Minuet Yachts: a 2m fun boat-can the design be improved?

[sharpii2]

Originally Posted by Doug Lord

To properly immerse the DSS foil at 2 chords below the surface the boat would have to sail at about a 20 degree angle of heel. The boat would use a 4.75" chord 63412 foil section for both the curved daggerboard and DSS foil. At approx. 8 knots,if the lee daggerboard was deployed it would be capable of producing about 76lb. of vertical lift along with the approx. 160 lb of vertical lift from the DSS foil for a total of 236lb of vertical lift at 20 degrees(minus sail down force(canting mast?)). The all up displacement as of now is about 350lb so approx. 67% of the boat would be supported by "foil assist".
However, the est. pounds per in immersion is 94, so if the foils develop 236lb of vertical lift then the boat will rise 2.5" + planing lift, reducing foil distance from the surface to 7" or 1.47 chords or a bit less. Unacceptable.
At the same time the lift would reduce the wetted surface about 5 sq.ft. or
5.1 times the planform area of the DSS foil. Good.
---
This is all based on approximations and estimates but what is clear is that the hull design will have to be substantially different than the first sketches show.

It looks like you are saying the hull has to sit deeper in the water for the DSS to be truly effective.

I may not entirely agree with your project, but I will say you are thinking like a designer.

Keep up the good work.

[Doug Lord]

Originally Posted by sharpii2

It looks like you are saying the hull has to sit deeper in the water for the DSS to be truly effective.

I may not entirely agree with your project, but I will say you are thinking like a designer.

Keep up the good work.

==========================
Thanks ,Sharpii. Have a Merry Christmas!

[Doug Lord]

Haven't talked to Hugh Welbourn yet, but what I think I know is that it is not necessary on this particular boat to have the DSS foil parallel to the waters surface. Since the foil is being used primarily downwind a small leeward component of lift will not be a negative and will help keep the foil properly immersed(2-2.5 chords below the surface). Given that consideration it is likely the foil will work in this application.

Originally Posted by Doug Lord

To properly immerse the DSS foil at 2 chords below the surface the boat would have to sail at about a 20 degree angle of heel. The boat would use a 4.75" chord 63412 foil section for both the curved daggerboard and DSS foil. At approx. 8 knots,if the lee daggerboard was deployed it would be capable of producing about 76lb. of vertical lift along with the approx. 160 lb of vertical lift from the DSS foil for a total of 236lb of vertical lift at 20 degrees(minus sail down force(canting mast?)). The all up displacement as of now is about 350lb so approx. 67% of the boat would be supported by "foil assist".
However, the est. pounds per in immersion is 94, so if the foils develop 236lb of vertical lift then the boat will rise 2.5" + planing lift, reducing foil distance from the surface to 7" or 1.47 chords or a bit less. Unacceptable.
At the same time the lift would reduce the wetted surface about 5 sq.ft. or
5.1 times the planform area of the DSS foil. Good.
---
This is all based on approximations and estimates but what is clear is that the hull design will have to be substantially different than the first sketches show.

[Doug Lord]

I've e-mailed Hugh Welbourn about this project and designing for DSS. This sketch represents the Little 60 at 12.5 feet. No decision as to final length has been made.
Advantages at this length:
--DLR of 78-about the same as a Laser
--Self-draining cockpit
--canting mast(self draining cockpit helps here)


Rough sketch:
click on image-

[ancient kayaker]

I don’t understand why you say the DSSF would be used largely to windward. That seems to be when it’s not needed as much. Also it will work at any angle to the horizontal - it’s just that’s the most efficient from the leeway and lift perspective. Intuition is telling me that the DSSF with a daggerboard or keel is going to be more efficient than a Bruce Foil, but I can’t put any math of logic to that, unless it is the ability to use an asymmetrical foil profile.

For balancing the DSSF combines with the rotating seat to increase the horizontal spacing between the COG of the crew and the combined center of lift and buoyancy (I am just stating that on the off-chance that I misunderstood the theory, nothing new). Given the extra complexity and work for the crew, is there any advantage in the combination rather than a rotating or sliding seat with greater reach?

