My improved dagger board and rudder

kmisegades

Swamp Goose
Dear friends, I recently designed a new dagger board that promises a 20% improvement in performance, based on the ratio of side force to drag compared to the composite/FRP board I am now using. I am currently making a composite prototype to test the design on my boat. When this is done I will share more details. I am turning my design attention now to the rudder. At 60% of the area of the dagger board and with a rather poor profile and planform, there should be much room for improvement. Is anyone aware of a more detailed drawing of the current rudder design other than that attached? My primary interest is on the hydrofoil's cross-sectional shape. I have reviewed a thread from 2017 concerning the need for more area (or not), the sweep of the rudder (weeds) and to reduce weather helm. I am not really concerned whether my board and rudder meet ISCA specifications, but both should fit existing hardware just fine. While my focus is mainly on improving L/D (ratio of lift/side force to drag) I am eager to know what other concerns people have. Many thanks. Kent Misegades, Seven Lakes, NC
 

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mixmkr

Well-Known Member
I'll be eager to hear more about the db. I extended a Barrington board by about 14 inches, sanded it more into a foil shape and glassed the final result.
A little more effort yanking it out when beaching, and I could find the bottom easier. Didn't really notice an improvement.
 

beldar boathead

Well-Known Member
The current rudder is slab-sided and not foil shaped. I am sure there is improvement to be had with the rudder. a

How will you measure the performance difference between a Sunfish with the racing board and current rudder vs your version? If one is night and day better than the other it should be apparent, but if that isn’t the case how will you tell if there is a difference? I’d be curious about the difference also with just your new rudder and with just your new board vs a boat with the racing board and normal rudder.
 

kmisegades

Swamp Goose
I'll be eager to hear more about the db. I extended a Barrington board by about 14 inches, sanded it more into a foil shape and glassed the final result.
A little more effort yanking it out when beaching, and I could find the bottom easier. Didn't really notice an improvement.
Thank you for the good comments - expert input is very important to me. A small difference in foil cross section and fin planform can make a big difference in performance, especially at for low speed flow in water. Lengthening a board will help if other aspects are considered. This is of course undesirable from a handling standpoint in shallow water. But everything is a compromise. Proof is in the pudding - I look forward to testing my board and expect to need to make multiple ones before knowing if they are better.
 

kmisegades

Swamp Goose
The current rudder is slab-sided and not foil shaped. I am sure there is improvement to be had with the rudder. a

How will you measure the performance difference between a Sunfish with the racing board and current rudder vs your version? If one is night and day better than the other it should be apparent, but if that isn’t the case how will you tell if there is a difference? I’d be curious about the difference also with just your new rudder and with just your new board vs a boat with the racing board and normal rudder.
Great question! It is the same for aircraft design, but planes mostly fly straight and level in calm air which makes testing much easier. Prediction methods (CFD codes) are so good these days for basic foils and wing-like shapes that such things are rarely tested anymore in wind tunnels or tow tanks. I am confident that the performance my work is showing will pan out - assuming the fabricated board and rudder are accurately made and I sail in ideal conditions - which of course never exist. I have a timed course on my lake between buoys spread a mile apart and will gather statistics from these myself. I have contacted my local rep for ISCA racing and hope they will test by parts in actual conditions similar to racing. Ultimately the only reliable source of performance data will be from experts like you.
 

LaLi

Well-Known Member
Ahem... devil's advocate here again :rolleyes:

What is the whole point of "improvement" here? You can't race with "improved" foils, and going a few per cent faster by yourself is pretty meaningless. I understand it if the goal is to make the boat more comfortable or easier to handle, but just "performance" for the sake of... what? Is going across the lake a few seconds faster enough of a motive?

_
 

kmisegades

Swamp Goose
Why do people climb mountains? It is an engineering challenge, and I like that. The current foils also have a lot of drag during maneuvering and I hope to quicken tacks. I doubt many people would want to sail with the original dagger board - the FRP ones are nice, but could be better. 2/3rds of all Sunfish owners are recreational boaters, I understand, but we too like going fast.
 

L&VW

Well-Known Member
What is the whole point of "improvement" here? You can't race with "improved" foils, and going a few per cent faster by yourself is pretty meaningless. I understand it if the goal is to make the boat more comfortable or easier to handle, but just "performance" for the sake of... what? Is going across the lake a few seconds faster enough of a motive?
It is, if the other boat is a Laser. ;)

.
 

beldar boathead

Well-Known Member
Ahem... devil's advocate here again :rolleyes:

What is the whole point of "improvement" here? You can't race with "improved" foils, and going a few per cent faster by yourself is pretty meaningless. I understand it if the goal is to make the boat more comfortable or easier to handle, but just "performance" for the sake of... what? Is going across the lake a few seconds faster enough of a motive?

