Tracking Under Power

[Jack O'Brien]

We all know how squirrely our X's are at slow speeds under power if we don't use a rudder and some centerboard.

Sail Magazine, August edition has several articles on Trailer Sailing and a page 46 description of the M says: "...it has a deeper V section forward for better tracking under power...."

Any boat design "students" know if this is correct?

Tony Houk has glued spray rails on his sides and some have glued thin protective rub strips to the keel. Anybody ever thought or heard of attaching a thicker, skeg-type something to the keel? Would it help?

[Steve M]

I have an and always keep at least 6" of dagger board down even under power. Helps keep the boat on track. Works for me.

[mgg4]

I have an and always keep at least 6" of dagger board down even under power. Helps keep the boat on track. Works for me.

I would be careful about using this technique going any faster than hull speed (6 knots). If you use this while operating at planing speeds, you are setting yourself up for a problem.

When a boat travelling at speed turns, it skids a bit by the very nature of how boats turn when they are planing. If you have your dagger board down, the boat will not slip, but rather will "Trip" over the board. Normally, the boat would lean into the turn, but with the board down, you will get a lean away from the turn. Very disconcerting, and if going fast enough can be very dangerous.

Remember, safety is the goal. At slow speeds, having some of the dagger board down makes slow speed maneuvering safer, but at higher speeds this is the first link in a chain leading to a knock down or capsize event.

--Mark

[Tom Spohn]

Having owned both and X and an M, I can confirm that the M does track somewhat better. We had no problem with our X at or below hull speed with the centerboard and rudders down and no problem at higher speeds with everything retracted. Yes it can be a pain to arrive at the Marina at high speed and have to drop the rudders and c/b just to enter at slow speed.

I think the advantage with the M is at high speed going through waves and currents. It does track better with less pounding.

[Scott]

Anybody ever thought or heard of attaching a thicker, skeg-type something to the keel? Would it help?

As MG states a boat slides a bit while turning. A fixed keel would creat problems. Your rudders can act as a skeg.

Second problem, Center of effort would undoubtably be affected changing your sailing performance in who knows what way.

[Jack O'Brien]

http://www.macgregor26.com/comparison_26x_and_26m.htm

The third paragraph explains the deeper V and several aspects thereof.

Yes, it helps tracking.

[Duane Dunn, Allegro]

I've always thought that adding a skeg to the boat would help. It would be a very small section fin that sticks out the leading edge of the centerboard. These small section fins were standard items on many flatter bottomed ski boats to give them just bit of extra directional stability and to add a pivot point for turning. Usually they were about 8" long made of metal and mounted just aft of 1/2 way forward.

I wouldn't think the fin protruding forward would hurt sailing with the board down. The only problem would be putting it on and off the trailer, but I think the stern floats high enough that you would still clear the rear trailer cross beam. You would also have to be careful beaching the boat as this fin would always be sticking down even with the board up.

[norbert]

I've always thought that adding a skeg to the boat would help. It would be a very small section fin that sticks out the leading edge of the centerboard. These small section fins were standard items on many flatter bottomed ski boats to give them just bit of extra directional stability and to add a pivot point for turning. Usually they were about 8" long made of metal and mounted just aft of 1/2 way forward.

duane, isn't this exactly what you get when you let a small amount of the cb down? i usually have the cb about 1 ft down when going under motor at slow or moderate speed (up to 6-7 knots). cb amount is easily to control on the old model with a cb cable where the rope/cable connection moves laong the jib car track (0.4 ft of cable is about 1 ft of cb down). i also use to have the rudders down (avoiding abrupt turns when going 6-7 kn). at higher speeds the boat runs like on rails with all fins up.

[Andy26M]

I know and agree with the theory of the boat "tripping" over the centerboard rather than sliding, but in my own experience with my 26M, this does not noticeably happen with the ballast full - I leave about 6" of daggerboard down even at w.o.t. (about 14-15 knots) if the ballast tank is full. What I believe is happening is that the daggerboard is located at or slightly forward of the boat's pivot point, hence what you note is that the boat takes a better "bite" into the turn (rate of turn is faster) but the boat still heels as you'd expect a power boat to heal (slightly into the turn). When trying to go straight, slow or fast, the daggerboard helps immensely if the ballast is full.

