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CSS 15 vs goat island skiff


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I once pulled up to a bunch of sport bikes parked at an ice cream store on my BMW touring motorcycle I used to own. All these kids with their carbon fiber laden bikes were looking with that "Check thi

Dave is absolutely right.  It is the height of foolishness to change a proven design from a great designer.  Raise your hand if you think building wooden boats makes perfect sense.

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Alex,

 

I read somewhere that economies of scale contributed to the continued development of wooden boats post WWII. In America, cheap FG boats made it possible for sailors around here to get sailing, and most design was in FG. The smaller population in other parts of the world didn't support the expensive tooling and design in wood continued. I read Wooden Boat and I am always amazed at the coverage from the other side of the world.  Whether this is true or not, I sure am glad.

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Yeah, this is true Steve, other countries delayed the change to 'glass production for some time, mostly because the recognized their markets, which weren't big enough to support the wholesale changes necessary, but there's more to it. A lot of companies looked at their staffing and realized they had some seriously good wood workers, that would be all but useless in a 'glass build, so they'd have to retrain or hire new - a difficult proposition in a newly emerging  industry. Shops would have to be reconfigured, equipment would need to be changed and a huge investment in molds and tooling, which might require the sale of a dozen boats, just to break even on start up for a single mold. So, if you're building a budget minded 16' fishing boat sold at 10K and have 100K tied up in a mold and new tooling . . .

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We have a Spindrift 12 with the standard rig and a 12' Amanda with a lug rig. The hull bottoms are pretty similar. I have been trying to find the time to make the rigs swap-able so that we can quantify the performance of the rigs. Just watching Alan sailing the S12 and Nat sailing the Amanda, the S12 seems to be faster upwind. We need to swap skippers but I would like to swap rigs as well.

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I don't think there's much comparison between the Goat Island Skiff and the Core Sound 15, besides similar length. I think a more fair comparison would be between the Bay River Skiff and the Goat.

 

The CS 15 is so much more boat than the GIS-- side decks are one huge difference, for starters.

 

The CS 15 has a deeper entry, a bow that doesn't hang up on waves, and deadrise to give her an edge to run on while level.

 

Most basically, the CS 15 feels stable with four crew members, while the Goat feels stable with up to two experienced crew.

 

It's a fairer comparison between the Bay River Skiff and the Goat, but the BRS is way more stable-- in that it affords one the opportunity to focus on things other than where to sit and which way to lean.

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A Bermudian cat will do better upwind against a lug cat, assuming typical proportions. The same would be true of ketches as well.

That is the entirety of the point I was trying to make, though at times maybe that wasn't clear.  I normally don't even enter discussions where people ask which boat they should build or buy.  It is way too subjective for my opinion to be worth considering.  The only topic I take part in less is choosing color   :P

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Sorry for posting this capsize video again.  But let me explain.  The boat in this video (a GIS) is on nearly a dead run.  This means that the CLE is way forward, within 2' of the bow, let's say.  Furthermore, the CLE is not only forward, but high, being a four-sided sail.  All of this is one great big lever arm, burying the skinny bow (not a big deal), and lifting the stern (a big deal, at least for the guy in the above video).  The cat-ketch rig lowers the CLE a bit.  More importantly for this point of sail, it shifts a fair chunk of the sail area well aft.  While I've sailed neither rig in these conditions, it is clear to me which one is going to be well-behaved.  

 

Then there's the subject of gybing.  Can you imagine gybing that GIS in the above conditions?  On the other hand, I have a video of Alan doing donuts solo in a CS15, mostly sitting on the wrong side of the boat!  It was a pretty blustery day.  I'd upload it, but it is 212MB.  You can find that video on the B&B site on Facebook.  Scroll down to my (Don Silsbe) posting dated December 1, 2104.  There's another video there, that I took of Alan on the same day.  The video is dated July 10, 2015.  This video shows how stiff the wind was-- not readily apparent in the other video. 

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If you looked at the respective CE locations on these two boats, you'd likely be surprised by the little difference in height (about 7"). Yes, this is leverage, but not much. The GIS can death roll and "auger in", both of these traits are harder to do in a CS-15, mostly because of volume distribution. Simply put (again) the CS series is a much more wholesome set of shapes than the GIS and a direct comparison is difficult to say the least and not really fair. Comparing a Camaro to a Corvette is about the same thing, both are sporty, but it's just not a fair comparison, once you have a good look at the two.

