Mast and boom


Frequently asked questions: How long is the mast?

Let's take a look at what is given for the mast:

The class rule specifies very little (this applies to all 2.4mR):

(Please read with interest first, explanations will follow later)
- Only one mast / boom set is allowed for each event. Exception total loss.
C.8.2. (Mast)
- Width of the measuring marks min. 10 mm
- Rotating masts are not allowed.
-Lateral play of mast foot / mast rail less than 10mm
-Side mast bending 2700mm over MDP (mast date point) less than 30mm
-The MDP must not be above the deck measuring point

C.8.3. (Tree)
- Width of the measuring marks min. 10 mm
-Lateral bend 1000mm in front of the rear measurement mark less than 15mm
- Intersection of the top edge of the tree with the rear edge of the mast not below the top edge of the lower luff mark.
-Position of the rear measuring mark according to the E dimension in the measurement report.

C.8.4. Shrouds / shrouds
- Position of the forestay on the bow according to the J dimension in the measurement report
-With adjustable shrouds, it must be possible to reach the "Max tight" position on both sides at the same time. (That does not mean that the pull has to be symmetrical, but that at the end of the adjustment both have the status "max. Tight" (right and left are max. Tight at the same time). This is to prevent someone from following With the mast tilted upwind.)

Continue with section F.
F.1. Components of the rig
F.1.1.Pflicht parts
- Fixed meeting (shrouds)
- Movable meeting (day before / after day)


F.1.2. Optional parts
Jib boom
- Jib boom for self-tacking jib
F.1.3. Prohibited parts
-everything not in F.1.1. and F.1.2. is called

F.2. Basics
F.2.1. Regulatory compliance
-A boat has to comply with the class rules. Should a boat fall out of the rules due to changes in the class rules in the meantime, it will continue to be compliant if it was compliant when it was first measured. (Protection of existence, analogous to special rules for vehicles with H-plates).
F.2.2. measuring marks
according to C.8. 2 + 3rd (min.10mm wide)
F.2.3. definitions
Mast Date Point (MDP)
The MDP is a point at the front of the mast that is determined by the height of the forestay. See G.2.4. (The forestay height is denoted by “I”) and G.4.2. ("I" must not be larger than 3750mm). It must be marked with a punch.

F.3. mast
F.3.1. material
Either wood, GRP or aluminum
F.3.2. method of construction
The mast should have a fixed receptacle for the luff over its length. This can be a separate solid component. However, it must be made of the same material as the mast.
F.3.4. Dimensions (there is no F.3.3.)
-External dimensions at the upper measuring point: min. 28 / max 66mm; transept min. 24mm
- External dimensions between MDP and a point 3500mm mm above: in the longitudinal direction of the ship min. 56 / max 66mm, aisles min. 38mm.
(In this section, the mast must be cylindrical, i.e. the same thickness everywhere). From there to the upper measuring mark, the mast may have a uniform taper.
-Height of the upper measuring mark max. 5000mm (via MDP)
-Height of the lower measuring mark min. 250mm
-Distance between upper and lower measuring marks according to the design. See value "P" in the measurement report.
-Forestay height according to design. See value "I" in the measurement report.
F.3.5. weights
- Mast weight min. 6,5 kg
-Mast tip weight min. 2,0 kg

F.4. tree
F.4.1. material
-Wood, GRP or aluminum
F.4.2. method of construction
-The tree including its sail grooves should consist of uniform material.
F.4.3. Dimensions
-Outer dimension vertical max. 75 mm
-Outside dimensions in the direction of the ship a min. 27 max. 55 mm

F.5. Fockausbaumer
F.5.1. material
One or a combination of the following materials: wood, GRP, aluminum
F.5.2. Dimensions
Length according to design, see point “J” of the measurement report, max. Length = 1,35 * J. What is meant is the total length, including the end caps.

F.6. rigging,
F.6.1. method of construction
Mandatory: a forestay, shrouds.

