Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 06-02-2008, 14:25   #16
Moderator Emeritus
 
GordMay's Avatar

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 31,583
Images: 240
Thanx - I didn't see the "L' shaped cockpit seating in the earlier dwgs.
__________________

__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"



GordMay is online now   Reply With Quote
Old 06-02-2008, 20:04   #17
cruiser
 
BigCat's Avatar

Join Date: May 2007
Location: Everett, Washington
Posts: 765
Sweet drawings, Nordic Cat-7 tons doesn't seem heavy to me. In fact, I think it will be an expensive challenge to make a 47' boat strong enough at that displacement. I visualize many hours for somebody making and installing Corecell planks and fairing with a long board sander. It is certainly much prettier than my developed easy-build style. (Developed, for those who don't know, means that you can make a surface using sheet material, ie. no compound curves.) Do you have a cost estimate yet?
__________________

__________________
BigCat is offline   Reply With Quote
Old 06-02-2008, 20:56   #18
Moderator Emeritus
 
David M's Avatar

Cruisers Forum Supporter

Join Date: Sep 2007
Location: San Francisco Bay
Boat: research vessel
Posts: 10,150
I'm curious, why is there so much hull volume amidships and very little at the bow and stern? Would this not encourage hobby-horsing? Wouldn't an inverted parabolic hull cross section give you maximum volume per amount of wetted surface area? It appears that there will be an unnecessary amount of wetted surface per amount of volume. Perhaps you could explain the reasons for the shape of the hulls cross section?

It is a good looking boat! For a large cat, I like the idea of two aft helms and a helm inside the salon forward, out of the weather....(like what Gunboat has.)
__________________
David

Life begins where land ends.
David M is offline   Reply With Quote
Old 07-02-2008, 01:48   #19
Registered User
 
Nordic cat's Avatar

Join Date: Jan 2008
Location: Denmark
Boat: FP Tobago 35
Posts: 721
Quote:
Originally Posted by David M View Post
I'm curious, why is there so much hull volume amidships and very little at the bow and stern? Would this not encourage hobby-horsing? Wouldn't an inverted parabolic hull cross section give you maximum volume per amount of wetted surface area? It appears that there will be an unnecessary amount of wetted surface per amount of volume. Perhaps you could explain the reasons for the shape of the hulls cross section?

It is a good looking boat! For a large cat, I like the idea of two aft helms and a helm inside the salon forward, out of the weather....(like what Gunboat has.)
Hi David,

I'm pleased that you like the looks of the boat, I think that too many of the new boats are very boxy, and are designed for comfort and ease of building only. I love good looking boats, regardless of type. Combining beauty (which is in the eye of the beholder) and functionality into one package is of course time consuming, and will end up with a more expensive build.

The reasons for the choice of hull shape are:
I want a "slippery" hull, this is best achieved with long narrow hulls. I also want plenty of living space. This is achieved by the large flares in the middle section of the boat.
It is correct that if the hulls are too narrow in the ends, and you have alot of weight in the ends, then "hobby horsing" becomes an issue. I find hobby horsing to primarily be a problem when motoring, or in light air. What I think is more important is the diagonal stability. By having sharp bows (at the waterline) I want to be able to cut through chop and small waves, and get the the major lift a bit further aft. If the sterns are too full, then they will push the bows down when the wave passes, so the 2 ends need to be balanced to some degree.
What is very important is the reserve buoyancy when the boat is being pushed hard. This is achieved by the large hull flares forward, and the rake of the stem. As the bow gets depressed, the volume increases not only from the flare volume, but also from the volume of the bows forward of the waterline. So the combination of the "tulip" shaped bows with high reserve buoyancy and sharp at the water is a good solution I think.
The prismatic coefficient is tuned to ensure a good compromise Basically I drew a 43 ft boot and extended her.
The lowest wetted surface pr volume unit is achieved with semi circular hull shapes.

