16' Keel boat-high performance

Thanks chaps - like i say its still a work in progress. There won't be any movable ballast - too complicated for a boat this size i reckon...but there will be a spinny chute on the deck near the bow, dinghy style. The original influences on this boat were the AC 4.5 designed a few years ago by Juliane Hempel and built by Speedwave, and the Ray Hunt 110 and 210 boats. I started doodling with 3 different hull styles - round bilge, multichine and sharpie, although I liked the simplicity of the sharpie hullform and its budget potential.

Interesting to see you on the same tack Tactic - I hadnt seen your boat till i searched the forums recently to see if anyone was up to anything similar! One thing I did wonder about was drafting a simple box rule for these boats (the sharpie is meant to be a one design which i thought could fit in a box rule) and posting it here to see what happens....like your boat too by the way!

Andy

 

Lorsail, re self-righting; in a capsize situation, how far from the C of G is the C of B? Wouldn't they be so close together that the bouyancy has comparatively small leverage to re-right the boat? What about the problems of trying to lever the mass of the seat against the water to rotate the boat upright? In winged classes this is a significant problem.

I could use an International Canoe as an example since the seat slides like your ballast beam. In an International Canoe, shoving the seat (which has significant buoyancy) down to leeward can sometimes help right the boat- but only when the boat has drifted so that the mast is to windward, and the boat then "trips" over the board and upright as it drifts to leeward. And even then, the boat (despite its small rig) requires the weight of the skipper on the centreboard before it will come up- and I think that's normally more righting moment than you are speaking of.

In other situations, if the seat is in the water, like wings it adds a significant amount of drag that actually acts AGAINST the sailor's attempts to right the boat. The wing/seat has to be rotated through the water AND (more importantly) it tries to "trip" the hull as it is being blown to leeward.

Secondly, there is the problem that if the wing is down in the water in a leeward capsize, your ballast/righting lever is also down to leeward - so you get into a situation where the boat can start to come upright, but then not be able to recover correctly. If the seat/ballast beam is providing righting moment by flotation down to leeward, then it cannot be providing righting moment by weight to windward. In a Canoe when the seat jams down, you can sometimes get the boat up (but rarely, as the tripping moment of the seat is so high) and then get to a point where you can't complete the recovery because your method of shifting ballast to windward is still to leeward, and your method of applying weight to the centreboard can't work because the angles are wrong and the CB is underwater. So within about 1/2 second you get into an impossible situation.

Will the ballast really help that much? It's been a long while since I tipped a 16' Skiff in but if I recall correctly, it takes all three crew on the centreboard to right the boat, just like an 18 does. You don't just stand on the top of the foil either, but actually lean back and bounce. That is a lot more righting moment than your ballast, yet it remains a struggle.

The 49er's wings provide some buoyancy but they are not exactly easy to right AND they have much more RM in the form of two men on the centreboard. Most of the small tris (Bethwaite HSP, Supernova, Tri Fli) I have sailed were significant problems to re-right because of the water drag of the wings. Moths don't have a massive problem but their wings are mesh, the skipper can exert a massive RM compared to the boat and rig size and weight, and they are not exactly Joe Average's boat. Older Moths normally had only the frames, no mesh, because of the windage and water-trap problems during capsizes.

All three of these boats also required considerable work (fast mainsheeting at times, fine groove steering) if they were to stay balanced on the main hull and not be slowed by dragging the floats, but I assume you've had experience with that in your old tri.

Agreed about the fun of sailing a small tri lying down (Waverider style). And about the fun of sailing a small tri in general; the HSP in particular as it was a wonderful creation.

 

SDB ( sliding deck ballast)/ Trapeze Wing System

CT 249-There are a number of aspects you may have missed or that I didn't explain well. For a disabled sailor SDB the keel will be ballasted as will the wing; the wing has buoyancy pods on it and also pivots athwhartship so that in a capsize it could be moved to center position with weight in the center but the whole thing pivoted so that the pod acts to right the boat in concert with the ballast keel. A non disabled crew could get on the centerboard if necessary. With both these testing is the only one hundred percent guarantee of performance but it looks feasible right now. The whole concept seems good to me because, assuming that the testing proves the theory, the boat will have extraordinary speed for a sit down inside singlehanded boat, be beach sailable, have a wide(huge) viable crew weight range(90lb. to 250 est.) at the same performance level, be easy to trailer and last but not least be self righting -at least in the disabled version.
I don't know how much fun a tacking dual in a lot of wind will be in the non-powered version but I think the skipper will forget about it off the wind....I think it offers a new way to sail fast with many of the advantages of a keelboat and coupled with "foil assist" or full flying foils where applicable it should be fairly fast.

