Getting out on the water this year

What does your design brief look like? What are your requirements for the boat? What do you want to use it for? What does your budget look like?
User avatar
Manik
Site Admin
Posts: 373
Joined: 27 Aug 2014, 15:41

Re: Getting out on the water this year

Post by Manik » 03 Feb 2015, 21:17

@old school: I'm a little confused. :? With the extra chine you're referring to having a pod, or...? As for steering, the cassettes seem like a rather good way to go to me (I hope we're talking about the same thing), but I'm all ears for other suggestions. :)

My reason for the deep-v ama is chiefly the issue of spray. Since the bow of the ama is pretty much to windward of any viable steering position, a lot of the spray it produces will be blown right at you when sailing to windward. Sven has said to me that sailing Pacific Bee to windward in 15 knots or more in cold waters, is best done in a wetsuit, and that's a 38-footer. I don't want to make that problem worse by having a flat bottom ama which will kick up a cloud of spray with every wave it slams into. That's why I want a deep-v ama. I think a tortured plywood hull can be built very rapidly as well, comparable to a flat bottom, but I admit the process of prototyping the shape, adds extra work which is not required for the flat bottomed hull. I get the feeling beachcats are rarer here than elsewhere in the world. While looking into Tornados and Tornado rigs I was surprised at how low the general availability of used beachcats seems to be, so sawing up a beachcat doesn't seem to be an option. Hacksawing an an SUP wouldn't have enough volume unfortuantely. All that said, I could always start with a flat bottom ama and build the tortured plywood one later...

@Rob: Maybe you're right, because this is a fast boat. What a monohull weekender can cover in a 12-15 minute nap, might be as little as 5 minutes on a fast proa, and while I have heard of people catnapping while sailing single-handed in the Gulf of Bothnia, an being far from having any close calls, the sheer speed of a multihull could well change that completely. It's definitely something to approach with a great deal of caution. I think I'll just sail it during the day initially, and leave the boat to its own devices but keep watch over it. That'll give me some idea of how safe or unsafe that may be. The problem with something like wind-vane self steering is that if the wind shifts while you are sleeping, you can potentially cover a lot of ground toward and rocky shore in 15 mins... Not to mention that if you and a container ship were heading right at each other, the container ship at 25 knots, and the proa at perhaps as much as 15 knots, you would be 10 nautical miles closer together by the time the alarm rings.

Cheers,
Marco
"Man's mind and spirit grow with the space in which they are allowed to operate." - Krafft A. Ehricke, rocket pioneer
User avatar
Skip
Posts: 236
Joined: 31 Aug 2014, 16:40

Re: Getting out on the water this year

Post by Skip » 03 Feb 2015, 23:08

For the ama perhaps a reasonable solution would be a tapered side, flat bottomed shape with a glassed foam shaped bottom. Pretty easy to build and easy to modify (if necessary) based on experience.

The idea of napping at 15 knots terrifies me AT LEAST as much as being blown over bothers you, I think. Part of it is the difference in venues; mine is never that cold and I can and have gotten in trouble while awake but just not observant enough, too much stuff above and below the water around here, particularly at 12-15 knots.

About being blown over. One time on P52 ..... early in the experiments with bidirectional sails the boom got completely away and the sail was flailing around attached only to the top of the mast. Not sure how long the dry mouth moment lasted while I let the halyard go but that was the closest and only time I was concerned about the boat being blown over. I did manage (unintentionally) to break the mast sailing upwind in heavy conditions and was hiked out as far as I comfortably could but didn't feel like the boat was in danger of capsize. My take is that a well sorted out pacific style proa doesn't need that much horsepower and the odds of being blown over are fairly small. That being said Nomad will have enough flare in the topside to theoretically come to rest on his (her?) side, my biggest concern at the moment is the potential damage in flipping back up but that's just a shot in the dark, the truth is in the doing.

I'm not really trying to convince anyone to abandon leepods, they may well be necessary or prudent, but my current opinion is they aren't really that necessary and felt it necessary to state my opinion.

