I realize that the GK24 was originally designed for racing, but I personally have no interest what so ever in racing. My interest is in having an easy to sail cruising boat.

As a bit of background, a large portion of my childhood was spent living aboard yachts and sailing mostly without engine.

Almost two years ago I bought an abandoned timber GK24 "Wolfhound" and am finally almost at the stage of pulling it out of the water to do a complete rebuild. Due to the very poor condition of the boat, I have not used it at all yet(the hull itself is good but not the deck), so have no practical experience of how it behaves. However, from first seeing it, I could see huge potential. A small, light, maneuverable boat, with a large amount of inside space for it's small size. My intention is to re-rig it with a 35 square metre cambered junk rig, remove the ill petrol inboard permanently and reduce or eliminate the cockpit. This should significantly increase the accommodation space and make it a low cost boat to operate and maintain. It will also require minimal effort to sail. I have a Rutland 913 wind turbine that I intend fitting for electricity and would like to investigate fitting wind-vane self-steering for the truly lazy sailor that I am.

My biggest concern is the GK24's ability to deal with bad conditions, particularly stability wise, with it's wide beam. I have seen an account on this forum of one crossing the Bay of Biscay, so I expect it is pretty good in that regard, but does anyone know how far over they can recover from?

I'm not intending on crossing oceans or anything like that, but my local cruising ground is on the edge of the southern ocean and I would expect to be out there for two or three days between harbours on occasion.

Has anyone else here developed the cruising side of their GK24 over the racing ability? What have they done to their boats? And what kind of passages have been done in a GK24?

Post edited by: stuartcnz, at: 2009/05/10 10:17

Just a very quick one - wrote a much longer one but the site timed me out... so lost it all...

Stability :-

GK's are pretty stiff for 2 reasons.

Good balast ratio, and good low CoG.
wide, so therefore good form stability

When overpressed to get the gunwales wet, due to the boats beam and dish shape the rudder immerses only its tip, cavitates & spins out, ending up in a broach. Time to reef ....

Very difficult except in wipe out broaches with the kite up to get the boat to lay down.

stability upside down - yep - very stable I'd imagine, but if the conditions are bad enough to get rolled over off the face of a breaking wave, the chances are the same wave type will roll the boat back over with a slap on the keel. I'm guessing AVS is about 120 degrees - not very good - but she'll come up easier assuming the rig was ripped out in the first roll .... !!

Observations on Junk Rig design (I'm no designer...) :-

CoE of the sail plan is ahead of CLR - Leehelm inducing when going to windward. Twitchy on a reach. Needs to be pretty much in line (it moves with apparent wind & sail shape), or preferably slightly aft to give the helm some feel. CLR includes both hull appendages.

CoE of sail plan is higher than standard, with a larger sail area - Heeling moment will be significantly increased (Lever arm length, and force applied) - May end up having to much sail in anything above 5 knots of breeze with reefs in.

Weight of rig and additional structure to support an unstayed mast is going to be all up front, plus the static weight of the rig when the boat is heeled is going to be greater - an unstayed rig, unless carbon / composite is going to be a heavier section, plus batten weights etc.

Dead downwind - GK's change from bMax quite quickly to low volume forward (though better than modern designs). I'd be concerned about the high CoE of the sailplan with the rig squared off pushing the nose down in gust and becoming a death roll (GK's like doing that anyway), leading to a leeward broach (fun but not funny....)

Larger sail areas generally - GK's have got a maximum displacement speed of around 6 knots - More sail area's not going to make it faster, just earlier to reef (which admittedly with a junk rig is easy).

Not criticisms, just observations/food for thought - keep us posted as to how you go - am sure you've spend enough time around boats to get it right...

Sounds like there's a long way to go with sheets of plywood before she's ready for a big test...

Good luck.

Keith in Singapore

Thank you for your informative reply Keith.