 

Hi Andy,
I have drawn several versions,round bilge,multi chine and the cheapo flat bottom.All look like goers to me.
I to used the AC4.5 as a guide and Martin 16 as well.
Mine are 4.7m long with around 120kg in the bulb.
I think a box rule would be great and make a nice little class,much cheaper than the Int 2.4m and prob a little quicker.

 

I think I got it all, Lorsail, but I should check. Aren't you thinking of something basically like Slingshot, the "canting proa", but using ballast in the beam rather than crew weight on the beam like Slingshot did?

If I have the concept right, there seem to be problems. I have punched some numbers and as far as I can see, the righting moment (when recovering from a capsize, including the ballast) is about 1/4 of the righting moment a 16 Foot Skiff has, and similar to that of a Canoe (which also has buoyancy to leeward at times, in the form of the seat). Neither of these boats pop back up quickly all the time. The 16 has a similar rig to your boat, the IC a much smaller one.

Furthermore, if the key to your stability is having the beam cranked to windward to create RM through its weight, then how come it's Ok to have the beam cranked to leeward when you are REALLY need righting moment (ie while recovering from a capsize)?

 

Ballast

I think the buoyancy pods plus wing buoyancy plus ballast in the keel will right the boat nicely....
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Note: it has been tested in several different rc models and works well. And full size testing will solve(or not) any unanticipated problems.

 

SDB(Sliding Deck Ballast)

Here's a cool shot of a rendering of Bethwaites 60+foot monohull equipped with buoyancy pods and sliding on-deck ballast:

http://www.sailinganarchy.com/fringe/2005/images/billoch2.jpg
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He has also designed an LAS(Lead Assisted Skiff), the UD 18 which will be used in the Paralympic Games. As I understand it ,the boat can feature a sliding ,rotating seat in combination with variable amounts of keel mounted ballast.
When you consider the design concept I have proposed using a crew that sits low in the boat with a sliding wing(or fixed side to side for that matter) that contains not only sliding lead but buoyancy due to its own volume combined with pods on the end of the wing
--it's really not too far from the concepts Bethwaite is experimenting with on both large and small design ideas. I think the application of movable ballast to small sailboats is wide open and can result in some unique ,very fast,"sit -inside " sailboats with loads of power to carry sail AND self-righting characteristics-boats that simply do not yet exist.
I think, too, that the concept could be brought to even smaller boats than I have proposed so far-in the 10'-12' region- as well.

 

LMAO ... they must have swapped the photos ... this is a trimaran ... hauling around some lead to slow it down ... too funny!

 

Trimaran?

Interesting "trimaran": the pods("hulls") aren't in the water at rest and they are not sailed "on". They are not used to generate RM in normal sailing just as backup in gusts. The boat is probably self righting both in pitchpole and in case of a knockdown. Uses sliding on-deck ballast for stability.
Bethwaite/Billoch article:
http://www.sailinganarchy.com/fringe/2005/pteradactyl.htm
The smaller versions I have proposed would definitely be self righting when used in a "disabled" format with a fixed keel.
Don't know of any existing self-righting trimaran's. It's a hybrid with some of the good points of both mono's and multi's....

 

Show that picture with no text to any sailor and ask what it is. The answer will be "A Trimaran ... with a keel".

Most high performance Tri's would not have a pod in water at rest if they had a great huge dangley bit under the hull either. They also don't have to accelerate a ton of lead after every tack. For a given weight they can carry more sail than this ... this ... thing.

It's a funny looking, slow trimaran. I guess if you want "probably self righting", you have to be slow. Mono-hulled lead mines have been doing it for years.

 

trimaran? Why no ,I don't think so...

