24/11/2014 at 08:11 #10007
Any body else interested in finding out.
I guess it is an exercise in weight loss and reduced drag. I have an idea for light weight keels and quick release clamps and faster lifting. I think no engine other than a small outboard.
It would be ideal for the round the island race.
I have no intension to do this to Mary as I want the cruising capabilities.
But the question remains….. How fast?
24/11/2014 at 08:45 #10008
I think you are correct about the weight. Peter Cranes boat Eirena is very light and sails very swiftly. I have been experimenting with sailing to windward in light airs with one keel fully raised (it was stuck up for a couple of days) and she was certainly swifter to windward like that. I also know that I gain almost a knot motoring in a calm when I fully raise both keels.
Not sure I would want to reduce the weight of the keels though – they have a low ballast ratio as it is. Of course it could be carbon fible keels with lead in the bottom! that would increase the righting moment without changing anything else.
I suppose my final comment would be that they are already fairly fast OFFSHORE. As in when there is wind F4 and above they keep up with boats which are significantly bigger. Perer Crane and I sailed from Falmouth to Penzance in winds of F4 to F6 from the SW. When on the moorings outside Penzance harbour we recieved comments from the crews of the 35 ft boats which also made that passage on the same tide along the lines of “those boats are fast, we couldnt catch you!”
To me it is important to have a boat which feels secure at sea, so while it might not be as fast as boats intended for racing, it inspires confidence in me. I have taken it out of shelter in some pretty strong winds! So I dont actually feel that the performance needs improving!
24/11/2014 at 21:26 #10009
Having raced in a mixed fleet local races a few years ago with Ereina: The technique for the first couple of years seamed to be – establish position at the back of the fleet and make sure nobody gets behind you. However, thinks did start to improve with the experience of racing most weekends through the summers and we even won a few.
I would not recommend an outboard (we did this for a year): you want to keep the weight out of the end of the boat. Also you will worry all through the race if there is any amount of wind on how you are going to manage coming into harbour and picking up your mooring: Ereina would not turn to port with the power so any sharp turns had to be to starboard. We had the new inboard fitted with a high pitch twin blade prop. which we alined with the steg and rudder while racing, although now I would go for a folding one like Trevor’s Calista (the faster you go the more the drag increases at a greater factor).
To further keep the weight out of the ends the ceramic and brass heads has been replaced with a portapotty (with pump out). During races we would store the anchour and chain between the front end of the keels. Also the inflatable, unless left on the mooring.
Keels – experiment – I would normally have the leeward one slightly kicked further back to lessen weather helm as the boat heels.
Mast rake – when you are hanging a weight from the top of the mast to calculate this it will be different if the keels are fully up or down. Any amount of rake appeared to increase weather helm (3/4 rig).
I wouldn’t change to full rig having sailed on both. The full rig is faster in light to moderate winds, but in higher winds we could claw away further to windward. We do have a light weight jib that we can fly from the masthead in light winds when just off the wind. I would like to try a masthead spinnaker at some point.
Keel box rubbers – these must be in good condition, turbulence in the keel boxes really slows you down.
I wouldn’t mess with the keels – you end up with a boat that is not an Atalanta. However, saying that I am going to try winching them with an 18v rechargeable drill, it would certainly be quicker at lowering.
There are lots of small tweaks that all add up, but in light winds they do not perform as fast as a lot of the plastic boats. In very light winds try joss sticks as a wind indicator (makes the boat smell nice and causes amusement as you drift past).
Would love to do the Round the Island Race in a year or two.
24/11/2014 at 21:29 #10010
Colin mentions a hull speed of 7 kts. But I believe the hull shape means it is able to plane. I believe the ability to plane must be restricted by weight. So I got to thinking about lighter keels. That would flatter the hull shape more so than an increased sail area.
Is anybody mad enough to skipper a round the island race attempt? It would be a fitting 60th anniversary? I will crew but there is a stupid number of boats involved and I fear I don’t have the experience. If we get a magazine involved some sponsorship and those interested put some cash or hours in. We do the boat up race it then sell it the proceeds go to the club?
Just an idea worth nothing if nobody is interested.
25/11/2014 at 11:41 #10011
As I recall the Atalanta had an annual group entry in the Round the Island in days of yore. Uffa Fox does not specifically mention the Atalanta with regard to planing in his published books on the subject. The lifting keel Fairy Fox 24, a beam of 6ft 3″ diplacement 1500lb and a sigle 6ft drop keel (of 65lb!!) designed with downwind planing in mind and to be sailed with a minimum crew of 4 (due to windage). Uffa in his book “Sailing Boats” has her recorded at 16kts. An Atalanta (I think A77) is featured in the 1963 “Uffa Fox Book of Sailing” , but no specific reference to planing. I remember an article in one of the sailing mags some years ago with a Fairey Fisherman on test planing downwind (I think under spinnaker) at 10kt!- surely the Atalanta could do at least as well. I’m sure other members have experienced surfing in displacement boats and the Atalanta has genuine ULDB credentials so one would suppose could be achieve planing given suitable rig set-up and conditions.