If you look at the hull flares, you will see that the inner flare is lower than the outer flare, this is to achieve greater stability when heeled. I have used 5 degrees. So at 5 degrees heel, both the inner and outer flares come into action. The inner flare also has the advantage if decreasing slamming under the bridgedeck, as waves passing through lift the hulls more. Also flares push water away from the upper part of the hulls, and work a bit like spray rails, this brings down the hull resistance to some extent, and bring down the spray a bit for the forward sections.

I hope this clarifies things a bit

Regards

Alan
__________________
Nordic cat is offline   Reply With Quote
Old 07-02-2008, 10:32   #20
Moderator Emeritus
 
David M's Avatar

Cruisers Forum Supporter

Join Date: Sep 2007
Location: San Francisco Bay
Boat: research vessel
Posts: 10,150
Thanks!...let me know when you have hull number one in the water. I will be buying a cat in a few years. I still have no idea which one. Many I have ruled out but there are still many to choose from.

Not to be argumentative, but if you take the length of the perimeter of a parabola (wetted surface area) and divide that by the surface area (volume) under the same parabola you will find that there is more area per amount of length than if you take a half circle. This gives you buoyancy per amount of wetted surface...the higher the better. Its not the same thing as a sphere (half-circle) which would count for something that is fully submerged but not for something that is partially submerged. (This in fact partially relates to why ships have bulbous bows) A boat hulls surface area is not completely submerged...this is the critical difference. It's an easy calculus equation if you want to prove it to yourself.
__________________
David

Life begins where land ends.
David M is offline   Reply With Quote
Old 07-02-2008, 13:13   #21
Registered User
 
multihullsailor6's Avatar

Join Date: Nov 2007
Location: Cruising in the SUN! Cruising towards Malta.
Boat: 37' Oldenziel cat
Posts: 442
Hi Alan!

I like the looks of your design, the hulls remind me of the Shuttleworth 47 to a certain extent - which surely isn't a bad thing!

I currently do some sailing here in Cape Town, most of it double-handed, on a bi-rig Schionning Radical Bay 8000 which is a fantastic little boat once you have learned how to tack her! And standing at the front beam, in your case sitting in the forward cockpit, and looking at the sea without any mast to look around is great! The bi-rig does have its own sailing technique, though.

I do find we are adjusting the sheets a lot to get best performance, so you should look into the sheeting aspects especially as you say sheets will be adjustable from both cockpits.

Which kind of engine drives are you planning?
How are the centreboards/daggerboards secured?
Which kind of rudders are you envisioning?
I ask these questions as we recently had the "nice" experience of hitting an UFO (Unidentified Floating Object) with our lifting port rudder when doing about 15kts - the impact ripped out the hold-down rudder attachment from the hull forcing us to sail on one rudder and abandoning the regatta. Fortunately the daggerboards were both up, otherwise the damage surely would have been more. Since then, for my own next boat, I am looking at ways of avoiding protruding fixed objects through the hulls as far as possible.

Best regards from sunny, but windy Cape Town
Roger
__________________
multihullsailor6 is offline   Reply With Quote
Old 07-02-2008, 13:33   #22
Registered User
 
Nordic cat's Avatar

Join Date: Jan 2008
Location: Denmark
Boat: FP Tobago 35
Posts: 721
Quote:
Originally Posted by multihullsailor6 View Post
Hi Alan!

I like the looks of your design, the hulls remind me of the Shuttleworth 47 to a certain extent - which surely isn't a bad thing!

I currently do some sailing here in Cape Town, most of it double-handed, on a bi-rig Schionning Radical Bay 8000 which is a fantastic little boat once you have learned how to tack her! And standing at the front beam, in your case sitting in the forward cockpit, and looking at the sea without any mast to look around is great! The bi-rig does have its own sailing technique, though.

I do find we are adjusting the sheets a lot to get best performance, so you should look into the sheeting aspects especially as you say sheets will be adjustable from both cockpits.

