Centerboard / Daggerboard Shape

[Eric O]

Yes, I'm following with great interest MM's CB mod. For those who have not caught his comments...

Per some of the questions on 'why modify the centerboard'.

#1 The stock board will not handle a heavy sea state. By that I mean contineous sailing (not motoring) in seas over 8 ft. & winds above 20 knots (usual heavy trade days down south).

#2 On the question of how well the 'wing' works. Honestly, it does not seem to make any difference one way or the other, except that it offers less resistance for the weight of ballast I needed to keep the board down. One drawback I'm hoping to correct by glassing the wing is the fact that it can sometimes catch weeds & kelp where the fins meet the board.

#3 After all is said and done, we all know the 26X points to windward about the same as the Penta, Nina, & Santa Maria did (i.e. pointing might look good but the boat 'slips away' when it heels). The board I use makes an amazing difference, and that is no joke. I can now point to windward well enough to not look like I'm going backwards when sailing next to bonofied racer/cruisers. If there is one modification I am most pleased with it is by far the new board. Maddmike

The thread is here http://macgregorsailors.com/phpBB/viewt ... 6&start=60

And some pics are here
http://www.sailboatowners.com/forums/pv ... 1223508.10

One thing we need to keep in mind though as we view these CB mods is that MM doesn't not have a large outboard on his boat so he is never motoring as fast as some Mac owners do. The extra board below the hull might create too much force at high motoring speeds. I wonder how much board you could have hang below the hull without creating problems while motoring at 20 knots.

Also something that I noticed about his board - from the pictures it does not look like it has a foil shape to it. All of the edges are rounded, but it doesn't look like it tappers fore to aft. Would more of a foil shape improve performance even more, or is as suggested in the quote at the beginning of this thread foil shape in the CB not really that critical?

[Gerald Gordon]

The extra board below the hull might create too much force at high motoring speeds. I wonder how much board you could have hang below the hull without creating problems while motoring at 20 knots.

Right on!! This is really my only concern!!

I don't plan to beach my boat. Having a small keel is not a problem. Motoring fast (max speed) could cause the boat to roll and go turtle.

So, who can build a high speed X-keel and test it?

[Frank C]

Gerald, rhetorical question, right? It's clear you'll not find anyone to test this for you, but why can't YOU perform a pre-test on your own boat?

I always extend the CB line by about two inches for slow speed motoring. This slight board depth doesn't impair straight line motoring at all, regardless of speed, it just improves tracking. I'm just guessing here, but isn't the familiar wobble-handling mainly induced by foil-lift? Such lift is materially non-existant when the board is mostly horizontal

Extend the CB line by ~5 inches and you'll be testing a skeg that's about 12" deep (I forget the actual multiplier from line-inches to board depth). Once the board is a foot deep, I'd be mostly attentive to whether the hull tends to "trip" over the skeg in higher speed turns? The board's still horizontal, and still shouldn't be inducing significant lift until it decends much closer to vertical.

[Gerald Gordon]

FrankC
sounds like a start

[normo]

Eric O:

Didn't mean to discourage your efforts to improve the performance of your powersailor. I gave it my best shot and was disappointed with the results. BWM is doing very good work and will hopefully influence future designs for the better. Unfortunately the biggie (bulb keel) is not in the picture for those of us with a 26X and probably not the M either. I still like the boat but wish it sailed much better than it does. The list of things I did are provided below:

