Trying to design my own cat.

Discussion in 'Multihulls' started by Richard Atkin, Aug 12, 2007.

  1. bobg3723
    Joined: Aug 2005
    Posts: 278
    Likes: 7, Points: 18, Legacy Rep: 95
    Location: Crystal, MN - USA

    bobg3723 Senior Member

    Richard,
    I agree wholeheartedly. Dinosour juice is noxious. :(

    But I think the expected sea conditions out in the Channel Island straits in differing seasons will no doubt guide your design accordingly. I prefer a multihull myself (to me, speed means having more time to spend frolicing at my destination), but a cleverly designed unballastesd lightweight daysailer with the displacement capacity for six souls on board and their gear that's managable to portage up the beach is of interest to many of us. I don't feel designing such is too tall an order to achieve. But I'm no naval architect. Far from it. :D

    The Channel Islands can be a great way to get away from it all that's also accessible by ferry and you can also get groceries in Avalon. I guess it's our version of Fraser Island. Getting there and back is not too long a journey for a two or three-day weekend.

    We all want you to blaze the trail, man, and write a song about the adventure! :D

    Cheers,
    Bob
     
  2. Gary Baigent
    Joined: Jul 2005
    Posts: 2,955
    Likes: 99, Points: 48, Legacy Rep: 509
    Location: auckland nz

    Gary Baigent Senior Member

    monohull skimmer

    Richard
    The CCS design could easily be enlarged to 6.5 metres, in fact my Belgian sailing mate is talking semi-seriously of one - but maybe it is just Belgian beer talk (which is the best around, by the way). He has done the mini-Transat in a 6.5 (came fourth) and likes the idea of a lightweight version. But he wants a single rig; that is not a problem.
    However I like the low 6.5 metre double rig on the 5.5, a lot of sail area down low and should make the boat plane like a crazed looney reaching and running. Beating to windward, the after rig can be cranked to windward to get it out of the disturbed air of the forward rig - and then centred on other points of sail after that.
     
  3. Richard Atkin
    Joined: Jul 2007
    Posts: 579
    Likes: 18, Points: 0, Legacy Rep: 219
    Location: Wellington, New Zealand

    Richard Atkin atn_atkin@hotmail.com

    Thanks for the words of support, Bob. I look forward to blazing the trail! :D
     
  4. Richard Atkin
    Joined: Jul 2007
    Posts: 579
    Likes: 18, Points: 0, Legacy Rep: 219
    Location: Wellington, New Zealand

    Richard Atkin atn_atkin@hotmail.com

    Gary,
    I am almost sold on a Skimmer 6.5 already. The 5.5 looks well built. It looks strong. I like the stayless wingmast double-rig idea. All that power without the heeling. I don't mind the compromise with windward performance.
    On a freak day....it might be possible to plane in a straight line for the whole 22 miles....WOW. That would be amazing. (well....I can dream).
    I know that glass over ply is strong....but what is the chance of water getting in and making the wood rotten and heavy? Would it be a bad idea to make the boat fibreglass foam sandwich? And what if the foam absorbs water....is solid GRP too heavy?
    I asked about this another time, but I didn't get an answer about the reliability of different building techniques. I don't want to build it myself.
    I want a professionally built, long-lasting, low maintenence boat if that's possible.
     
  5. Gary Baigent
    Joined: Jul 2005
    Posts: 2,955
    Likes: 99, Points: 48, Legacy Rep: 509
    Location: auckland nz

    Gary Baigent Senior Member

    building materials

    Whoever started up the weird fantasy of water soak age into closed cell foam was inhabiting Pluto, and the far side of Pluto at that. Swerve away from that nonsense. Similarly, two coated epoxy and glass/carbon over ply will not soak water either. As for strength, epoxy/glass over thin skinned tensioned ply is a very good, low tech and therefore reasonably priced way of getting a light boat that will last probably as long as you will. However if you plane at 15 knots into offshore California rocks or reefs as in your dreams .... well, few materials can handle that - maybe steel .... but then that is a hopelessly heavy material for small boats. IMHO laminates of solid glass is also too heavy - but foam/epoxy glass/carbon sandwich is an excellent and lightweight way to build - but more expensive than the bent ply combinations and also slower. You can have a tensioned ply hull formed in less than a week - but it is more art than the established way of boat building and therefore does not appeal to the average conservative mariner. Check out the Gougeon's book on this subject.
     
