Advice on most likely mast failure modes and insurance claims

The class association has been working with top UK dinghy insurance company Noble Marine Insurance to produce a guide that will help individuals in the unfortunate situation of having broken their mast.

The majority of insurance companies covering dinghy classes will use a standard response to a broken carbon fibre mast of requesting a quote for a new mast and a repair. This is based on most classes have a one piece mast, which is going to be very expensive to replace. However, one of the original design criteria for our class was that the mast should come apart so it can be transported inside the length of the boat.

The mast is therefore manufactured in three separate sections.

Bottom section – from mast foot to immediately above spreader bracket. (Ovington part number 61022, which retails for £878.70 2010 prices)

Mid section – from spreader bracket to hounds, This is the point where the wire shrouds and forestay attach to the mast. (Ovington part number TBC)

Top section – from hounds to top of mast, which is the tapered part. (Ovington part number TBC)

As a class, we are in an unusual situation where a broken mast often does not need to be completely replaced. It is very important that you make this clear to your insurer, as any work not required will affect the annual policy premiums the class members will pay.

Most sailors know that the mast comes apart just above the spreader bracket by sliding the mid tube off the lower tube (we’ll call this sleeve B).

The mid and top sections are factory joined at the hounds. (You’ll see a slightly tapered grey or blue plastic collar that acts as a step down join between the two components.) These two tubes are joined by a sleeve (A) approximately 500mm long equally spaced inside, and bonded together. This is done prior to the plastic luff track being attached to the back face of the mast. It is therefore possible for a professional to take these two tubes apart, and fit a new join sleeve and is well worth mentioning to your insurance company.

Known modes of failure (in order of most common, as I see it):

1. Early masts join sleeve ‘A’ failed prematurely due to being slightly too weak and this was strengthened. I do not think there are any masts sailing now with this weaker ‘A’ sleeve. It has always been the intention that join sleeves A and B fail first, as these are relatively easy and cost effective to replace.

2. Current boats most common failure mode is still sleeve A. The mast can then be cut through at the step down collar, and the old sleeve removed (which is bonded in) a new sleeve is then inserted, and the mast is re-assembled. It is common that the step down collar requires replacing. It is also obviously necessary to carefully cut through the luff track. Repaired masts then only ever show a saw line adjacent to the step down sleeve, and this is perfectly acceptable to all.

3. In something like 30% of cases the top mast snaps off usually around 500mm down from the top. In which case, the top section can be cut away from sleeve A, and a new top section fitted. It is most likely that the luff track will need replacing on both the top and mid sections, as it’s quite difficult to re-align.

4. In a very small number of cases the lower mast section fails. This is very rare (probably only one every couple of years) it’s only really ever caused by the lower shroud snapping when sailing. The sudden unloading then causing the carbon tube to fail due to catastrophic loss of local rig support. In cases such as this, it would be necessary for a new section to be supplied. A repair here would likely stiffen the tube in this area, giving sailors a possible performance advantage.

As a rule of thumb, almost all examples 2 and 3 occur when the mast hits the bottom in strong tidal conditions (especially when in wind against tide wave action)

For your reference,

Ovington part number 61105 – upper carbon join sleeve £152.90 retail inc. vat
Ovington part number 61108 – carbon top taper tube £372.65 retail inc. vat
Ovington part number 61121 – mast sail track per metres £14.50 inc. vat
Ovington part number 61110 – middle carbon join sleeve £135.57 inc. vat

There is obviously labour to be added to these,

if you broke the upper join sleeve (most common failure) you’d be looking at £152.90 + (£14.50 x around 4 metres)

Or,

If you broke the top taper tube (second most common failure) you’d be looking at £372.65 + (£14.50 x around 4 metres)

FYI, a complete top section is part number 61025 which retails for £816.35 inc. vat.