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Old 30-09-2010, 13:09   #1
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Design / Construction Preferences in an Offshore Cruising Cat

For whatever it may be worth, I have decided to start a thread to debate various aspects of catamaran design and construction and how they impact suitability for offshore cruising. No, cutting off one hull and adding ballast is not (even if funny to some) a design for a catamaran.

The subject is of interest to me (and I suspect some others), because of the significant changes to the design of crusing catamarans over the last few decades. The trend is certainly towards wider cats with high freeboard, large windows, galleys up, huge flat-top mainsails (or at least, significant roach) without backstays and 'lighter' construction schedules. There can be little doubt that most modern cruising cats are faster, sail better to windward and have brighter, more commodious interiors than their predecessors. Higher rigs with flat-top mains provide more 'horsepower', particularly in light air. Increased beam adds additional interior space while also improving form stability, at least in relation to capsize resistance. 'Sugar-scoop' transoms permit increased LWL's (and hence increased speed potential), as well as more convenient boarding for swimmers/from inflatables. Large windows increase the brightness of the interior and higher freeboard eliminates the 'wedding-cake' appearance of some older cruising cats, all while increasing interior volume. And of course, lighter construction schedules reduce weight, again increasing the performance potential.

While recognizing the foregoing, few design features are a plus/plus. There are a number of stories of serious problems with delamination and stress cracks that did not seem to plague the earlier British cats that were built out of less exotic materials, but to heavier schedules. There are numerous reports of flimsy, creaking interior joinerwork and of large curved windows that are not only expensive, but extremely difficult to replace; apart from sagging vinyl headliners, the interior joinerwork and tempered glass fixed portlights of many of the early British cats seem almost indestructible.

Higher freeboard does increase interior volume (and to my eyes, improve the appearance of cats over about 35 feet); however, it increases windage and increases the difficulty in boarding/deboarding the boat at a dock. Sugar scoop transoms have the advantages listed, but they can also tend to 'scoop' up and spray water when powering in reverse.

Placing engines towards the back of the hulls so that they are accessible outside increases convenience and opens up more interior space, but it also puts weight towards the end of the boat and typically eliminates an aft collision bulkhead/water-tight compartment (for the result, one can recall recent pictures of an inverted Lagoon with the aft part of the hulls awash).

Flat-top/large roach mainsails do increase performance, but these huge sails often require an electric winch for the halyard; regardless, they eliminate the possibility of backstays and tend to place the aft shrouds further aft, interfering with the main on a run.

Galleys up allow for great socializing for the chef and easy access to the cockpit, but they also place the weight of the heaviest part of the accomodation up higher (raising the CG), tend to reduce available storage space and, provide for a less enclosed/secure setting for the cook while offshore.

Lets face it, the list goes on and on. What I envision here is a debate of some of these design features (recognizing that they have, in many instances, already been debated under individual headings), but with a particular referece to offshore sailing. Do I expect consensus? No, but I hope we can stimulate a lively and interesting debate. It will also allow the owners of older boats to participate with their own opinions/experiences concerning design attributes that are now considered by many to be obsolete, but which may still have some advantages.

Perhaps we can start with performance orientation in general. Everyone can see the need for a boat to be able to sail off a lee shore, but are there actually moderately sized catamarans that can out-sail a storm front? Is that a viable goal and is it obtainable at a 'reasonable', or 'mass-market' cost. And what would the impact be on interior space/accomodation/comfort?

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Old 01-10-2010, 06:16   #2
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Lagoon & Fountaine-Pajot out of France are setting most of these trends


The trends in catamaran design today are coming from the two largest producers.
Lagoon & Fountaine-Pajot out of France are setting most of these trends.

1) Galley up on all their models
2) Engines in their own large stern engine rooms for easy maintenance
3) Larger engine options
4) Folding prop options
5) Sail drives on most all of the models
6) Foam core infusion construction
7) Lexan vertical windows in the saloon for panoramic views from the galley
8) Window brow to keep the sun out of the saloon
9) Windows bonded on with no screws using automotive 3M adhesives
10) Large foam blocks in the bows, mid section and under the stern bunks for CE offshore rating and flotation
11) Flat top sails as an option on most models.
12) All lines lead back to the helm
13) Length / 2 = Width
14) Bridge deck clearances of 28 or more inches
15) Floating cabinetry to prevent wood to fiberglass rubbing and squeaking
16) Larger interiors with lots of storage
17) No or little wood on the exterior
18) Anchor and chain close to mast with longer bridals off the bows for better weight distribution

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Old 01-10-2010, 07:38   #3
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Catamaran Design Features

At there is a "Technical" section and in the pull down menu a link entitled "7 questions to ask your builder" by Ted Clements (designer of the Antares and PDQ catamarans).

While written in sales pitch form the comments are worth considering and from practical experience make a lot of sense.