So much for the class rule.
Some may have read more question marks than aha effects while reading. I hope it is now clear why I said that a translation of the class rule often does not produce the desired result.
In particular, there is no clear answer to the initial question of how long a mast should be.

But one after anonther.

We have seen that those who want to buy a mast from a well-known mast manufacturer no longer have to worry about most of it.
What else is important:
-MDP not above deck measurement point
-MDP to the anchor point of the previous day max. 3750 mm
-MDP to the upper edge of the lower luff mark min 250mm
-MDP to the lower edge of the upper luff mark max. 5000mm
-Position of the Lümmel fitting so that the upper edge of the tree is not below the upper edge of the lower luff measurement mark.
Believe it or not, now we know how long such a mast is.

If you want to know it to the millimeter, you have to read to the bitter end, for everyone else:
The deck measurement point is approximately at the level of the top edge of the deck on the mast. With MEINER MKIII it is about 2mm above the small collar that surrounds the mast hole.
The MDP must not be above it. But since the MDP determines the length of the mast upwards and we all want our sail to be as far above the water as possible, we don't really want to be below it either. So we take a ruler and measure from the mast foot rail to the deck zero point.
We add the 5000 mm max dimension to this dimension up to the lower edge of the upper luff measurement mark. We take the maximum, because we want to sail as big as possible.
Then you need a little space for the deflector plates of the traps and the gallows. But we want to be as stingy as possible, because that's unproductive material.
A mast is just as long. Ideally.

How do I measure my masts now to the millimeter?
Here we get down to the nitty-gritty, explanations from the ERS (Equipment Rules of Sailing) are necessary.
The ERS is here[20912].pdf .
Furthermore, you need suitable measuring equipment, i.e. a tape measure of quality class I. A folding rule has quality class III, i.e. a deviation of up to + -4,6 mm at 10 m. At least a quality rule. Promotional items without a class specification are only to be used here as an aid to estimating. Class I requires max + - 1,1mm at 10 meters. Furthermore, a certain precision is of course required when working. The measuring tape should be 5 m long and when measuring, we should note that there is a sliding hook at the beginning. So make sure that we really start measuring at "0". With most dimensions, it is also easier to feel when you work in pairs.

The starting point for mast measurement is always the pivot point on the previous day.
For pelican hooks, which most of us have, we take the lower edge of the slot in which the hook is hanging (F.2.3.e of the ERS). From there we go down 3750mm (I dimension). There should be a grain mark there. If not, we draw a line there, measure again carefully and then set the marking. Then we have the mast-date point MDP.
From there you can check the positions of the measuring marks. This also gives the position of the lumber fitting. Please make sure that the measuring tape can lie on the mast and does not run around shrouds or the like. Preferably you transpose the MPD to the side or to the back. Work meticulously with the stop angle.
The deck measurement point is still missing.
Place the mast and bring it into a vertical position.
Lay a straight bar across the mast. From the outer edge of the deck at the level of the bar, you go 15mm inwards on each side and make a line. Now you take 2 small strips of the same width, 40-50mm wide and not more than 40-60mm long. Write down the width of the lasts. Well-equipped hobbyists are welcome to take final measurements.
You then place it as a spacer between the deck and cross bar so that the inside edge lies on the line and the width is perpendicular upwards.
Assuming that your spacer bar was 45 mm wide, the cross bar is now 45 mm on each side above a point on the deck and 15 mm from the outer edge.
Now you make a mark on the front of the mast, where the lower edge of the cross bar is.
Now the cross bar and the spacers can be gone. We now go down from the last mark so far that we come to a point that is 36 mm above the outer edge of the deck.
In our example, the spacer bars were 45mm, down 9mm. Then we put a line again.
We measurers have created a template for this, but quite complicated procedure.
It is best to remember where this line is in relation to the mast collar, then it will be easier when checking a new mast.