1. Purchased a new full batten, loose footed main with two reef points from a quality sailmaker for $1000. It is better in heavier air but probably worse in light air.
2. Shortened the forestay about 4 inches to get a mast angle of approximately 88 degrees. This significantly reduced tendency to roundup. (best change I have made)
3. Installed a cabin top traveler which now allows the main to be adjusted much better than that pedastal mainsheet arrangement. (2nd best change I have made)
4. Temporarily removed the furler and installed hanks on the jib while I toy with a light weight headsail on a short sprit. Furlers are convenient but they penalize performance slightly.
5. Removed the rudders in hopes of reshaping to a NACA0012 shape. To my surprise the stock rudders have that shape.
6. Put the boat on the lift and checked the centerboard to make sure it was smooth. The centerboard does not fit snugly in the trunk. This allows the board to move sideways considerably while underway. Some of the energy that should go into lift from the centerboard is wasted. This is one of the first things that Catalina 22 racers fix. As the Mac centerboard is very light it probably wouldn't go down if it this was a snug fit but it could be improved.
7. It seemed that with the stock location of the jib tracks on top of the cabin tracks it is easy to overtrim the jib. Rigged up a temporary (have used it for a year now) setup where the jib block is attached to a block on a line stretched between the lifeline stanchions. It can be adjusted fore and aft which simulates an adjustable genoa car.
8. I pay attention to weight. For our weekly beercan races I try to limit fuel to six gallons, only carry drinking water, one battery etc.
9. I keep my boat on a lift so the bottom is always smooth and clean.
10. Don't have a genoa. I have concluded that a 150 genoa is too large for the majority of conditions that I sail in during the year. Sailing with a rolled up headsail is not fast. I am considering a 130 headsail for lighter air days.

It is fun to conceptualize new ideas and changes. Everyone does it. I can save you some time by telling you with great certainty that considering a flat plate design for a centerboard or rudder is a huge step backwards. I have spoken with the Ida folks and I believe they do have designs that will improve the performance, particularly for the older Ventures which had flat plate rudders. Since the 26X already uses a decent rudder shape I would not spend several hundred dollars without seeing data or controlled results quantifying what the improvement is and how it was achieved.

Over the past year I have developed a good sense for how the 26X performance compares with other sailboats. I sail my boat at least 40 times a year in beer can races in a wide range of conditions with a variety of other boats. Regulars in our club include - Ranger 23 (PHRF 221), Catalina 22 (270), 25 (230), and 27 (215), Flying Scots (210), Island Packet 32 (212), Cal 25 (224), Soverel 28 (217), Bristol 32 (199), J22 (180), Sonar (176), J24 (169), J105 (82) and others. I have been assigned a phrf of 300 for convenience as we use a pursuit start. So far I ALWAYS 3-4 minutes behind all the majority of boats in a 4 mile race. In light or heavy air I am further behind. My 26X prefers 10-12 knots winds.

Before I bought a 26X I checked around and remember seeing reference to a phrf of 369. I chuckled and blew it off. As it turns out I raced a well prepared Catalina 22 for several years; it has a rating of 270. In case you don't know, the C22 One Design class is very competitive and loaded with good skippers. A well prepared C22 will surprise you. My C22 could easily and virtually sail circles around the 26X. A rating of 370 for the Mac is, in my opinion, too low for most conditions. Off the wind the 26X is mediocre but sailing to windward it's performance is poor at best. For now I can live with that.

Good luck with your changes.

[Gerald Gordon]

So ,Normo, what to do?

Let's say for the heck of it that the X had a heavy keel with personality. Do you think that that would improve the boat's sailing performance?

[maddmike]

While I'm not running a 'big' engine, I have powered with all 3 engines going at the same time 2 x 6hp + 1 x 18hp = 30hp, (extra shaft drag). Without ballast, rudders up, calm conditions, 6 gal. fuel, & only me on board I can just top 10 knots, which I believe gives a good idea of stability at (some) speed. The boat is OK board up, seems to be only a slight difference from the stock board. However, in a very tight turn the added turbulance from the 'keel' creates additional cavitation and the engines tend to 'over-rev' more than with the stock centerboard. Otherwise it remained quite stable. Board down?, Don't even think about it. As for pulling on the beach, I still do it, and have to admit I'd rather run the board into a coral reef than the bottom of the boat (yep, I done did that on a couple of occasions, oops!). Maddmike

[delevi]