_
If it’s fun to do, why not? On the other hand if the objective is to commercialize the product and make money, then it’s not a good idea.
 

Coastal Redneck

Active Member
Why do people climb mountains? It is an engineering challenge, and I like that. The current foils also have a lot of drag during maneuvering and I hope to quicken tacks. I doubt many people would want to sail with the original dagger board - the FRP ones are nice, but could be better. 2/3rds of all Sunfish owners are recreational boaters, I understand, but we too like going fast.
Speed is of the essence, even for recreational boaters... whenever two boats are traveling in the same direction, the race is on, LOL. :rolleyes:

It is, if the other boat is a Laser. ;)
Haha, L&VW, you funneh... :cool:
 

mixmkr

Well-Known Member
I made my daggerboard longer in hopes of being able to point higher and less sideways slipage. My launch is often at the end of a cove, with the prevailing winds usually blowing staight out the mouth. Tacking angles of 45+ degrees getting home, make one late for delicious suppers. I usually try getting better angles along the shore line, but wind speeds are typically less. Downwind runs back to launch sites are usually a factor, determining where to put in.
 

wjejr

Active Member
Hi Kent. You may be interested in my efforts to build an improved rudder for my 1971 Sunfish. The thread is here: Making new style rudder for old style boat .

It was a fun project, but I've never been able to determine if it's made a measurable performance difference. I think it's better, but I don't race the boat, and there are no other Sunfish where I usually sail. Sure looks cool though. :)

I hope you find my thread helpful. Good luck!
 

Webfoot1

Active Member
You'll eventually hit the problem of the daggerboard slot
being too narrow for the NACA airfoil most commonly used
for keels. Find a way around this and you may have a shot
at something better. Remember that the optimum L/D ratio
varies with the hydrodynamic speed so it's always a compromise.
X-Plane uses Blade Analysis so perhaps components could be
modeled using that program.
 

kmisegades

Swamp Goose
Ahem... devil's advocate here again :rolleyes:

What is the whole point of "improvement" here? You can't race with "improved" foils, and going a few per cent faster by yourself is pretty meaningless. I understand it if the goal is to make the boat more comfortable or easier to handle, but just "performance" for the sake of... what? Is going across the lake a few seconds faster enough of a motive?

_
On our lake, anyone can race any sailboat and in any condition. No One Design events here. Most sailboat owners are recreational sailors, but that does not mean that they do not like to see how well they do against others. Sort of like street drag racing. Welcome to the South, y'all!
 

kmisegades

Swamp Goose
Hi Kent. You may be interested in my efforts to build an improved rudder for my 1971 Sunfish. The thread is here: Making new style rudder for old style boat .

It was a fun project, but I've never been able to determine if it's made a measurable performance difference. I think it's better, but I don't race the boat, and there are no other Sunfish where I usually sail. Sure looks cool though. :)

I hope you find my thread helpful. Good luck!
Many thanks. You are a skilled craftsman and your work is impressive. I am wondering why rudders and dagger boards are not built more like aircraft wings, with a central spar running from the root to the tip? They are essentially the same, and the loads on them from dense water are quite high. Massive wood is surely fine, but relatively heavy. But then weight is not much of an issue on a sailboat, plus a light daggerboard will probably float right back up the trunk, the reason clips are required for wood. Has anyone tried making these parts directly with a CNC milling machine? A simple ShopBot or similar should be adequate.
 

kmisegades

Swamp Goose
You'll eventually hit the problem of the daggerboard slot
being too narrow for the NACA airfoil most commonly used
for keels. Find a way around this and you may have a shot
at something better. Remember that the optimum L/D ratio
varies with the hydrodynamic speed so it's always a compromise.
X-Plane uses Blade Analysis so perhaps components could be
modeled using that program.
Thank you - yes, the legacy of the early Sunfish dagger board left us with only 27/32" for the maximum thickness of the board. If the full width of the trunk is used, this results in a maximum thickness ratio of only 8.8%, far below the optimum for such conditions. If you look at the FRP board, you will see that the designer went with a 9% foil with the maximum thickness at 35% of chord, but this was too thick in the upper portion and there is a flat of an inch or so until the taper starts in the lower portion. Not exactly ideal but everything is a compromise.

I have found a way around this thickness restriction. The foil shape is also only part of the design variables - other things like the length (span), taper, sweep, tip shape, trailing edge details, etc. can be as important as the foil cross-section, if not more so. Then there are the practical aspects - like snagging weeds, ease of retraction, durability, appearance, and of course cost. I have looked at all these things in my computer studies and found a few combinations that look promising. I am making these now from foam/fiberglass. The board (and new rudder) will fit into existing hardware and will be approximately the same length as the existing FRP parts. I am making no attempt however to adhere to One Design rules as this pretty much eliminates any chance for real progress.