About the junk rig. This design was done based on the existing mast head rig, so the COE should be about 6% abaft the standard mast head bermudan rig. The measurements were taken from the CAD drawing on this site. The height of the COE is just a quirk of the sail aspect ratio, which changes often with reefing.

According to "Practical Junk Rig" (Hasler/McLeod) which is referred to as the bible by most everyone that has practical experience with junk-rigs, The COE should be about 5% forward of the CLR. However, by way of disclaimer they say that performance of specific boats under their traditional rig should be taken into account. So if the boat traditionally has lee helm, then the COE should be moved back 1 to 5% of the LWL. Also the COE of a junk rig can be adjusted a fair bit, on the go with the hauling parrels. Generally people adjust for their current position to the wind. This is where input from you guys will be invaluable to me.

How is the helm on GK24's? A tendency to weather/lee, or is she well balanced?

As to the size of the rig, bear in mind that is the full rig, including spinnaker. Most of the time it should be reefed and it can be reefed a long way!

I too, was concerned about the weight in the bow, but as fortune allowed, Annie Hill (author of Voyaging on a Small Income, who has done in excess of 100,000 miles of blue water sailing with a junk rig) happened to be in the same marina as Wolfhound a few weeks ago. She had a look at Wolfhound for me and when I explained what I had in mind, she was very encouraging, saying that she knows someone in South Africa who has successfully converted a similar design. She also thought that the mast placement looked about right.

Sounds like there's a long way to go with sheets of plywood before she's ready for a big test...

That could prove to be an understatement. Essentially the only original parts of the boat will be the hull, keel, rudder, and a couple of bulkheads. Even the transom will need some repair for a bit of rot. But considering what I payed for it and the fact that I am very taken with the shape, I still think it is worth it.

Ah hah... I was brought up on "Skene's Elements of Yacht Design" by F.S.Kinney - Who admittedly never went near a dish like design, and advocated adding some positive weather helm / feel by having the CoE 'slightly' aft of the CoE... As you say, the CoE moves (and can be moved) much more than the appendages, so there's obviously some significant 'float' in the principles.

Have to admit my calc. for CoE height when I measured up for a high aspect No.2 was lower than yours (about 20% lower from what I assumed was centre of bouyancy), but as you say, reefing aint an issue with junk rigs - you just keep lowering it a bit more.

GK's general handling - I have to be biased here, having sailed long periods on Mumm 30's and other performance designs - very very sweet and well balanced - considering the dish shape of the hull and rounded forefoot. By no means 'hands free', but in 10 knots of breeze with full main & No.1, she'll track almost without touching the helm.

Of course add a bit of heel and some waves / breeze, and she holds a 'polite' amount of weather helm - never lee helm except when the breeze drops to virtually nought... Blowing dogs off chains and overcanvassed with no crew on the rail... yep... tiller behind your ear... but then there's lots of options to fix it (Err... reef...)

Reckon your advice on rig location will be good - again, I'm no expert in junk rigs.

Good luck with the plywood - By it when the market is down.

Cheers,

Keith in Singapore

When I had DS surveyed, the surveyor told me he knew of someone who had rolled a GK24, twice, in the Solent and on both occasions it came up the right way again. No reason to disbelieve him.

rolled or just put her on her side, seems somewhat imploresable to roll a GK24 particuarly in the Solent! It would have to be a very big wave.....

Chris Hawkes
Minx

Agree - shaggy dog story - bet the surveyor was wearing a Captains hat, grey wooly beard, smoked a clay pipe, had a squint in one eye, and wore a Cap't Baines greatcoat.

Bet he catches massive fish as well.....

I can't get Slingshot to lay down anywhere near past 50 degrees off vertical - She just skips sideways because the gunwhale doesn't dig in .... different with a windward broach downwind avec kite, but 'rolling' a GK24 .... call me a sceptic but I wouldn't think you'd get the spreaders wet....

Anyway - we've all got the odd story to embelish aye

Keith in Singapore