Cheers,
Skip
who cut out all the parts for Nomads' trailer today!
User avatar
Rob Zabukovec
Posts: 555
Joined: 27 Aug 2014, 21:20

Re: Getting out on the water this year

Post by Rob Zabukovec » 03 Feb 2015, 23:14

Marco,

Deep V bows throw spray pretty much straight up, whereas flat bottoms throw it out flat, so I am not sure about your logic.....Read also p 108 and p 1113/4 of Skenes Elements of Yacht design (Planing Powerboats) And if your ama is being lifted dynamically as well, the spray zone should move further aft. We are talking seriously narrow hulls here compared to powerboats, so pounding shouldn''t be an issue.

Speaking of flat bottoms and sidehung rudder systems etc, FWIW here is a link which might be interesting for those who haven't seem it before:

http://fionamsinclair.co.uk/yachts/smith/page25.htm

Rob Z
old school
Posts: 226
Joined: 30 Dec 2014, 00:18

Re: Getting out on the water this year

Post by old school » 04 Feb 2015, 00:24

Marco,
What I am saying is that choosing a flat bottom for the sake of simplifying and speeding up the build makes more sense for the ama than it does for the vaka……..if the vaka is always to lee.
Sure I can understand what Sven says about wet sailing…..on a small proa it gets wet going downwind too, because an ama of just about any shape (and I have tried a number of different shaped ama’s in my time) will kick up spray which you ride into at speed.
Solution is to sail from an enclosed cockpit or wear the wetsuit. The wetsuit option is certainly the quick, cheaper and proven option, but like I have already said – I commend you for having a go and add that trying to achieve what has not thus far been proven is also good.

Working within the parameters of known hull characteristics however, will result in a realization that on a small craft, displacement, draught and hull lines favour less boxy shapes.

Having said that, I need to make it clear I agree a flat bottom craft when kept very light will have good speed capability.
Problem is you are building a small proa for cruising and will need a better load carrier, which will have better lines if you add another chine to make a V bottom………….so hope this explains better what I was getting at before.

As for the cassettes………..there is a quicker and much less complicated way to make steering foils, so why do the extra work. Making cassettes and hardware to hang them, plus fancy tillers, is not going to be any less work than making in hull cases and dagger-rudders. At least the dagger-rudders are using the flat bottom to good effect, if the flat bottom is obligatory.

Hey, I’m not trying to sell you my rudder design, I’m just saying that I think a V bottom (which makes it more difficult to accommodate dagger cases compared to a flat bottom) makes for very little extra work, given benefit to load carrying hull lines.
If you prefer the flat bottom and the side hung cassetes, then I hope you fare well with them.
User avatar
tdem
Posts: 146
Joined: 31 Aug 2014, 22:08

Re: Getting out on the water this year

Post by tdem » 04 Feb 2015, 03:13

old school wrote: As for the cassettes………..there is a quicker and much less complicated way to make steering foils, so why do the extra work. Making cassettes and hardware to hang them, plus fancy tillers, is not going to be any less work than making in hull cases and dagger-rudders. At least the dagger-rudders are using the flat bottom to good effect, if the flat bottom is obligatory.
(...)
Hey, I’m not trying to sell you my rudder design....
I for one would like to hear about it. If I remember correctly you favour rudders connected to the crossbeams with "rigging", somehow?
The most important thing is to keep the most important thing the most important thing.- Donald Coduto
old school
Posts: 226
Joined: 30 Dec 2014, 00:18

Re: Getting out on the water this year

Post by old school » 04 Feb 2015, 10:05

It’s possible to show a pic of a model with the rudder design spoken about, but there are so many variations based on the principle that showing only one example isn’t good enough. Neither is it a design worthy of a beauty contest, so just bear with me trying to explain it all.

