailing dinghy so not much opportunity for looking at internet.

Yes, pushing might work, or perhaps towing from a pole extending from the side of the towing boat. We will try again some time.
John Perry 8


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