Here's an idea: how about linking the seat swivel to the DSSF slide? Then the crew doesn't have to think about the foil, it would happen automatically. I don't think this has come up before - at least in the forum - although it seems a bit obvious. There is the possibility of gravity overcoming the crew's efforts and the foil deploying on the wrong beam, but a simple gravity-operated rachet lock would prevent that. Of course that is more complexity, but it would pay back in easier operation of what promises to be a busy boat. I think I would try to gear it so the foil deploys before the seat is at maximum offset so the crew is not fighting the full heel and the foil's buoyancy simultaneously.

[Doug Lord]

Originally Posted by ancient kayaker

I don’t understand why you say the DSSF would be used largely to windward. That seems to be when it’s not needed as much. Also it will work at any angle to the horizontal - it’s just that’s the most efficient from the leeway and lift perspective. Intuition is telling me that the DSSF with a daggerboard or keel is going to be more efficient than a Bruce Foil, but I can’t put any math of logic to that, unless it is the ability to use an asymmetrical foil profile.

For balancing the DSSF combines with the rotating seat to increase the horizontal spacing between the COG of the crew and the combined center of lift and buoyancy (I am just stating that on the off-chance that I misunderstood the theory, nothing new). Given the extra complexity and work for the crew, is there any advantage in the combination rather than a rotating or sliding seat with greater reach?

===========
AK, thanks for your comments-you may have mispoken here. What I've said is that the foil will be used primarily off the wind-not to windward. There are two main reasons for this:
1) with more than a 20 degree angle of heel the foil will develop a component of lift to leeward screwing up progress to weather,
2) upwind speed will be fairly low and there wouldn't be much lift.
However, the boat will have an inclinometer in it so the skipper doesn't have to guess at the angle and the foil may be productively deployed at 20 degrees or less upwind-we'll have to see. I'm anxious to see what Hugh Welbourn says about this application.
----
The daggerboards are there because we don't want a board in the center between the skippers legs-so since they are there why not make them lifting boards like on the real thing? The lift of the daggerboard does not add to RM
but it does slightly reduce displacement. I think the two -DSS and curved lifting daggerboard are a good foil assist combination allowing around 70% of the weight of the boat to be lifted. The rotating "swivel and push" seat is moving to the max as it is now-there is no further for it to go. DSS allows for a much bigger asy spin to be carried than would otherwise be possible.
Seems to me that using these elements of the full size design* in a small boat will be a heck of a lot of fun to play with and we'll learn alot in the process.

-DSS is not presently used in an Open 60-but is approved by the class association. However, the class is considering going one design which will flat out squash innovation more thoroughly than the economy has!
=======

Originally Posted by Doug Lord

Haven't talked to Hugh Welbourn yet, but what I think I know is that it is not necessary on this particular boat to have the DSS foil parallel to the waters surface. Since the foil is being used primarily downwind a small leeward component of lift will not be a negative and will help keep the foil properly immersed(2-2.5 chords below the surface). Given that consideration it is likely the foil will work in this application.

[ancient kayaker]

Sorry Doug: I read you correctly but in my post I started off writing that the DSS seemed more useful to windward: then edited myself beyond all comprehension. Amazingly you managed to see through the fog . . . I had failed to pick up on the lack of speed upwind.

I assume the foil angle of attack is not variable.

I think the crew will be unlikely to become bored epecially in a brisk breeze!

[Doug Lord]

Originally Posted by ancient kayaker

Sorry Doug: I read you correctly but in my post I started off writing that the DSS seemed more useful to windward: then edited myself beyond all comprehension. Amazingly you managed to see through the fog . . . I had failed to pick up on the lack of speed upwind.

I assume the foil angle of attack is not variable.

I think the crew will be unlikely to become bored epecially in a brisk breeze!

==================
You bring up a good point about the foil-I've been curious on all the DSS stuff I've researched why that is never mentioned. I'd say it was absolutely critical that the foil angle of incidence (relative to the boat) is adjustable. I'm sure I'll get advice on that from Hugh Welbourn. I can't see that it would be
possible to have it right for every condition -much less right the first time-but I've got a lot to learn about this system. Seems like you can't lose by making it adjustable-you can always lock it in position.

[ancient kayaker]

Originally Posted by Doug Lord

==================
You bring up a good point about the foil-I've been curious on all the DSS stuff I've researched why that is never mentioned. I'd say it was absolutely critical that the foil angle of incidence (relative to the boat) is adjustable. I'm sure I'll get advice on that from Hugh Welbourn. I can't see that it would be
possible to have it right for every condition -much less right the first time-but I've got a lot to learn about this system. Seems like you can't lose by making it adjustable-you can always lock it in position.