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Hi Don,

I'm not following your idea about carrying more sail aft to improve down wind behavior. Having the sail in font is more similar to pulling the boat from the bow. Also, spinnakers go in front. In an earlier discussion n someone mentioned that the secret sauce of the cat ketch downwind is that you can ease the sails forward. Bob

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Hi Bob,

Thanks for not understanding.  It gave me an opportunity to get out some instruments, and do a little calculation.  (I'm a retired engineer, and this was "fun".)  If you watch the capsize video closely, you'll see that what happens is that the transom lifts out of the water, making the rudder useless.  The lifting of the transom is the result of the rotational force of the sail.  When sailing on a run, the sail is let out.  This moves the CE forward to approximately even with the mast.  The rotational force (aka "torque") lifting the transom is the sail area times the distance of the CE off the waterline.  For the GIS this is Tg = 105 sq. ft. X 9' = 945 units.  For the CS15, it is Tc1 = 59 sq. ft. X 8' = 472 units.  That's exactly half the torque of the GIS.  The mizzen (Tc2) doesn't come into the equation, since it is so far aft-- it has the resisting force of the hull to overcome.  Granted, the GIS mast is about 3' further aft than the CS15, but the GIS has a slender entry-- there's not a lot of buoyancy ahead of her mast.  Anyway, this is the basis for my opinion

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Hi Don,

 

As a not-yet-retired physicist, I'm right there with you.    Warning:  it's about to get geeky!

 

For stable operation, all of the forces have to balance and all of the torques have to balance.   The forces and torques come from the sails at their COE's, the mass of the boat at the center of mass and the buoyant force, wherever the center of bouyancy is.  The center of buoyancy moves around as the boat heels or trims bow down or bow up.  I think the torque from the CS mizzen "counts"  in the pitchpoling torque you calculated.  It's force times height of the COE just like the main.  The mizen exerts a little less torque than the main, but the torque is the same whether it's fore or aft.    

 

(Just to be clear, i'm only talking about the torque that would tend to make the boat pitch pole.  Moving the mizzen forward of aft would be very important for balancing the helm)

 

As I watch the video, I think the capsize starts with the skipper sheeting in the sail.   The next thing that happens is that the boat starts to heel.  Now the sail with its driving forces is out over the water to port. That creates a torque to turn the boat to stbd.  Also it looks like the crew sort of stumbles a little to port, increasing the heel and the turn to stbd.  The port chine sort of digs in and _then_ the stern lifts when it's pretty much all over.  

 

The cat ketch has the reputation of being better going dead downwind, and I won't argue.  I just dont think that there's much difference in the GIS and CS sail plans in terms of a torque that would tend to pitchpole the boat.  The bow profiles are quite different, and I think that aspect is worth investigating.

 

My son says too much pi will give you a large circumference.   Gaaak!   Happy Thanksgiving.

 

Bob

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Hi Don,

 

As a not-yet-retired physicist, I'm right there with you.    Warning:  it's about to get geeky!

 

 

The important thing is you recognize when it's happening............otherwise you start "scaring the straights". :)

 

In later videos, that same GIS can be shown to be sporting a small mizzen. And in yet other places, it is discussed how to sail that same boat, with a mizzen, when the wind is up and honking.......

 

http://www.storerboatplans.com/wp/design/rig/sails/sailing-unstayed-cat-ketches-and-cat-yawls-safely-and-efficiently-downwind-in-strong-winds/

 

That "by the lee" technique appears to be a good one and something most sailing a cat ketch should be aware of.

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Thanks for the link, Howard.  There's some good stuff in there.  I did notice that they were sitting well aft in the photo on the link.  I think they were more forward in the capsize video.  That's not a good idea, given the slender entry (less buoyancy in the bow) and all that torque stuff I already mentioned.  But I'll print that out, so I can thoroughly digest it (literally, not physically).

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I have found this thread to be very useful as I am considering building one of these boats as a beachcruiser for use in the Georgian Bay/North channel region of the Great Lakes. Could anyone comment on how the "rowability" of these boats compares? ( And by this I mean extended rowing) And if I am not hijacking this thread too much could anyone comment on how the Argie 15 stacks up against these two as per the discussion. I do really like the Core sound 15's, but i also appreciate the weight savings of the GIS and Argie. Thank you, Allan.

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