Why does my boat surf so fast?

Discussion in 'Multihulls' started by pir8ped, Apr 16, 2014.

  1. Richard Woods
    Joined: Jun 2006
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    Location: Back full time in the UK

    Richard Woods Woods Designs

    I checked the sail plan I drew. The masthead genoa is 35sqm, the regular one 18sqm, the storm jib I suggest is 5sqm. So your storm jib is twice the size I recommend.

    I know you have made your boat lighter since you bought it, but the original builder built it over weight (he didn't discuss the changes he was making with me, as you know).

    I will be flying back home to the UK for a while on Wednesday, down in Millbrook at the end of the month

    Is your boat ashore at Jolly Harbour?

    Richard Woods of Woods Designs

  2. pir8ped
    Joined: Jun 2008
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    pir8ped Junior Member


    It's at North Sound boatyard - a lot cheaper than Jolly Harbour.

    Those sails - I guessed they might have been bought second hand, rather than being made to spec. Funny to think your genoa spec was 35 sq m, and at times, with the jib and genoa hanked on together, I've had almost 90 sq m up...:rolleyes:

    End of the month I'll be in Ireland...


    Even on the darkest days, I was never very short of electricity. My 2x80w panels had long cables on them, so I could, if needed, optimise their position. Even on cloudy days, the panels would generate as much as the boat was using, and my charge levels would just go down at night. A few hours of sunshine was all I needed to top them up again. So the hi-tech drogue/generator doesn't have that much appeal to me personally.

    I suspect such a drogue would produce so much electricity at full power that it couldn't be stored, and would have to be dissipated as heat. My rope and chain was very adjustable, and I think sufficient for the conditions. If things got really hairy, I have a series drogue, but it remains unused so far in its bag.
  3. dialdan
    Joined: Jul 2008
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    dialdan Junior Member

    The reason your Sagitta surfs too fast or faster downwind than the Shuttleworth has probably more to do with the windage on your boat being greater downwind .
  4. cavalier mk2
    Joined: Mar 2010
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    cavalier mk2 Senior Member

    pir8ped, I was more pondering the idea in general. Especially for electric drive or hybrids the idea is interesting. A straight mechanical version would be lower cost and less complicated. My budget too is in the rope/tire/chain range but such a self adjusting drogue has appeal for those with bigger boats/budgets.
  5. Richard Woods
    Joined: Jun 2006
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    Location: Back full time in the UK

    Richard Woods Woods Designs

    I don't actually think that is the case. The Shuttleworth is 1m wider than a Sagitta so even though it is an open deck design the aft beam and cockpit windage will be greater than on a Sagitta.

    The Sagitta actually has a low windage coachroof,as it only has 5ft headroom inside

    The Shuttle rig is much taller than the 12m Sagitta mast, so that will add windage

    As already mentioned, the wind at sea level is much less than higher up (wind sheer and wave interference)

    So the differences in windage are actually marginal. If you know the difference in areas it is then easy to calculate the relative speeds, assuming the same windstrength on each boat. But there has to be a big difference in "sailarea" to make a noticeable difference in speed. As an example, the Laser Radial is only 2% slower than the standard Laser, yet has 20% less sail area

    I see Aleph is for sale

    Richard Woods
  6. pir8ped
    Joined: Jun 2008
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    pir8ped Junior Member

    Yes, Aleph - that's the one.

  7. elhix
    Joined: Feb 2005
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    elhix Junior Member

    Faster? Whoa there chief! I'm not sure - as the Shuttleworth in question - I can let that slip by! Having sailed with the Mr Pir8ped many times in a wide variety of conditions I can say (and he'll agree, with a surly scowl) that our Shuttleworth is always very significantly faster than the Woods cat - a great boat in every other respect.

    Pir8ped and I took the same time to cross but used different methods to manage the horrible conditions - a t-shirt sized storm jib in our case and the use of towed rope/chain drogues by Pir8ped. The fact that our boat is way more easily driven than the Woods meant the small sail was enough to keep us going yet didn't encourage excessive surfing. In retrospect I actually wish - at times - I'd copied Pir8ped for a possibly higher average speed but in the gusty, squally and very rough conditions we choose to leave things be and read books. We are lazy sailors. We were in nasty, gale force conditions off Morocco late last year and I have no doubt we'd have seen 20 knot surfs then if not for the bare poles and double warps of rope and chain slowing us down. Despite the huge reserve buoyancy in John Shuttleworths designs I am always very cautious when we start to surf in larger, steeper seas.
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