New Design for a 17' Daysailer/Racer

Doug, I am working away at it; and I can see now what you mean. Hydraulics just aren't feasable on a boat of this size. There is a good reason why the skiffs and 5-0's don't run them any more, namely that they aren't very reliable, and in the case of a failure, it is not nice to be sailing around in a boat full of hydraulic fluid! I would still rather have the electrical option only as a last resort. I am now looking into the option of having a mainsheet-style track moulded into the deck, just forward of the keel "trunk", that operates a purchase system. See the dodgy-paintbrush-diagram(TM) attached to this message to get an idea as to how it might work. The idea is that as the 4:1 purchase is taken up on the opposite tack, a further 2:1 PBO/Dyneema purchase hauls the keel head from side to side, and the tensions are taken up either side proportionally to how far over the car on the track is pulled over. The spare line can be taken up using shock cord aft of the skipper. Upon tacking, the crew's main job is to get the keel over, instead of changing the jib sheets, as the jib will be self-tacking, so the keel controls will be on either side of the cockpit in the crew area.

as this may be a pain to model in rhino on the boat, I think that I'll simply do the canting keel as a series of diagrams.

Cheers,
Tassie

 

P17

T, do you think that if the line came off the inside "lever" closer to 90° from the keel fin's cl it might be easier to pull?

 

remember to keep it simple and sturdy, basically you need just a shaft, a couple of ball bearings and few blocks, nothing else, it must be so simple that you can check it in a wink of an eye while you sail or before you launch the boat; it's not so important if a bit of water leaks inside from the canting shaft as long as it's few centimeters above the waterline and you have a self-draining cockpit, that's what happens everyday in a dinghy form the daggerboard case, just few cm above the waterline

fair wind
mistral

 

Guest

Guys,

Sorry for the delay in getting back into this thread. To be perfectly obvious, I didn't think that it would generate this much discussion, so I put it on the back burner. My apologies.

The original design brief was spurred by the RS K6. That seems like a fast, exciting boat that a non-athletic crew can have fun with. I've sailed everything from Sabots to a Choate 40 IOR boat, with stops in between for J24's and Hobie 16's, but I'm at the point now where I don't want to use a trapeze or hike excessively to keep a boat down. On the other hand, I also don't want to sail a boat that's uncomfortable and slow.

I also want to drysail it, so that means optimizing the rig so that it's quick and easy to rig and de-rig. So. What does the brief look like: a light, narrow, handsome boat that's ergonomically well thought out, fast upwind, quick and easy to plane on any kind of a reach, and within the capabilities of an amateur builder (me--a complete hack) to build for a reasonable amount of money.

BTW, I thought that Paul B's renderings were headed in the right direction.

 

So, that logically puts canting keels out of contension, for it to be "within the capabilities of an amateur builder... ". Regardless of their obvious advantages in terms of performance, they blow the boat away in terms of complexity to construct, and complexity to rig and use. Easily dealt with!

Just a few pics of the latest evolution of the renderings... 2x CK version of boat, 1x lift keel version, both with a representation of the rig.

Cheers,
Tassie (in Queensland... if that works!)

 

P17

T, I totally disagree that the canting keel boat is beyond a home builder. If the boat is designed well and speced out properly there is no reason a homebuilder couldn't do the job.
Nice renderings-brings it to life....

 

Cleve,
It sounds like you're looking for the Johnson 18
Steve

 

Guest

Pretty close . . . maybe an updated version aesthetically. But I'd really like to have comfortable seats with adequate backrests, for those times when we're not on a screaming reach.

I like narrow boats, with long bow runs flaring to a shallow midsection just past the halfway point. Sort of a mini ACC boat or ocean racer.

 

Sailed J24s out of SB? You must know my bro Kenny pretty well. Sailed lots of J24 miles with him, and had loads of fun racing MORC Internationals together, not to mention various Ventura Cups, LBRWs, etc.

 

Your pic doesn't seem to work. I think you mean something like this attached pic.

Why not eliminate the rack from one side, add a float onto the outboard end of the remaining rack, make the hull much narrower...

What the heck, make the outboard float the same as the hull.

That's been done before as well. Have a Hobie day.

 

Must be nice to be a young student with access to nice software like this. You're doing pretty darn well for a first attempt. Sadly, when I was at your stage of education I was using a slide rule. But not bad for a "Maintenance Worker", eh?

