Harveys' maps suggest that two of Arran's subbies (SubMarilyns) have in excess of 150m drop. In the case of Sail Chalmadale the drop is a suggestive 153m, and I felt this deserved some investigation on the ground. Hence a recent trip across the water.
Having crossed Beinn Bharrain, I descended to the col below Sail Chalmadale, which Harveys mark as 328m. I waited there for a couple of minutes, as close as I could reckon to the highest point, then noted a reading of 320m on my wrist altimeter (Suunto Vector). I trudged up to the summit, waited another few minutes, after which my altimeter read 480m, a difference of 160m from the col.
Now I am definitely not proposing this proves anything. I am aware of the problems with wrist altimeters and would guess that 10m is within their margin of error. However, I carried out the same procedure on the other suspect subbie - Beinn Tarsuinn - finding that the drop was reading 145m, quite close to the OS drop of 148m. It was a perfect day and there were no obvious reasons why the pressure should have changed in the few minutes between cols and summits. I conclude that there are at least a few metres of difference between the drops on the two hills.
In the absence of definite information from the OS, I doubt that it's possible to speculate further. However, the moral, surely, is clear. If you're visiting Arran, you'd be well advised to climb this one, just in case of future surprises.
After the report in Marhofn 58 I was dreading completing this hill. Being a purist (or a pedant, take your pick), I always try and make at least a bit of a walk out of a tick, and try to aim for a minimum of 30 metres of ascent by my own muscle power. How could I claim this hill in the Sennybridge army training area, when the only way of bagging it seemed to be a panic-stricken dash of a few metres to the trig point from a car with its engine running?
HM Forces came up trumps. Purely as a speculative planning move, and knowing I was staying within striking distance on the first weekend of 2003, I wrote to Army Training Estate (Wales), Sennybridge Training Area, Sennybridge, Brecon, Powys, LD3 8PN asking about the access position (see also http://www.defence-estates.mod.uk/access/accopplocations/accopp_sennybridge.htm).
I received a very friendly letter back from a captain at the base. He saw no problem in arranging access over this period and invited me to attend the base on Friday 3 January for a safety briefing and a range pass.
I duly arrived on the appointed day and was treated in a friendly and very helpful manner by all the staff at the base. I discussed with the sergeant my proposed route onto Mynydd Bwlch-y-Groes (and Mynydd Eppynt) and he saw no problems. It seems the western end of the area is mainly used for infantry training, and when I visited it was still closed for training for the holiday period.
Armed with my range pass I set off to the car park at Halfway Forest (SN835330) and up the higher forest road on the east of Nant y Dresglen, passing a sawmill and into the danger area. Navigation was easy by the forest roads, and the only ordnance I saw were a few empty smoke grenade canisters. On reaching a gap in the forest above Garn-rhiw I headed up the hill by a clear path onto the ridge. An army track (not shown on the Landranger map) follows the crest of the ridge above the public road. Apart from a couple of flooded sections (deliberate I think) this made for better walking than the road. The smartly repainted, whitewashed, trig point was easily gained by this route.
I had time to savour this difficult tick and explore a little. The weather was cold and sleety but quite clear, and the summit area not in doubt. The top is flat with no easily identified highest point. Those who have been satisfied with a mad dash from the road for the trig point will be pleased to read that there is no ground which appears to be higher. Various tussocks within a few metres of the trig point may look higher, but seem to be the same altitude when you stand on them.
I returned by my ascent route, making a total walk of 10 kilometres with 310 metres of ascent. All very satisfying, and I saw no-one for the whole walk.
In Marhofn 84 Mark Trengove suggested that Mynydd y Cwm might well be a new Welsh Marilyn. John Barnard has been to see for himself and offers a second opinion:
The summit is marked by a reasonably-sized cairn with a wooden cross sticking out of it, located in a small clearing in a rather inhospitable 'plateau' covered with brambles. I thought that a point about 50m SE could be higher. Looking back the cairn seemed lower but I would not swear to it, since the undergrowth makes it even more difficult to tell.
The OS map shows a 305m contour at the summit. I estimate this contour to be about 0.8mm in diameter, indicating that the contour should be about 20m in diameter on the ground. I would say that the ground drops away by about 0.5m, so I think Mark Trengove's estimate for the summit of 305.5m is not a bad guess.
The best place to start is SJ079768, where there is a wide area you can park without obstructing the forestry gate. Just follow the track until it gets as near to the summit as possible and then make a direct line to it. I found a number of tracks of varying quality but getting to the summit did not present any difficulties.
I think this is the key to the status of this hill. I have scanned the map with a magnifying glass until cross-eyed, which for me does not take long. I am quite sure that Mark's assessment of the rough position of the bwlch between this and Penycloddiau is right.
I also agree with the spot height position marked at 156m on the small road at SJ173678. Certainly the road drops into the field on either side by about 1.5m. On the map there are 155m contours east and west of this road that define the col as in this region, so an estimate of slightly below 155m for the col seems reasonable. But by how much? Some surveying equipment is really needed in the field to the east of the road to confirm this absolutely.
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