  6. bobg3723
    Joined: Aug 2005
    Posts: 278
    Likes: 7, Points: 18, Legacy Rep: 95
    Location: Crystal, MN - USA

    bobg3723 Senior Member

    Gougeon Brothers is a must have in anybody's collection. In fact, all the popular plywood boat building books on Amazon dot com for that matter.

    Gary,
    You Kiwi's have a world of experience traversing some truly hairy seas between Kiwiland and Oz in skinny multi's. Give us your assessment of what would be the minimum requirements for a daysailer to sail across the Channel Island straits in either a mono or multi, if you would please? :?:

    Regards,
    Bob
     
  7. Gary Baigent
    Joined: Jul 2005
    Posts: 2,955
    Likes: 99, Points: 48, Legacy Rep: 509
    Location: auckland nz

    Gary Baigent Senior Member

    sea crossing light multihulls

    Bob
    No way am I going to give advice on this subject - I haven't crossed the Tasman in a light multi - but have done some very wild coastal sailing here in a Newick 36 with foils named Mokihi (Maori for a lightweight raft) - and also on some light cats and tris. The Newicks are not that light (but still light enough) but they are real sea boats that do everything well, not nose bleeding top speed but fast on all points of sail - you cannot go wrong with his above 30 foot designs, again that is just my opinion.
    This subject (light multis offshore) can be very controversial - but people have crossed seaways in all sorts of multihull craft.
     
  8. bobg3723
    Joined: Aug 2005
    Posts: 278
    Likes: 7, Points: 18, Legacy Rep: 95
    Location: Crystal, MN - USA

    bobg3723 Senior Member

    Gary,
    What do you know about some of the Malcom Tennent designs like his Great Barrier Express for example?

    Bob
     
  9. Gary Baigent
    Joined: Jul 2005
    Posts: 2,955
    Likes: 99, Points: 48, Legacy Rep: 509
    Location: auckland nz

    Gary Baigent Senior Member

    kiwi multihull designs

    I used to have an altered (by me) Tennant 32 foot Bamboo Bomber named Supplejack - there are some jpegs of it in the back blocks of this site (Pahi cat). And I was around when the first Great Barrier Express (Richard Pilkington's) was launched. They are excellent designs. The local multihull club has introduced an 8.5 class based on a one or two steps-up-the-ladder performance version of the GBE - and the class is strong with fervent loyalists keeping the class very much alive. IMO they did not go far enough into introducing a more performance oriented class - but I'll say no more having incensed them enough already. The new 8.5's are very quick especially Dirty Deeds. The GBE's have to be heavily modified to keep up - therefore any original models have become almost obsolete for racing. If you can be bothered ploughing through this stuff, here is a bit of the early history of Tennant and Given designs:

    24. open wing deck design
    AUSTRALIAN MULTIHULL DESIGNER Lock Crowther had appeal in Auckland with some Kraken 33 and 40 racing trimaran designs plus his racer/cruiser 40 foot catamarans being built here. Local multihull designers like Young (still interested despite early bad press), Ron Given and Malcolm Tennant had gained recognition
    few larger cruising catamarans. Given designed his own 36 foot lightweight racing catamaran Tigress in 1971, an open wing deck design like an enlarged Paper Tiger; it looked extreme and observers were impatient to see it line Given, Tennant had drawn larger designs but his examples also took time to build; multihull sailors invariably had little money and usually built their own yachts. Tennant had earlier built a few Australian B2 Class Stingray catamarans and tried unsuccessfully to get the class established here; then he designedcruising 36 foot catamaran named Vorpal Blade – but the owners took a decade to construct the boat. In 1972 he published his ideas on a 9.8 metre high performance wing masted catamaran he named Bamboo Bomber which had flared and stepped hull topside shapes with blister cabins fore and aft of the central cockpits; the boat looked a bit weird and spacecraft-like and nothing came from it. However in late 1972 I asked him to redraw the concept, clean up the lines by discarding the stepped cross section hull shapes and the result was an attractive and very modern (for those days) racing design – two examples of which began construction soon afterwards. Both yachts Supplejack and Superbird were launched in 1977 and were built in tensioned ply like large versions of the (then) Olympic class Tornado. Both wing masts ended up heavier than intended and made the light platforms pitch in some sloppy seaways and light winds – but given sufficient wind power to drive through waves, both yachts were very fast. Continuing loosely to the Bamboo Bomber theme he had first shown in Sea Spray, Tennant drew a clean looking, aft cockpit, blister cabin 8.5 meter racing/cruising catamaran named Great Barrier Express - which Tennant said was inspired by a Hawaiian beach cat developed Mickey Munoz. Compared to the second version of Bamboo Bomber, Great Barrier Express had more rocker in hull underwater profile (for easier tacking) and sloping transom hung rudders which could be lifted, whereas Bamboo Bomber rudders were fixed down and under hung. The latter rudders also sloped and had skegs – retrospectively bad mistakes - as too was the sloping GBE rudder design – which tended to lift the sterns and push down the bows when sharp helm movement was made - later versions had vertical rudders to counter that problem. The original Great Barrier Express built and owned by Richard Pilkington was launched in early 1977 beating the Bamboo Bombers into the water. The cat had sensational speed and quickly became known as a giant killer; it was also instantly popular and went into production at Pilkington’s boatyard.
    The original group of Given, Tennant and Fay had broken up by the early 1970’s; Given and Fay, who had collaborated on the Paper Tiger had split over disagreements with the design when it went into production which culminated in a court case. Then Tennant’s Great Barrier Express and Given’s Gulf Tiger competed for the quite lucrative fast cruising/racing catamaran market – and earlier friendship quickly evaporated. The Great Barrier Express hull was based closely on tensioned ply Bamboo Bomber and was round bilged while Given’s Gulf Tiger continued his Paper Tiger theme with hard chined hull cross sections. The GBE was more
    performance oriented with the elliptical shaped cross section hulls having less wetted surface area than the flat sided, chined Given design. The after sections of Gulf Tiger were almost flat like a planing hull dinghy. The two also differed in rig design; Given aiming his Gulf Tiger to the average sailor by keeping the rig simple with a non-rotating mast and similar (although spreaders were much wider) to bendy, fractional setups of New Zealand dinghies – while Tennant drew a rotating mast and a high aspect ratio B Class catamaran-type rig for his design, making it higher performance and requiring some extra skills to handle. Given supporters were adamant that large spinnaker carrying Gulf Tiger would be the faster yacht – but were proven wrong.
    Many club members considered open wing deck, lightly constructed multihulls outrageous and that these designs were nothing more than overblown day sailers with afterthought accommodation – which was correct. Duncan Stuart, who owned Kraken 40 Krisis, cracked, “If you close your eyes when on Supplejack’s deck and step onto the tramploline, you can’t tell any difference.”
    With the success of the Great Barrier Express design Tennant was pressured by people with a non-surfer-type philosophy into making a larger hull design with more accommodation. So Tennant drew the Turrissimo version which was more inflated in hull crossection, higher wooded and slightly longer than the GBE. After the sleek lines and minimalist earlier surfer inspired boat, Turrissimo appeared gross to some eyes but Tennant had listened well – if people thought accommodation more sensible than balanced aesthetics, then he was going to give it to them – and fat Turrissimo turned out to be a faster sailer than its appearance belied.
     