25/11/2014 at 14:02 #10012
Yes they are supposed to plane. I spoke to Simon West (A5) who was describing how they had A5 planing, when we were last at Beale Park.
More surprised to hear that a Fairey Fisherman planes, are you sure about that? The Fisherman is a lifeboat hull. Designed as something to do with the mould after fairey failed to get the contract to build ships lifeboats.
06/03/2018 at 22:21 #15128
Yes It is correct A5 was planing down wind surfing waves , keels were half down with the spinnaker..Diaphony had a sumlog fitted which I believe went up to 12 knots and was on its stop the boat stil surging a head but the most memorable sight was the look of Horror on my father’s face..
We really did break out of forced mode that day.
25/11/2014 at 15:12 #10013
Very qualified though. The Fisherman article was a test sail in either – YM, PBO or ST. It was clocking 10 kt under sail in a blow, (to the surprise of the journalist), so planing/surfing down waves, but exceeding hull speed in any event. I seem to recall that the owner was also a racing yachtsman who used the FF for family sailing. The underwater profile is rounder and flatter than a normal displacement motor sailor, so I suppose there is less grip on the water.
25/11/2014 at 15:45 #10014
I just managed to find an extract of the original PBO FF review from Dec 1998. The actual reference to 10 kt was anecdotal from the owner “while sliding down a wave in similar conditions under spinnaker”. So that is pretty qualified and obviously not bestowing general planing ability on the Fisherman.
27/11/2014 at 12:21 #10015
Just a thought.
I have been looking at a photo of an atalanta sailing hard on the wind with one keel box totally out of the water.
I wonder if she would be faster with tha windward keel fully raised? My thinking is that the keel weighs more out of the water – so lifting it would increase the righting moment, and reduce the wetted surface area.
Would that balance the loss of keel area stopping sideways motion?
27/11/2014 at 20:41 #10016
Needless to say post the photo.
My guess is that the keel being down increases then leverage of the weight.
Has anybody calculated drag forces on a standard Atalanta? I believe it can be done by a towing one using a newton meter, or hanging scales. If we graph this against speed we would to see an initial upwards curve showing the wave forming drag that defines the hull speed then a kind of levelling off as the planing comes in.
Be a good article…
27/11/2014 at 20:45 #10017
Sorry there is a good discussion here including graphs.
23/06/2017 at 00:19 #10018
Interesting discussion I wish I had chimed in on earlier. My thoughts are definitely do not lighten the keels. The keels are your righting moment, which is your horsepower. The higher the righting moment the more sail carrying ability. With that in mind if the boat is to the point of the windward keel box out of the water I would definitely have the windward keel down. With the keel down the Vertical Centre of Gravity (VCG) of that keel is lowered by 2 feet or so, a significant increase. I agree on the ability to at least semi plane. We were off the south coast of Nova Scotia in 1996 and had a great breeze out of the north. We were beam reaching with the asymmetrical spinnaker on the bowsprit and full main and hit 8 knots consistently. The boat was not light, we had been living on her at that point for 2-1/2 months having sailed from Boston to Bermuda then to Halifax and all around the Canadian Maritimes.
Keep the boat light. Get weight out of the ends. Fair in the forward and aft ends of the blocking on the bottom around the keel trunks. As mentioned have good keel sealing strips. Get rid of roller furling, rig a down haul looped over the top hank, lead it to the tack then back to a cleat at the cockpit. Lighter and you can get rid of the sail much more quickly. Without the roller furling the jib also does not need the weight of the sun cover. Fair the keels and rudder. IF you have an inboard, get a folding or feathering prop. If an outboard take it off the transom and stow in the space under the cockpit seats. Rig a backstay adjuster, a simple way is to have a block on each leg of the backstay linked together with a block in the middle. Have a continuous line led from a cam cleat on one side of the aft hatch, to a block on the deck, up to the block on the adjuster, down to another block then forward to a cam cleat on the other side of the aft hatch. Makes it very easy to open and close the leech of the main, especially if you have a fractional rig. Clean the bottom. We moved the anchor chain from the bow to just aft of the main bulkhead. We are definitely going to be looking into synthetic rigging when we finally rebuild Le Bateau Ivre. Less weight although a little more windage.