Eric, I feel your pain. I had problems with my DB after the first 6 months of buying my boat and have been contemplating a DB modification for some time now as well. I think adding some weight should improve performance nicely, particularly in higher winds. I just took my boat in to the dealer, since it has been just over a year since I bough it, and I needed to have him take care of some minor problems. Prior to trailering it there, I took out the DB to inspect it. I did this because I had my original board literally break on me about 5 months ago. To my surprise, the new board had huge chunks etched out of the top part of the board, at the front and back, the area which stays in the trunk to be supported and has the most amount of friction on the trunk fore & aft. It looked like a shark to a couple of bites out of the back edge and a bite off the front. My guess is that this happened from sailing in heavy chop. The dealer was baffled. At first, he tried to say that it was from the type of sailing I did.??? That didnt fly. He is going to the Macgregor factory in a week, and will take it in to have it looked at. Im hoping it will be replaced.

This, once again sparked a desire to modify the board. It is obvious to me, especially after having problems with two boards, that they are not built well. I poked my finger inside the holes at the bottom of the board and found the fiberglass to be paper thin.

What I'm thinking about doing is filling the board with lead shot, mixed with some resin. I am also thinking about wrapping 1/4" thick rubber around the top 12" of the board. I'm hoping this will protect it from damage and will also provide reinforcement for the added weight pushing on the trunk. Unfortunately, I had the dealer dispose of my old broken board, so I don't really have a cross-section to see where to drill holes and to pour the shot/resin mixture. I also have no experience doing this sort of work, so I would really welcome any suggestions from some of you handier folks.

By the way, has anyone had a DB with similar problems on an or just had it all out snap in half?

[adm]

Lets size it up.
There is difference in angle at which flat plate moving trough water will "stall" comparing to foil (Someone mentioned NACA 12). At speeds around 7 - 9 knots it is about 9 degrees and 15 degrees respectively. Thicker profiles will stall and bigger angles. But even when foil is better, in normal sailing the flat plate is quite sufficient. There is no reason to go overboard. Manifacturing require tight tolerances and may be quite impossiblewithout expensive tools.

To minimalize drag you need to shape leading and trailing edges of board.
What are you going to do is to create "foil which is cut at 30 percent of the chord and have some lenght of paralell sides "extensions" between trailing end. For example when you need 24 inch wide board 1 inch thick using NACA0024 profile round up first 3 25/32 inches of board edge using doubled values for NACA0012. Leave 12 inches flat and taper remainig 9 7/32 inches as trailing edge (also using doubled values from NACA0012, column) leaving edge itself very blunt - NOT rounded!!
You will have profile almost as good as NACA foil itself.


Here are offsests in percents of profile lenght:

Distance
From Nose NACA0012 NACA0015 NACA0018
1.25 1.89 2.37 2.84
2.50 2.62 3.27 3.92
5.00 3.56 4.44 5.33
7.50 4.20 5.25 6.30
10.00 4.68 5.85 7.02
15.00 5.34 6.68 8.02
20.00 5.74 7.17 8.61
30.00 6.00 7.50 9.00
40.00 5.80 7.25 8.70
50.00 5.29 6.62 7.94
60.00 4.56 5.70 6.84
70.00 3.66 4.58 5.50
80.00 2.62 3.28 3.94
90.00 1.45 1.81 2.17
95.00 0.81 1.01 1.21
100.00 0.13 0.16 0.19

Good luck

[normo]

Gerald:

So ,Normo, what to do?

First, I wasn't paying close enough attention to eric O's question and didn't realize that he had a Mac 19. Interesting boat. My comments were directed to those with 26X models. Fiberglass is great stuff and you can repair major damage with it. If you want to try something different you may find a thick piece of aluminum plate at a recycling facility. Locally they sell recycled aluminum for $1/lb. Unless you sail a lot with other like sailboats you may never notice the difference between a flat plate shape and a optimum airfoil shape. Grinding a nice leading edge and tapering the trailing edge some using the NACA coordinates will help. If you aren't satisfied with a flat plate you can reshape it later.