Which kind of engine drives are you planning?
How are the centreboards/daggerboards secured?
Which kind of rudders are you envisioning?
I ask these questions as we recently had the "nice" experience of hitting an UFO (Unidentified Floating Object) with our lifting port rudder when doing about 15kts - the impact ripped out the hold-down rudder attachment from the hull forcing us to sail on one rudder and abandoning the regatta. Fortunately the daggerboards were both up, otherwise the damage surely would have been more. Since then, for my own next boat, I am looking at ways of avoiding protruding fixed objects through the hulls as far as possible.

Best regards from sunny, but windy Cape Town
Roger
Hi Roger,

I'm glad you like the looks. I would definately like to hear some more about sailing and tacking a bi-rig catamaran, there is not that much experience around! How do you tack by the way? Do you lock the leeward boom before going around, and thus let the now windward sail push you around?

The sheets will be adjustable from both cockpits, no traveller as the vang will be fixed. One end of the sheet is traditional, led to the aft cockpit winches, the other end is led forward to the masts under the boom, and then down to the forward cockpit winches. There will be 4 winches in the forward cockpit and 3 in the aft cockpit at the steering position. All other adjustments will be on the masts.

Engines will be 39 hp Yanmars with the new 3kVA generator fixed to the flywheel. Final decision on shaft/saildrive is not made, but I prefer shafts.

2 asymmetric daggerboards with up/downhaul in a lined casing that will be built like the proverbial brick s*** house.
The Shuttleworth 47 hit a sunfish at 12 knots, dented the daggerboard and not a mark on the casing! Shuttleworth sure knows what he is doing, and doesn't skimp on weight when safety is involved.
Ruuders will be balanced spade rudders, and not kick up. They will not be deeper than the hulls.
I am considering a couple of 30 cm short keels, primarily for standing on when hauled out, or beaching.

Where do you keep your boat?

Regards
Alan
__________________
Nordic cat is offline   Reply With Quote
Old 07-02-2008, 13:38   #23
Registered User

Join Date: Oct 2007
Location: Winters cruising; summers Chesapeake Bay
Boat: Catana 471
Posts: 1,239
Quote:
Originally Posted by Nordic cat View Post
So the combination of the "tulip" shaped bows with high reserve buoyancy and sharp at the water is a good solution I think.
........and an already proven feature.

Dave
__________________
2Hulls is offline   Reply With Quote
Old 07-02-2008, 14:46   #24
Registered User
 
multihullsailor6's Avatar

Join Date: Nov 2007
Location: Cruising in the SUN! Cruising towards Malta.
Boat: 37' Oldenziel cat
Posts: 442
Quote:
Originally Posted by Nordic cat View Post
Hi Roger,

1) I would definately like to hear some more about sailing and tacking a bi-rig catamaran, there is not that much experience around! How do you tack by the way? Do you lock the leeward boom before going around, and thus let the now windward sail push you around?

2) Engines will be 39 hp Yanmars with the new 3kVA generator fixed to the flywheel. Final decision on shaft/saildrive is not made, but I prefer shafts.

3) 2 asymmetric daggerboards with up/downhaul in a lined casing that will be built like the proverbial brick s*** house.
The Shuttleworth 47 hit a sunfish at 12 knots, dented the daggerboard and not a mark on the casing! Shuttleworth sure knows what he is doing, and doesn't skimp on weight when safety is involved.

4) Ruuders will be balanced spade rudders, and not kick up. They will not be deeper than the hulls.
I am considering a couple of 30 cm short keels, primarily for standing on when hauled out, or beaching.

5) Where do you keep your boat?
Alan,

1) The wisdom says "release the windward sheet and sail head to wind
on the lee sail, then dumping that and sail off with the leeward
sail? Could also try doing the same with the centreboards. Lift the
leeward one pre tack, sail away with the ww one up, lw one down".
I guess you've read the threads on Boat Design Net - the Boat Design and Boat Building Site (which shows no interest in your design?! - or is everyone HERE?)