I think you'll learn a bit more from some constructive comments rather than cheerleading, so here's the requested commetary:

Your bulb looks a bit cartoonish. I'm sure you can take a quick look at pictures of modern boats and do a more realistic bulb pretty quickly. You could also jump down to the local boatyard and steal a few dimensions. Don't look to my bulb, that's not a correct section for a bulb either. Yours doesn't have to be exact for a study such as you are doing, but it need not look so out of place.

What's the height of the gunwhale (seating) to the cockpit sole? Looks high from an ergonomic point of view. You need to be able to plant your feet for some good leverage with flex in the knee while seated. Might be a scale thing, but it looks too high. Compare your dimension to normal home seating. It should be a lot less in this type of boat. The deck area used for seating looks too narrow as well (so is mine, because overall my model is too narrow). Maybe your overall freeboard need to come down a few cms?

I think your overall dspl is too high for the requested type. The RS K6 weighs in at 260 kg. This design was to be a scaled down version of that boat.

I also think you have too hard a turn at the bilge, especailly aft, although there is no good view of the hull from lower angles and you seem to have an immersed transom. This looks to be a wetted area monster, possibly sticky in the light. Will probably be more stable this way though. Combined with the high freeboard it gives a "floating loaf of bread" impression.

Small changes can really change the perception of the overall aesthetic. I think you could be close, just some tweaks can change things a lot visually.


Nice to see someone put out the effort. Be sure to keep your field of study wide open. Not many make it in the boat design business, even those very talented. Generally getting out of the boating focus will give you a much larger choice of options that pay well. You can always start off in the boating thing, but with skills and a portfolio that include a lot of other design and engineering aspects you'll have a nice fall back.

 

Are you suggesting that the "keel trav" needs to be pulled to leeward, then the 4:1 taken up to pull the keel top to leeward, levering the bulb to windward? That adds yet another control. Doesn't sound too simple.

If you try to have the car auto-locate to the leeward side that might be difficult. When you tack the top of the keel will move to windward, keel to leeward. If you simply pull on the 4:1 the line will tension and the keel will not be able to rotate, since the distance of the 4:1 will increase as the keel becomes closer to upright (think about it).

Have you calculated the loads? What, 100 kg located approximately 5' below the fulcrum? What's the length above the fulcrum? Say 1.5 feet? Load would be 333 kg? At 8:1 that's 42 kg. Hope you have a Starboat crew sailing with you. Is the upper end of this keel with all the purchases flailing about in the cockpit?

You will have a hole in the bottom of the boat (going into a full height well, but a hole never the less) that is fore and aft slighly bigger than the keel chord length (let's say 1 foot) and the entire width of the keel swing (100 degrees). That's a hole, what, 1 foot by 2 feet? You show a mylar cover of some sort. Mylar is not very elastic, so how will the mylar allow the movement through 100 degrees? The mylar will have to slide. The mylar will also have to be very stiff to cover roughly 2 square feet of surface without deforming from pressure while sailing.

You should engineer this before going any further. If you can't solve this you cannot make the canter without the hull bump (not saying a hull bump is any sort of deal breaker). Making a canter work is much more than making a model with the keel sticking though a virtual hull at any angle you want.

Others may post "beliefs" here without calculations or problem solving. But if you're a serious student you'll address the real problems, solve them, and move forward to the next problem.

 

Paul,

Thanks for the commentary. I agree that the keel bulb isn't realistic, I'll put that one down to ineptitude in modelling. I did try to make it look good from a quick knock-up point of view, but it isn't particularly representative of what the final product could, would, or should look and act like. The hull too, may not fit the bill (after having later aesthetic and ergonomic thoughts), as it is quite simply too dinghy-like to please the perceived "customer". The aft of the boat is quite squareish, I'll agree with that, but I couldn't figure out another way of making the underside of the boat rounder without eliminating the flares from the boat. Maxsurf (especially the student freeby version of it) can be a bit silly when reverse curves in profile are desired. Freeboard-wise, well... I think that is usually in the eye of the beholder. While excess freeboard does add excess weight, it also means that it takes more effort to put the boat "down the mine", or even to simply take an inadvertant salty, cold bath

In reference to my keel canting "track" solution, and the associated "Starboat crew" required... I don't have one, and most people I know don't have one in their crew roster either, and neither do I have any dimensions of the keel above the fulcrum. A lot of this work is only very quick and extremely rough, and it'll do for me, but I am sure that if my design were passed off to a professional yacht designer or Naval Architect, a more logical and reasonable keel and canting arrangement would be developed very early on. I agree that this isn't a good attitude, but there are time constraints on how long I have to actually play with Rhino, namely due to having a menial uni-student day job! I haven't, and probably won't be bothered going into too much more detail with reference to canting keels, as they are a bit too complex for my liking, irregardless of what quick thinking I try to put into the solution. I also consider electrical actuation as a breach of the normal "sails only" propulsion stipulations as set by the ISAF, so (sorry Doug), I don't think of it as an option at all from my perspective.