It's important for 26X sailors to remember that the 26M daggerboard moves vertically, i.e. it's center of effort remains right below the mast no matter how much of it is deployed, whereas with the 26X's swing centerboard the center of effort moves aft significantly when the board is raised. If the 26X centerboard was partly down such that its center of effort was aft of the boat's "natural" pivot point, then the "tripping" situation would come into play much more noticeably.

BTW, in any case, I always raise both rudders before exceeding 7 knots. The rudder(s) effect is to totally screw up the "fishtailing" ability of the stern under power and makes the boat very uncomfortable, not to mention the hydrodynamic instability and the potential to damage the rudder/steering due to increased loads.

Conversely, with the ballast empty, I find the boat steers much straighter and easier with the daggerboard fully retracted. I'm not entirely sure why this happens, it must have to deal with the changed hull geometry when the ballast is emptied and the fact that the boat gets up much higher onto a plane than it does with the ballast full.

As to coming in/out of the marina - I always raise both rudders, and leave as much daggerboard down as water depth allows. Leaving the rudders up allows you to push the stern left<-->right at will with the engine, and the daggerboard fixes the pivot point (without something like a daggerboard, remember that a boat's pivot point naturally moves aft when the boat is moving in reverse). I've found that with a little work you can move a 26M virtually sideways if you keep the rudders out of the water.

- AndyS

[Duane Dunn, Allegro]

Norbert,

You can get sorta the same effect by dropping a bit of centerboard. The problem is getting just the right amount. Ideally if you can get just the leading edge down a bit with most of the body of the centerboard still in the trunk you can create a skeg, but it ends up being a bit too far aft. With just a small fin you can run at speeds higher than 6 - 7 knots without worry about breaking the board or generating lift in the turns.

I find at anything below 7 knots I put down a foot or two of centerboard and a rudder and the boat is on rails as far as tracking. With all fins up it also tracks well at speeds above 10 knots. It's that slow cruise in the 8-9 knot range, with the engine noise much more acceptable, where my boat does not track well. It tends to hunt from side to side in any sea state higher than dead calm. Up to now I have always had all the fins up at this speed, but I think with a little something forward on the boat to supply some side to side resistance the boat would keep it's course better. I think a small flat fin on the leading edge of the centerboard up near the forward pivot point would add to the boats directional stability quite a bit.

[Mark Prouty]

When a boat travelling at speed turns, it skids a bit by the very nature of how boats turn when they are planing. If you have your dagger board down, the boat will not slip, but rather will "Trip" over the board. Normally, the boat would lean into the turn, but with the board down, you will get a lean away from the turn. Very disconcerting, and if going fast enough can be very dangerous.
--Mark

I accidently left the centerboard partially down under full power after maneuvering into a dock. On a straight course under full power, the boat wanted to trip.

[Duane Dunn, Allegro]

Actually what happens on both the X and the M at high speed with the board down is not really tripping in the sense of a outside lean. Both the boards are foil shapes and at higher speeds they develope lift. In theory this is a help going to weather when sailing but the speeds are low enough that the effect is not really noticed. What will happens at high speeds under power is the boat will start a lean off center to one side or the other and then the lift from the board will begin to roll the boat. This will happen even when you are going straight.

How much board it takes to induce this varies. Full down will do it every time. Sounds like on the M having a foot down does not give enough surface area for this to come into play although when the M first came out we experienced this on a demo run when not all that much board was down.

The same is true on the X. Having just a small part, about half the board width down, doesn't cause rolling under power at any speed. Any more than that and you do notice the lifting effect. The difficulty I have is consistantly getting just this little sliver of board out for better tracking but not lowering it so far as to get the rolling motion from the lift from the board.

[Dimitri-2000X-Tampa]

Theoretically, if the board is completely vertical, the lift from either side will be equal and you shouldn't have a roll moment...of course, in the real world, this wouldn't happen since the slightest wave, turn, or weight shift will leave that nice equilibrium and start rolling the boat. This is really obvious when sailing a laser or windsurfer fast with the board down. Go fast enough and it will fully capsize you.