Isn't that the old idea of telling what a book is about by just looking at the cover? Or is it: "Don't confuse my mind with facts-it's already made up" ?
Some people including me , Billoch, Bethwaite Langman and probably many others look at the facts of how the boat sails- not ,necessarily, just what it looks like. This is a new type of boat: it has some visual characteristics similar to a trimaran but it does NOT sail like a trimaran-in other words the pods are not used for buoyancy in the normal course of sailing.Further, the ballast is not just in the keel but the boat is designed to use additional on-deck sliding ballast in the "wings".It derives it's normal sailing stability entirely from ballast-not from buoyancy in the pods. In fact, use of the pods for buoyancy and RM would be slow with this new type of boat.The smaller , somewhat similar, versions I have proposed would also be slow if the pods were immersed but it's great to have them for backup.
Mr. Hough, Mr. Bethwaite thinks this is a very fast concept and, with all due respect, you're probably wrong. I think I'll stick with Mr. Bethwaites analysis of the concept...

 

it looks like a trimaran but will be slower. It is as wide as a trimaran but cannot generate the same righting moment.

Doug, do the math. it will be slower than a Tri of the same length and weight. It will only be fast in the context of mono-hulls, and then only if someone finds a half blind official to allow YARGYD (Yet Another Rube Goldberg Yacht Design) to sail as one.

Claiming this thing is a mono-hull because the amas are only in the water in gusts, is the same as saying that Cheyenne is a mono-hull because her windward ama is only in the water in lulls.

The pods/amas/hulls have bouyancy, the boat uses them to increase RM at times. This is an accurate description of any multi-hull. It is not the description of a mono-hull.

 

Monohull?

To say this is a trimaran because of the buoyancy pods doesn't make sense to me: they have nothing to do with RM in the normal course of sailing and do not contribute ANYTHING to the speed of the boat.
Bethwaite says that this boat will be MUCH lighter than an equivalent length trimaran and I'd bet that with a two foil system like a Moth the boat would hold its own or be faster than the eqivalent sized tri. The fact is that a two foil Moth can hold it's own with multihulls that are much larger with more SA and much more RM.It's also true that Bethwaite, Langman and the Out 95 group are all going to be using this configuration to experiment with the use of a two foil monohull hydrofoil system.
Frank Bethwaite called his HSP a trimaran because of the small pods but they were used in sailing the boat and did provide RM when sailing at speed . Bethwaite/Billoch's configuration sailing at speed will not use the buoyancy pods for anything except holding the crew and develops all its RM from ballast like any other monohull. So ,again, like any other monohull keelboat this thing uses a ballasted keel and on-deck ballast to stay upright. I don't believe the incidental use of buoyancy pods as emergency backup takes anything away from the basic characteristics of the boat as a ballasted keelboat albeit a very ,very fast keelboat.
Like I said earlier, I'll go with Bethwaites analysis....
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Ah, the big cat's windward hull is only out of the water for short periods in gusts! The Bethwaite monohull(hybrid)'s pods are only in the water as emergency backup -and slow the boat when in the water. If it uses a ballast keel and deck ballast to stay upright, if it is self righting-then it must be a monohull, right?

 

people shouldnt be dumb enough to design a monohull in the first place that will actually need the help from buoyancy pods. Any reasonably designed monohull will self right if the keel still provides a righting arm when the boat is fully knocked down. If the canting angle of the keel is so high that when the boat is knocked down 90 degrees, and the keel doesnt provide any RM at this point, you shouldnt be sailing it. Genuine Risk doesnt use buoyancy pods and she is wicked narrow-90' long only 11' wide. Of course, she is relatively slow too(compared to multis). A "hybrid" boat is not a smart idea. And what happens if you stuff one of these "pods" into the water about 10 feet under at 30 knots? It will either get ripped off or cause the boat to completely wipe out.

 

I agree. It adds something. HULLS!

Sorry I'm not with you on this, Doug. I agree with you that this is an exciting experiment in naval architecture, with interesting people involved. I'm glad you're into it, and I hope you'll keep us posted.

But the semantic game is dopey. A monohull has one hull. A boat with three hulls is a trimaran, whether it has ballast or not.

Did I ask you at some earlier point in this thread if the Bongo is close to what you mean about a ballasted 16 footer?
www.sailabongo.com