25/06/2017 at 07:35 #10019
Thanks. a couple of questions. Bowsprit? How have you attached this. Also synthetic rigging can you send a link to what you are thinking about, what kind of weight saving? Are we talking skipping lunch or a crew member 🙂 . Also are you still running wooden spars? What is the relative weight by comparison wood, aluminium and carbon fibre. I understand carbon fibre is not that robust and is still expensive.
12/03/2018 at 17:29 #15130
The hull speed (c6.5 kt) is relatively high in the Atalanta compared with similar sized displacement cruisers due to the long waterline (c24.5). This in itself makes her faster in a decent blow than many larger displacement yachts with less waterline length and/more wetted area. Reducing weight will increase acceleration up to to hull speed, as will fairing and smoothing anything below the WL. Even though she is already light at 2t (depending on payload etc), it would take much further reduction in ballast (and hull modification) to achieve any chance of true planing – as opposed to surfing and slipping down waves etc.
As mentioned way back in this thread (citing UF’s book “Sailing Boats”), the Fairey built Uffa Fox designed 24 ft “Fairey Fox” (displacement 680 kilos) was a planing design with a superficial similarity to the Atalanta with a waterline of 24ft. This design could achieved planing with a hull form specifically designed with a long flat run with a chine aft; the flat run began about one third back from the bow. She had only an 85lb drop keel (3/8″ thick) with sharpened leading edge. The drop keel was so narrow it avoided the need for a rubber strip over the slot. So roughly scaling that up to the Atalanta – maybe 50lb per narrow keel! The Fairy Fox also required a crew to provide ballast as on any performance boat – Uffa warns that she should never be taken out with less than four people because of the windage in her topside mast and rigging.
08/06/2018 at 17:37 #15699
KEEL SEALING STRIPS
This seems like the ideal post to ask some advice about keel sealing strips. As most of you know, Uncle Bernard built A89 Colchide from 1958-1960 and uniquely sheathed the hull with Marglass. He never fitted keel sealing strips and I really don’t want to screw 60 or so screws into the Marglass and risk water penetration between the Marglass and wooden hull. I don’t have the courage or skill to do this work, and there was much “sucking of teeth” when I asked a boatbuilder last winter, having mentioned the Marglass.
One option next winter would be to make and fit the keel box slabs, but there have been some accidents with these.
Any thoughts anyone?
09/06/2018 at 17:18 #15700
I am interested in the different ways of sealing the keel box slots. I have heard about automatic arrangements which allow the original blocks to rise and fall – but I have never really understood how they work.
Calista has had rubber sealing strips since I have had her – and they have had to be replaced at regular intervals. However I suppose replacing them 3 times in 20 years is not too bad – it is just that I hate doing the same job again – and again.
I would have thought the standard original arrangement would work for you. What exactly are the problems that others have had with these?
On the other hand if the Marglass is really clean you might get away with bonding rubber strips on to the hull using something like sikaflex. Holding them in the correct position while the “glue” sets might be tricky – and there is always the risk that the glue line might fail.
12/06/2018 at 07:03 #15724
I heard that the original blocks can stick and not kick up if a keel strikes ground, in which case the blocks are forced through the rear of the keel box. Ouch!
How long are the screws on your rubber sealing strips and how many screws are there total?
12/06/2018 at 21:19 #15726
Im not sure that sounds right. The front has to come up as the front of the keel rises – unless it is detached from the stirrup. Even then I think the force on the block would be more upwards than backwards. So where did you hear that – and which boats – I want to know more!
13/06/2018 at 19:51 #15727
Ah I understand the question now. I have keel ‘blocks’ on Mary and there is about an inch behind the blocks as they sit with the keels down. This means the keels have to raise, pretty much, half way before they run the risk of hitting the back of the box. Then there are the stirrups that hold the block back these have some spring. I usually notice this when lowering.
I think my ‘blocks’ are too long and when trying to lower the keels after spending the winter on the trailer meant I need to lower the blocks to below the hull line before lowering the keels otherwise they jam against the back if the blocks.
So I guess if I did try to raise the keels by such significant amount I would run foul of this problem. Using some form of collapsible extension to the block at the rear like a loop of thick rubber would make this safe. Replacing the loop of rubber on a removable block would be easier than anything that attaches to the hull?
Another thought is that these are a wholly detachable part of the boat so could be made of something other than wood that would bend in preference to damaging the keel box. Mine unfortunately (depending on how you see it) are made of a wood heavier than water. So are unlikely to act is such a sacrificial capacity ;-(
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