Initially the design had a sleeve over a tubular connecting beam/aka, which served as the horizontal pivoting axis. Then there is a pintle rotating mid way on this sleeve in the vertical axis, fixed to the rudder blade near it’s leading edge –remember that only the after rudder is operational.
Pivoting on it’s attached metal pintle, the rudder blade has a deep cut notch or slot where it crosses the horizontal sleeve ( the sleeve actually passes through the aperture behind the pintle), which allows the blade to turn until the back edge of the slot stops against the sleeve, Turning arc of the rudder is as per normal , being +- through 100 deg of arc.
Bracing in the lateral plane is by a diamond staying arrangement . The rudder pintle is the vertical strut and the sleeve is the horizontal strut in a tensegrity like structure.
Tension in a tackle taken forwards from lower point of the diamond stayed plane (let us call this the ‘virtual transom; the lower point being the lower pintle and gudgeon) stops the rudder from swinging backwards. This tackle is also used to lift the blade out of the water and stops on a fuse pin/dowel to allow kick-up on impact.

Based on the same principle, minus the stay wires, and having a single, solid cruciform piece instead of separate sleeve and pintle, is a version I have also devised, working as a linked tandem set of rudders. But this was before I had sailed in high latitudes, so have since canned the idea. However I have adopted the solid horizontal member of the cruciform, in place of a sleeve slipped over an aka, on my current proa in the build stage. This way the rudder is independent of aka or kiato.
Here’s hoping this explains things sufficiently……. Otherwise I will need to get my wife to take pics with her I phone and mail then to me, since existing pics are in my non-operational computer. I am going to have a hard time justifying the need for new pics…. She thinks that I have better things to do.
Mark

Re: Getting out on the water this year

Post by Mark » 05 Feb 2015, 13:41

For a quick build method have a look at:
http://www.thecoastalpassage.com/cheapcat.html
old school
Posts: 226
Joined: 30 Dec 2014, 00:18

Re: Getting out on the water this year

Post by old school » 05 Feb 2015, 16:48

Looking at that (the above video) I see a single chine V bottom as a time and labour saving benefit, along with using foils outside the vaka. A steel shoe strap fitted to this V bottom will also be good for taking to the ground, where a flat bottom just presents more area to be damaged.........not mention extra work and complication associated with slots and cases opening out on a flat bottom.
petermirow
Posts: 37
Joined: 13 Jan 2015, 09:34

Re: Getting out on the water this year

Post by petermirow » 06 Feb 2015, 10:42

Hi,
The cabin seems an important item for you. And, considering your sailing grounds, I can understand that. Therefore, I think the leepod is a good idea, and preferable to the safety ama. I'm not sure whether you have seen my boat, specially internal pictures. But the "leepod" (kind of odd name if you consider it is a tacker), really makes all the difference.

But if you go for a safety ama, then I agree with Rob and Old School, above. The safety ama should be flat bottomed. It provides dynamic lift when hitting the water.
Cheers,
Peter
old school
Posts: 226
Joined: 30 Dec 2014, 00:18

Re: Getting out on the water this year

Post by old school » 06 Feb 2015, 21:01

Correction to what Pater writes above…………I do not suggest a leepod large enough to house a bunk and replace the safety ama.
Most definitely I use structure to w/ward for supporting the mast step as well as creating bunk space…….. on any proa I build with a cabin.

Sure, I started out with the idea to combine a leepod buoyancy with bunk space, as a result of reading Project Cheers, back in the 1970’s, but have moved on from that.
It is as convenient to have a detachable safety ama to leeward as it is for having the w/ward one separate. What’s more, the safety ama can be inflatable and used as a dinghy/raft/paddleboard at the same time as reducing overall beam when not needed for sailing safety.
Just think of the saving in material and building time of structure when the cabin bulk is to w/ward; it provides a deper structure to take mast compression and the bunk base need not be as high up from the water as on the lee side. This also allows the safety ama to be lifted as high as you want for it’s purpose of capsize prevention.

I have sketched out my ideas of a design we are talking about on this thread, but living up to my old school moniker it is a scribbled pen sketch and not a computer generated rendering. So I don’t have a quick way to show it here…..hull section of vaka is V bottom (something like you have Peter, but with vertical hull sides) and the w/ward ama is an inversion of this shape, with V on top. Safety ama shape can be any number of things, although an inflatable paddleboard is the best thing to make first contact with water when heeling.
Post Reply