Here is a comment from the owner/skipper of this cat: "We have tried the sail configuration as explained above, but had still best results sailing up to the point rudder not to tight, releasing lee sail to reduce drag of lee-hull until new lee sail tacks and hauling close new windward sail."

So still experimenting but tacking a bi-rig is definitely not as easy as with a sloop rig!

2) Would recommend shaft drives with folding props for mentioned reasons, don't like saildrives any more. Or use the Gunboat solution of having the shaft coming out the side of the boat under the bridgedeck.

3) Any thoughts on having the "2 asymmetric daggerboards with up/downhaul in a lined casing that will be built like the proverbial brick s*** house" next to the hulls, for aestetic reasons on the inside, to make it a real watertight solution?

4) Put these keels in front of the rudders for protection!

5) This Radical Bay 8000, not mine by the way, is moored in Simonstown but sailed extensively from there in False Bay and regulary round Cape of Good Hope to Cape Town and further on the Langebaan. Do you know the area?

Roger
__________________
multihullsailor6 is offline   Reply With Quote
Old 07-02-2008, 15:45   #25
Registered User
 
Nordic cat's Avatar

Join Date: Jan 2008
Location: Denmark
Boat: FP Tobago 35
Posts: 721

Quote:
Originally Posted by multihullsailor6 View Post
Alan,

1) The wisdom says "release the windward sheet and sail head to wind
on the lee sail, then dumping that and sail off with the leeward
sail? Could also try doing the same with the centreboards. Lift the
leeward one pre tack, sail away with the ww one up, lw one down".
I guess you've read the threads on Boat Design Net - the Boat Design and Boat Building Site (which shows no interest in your design?! - or is everyone HERE?)

Here is a comment from the owner/skipper of this cat: "We have tried the sail configuration as explained above, but had still best results sailing up to the point rudder not to tight, releasing lee sail to reduce drag of lee-hull until new lee sail tacks and hauling close new windward sail."

So still experimenting but tacking a bi-rig is definitely not as easy as with a sloop rig!

2) Would recommend shaft drives with folding props for mentioned reasons, don't like saildrives any more. Or use the Gunboat solution of having the shaft coming out the side of the boat under the bridgedeck.

3) Any thoughts on having the "2 asymmetric daggerboards with up/downhaul in a lined casing that will be built like the proverbial brick s*** house" next to the hulls, for aestetic reasons on the inside, to make it a real watertight solution?

4) Put these keels in front of the rudders for protection!

5) This Radical Bay 8000, not mine by the way, is moored in Simonstown but sailed extensively from there in False Bay and regulary round Cape of Good Hope to Cape Town and further on the Langebaan. Do you know the area?

Roger

Thanks for the input on tacking, I guess time will tell how mine reacts.

2.) I agree with you. A third option is to angle the drives at around 45 degrees inboard, this has been done on some F41 Farrier cats with yanmar saildrives.

3.) They would then have to be in the saloon! I have been thinking af angling the hulls out by around 5 degrees like on some of the Loch Crowther designs, but this will need alot of redesign work! The daggerboards will then be more vertical. I also considered a Chtis White style board that emerges from the LAR keels, but have decided to go asyymetric with the bottom half meter symmetric for downwind. The boat should track well without boards downwind, but just in case...

4.) That is the plan

5.) Yes, I have some friends in Kalk Bay, and spent a couple of weeks in the area last year while checking out boatyards.

If you have any reccomendations for good yards, please contact me offline

Regards

Alan
__________________
Nordic cat is offline   Reply With Quote
Old 07-02-2008, 20:33   #26
Senior Cruiser

Cruisers Forum Supporter

Join Date: Nov 2005
Location: Out there doin' it
Boat: 47' Olympic Adventure
Posts: 2,635
Looks very nice, Alan. Very seaworthy, as well. I like the forward cockpit - besides some of Chris White's designs, the SMG 50 has this feature. Now can you make it affordable?

