Underwater lines for a performance cruiser

[BigCat]

Hey 44'cruisingcat, I love it when you take untenable positions, zealously defend them with irrational arguments, and then top it all with rudeness. Adding profanity has got to be a personal best for you! ***** ***** ***** ***** ***** ***** ***** As anyone who knows anything about yacht design would tell you, you don't want the transoms immersed in a sailboat. I have too high an opinion of Oram to believe that he intended to immerse the transoms, and this probably means that his bows aren't all that deep, either. In the photos which anyone can see by following the link in my last post, that boat has its transoms slightly immersed, with no dingy on board. I'll leave it to others to interpret what the boat's hard times have to do with this, as I can't begin to imagine. 3 cyclones, running on a reef, and being hit by lightning definitely qualify as hard times, but they won't affect the boat's level of floatation unless it is waterlogged. Please don't suggest that-I like balsa, though not in the hull below the waterline. But then, I don't aspire to a fully loaded, cruising DL ratio of 60, either, which does seem a little ambitious to me.

[Nordic cat]

Originally Posted by masalai

The initial poster brought to mind the John Hitch design "X-IT" which is cruising somewhere - 50 something LOA and a beam WL any lady would be pleased with, NO rocker and head on looks like a "manta ray" lifted above the water... Impressive performance from a very quiet sailor.... some pictures exist on boatdesign.net if a search of X-IT or John Hitch or Hitchhiker rig - my idea of a cruising yacht if you are not (NOT) a hoarder as weight KILLS multihull performance... Googling Michelet-Godzilla will find a site to download that software - it works with Freeship-plus and on win 2000 or lower... both are free to download...

Thanks. Found the pictures, great looking boat and a very intersting concept.
I will be using Michelet and another CFD program to look at hull resistance and wavemaking when we get a bit further down the road.

Weight is a killer, and I'm working hard to bring it down and keep it reasonable. I am hiring an expert to come out and train the boatyard crew how to infuse the hulls. (foam epoxy with kevlar inside) Have extended the boat to 49', but started out at 43', kept the same beamCL. At the moment I expect us to end up with a lightship weight of around 7 tons, and a payload of 2-2,5 tons for performance sailing. We have at the present time identified about 1000 objects that will go into the boat and defined the weight of every single piece, so there shouldn't be too many suprises.

Having read the articles BigCat pointed me to,I am going to look at increasing the cp to around 0.62. Will also be looking at shaping the hulls to minimise spray and secondary friction from water running up the sides.

Thanks for the great input guys.

Regards

Alan

[BigCat]

Hi, Alan - Check out Yahoo! Groups - It's got all my resin infusion links.

[BigCat]

"Will also be looking at shaping the hulls to minimise spray and secondary friction from water running up the sides." If this means adding a chine in the topsides, do give so thought to the effect of a sudden increase on the boat's motion if it is placed low enough down and far enough forward to be plunged underwater when the boat pitches. The typical chine added for this purpose is placed fairly low, to provide more room inside the hulls, but it can lead to sudden increases in hull volume forward when pitching.

[44'cruisingcat]

Originally Posted by BigCat

Hey 44'cruisingcat, I love it when you take untenable positions, zealously defend them with irrational arguments, and then top it all with rudeness. Adding profanity has got to be a personal best for you! ***** ***** ***** ***** ***** ***** ***** As anyone who knows anything about yacht design would tell you, you don't want the transoms immersed in a sailboat. I have too high an opinion of Oram to believe that he intended to immerse the transoms, and this probably means that his bows aren't all that deep, either. In the photos which anyone can see by following the link in my last post, that boat has its transoms slightly immersed,

No it doesn't. Outahia's transoms are not immersed. Simple as that.
I've seen the actual boat. Of course that's not as good as you having seen the photo's is it? Do you know the actual shape of the transoms? Have you ever actually seen them?

I don't really care what you think you can see in the photo's. I know the boat, I know the owners, and I know Outahia isn't overloaded.

[BigCat]

"I've seen the actual boat. Of course that's not as good as you having seen the photo's is it? Do you know the actual shape of the transoms? Have you ever actually seen them?" 44'cruisingcat, you have, at least, the virtue of consistency. If that is a virtue when both mistaken and belligerent. There are 2 pages of photos on Oram's website devoted to this boat. On the first, you can see the boat dried out from the side. On the second, you can see a number of photos taken while the boat was in the water. Each person can judge for themselves by looking at the photos. There are photos of other 44s on his site. On none of them can you see any sign of overhang at all, in those photos which were taken while the boats were in the water. I suppose that they all were loaded with a year's supplies? I don't mean its way under water, just that the transom is just slightly immersed. See http://www.boboramdesign.com.au/zenphoto/index.php?album=44c-outahia&page=2 and http://www.boboramdesign.com.au/zenphoto/index.php?album=44c-outahia&page=1

http://www.boboramdesign.com.au/zenphoto/index.php?album=44c-xtra-chilli
http://www.boboramdesign.com.au/zenphoto/index.php?album=44c-just-add-water ***** ***** ***** ***** ***** ***** ***** ***** ***** ***** *****