For the X owners I would offer the following for consideration:
The changes I have made were not expensive (you will have to replace the light weight mainsail soon anyway) and they did help performance some but not to the degree I had hoped. I improved from very very slow to very slow. Will anyone ever get a modestly modified 26X or M to sail a true 250 phrf (possibly even a 300 phrf) in a wide range of wind conditions? Not a chance in my opinion.

BWM's highly modified M gives an indication of what is required to achieve a significantly improvement in performance. They are very up front in stating that their boat is a one-of-a kind design which incorporates several key changes that are not yet ready for production or retrofit. This is really neat stuff. Their website also gave a preliminary report on performance of this boat. It noted that it did a horizon job on a San Juan 24 in 45 minutes. No doubt this is true however I can't help but wonder what they are comparing. Were they beating? Was the San Juan skipper aware he was in a race? Did he have UK like Tape Drive sails, a clean fair bottom, good crew and was he even a racer? These factors matter - a lot.

A San Juan 24 has a PHRF between 216-220. If an M, with a 50/70 hp engine on the transom, can be made to be even competitive with, let alone do a horizon job on, a boat with a 220 phrf it will set a new standard for sailboat design. I wish BWM nothing but the very best but I would be very surprised if this result could be repeated in bonafide PHRF races in a wide range of conditions against a mix of equally well prepared 220 phrf boats, skippers and crew.

My advise to current X and M owners is to enjoy the boat for what it is and beware of expensive upgrades that advertise major performance improvements. If anyone finds an upgrade that will make my 26X perform like a 240 phrf boat please let me know ASAP. IMHO, with the large freeboard, modest sail plan, narrow beam, water ballast, heavy outboard and that draggy transom protruding several inches below the waterline at all timesthis boat will never be a good performer compared to the majority of conventional non-water ballasted boats of this size.

[Terry]

Yes, I also have what looks like a shark was nawing on the top edges of the dagger board, right at the trailing and leading edges and on the top surface. I am at a loss as to explain how it happenned as there is nothing sharp enough in the trunk to cause this. Perhaps when it is completely raised while trailering it may happen, I am not sure. The one thing I am sure about though is (if someone comes up with a good mod) replacing it with an improved foil shaped one with added weight. I look forward to seeing someone design something (I am not that handy).

[Gerald Gordon]

Question about the CB pull string...

Who knows for certain if the CB pull string which raises and lowers the CB comes straight out of the compression post and attaches to the CB directly without any additional bends or pulleys?

[Moe]

It goes directly from the bottom of the compression post through a hole in the CB and is then knotted.

[Eric O]

Normo,

Thanks for sharing the results (or lack of) of some of your changes.

From what I have read about rudder mods to the X, the biggest difference was not from trying to improve on the shape of the rudders, but strengthening and adding about 3" to the leading edge the change the balance of the rudders in relation to their pivot point.

The M19 has stubby little rudders compared to the other boats. They are designed to be in the water under both power and sail. I'm wondering how much performance would be enhanced by putting on some X, M, or Classic rudders. The mod will require changing the mounting brackets and rigging a system to pull them up when under power.

As far as the CB goes - sounds like MM is onto something that has made a significant enhancement. Maybe building on that would get you closer to the PHRF rating you'd like to see.

[Eric O]

Leon & Terry,

Sounds like your DB is shifting back and forth in the fore/aft direction. If not every M owner has this problem maybe there is a problem with the fit of your DB in the trunk. Some boats with a DB have a way to lock them down when they are lowered (West Wight Potter 19 for example). Maybe there is a way you could do that on your 26M.

Adding weight to your board is liable to make the tendency towards fore and aft movement worse. Todd at BWY indicated that was one of issues they had to address with their weighted bulb at the end of the DB. I did not hear what he did about it. More than 50 lbs or so extra weight will probably require DB trunk reinforcement and some mechanical aid for lifting the board, but it sounds like Todd believes the weight, even only 50 lbs., would be an improvement.