Kevin
__________________
Lodesman is online now   Reply With Quote
Old 08-02-2008, 03:08   #27
Registered User
 
Nordic cat's Avatar

Join Date: Jan 2008
Location: Denmark
Boat: FP Tobago 35
Posts: 721
Quote:
Originally Posted by Lodesman View Post
Looks very nice, Alan. Very seaworthy, as well. I like the forward cockpit - besides some of Chris White's designs, the SMG 50 has this feature. Now can you make it affordable?

Kevin
Thanks Kevin, Yes I forgot the SMG 50, I wonder how well she goes to windward, my understanding is that she has no daggerboards or LAR keels.

Making it affordable - a good question. I have of course done preliminary costing, and the key area where costs can be brought down is in the number of hours needed to build her, and what you have to pay for those hours. I will be building in South Africa to keep the hourly rate down while maintaining high quality workmanship. The first unit will be produced using plugs, as the cost of moulds is nearly the price of a finished boat,
If we can get a few orders in, then I will consider investing in moulds, that will be able to save on manhours and materials. This would be by moving from vacuum bagging to infusion.
I will not skimp on the quality of materials and workmanship! Using fireproof epoxy, loads of carbon fibre, aramid/kevlar, high quality cores, fittings and fixtures, good sails etc will not be compromised. I have already purchased the forst 500 kgs of unidirectional carbon, which at the present prices is around 45,000 USD. Just the engineering and design of the masts is also a big investment.
I have a French boat at the moment, but all fittings and sail handling gear has been upgraded to a couple of sizes bigger and better quality, but it is really annoying to have to do, and much more expensive to replace than do properly from the beginning.

The base price looks like being in the same price range as a 42-44' French roomaran, but lets see where we end up after the prototype is built. Up to now the design cost is practically nil, but by the time we have finished doing the CFD analysis and tuning, FEA, and fulfilling CE RCD requirements and final design I expect that just this will be around 70,000 USD.
I expect around 12000 manhours for the first one. Interior finish can easily change this by a considerable amount.

Regards

Alan
__________________
Nordic cat is offline   Reply With Quote
Old 09-02-2008, 11:13   #28
Marine Service Provider
 
fastcat435's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Location: Amstelveen Netherlands
Boat: FastCat 445 Green Motion
Posts: 1,649
Images: 10
Send a message via Skype™ to fastcat435
Quote:
Originally Posted by Nordic cat View Post
Thanks for the comments, I agree with the idea of having the helms at the same level as the bridgedeck accomodation where possible, but boat design is the art of attempting to master compromise
The saloon and cockpits are all on the same level, so the inside and fwd helm are on the same level. The aft helm is 2 steps up. Gives redundancy as each of the outside helms run to their own quadrant, with a rod between the 2 rudders. Anything happens to one, I can just disconnect it and continue.

The forward cockpit, in its true sense is at present only offered by Chris White as far as I know. Whether it is a fad or not, only time will tell, alot of fads have come to stay - like multihulls, flat top mains, unstayed masts, chartplotters etc. It does limit accomodations a bit, but I hate bunks on the bridgedeck, they are only any good at anchor or in harbour, even with more than 3 feet of bridgedeck clearance, the odd wave is sure to hit, and at least disrupt your beauty sleep.

Having 2 really nice aft cabins, and a smaller forward cabin on a 47 foot boat clearly signals that this is not a condomoran. Stringent weight saving and weight control, without compromising strength, as well as meeting CE regulations, that adds unneccesary weight without the strength, will have the boat at around 6 tons, start adding luxuries we get up to over 7. (this is for light ship, i.e. all equipment onboard including safety equipment, but no liquids and personal items). This is a performance cruiser, if I define the weight like most marketing people do, then I could bring it down below 6 tons, let everything else be an option. Small standard engines, minimum safety equipment, minimum instrumentation, thin matresses, no solar panels, no water cooling of the refrigeration - lots of stuff to make it look good!
I have chosen to design top down,i.e. starting with a really luxurious fitout, and then remove what I don't want, instead of the normal way, which always leads to an overloaded and under performing boat. But with this approach I hope to be able sell a few boats, to the kind of people who would love a Gunboat but are sensible enough to look for better value for money. I also think the boat looks nicer than a Gunboat - but now we are getting subjective methinks...

