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June 2009

The OCSG Coniston Water Training Weekend Meet was an opportunity for me to practice a technique recommended by EddieVB to escape from the irons, namely to push the sail to windward. This is something I learned while dinghy sailing several years ago but that I'd subsequently forgotten. And yes, it does work. Thanks for reminding me Eddie. I was able to reverse onto both port and starboard tacks, although my Raptor still has a preference to remain on a port tack and would sometimes over-ride my rudder position when reversing i.e. would reverse onto a port tack despite the starboard rudder pedal being depressed. So there will still be times when I need to resort to "pedaling".

Video clip: Large/small

I also practiced flying the ama without the foil deployed, to improve my mainsheet and rudder control, although this was complicated by the variable winds. Flying the ama is actually not recommended when beating on a starboard tack. The Raptor handbook states that the boat sails fastest by maintaining the ama "at roughly its natural waterline with the foil". By contrast, flying the ama is recommended when reaching on a starboard tack. I find it easier to control the ama flight with the mainsheet rather than with the foil control handle, although the latter may maintain boat speed better. One thing that I noticed while watching my ama flying videos: as the ama lifts while on a starboard tack, the wind resistance from the sidecar increases, which in turn increases the tipping tendency of the Raptor. It may be that this could lead to a capsize, even if the mainsheet is released, if the ama is allowed to lift too high in strong breezes/gusts.

As mentioned on previous occasions, deploying the foil considerably increases drag. Since the foil position is several feet to the starboard of the main hull centreline, one effect of deploying the foil is to cause a large rotational moment, turning the boat clockwise (to starboard). Deploying the foil inevitably slows the boat down and causes a large splash as it enters the water, since initially the end section of the foil is at nearly 90 to the water. This reduction in speed means that the flow of water over the rudder is reduced and directional control is lost. This in turn means that it is initially impossible to over-ride the clockwise turn as the foil is deployed. It is therefore important to bear away from the wind before deploying the foil, sailing on a beam or (preferably) broad reach. This will give you time to sheet in and gain enough forward momentum to achieve directional control before the foil drags you into the irons. I've posted a short video, which shows the effect of deploying the foil. Even though initially on a beam reach, I almost ended up in irons.

I left my Raptor with Solway Dory after the meet and plan to collect it again prior to the next one in July. This will give them a couple of weeks to make the various repairs and modifications that I've requested (more details of these next month). It will also allow DaveS to make a couple of new (wood) daggerboards for GeorgeF, to replace his original board, which snapped earlier this month, using my Raptor and board to create a template. Hydrovisions were unable to help him out with a replacement board.

I had planned to ask Solway Dory to also make me a new board to use solely for racing, since my current board has suffered some damage from numerous groundings. However, after talking to them, I decided first to undertake some testing to determine the optimum daggerboard size. DaveS explained that the daggerboard area was generally 2 - 5% of the sail area. My Raptor has a 62 sq ft sail when fully unfurled and approximately 2 sq ft usable daggerboard area (below the hull), equivalent to about 3% of the sail area. However, based on an analysis of my GPS track data, I believe this area might be inadequate. I think this because I have never achieved track angles of 90 or less between two tacks, despite my tactical compass showing that I often make 90 turns between tacks. I believe the difference is because my Raptor is making too much leeway. I plan to conduct some tests with my sail reefed to the OCSG area (44 sq ft) and with my daggerboard fully down, which will be equivalent to almost 5% of sail area. If this leads to a significant reduction in my actual tack angles then it will indicate that the original daggerboard dimensions are suitable for a smaller sail area but insufficient for the Raptor's full sail area. This testing will need to be done in light to moderate winds, since excessive leeway is inevitable in the F6+ conditions experienced at recent meets.

I had thought that a shorter board would be best for racing, but it may be that I ask Solway Dory to make me a longer board for normal use. Note that EddieVB recently had Hydrovisions make him a custom shorter board, but I haven't heard yet how successful this has been, especially since his sail area is even larger than mine.

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