I am not saying that the design is bad, but it obviously is meant to demand a great deal of discipline from the owners. Much more than I am willing to believe the average owner will demonstrate when it comes to deciding whether or not to bring along a case of wine, a barbecue, a half a dozen friends and neighbors, etc. etc. With no margin, the transoms will be under water when the boat is well loaded, and with no margin, the stern wave will climb up the transom when underway. That is why most designers give some overhang on sailing catamarans. I keep saying something you don't seem to get. I think well of Oram and his designs. The very nature of yacht design is that as you optimize one trait, you pay a price by losing some other trait that is a virtue, in at least some circumstance or to some degree. I think it was Bill Crealock who said, "You can't put a camper back on a Ferrari and have a live aboard sports car."

[catty]

Gee 44c why so upset?, maybe if you get your mum to read the posts she can help explain the big words.

Yep, the transoms looks immersed to me bigcat. Looking at the other pictures I'm suprised how streamlined the cabin structure is. Those outboards should have no problem reversing into 10 knots of wind. The flat bottom hulls are a great idea for simplification by amateur constructors.

At the end of the day most cruising boats are going to end up down on their lines a little. Big Deal. I suspect most designers never realise the amount of crap us end users consider necessary. By the same token it would be nice if the designer put sufficient rocker in the hull so you weren't dragging the transoms around even without any wind in the sails.

[BigCat]

"Yep, the transoms looks immersed to me bigcat" There is an Irishman making a Derek Kelsall designed catamaran who has made a website at Connemara Catamarans
Anyone interested in home boatbuilding should check it out. To quote him, "We wanted to increase the all up weight from 6.5t to 7.5t to allow for extended cruising gear, this was done by increasing the rocker on the hulls."
It looks like the Oram 44 could do with a bit of that, as well. That's exactly what I would do if I wanted to change the displacement of a stock design of mine--increase or decrease the rocker a bit.

[masalai]

God you guys appear to be crazy... A design is paid for and you change it "willy-nilly" - are you better than the original designer - A boat is designed for a specific set of criteria - All this chopping and changing of a design (as implied in this recent thread posting is nothing short of stupid - 1) the designer will DIS-OWN your efforts, 2) Your build will become un-insurable. 3) no designer worth his salt will sign off on your project. 4) you run the risk of bearing the costs and everything in litigious action. 5) If it was my design I would sue for defaming my efforts or whatever bad rep your mis-taken idea in alluding it was someone else's work...

If you do not like a design get a design that meets your needs... Why buy a sports car and demand it carry a couple of tons of bricks to your house building project...?

Sorry for the blast but please remember what it is designed for and keep to those limitations... Then it will work as expected and give lots of pleasure with minimal trouble..

Fair winds and calm seas to you all...

[BigCat]

" 1) the designer will DIS-OWN your efforts" You've got it all wrong, the idea is for the designer to make the changes. Kelsall changed his design for his client, and I am a designer. I am talking about changing my own designs, and if I wanted an Oram 44, I would ask Oram to add say 1000 pounds worth of rocker (16 cubic feet or so,) to change his design. If he didn't want to, I wouldn't fight it. I'd either accept it or not go with that design. Adding 10% to the displacement of a given design by slightly increasing the rocker probably isn't going to be any big deal, for most designs.

[masalai]

OK Oooops, My view was different, but yes it is ONLY the designer who should make any changes or as has happened here in Aus with someone else I know - refused to allow builder to identify him with the design or construction...

[cat man do]

Instead of adding more rocker, more draft, more dragm why wouldnt you just go same accom. on longer hulls ?

More seakindly, better ride and faster.

Dave

[catty]

I suppose the only problem with not immersing a flat bottom transom is that it will slap like hell even at anchor and drive you nuts. I was aboard a lovely jenson 12m in koolama bay in the kimberly for dinner one evening and the slapping from a small swell wrapping around the point shook the whole boat on impact. I notice tony grainger has observed this and has attempted to correct his designs( judging by a recent article). Maybe outahere is doing the same in a simple and more drastic manner? mmmmm. Sink the stern and get some sleep.

[cat man do]

Pescotts do the same, pain in the arse, but you notice the difference in performance under sail.

I reckon I picked up a knot + by extending the steps until the transom was free on my last boat, but maybe it was extra waterline length as well.

Loved the steps in the Jensen that allowed a croc to get up easily and the Back cabin windows that allowed same croc access to dinner.

Dave

[catty]

With any sort of following sea the croc could swim unimpeded into the galley via these steps. yer there the ones.