Regards

Alan

A nice design Alan , the hulls are very narrow so you will have to keep the boat extremely lightweight.7 tons will be over weight and will sink the hulls right in
Around 4.5 tons is what you should be aiming for to keep it fast and lively, do not forget that 2 tons will be added in water diesel and everything else brought on board
Good Luck but recalculate the buoyancy on this one

Gideon
__________________
fastcat435 is offline   Reply With Quote
Old 10-02-2008, 13:59   #29
Registered User
 
Nordic cat's Avatar

Join Date: Jan 2008
Location: Denmark
Boat: FP Tobago 35
Posts: 721
Quote:
Originally Posted by multihullsailor6 View Post
Alan,

1) The wisdom says "release the windward sheet and sail head to wind
on the lee sail, then dumping that and sail off with the leeward
sail? Could also try doing the same with the centreboards. Lift the
leeward one pre tack, sail away with the ww one up, lw one down".

Roger
Hi Roger,

Here is a link to a guy who explains how he sails his bi-rig boat,so maybe a source of some inspiration??

Francesco Fabbrovich Yacht Design

regards

Alan
__________________
Nordic cat is offline   Reply With Quote
Old 10-02-2008, 14:23   #30
Registered User
 
Nordic cat's Avatar

Join Date: Jan 2008
Location: Denmark
Boat: FP Tobago 35
Posts: 721
Quote:
Originally Posted by fastcat435 View Post
A nice design Alan , the hulls are very narrow so you will have to keep the boat extremely lightweight.7 tons will be over weight and will sink the hulls right in
Around 4.5 tons is what you should be aiming for to keep it fast and lively, do not forget that 2 tons will be added in water diesel and everything else brought on board
Good Luck but recalculate the buoyancy on this one

Gideon

Hi Gideon,

When you state that "around 4.5 tons is what you should be aiming for - "What do you base this vast insight into engineering on?
You should know that there are scantling rules that need to be adhered to when designing and building to ISO and ABS rules to achieve CE approval for different categories. You need a certain amount of foam, a minimum of 1200 g/m2 fibre on the outside etc. On a 47ft boat we can maybe save 200 -250 kgs by infusion compared to vacuum bagging. Yes, the boat is painted, we use lightweight stuff wherever possible, but there are certain minimum requirements, either morally or rule based.
When you make fantastic weight claims -what weight are you using? Is it just the shell with no outfitting, or is it real lightship, which I take to mean including all normal equipment, safety equipment for the boat and crew etc.
The 7 tons I state is with everything onboard, including spares,sails, 4 anchors, bedding, charts, almanacs, dinghy, outboard etc. but no liquids and personal stuff and provisions. That is why I calculate a max displacement of around 9.5 tons fully loaded for long term cruising with a crew of 4, with dive tanks, compressor etc. This will be with the maximum fitout. The draught will then be less than 65 cm.
As I stated in the first thread, we still need to run Michlet on the hulls, and maybe the decision to change some things will be made, but these will be informed decisions and not just marketing claims.

Regards

Alan
__________________

__________________
Nordic cat is offline   Reply With Quote
Reply

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Centerboard Performance zippy Monohull Sailboats 14 06-03-2012 05:15
Can You Junk Rig a Cabin Cruiser? ChuckMills2000 Construction, Maintenance & Refit 6 12-11-2009 11:10
Underwater lines for a performance cruiser Nordic cat Multihull Sailboats 183 04-04-2008 14:45
Board Performance TaoJones Forum Tech Support & Site Help 3 26-09-2007 21:29
J30 as family performance cruiser O25 Monohull Sailboats 1 31-10-2005 10:04



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 06:05.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.