  10. Gary Baigent
    Joined: Jul 2005
    Posts: 2,955
    Likes: 99, Points: 48, Legacy Rep: 509
    Location: auckland nz

    Gary Baigent Senior Member

    Sorry I messed up some areas of the cut and paste - but you get the gist.
     
  11. bobg3723
    Joined: Aug 2005
    Posts: 278
    Likes: 7, Points: 18, Legacy Rep: 95
    Location: Crystal, MN - USA

    bobg3723 Senior Member

    Hey Gary,
    I've been diligently going over some pictures of hull to beam connections and the one thing that always gave me pause for thought was the the connections themselves. They appear to my eyes as some sort of clamping affair like that on construction scaffolding and I can't help but wonder how tremendous a racking effect would exert upon that juncture. This leaves me somewhat more concerned for the integrity of the beam at that point than I am about the bending modulus central to the tube. To my eyes', something more substantial is what's called for. I don't know...maybe of a solid spade-shaped pad to distribute the torsional load down into the hull structure seams a prudent design step.

    If the connection had some sort of give like that of that you would find in timber lashings, that's not too bad. You would have to gain stiffness by haveing four or more crossbeams. But solid clamps on the end of two beams doesn't have the sort of give a rope lashing has, and so more surface area for the connection would be needed, like a buttressed Cypress tree in the swamp, sort of connection.

    I don't know. What say you?

    Regards,
    Bob
     
  12. Richard Atkin
    Joined: Jul 2007
    Posts: 579
    Likes: 18, Points: 0, Legacy Rep: 219
    Location: Wellington, New Zealand

    Richard Atkin atn_atkin@hotmail.com

    Gary, thanks for the information about building materials. It might be quite some time before I email you (depending on how things go with my non-boat related plans), but I would like to discuss with you a larger Skimmer in the future if you are available.

    Thanks again for all the advice and earlier suggestions.
     
  13. Gary Baigent
    Joined: Jul 2005
    Posts: 2,955
    Likes: 99, Points: 48, Legacy Rep: 509
    Location: auckland nz

    Gary Baigent Senior Member

    beam connections

    Bob
    If you look at Tornado tubular beam/hull connections you will see they are very carefully done with the clamps fitting perfectly with no gaps or hard spots and resting on bases that also are carefully done and which spread the loads through frames below the connection areas. There is another method making moulds by glassing over the tubular beams (which are wrapped initially in plastic to stop adhesion to the alloy) so the beams are solidly set to the hulls in sleeves which in turn are set over bulkheads or ring frames - these spread the loads throughout the immediate area of the hulls - and work fine. Or you can build wing shaped composite beams that do a similar job.
     
  14. bobg3723
    Joined: Aug 2005
    Posts: 278
    Likes: 7, Points: 18, Legacy Rep: 95
    Location: Crystal, MN - USA

    bobg3723 Senior Member

    Gary,
    Thanks for the description on how the beam ends are bedded. Well I guess tubular stock aluminum crossbeams have had several decades on its track record.
    Are aluminum crossbeams an easy to order item for multis that are no longer manufactured, let's say as a owner installed replacement part? Or does one need a naval architect to sign off on a custom spec'd replacement? Just curious.
     

  15. Gary Baigent
    Joined: Jul 2005
    Posts: 2,955
    Likes: 99, Points: 48, Legacy Rep: 509
    Location: auckland nz

    Gary Baigent Senior Member

    obtaining beams

    Bob
    I'm not ofay on this, getting alloy beams where you live, (most new multihulls have stopped using alloy by the way) and because the beams on my boat are composite wing shaped ones that are carbon/glassed solidly into the floats as well as into the main hull - and I recommend this way instead of using alloy. But you could hunt down some local mast sections and maybe even get some extruded oval beams (it is still possible to do so in Auckland) but with mast sections you end up with the unnecessary luff track - or you could build some carbon ones ...... or get perhaps a broken set of Volvo 40's carbon beams and patch them up - bad joke. As you can gather I'm not someone who employs marine architects to use their expertise in telling me what to do - I'm just a suck and see kiwi bloke, mate.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.