I do not use X-Plane. The methods in it are OK for what it does, but not accurate enough. My background is in real aircraft design, so fortunately I have experience with the same tools found at places like Scaled Composites (Northrop Grumman), LockheedMartin, Boeing, etc. Just saying.

Does it matter, since it will be hard to test? Yes - computational methods for basic wing-like parts are very mature, the reason that wind tunnel and tow-tank testing of such things is pretty rare these days. (they are of course an absolute necessity for complete models with all details). Fluid mechanics though is highly non-linear, meaning you don't know 100% if your ideas will work until you try. And I am not much of a sailor, but sure have fun trying. I do look forward to having the experts give my stuff a try though to see if they bring the expected improvements.

Just got a new wet suit and am ready for cool weather sailing here in NC.
 

kmisegades

Swamp Goose
Regarding staying in the class rules. If you race the parts have to be approved for use. This can take years.
Yes, I am in touch with leaders in the US ISCA organization and appreciate why this is necessary for One Design boats. My local sailing club races all boats at one time and has a handicapping system. One Design rules do not apply.
 

beldar boathead

Well-Known Member
Yes, I am in touch with leaders in the US ISCA organization and appreciate why this is necessary for One Design boats. My local sailing club races all boats at one time and has a handicapping system. One Design rules do not apply.
Are the ISCA leaders interested in new designs for racing?
Also, handicapping of small boats is typically based on the Portsmouth handicap system. How does your local club do the handicapping?
 

LaLi

Well-Known Member
The Sunfish is a Single Manufacturer One-Design, which means that all major parts (including foils) come from the builder, at least indirectly. You can't take your own designs to the class association to be "approved" - they won't and can't do that.

One-design rules do apply to handicap racing if you want to race with a standard rating. Any "improvement" should change your handicap number. (If not, there's something wrong with the system, or it's run incompetently.)

8.8 % isn't "far below" the optimum. The Laser centreboard is about 8.5 % and I have never heard anyone consider it too thin. Some classes like the Finn and the Lightning have nearly-flat plates that are 8 millimetres thick, and doing just fine. 9 - 10 percent might theoretically be "better", but as I understand it, the current Sunfish centreboard is very close to "good enough". The rudder may be another story.

If you want to "quicken" your tacks, get some coaching and practice. Beats anything you can do to your foils :rolleyes:

_
 
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kmisegades

Swamp Goose
Are the ISCA leaders interested in new designs for racing?
Also, handicapping of small boats is typically based on the Portsmouth handicap system. How does your local club do the handicapping?
The ISCA people I have corresponded with are not considering new rudders or boards. My interest is to seek an experienced competitor in my area to comment on my parts and try them out when not competitive. I will not live long enough to gain their expertise.
 

kmisegades

Swamp Goose
The Sunfish is a Single Manufacturer One-Design, which means that all major parts (including foils) come from the builder, at least indirectly. You can't take your own designs to the class association to be "approved" - they won't and can't do that.

One-design rules do apply to to handicap racing if you want to race with a standard rating. Any "improvement" should change your handicap number. (If not, there's something wrong with the system, or it's run incompetently.)

8.8 % isn't "far below" the optimum. The Laser centreboard is about 8.5 % and I have never heard anyone consider it too thin. Some classes like the Finn and the Lightning have nearly-flat plates that are 8 millimetres thick, and doing just fine. 9 - 10 percent might theoretically be "better", but as I understand it, the current Sunfish centreboard is very close to "good enough". The rudder may be another story.

If you want to "quicken" your tacks, get some coaching and practice. Beats anything you can do to your foils :rolleyes:

_
Thanks for the great comments! Forums like this are a terrific means to gain ideas, even when one question sometimes generates conflicting opinions.
 

beldar boathead

Well-Known Member
This seems like a fun project. I strongly suspect that the daggerboard changes will only have an incremental improvement that will be hard to measure. The rudder has more potential - reducing weather helm is the easy improvement, and it should be able to generate some amount of lift more than it does today - but who knows if that will be noticeable. Regardless of whether the improvements are noticeable, it is a fun project. If you really want to improve the performance of a Sunfish, I'd look at the rig. A lateen rig is not a performance rig. Some version of a Super-Sunfish-like cat rig would provide a noticeable performance boost in speed and pointing ability.

Here is a bit of info on the late Larry Cochran who led development of the new board. He worked with the late Bruce Sutphen on the project. Scroll down to Larry's info International Sunfish Class Association . Here is some information on Bruce Eight Bells: Bruce Sutphen >> Scuttlebutt Sailing News They each had a lot of theoretical and practical engineering, sailing and Sunfish knowledge.
 
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