Now we have the punch on the mast that designates the MDP and a line that represents the deck measurement point. The MDP must not be above the line. But that doesn't cause any problems because the mast manufacturers like to save material, so the mast is rather 2mm too short. At the World Cup we had a boat, however, because a plate was built under the mast rail for load distribution. Then of course the mast may rise too far.

What other conditions do we have that a mast has to meet and how can I control it?
Mast weight: (F.2.3q. Of the ERS)

Total weight of the mast including all attachments. So also a possibly existing compass holder.
Ribbon on balance, zero balance, loop ribbon around mast and lift in the center of gravity. logical.
Mast tip weight (F.2.3.r of the ERS):
Place the mast on 2 trestles. Support points: upper edge of the lower luff measurement mark and area at the height of the trap deflection disks.
Tighten the shrouds and stays towards the mast base, if necessary fix them with Zeising in the area of ​​the lower measuring mark. Pull the shackle of the traps all the way up. Traps and shrouds may lie on the floor in the area of ​​the mast foot.
Fasten the loop of the scale bundle at the level of the lower edge of the upper luff measurement mark. Raise the mast slightly, remove the trestle if necessary. Read weight. Finished
Lateral mast bending (F.2.3.m of the ERS and C.8.2.a of the KR)
One side of the mast rests on two trestles, so the spreaders point up / down. Support points: upper edge of the lower luff measurement mark and lower edge of the upper luff measurement mark.
We measure a point that is 2700 mm above the MDP and make a mark there. Now we take a thin line (fishing line, mason line or similar) and tension it so that it is fixed to the measuring marks on the mast. Really tension, no slack. Now we measure the distance between mast and cord on our 2700mm marking. This must not be more than 30mm, otherwise the mast is too soft. But nothing can happen there. Your value will usually be less than 15.
Position of the lumber fitting:

If the angle between the mast and boom is 90 °, the intersection of the top edge of the boom and the rear edge of the boom must not be below the top edge of the lower measurement mark on the mast.
(Raise the tree with the large fall so that the top edge of the tree is 90 ° to the rear edge of the mast. You are welcome to use an angle. The corner of the angle on the mast must not be below the top edge of the measurement mark on the mast. This measurement mark gives the maximum luff length of the mainsail.)

So now we have discussed what the class rule gives about the mast.
Any questions?
Yes: What about the spreaders? How long, wide, high should they be and where should my shrouds start?
Well, there are no stipulations in the class regulation.

Then the recourse to the OD rule comes into play. If you take these measurements, you have a clue, which is apparently reasonable. At least for an MK III.
But as I said: If you do not have or are not striving for an OD certificate, they are not mandatory.
Here is a link to the official form for the mast dimensions for OD:

At the end...
You saw that the class rule for us is quite complicated and does not provide an easy answer. So please don't be surprised if my answers are not always easy.
You have seen that the "measuring" cannot be done completely in passing if you do not have aids and specialist knowledge.

As Detlef said: Just ask if something is unclear. But only if you are really interested in the answer. And if you are able to follow a technical description.
Is not meant bad, some are not really good at it. I don't have any musical talent for that.

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  • Peter Strubel

    hello dear sailing friends,
    maybe someone can give me some advice
    I'm just rebuilding an old sailboat, it was badly damaged, actually
    there was only the hull left, no mast and no sail. Unfortunately, I am not at all familiar with the proportions. How long or high can the mast be when the boat hull
    measures 70 cm in length and 35 cm from the keel sole to the deck! The boat also has a low cabin structure with portholes on both sides. It's a shame that I can't bring a photo of the property here. I would be very grateful if someone could tell me something about this.
    Sorry that I ended up on your site, where I certainly do not belong. I would be very happy to get a positive answer.
    With kind regards Peter Strubel, Eckernförde

  • Rudi GER 793

    Hello Peter,

    the mast length should be between 70 and 100 cm, depending on the balast and hull shape, more.
    Have a look on the net for model tippers or similar sites.


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