Thin sheets of Mylar are in fact, quick flexible. I have built model boats as parts of assignents out of the stuff, and it flexed beautifully, and most importantly it is light and cheap and very easy to replace, should a flap/gasket be lost or damaged. Provided that it doesn't get caught in a tight jam and get creased (as when that happens, the mylar itself starts breaking down very quickly), it usually forms quite a nice fair curve between any two required surfaces. Anyway, I partially did the canting keel model out of a combination of boredom and a slight anxiety to see how well rhino would perform in the task, and thankfully it came through with flying colours.

With some of the ergonomic issues at hand, I will consider making the floor of the cockpit slightly higher, and add some toestraps and footstops to further increase the reality of the model. The sidedecks are narrower than those of a Laser (which is an ergonomic disaster irregardless of how you look at it, IMHO), so for a design that has been done by a teenager who has only just finished 1st year Engineering, and that has only really been done as an exercise and a bit of fun, I think that it will more than do for the time being.

With respect to the hull, the transom is immersed, but in return, the boat has a very low rocker profile, and quite flat sections aft. This is such that downwind the boat would be a bit quicker to plane and also to increase the probability of planing upwind. With a canting keel, this would indeed be a hoot to sail downwind, but god forbid upwind in less than 5 knots of breeze. Yet again, this boat is a bit too much of a skiff-based dinghy to really be what the doctor ordered, to use that time-honored cliche.

If I can find some time off from work, I might just see what I can do in terms of a flareless boat, a boat that actually resembles the K6... however, keep it in mind that I'm in Australia. The fact that there aren't any K6's, or for that matter, any classes of boat that meet this design brief down here, makes this quite a visual exercise... so no guarantees on the results!!

Thanks again,

Tas

 

Tas,

I'd say you are well ahead of the curve for your age and experience. Most of your peers at the uni are more apt to spend the time getting pissed than adding another project outside their normal coursework and existence-level job.

Maybe you can raise up the point of your bilge turn aft, keeping the hull centerpoint the same. That would add more curvature to the bottom (athwartships) and even add flare to the topsides. A small change here might make it look/sail a bit better.

I'm sure Andrew Mason can help out with any questions you have about adding reverse curves in the program. I have no doubt it can be done, and Andrew will probably have a very quick way to accomplish this.

I think Mylar film can be OK for a dinghy centerboard slot, but here you are talking about a lot of area. The film I had on my old I14 would not be strong enough to span an area as large as you'll need for this hole in the hull. Hopefully you'll get a look at some CFD of small boats planing. You'll see the area under the keel is highly pressurized to create the dynamic lift. Here's an example from the Cheetah 30 sportboat testing (scroll down): http://www.sailingsource.com/bana/cheetah/descomnt.htm

A 1 foot by 2 foot flap of mylar would be flapping about under the boat, giving you some serious drag, and would deform and tear off pretty quickly.

Per RRS 86, class rules can change RRS 51 and 52, so canting ballast and powered actuators can be used. Most of the newer maxis have canters powered by their engines. While that might be a good solution at their scale, it might not be viable at 17 feet.

I've also never seen a K6, only photos on the internet.

I'm looking forward to seeing your next iteration.

 

P17 canting keel

Tassie, "Paul b." is right; the rule is 86.1 (c) and it says that the rules against movable ballast and the limitation to manual power can be changed by the class rules.
I'm certain that if you do the research you'll find off the shelf electrical components that will do this job with a high degree of reliability-and relatively low power consumption-as I pointed out in an earlier post. As you get time check it out; you'll probably be surprised at what you find. You're too young to be set in your ways or to close your mind to new technology or to old technology done in new ways...Good luck-you're off to a great start!
The canting keel on this size boat allows a high performance boat to be doublehanded and still have the advantages of a keelboat. Being able to move the keel easily and quickly fits the concept perfectly. You can't buy a boat in this size range that has what this boat has to offer; it is a unique type with tremendous potential...