Oops, that could make another thing for our busy crew to worry about, but hopefully it won't need continual changes. Perhaps it can be adjusted for conditions on the day and left, or possibly it may merely need a one time adjustment to suit an individual hull and rig. I think it should be adjustable; getting it right first time in the design and a first-time build is asking a lot . . .

[Doug Lord]

Originally Posted by ancient kayaker

Oops, that could make another thing for our busy crew to worry about, but hopefully it won't need continual changes. Perhaps it can be adjusted for conditions on the day and left, or possibly it may merely need a one time adjustment to suit an individual hull and rig. I think it should be adjustable; getting it right first time in the design and a first-time build is asking a lot . . .

=================
I don't think it would require frequent adjustment. Probably more like a "gear shift" for major changes in conditions and/ or "set and forget" for the day.

[upchurchmr]

I really liked how simple, elegant and nice sailing the boat was that started this post.

We are mostly people who want to put our stamp on things or we wouldn't follow these posts.

The complication that is being generated here is amazing.

Perhaps we should follow a Herreshof (SP?) idea if some complexity is acceptable. In "The Common Sense of Yacht Design" he offered the idea of a trimaran with a moveable crossarm/ ama set that could be moved to Leeward to form an Atlantic Proa on each tack. This would increase the moment capability like the swiveling seat. If you then could then rack the crossarms to move the ama fore and aft you could balance the sail force without a rudder (less drag to weather or reaching). If you really wanted you could put a curved foil in the ama to get dynamic lift (or just use a Bruce foil to experiment).

You could use the rig as an Atlantic or Pacific according to your desire. We could get Chris White to throw in his tilting mast patent to avoid reefing and minimize beam.

I really like the idea of being totally inside the hull, but we would probably need a windshield and a wiper since we would be going so fast. Do we need a spinaker?

Lets start with the 3M Trimarans designed some years ago, at least it would be similar to the original boat in the post (concept).

Merry Christmas or Happy Holiday or both.

Marc

[Doug Lord]

Marc-and everyone else-, Merry Christmas and happy New Year! While the Little 60 was inspired by the Minuet it certainly isn't meant to be in any way similar. Some of us love the idea of a "techno" boat where half the fun is learning to effectively sail the thing-and being patterned after one of the most complex full size, sometimes singlehanded, ocean racers guarantees that.
Of course, I like the power and majesty of a foil assisted trimaran as well which is the boat I'm working on now-model first and then-maybe- fullsize(main hull rig and foils already done).
I think there are all kinds of ways to have fun on the water and sailing a mini 60 with effective, working systems that actually increase speed will be one of those for me.

[Submarine Tom]

It's all coming back to me now Doug. They were mini 60's I sailed in. The guy had two of them. Unbelievably fun! Only 2m long, maybe 2.5 but no more. Like I said before, my girlfriend and I both fit in it two-man-luge style. She was a great girlfriend...

Merry Christmas to you too.

-Tom

[Doug Lord]

There is something not quite right about DLR as applied to certain hulls.
DLR =Displ. in long tons*/ (lwl in ft/100)^.667
*Displ. in long tons=displ. in pounds/2240
So:
1) Example 1: 8' boat with 300 lb displacement DLR=253
--minimum planing SA=(500sq.ft.per ton required to plane)=2240/300=7.47 ; 500/7.47=66.9 sq.ft..

2) Example 2**: 7' boat with 240lb displacement-DLR=312
-- minimum planing SA=500/9.33=53.59sq.ft

=================
It's been said by many people I've talked to that it would be damn near impossible for boats with DLR's this high to plane
**Consider that Example 2 is the same length and weight(60lb with a 180lb crew) as--hold your hats- a typical windsurfer! And we know it planes.
So, does this mean we can do a very small planing L60 afterall?? Cost of a 12 footer built to the standard we want is THREE times higher than for an 8-9 footer!

====================

Just discovered this: enter the parameters of your boat and it solves some common ratio's such as DLR and SA/D- http://www.gosail.com/boatRating.html

[Doug Lord]

It's occured to be that the DSS foil need not 100% retract allowing a longer foil. Until now it was only an idea, but I was going over the Quant 28 site with my new translate facility and found this that I hadn't seen before:



picture-foil sticking out both sides-allows for a longer foil-
click on image-