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Old 01-10-2010, 08:06   #4
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Ignoring money etc. etc...One of the features I feel has a lot of merit that we don't see very often is the forward cockpit coupled with an interior cockpit as seen on designs by Chris White (Atlantic series) and Morrelli & Melvin (Gunboat series). Obviously there is a size constraint because this would be impractical on smaller boats. Aside from the practicality behind the move, I like that is highlights the overall design of cats. Specifically that the front half can be used as a comfortable social area. It makes the whole boat feel useful and livable.
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Old 01-10-2010, 12:28   #5
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Mark, I agree with your assessment of current design trends and the genesis, especially as relates to production cats that are moderately priced (which is, in fact, the type of boat I wanted to discuss). I guess what I was attempting to get at is whether all of these trends are, in fact, beneficial - particularly for a boat intended to be sailed offshore. To your list I would add the following (as distinguished from many of the earlier cruising catamaran designs):

19. plumb, or nearly plumb bows.
20. no full width bow pulpit
21. only netting between the hulls forward of the bridgedeck (no solid foredecks, or center walkways)
22. no, or minimal fiddles on counters/tables
23. no backstays
24. single centerline mounted windlass
25. high freeboard to permit a flush deck except for the bridgedeck accomodation.
26. fractional rigs with the preponderance of SA in the mainsail.
27. wider hull beam, and/or large knuckles/bridgedeck tunnel protrusioins to increase interior accomodation.
28. shorter bridgedecks
29. large sliding glass companionway doors
30 higher CG due to increased bridgedeck clearance, galley up and, in the case of the Lagoon 44 etc., elevated helm stations.
31. higher CE for the sailplan.

Let me start by saying that the increased BOA (or more significantly, centerline beam ) permits a greater SA, a higher CE for the sailplan and a higher CG while maintaining equivalent transverse stability (although the raised cockpit Lagoon 44 with its concurrently raised boom makes me wonder...). Neverhteless, the result is a boat that is faster while being equally resistant to capsize.

Furthermore, the increased bridgedeck clearance and the shorter bridgedeck than on many of the older designs, reduces the tendancy to pound (again, being mindful of some South African designs that have had minimal bridgedeck clearance; and, of course, boats with large protrusions close to the waterline in the bridgedeck tunnel).

Of course, most NA's believe that bridgedeck clearance must increase in proportion to increases in beam (and many believe centerline beam/tunnel width is more relevant than LOA/LWL in determining the appropriate clearance). Furthermore, according to many naval architects, as the ratio of BOA to LOA increases past a certain point, so does the risk of pitchpoling. Nevertheless, IMO the advantage here goes to the more current designs, so long as they are not too extreme: the BOA:LOA ratio does not substantially exceed 1:2 and the CG of the vessel and the CE of the sailplan is not unnecessarily high.

Netting forward, rather than solid foredecks/walkways between netting; no full-width bow pulpit? Clearly the elimination of these reduces weight forward and accordingly, reduces the tendancy of many of the early cats to hobby-horse; it should also reduce the risk of pitchpoling, particularly if one were to bury the entire foredeck.

Yes, it is hard to beat a solid foredeck for lounging (although that is not as significant in a boat intended to go offshore). Furthermore, although a solid foredeck provides a sure footing for retrieving anchors, repairing jammed furlers etc., the same can be said of netting divided by a solid walkway to the seagull striker/furling gear.

Personally, I believe that the latter is the ideal compromise between reduced weight forward/reduced risk of pitchpoling and a sure footing for repairs of jammed furling etc. (admittedly rare, but when it happens it tends to happen in bad conditions). As to full-width bow pulpits - IMO while they have a deleterious effect on the lines of a boat, the added security forward for repairs/spinnaker sets more than makes up for that and the minimal increase in weight at an extremity of the boat.

Galley up, versus galley down? IMO, in this area the advantage goes to the earlier design tendancy towards a galley down - for a boat that is intended to sail offshore.
Yes, placing the weight of the heaviest part of the accomdation (and the heaviest stores) down increases the transverse stability of the boat. More significantly, IMO, that location provides a more secure setting for the cook (and the motion in cats, as we all know, can be fairly substantial in boisterous conditions). Furtherthermore, especially in cats under about 45 feet, there tends to be mcuh more storage space available in a galley down. Finally, in my experience, the inclusion of a galley up, especially in cats of about 40 feet or less, tends to reduce the space available for a chart table/nav station (or the seating in the main saloon - something has to give).

The absence of fiddles on counters/tables? Inexcusable, in my opinion, in any offshore boat. No, they do not have to be as high as in a monohull (for obvious reasons), but they should at least be able to stop knives and plates sliding off a counter or table when underway in heavy seas.

The modern trend in rigs? Here I am of mixed emotion. My Sunstream 40 has a cutter rig with a forestay, a staysaill stay, twin backstays and the aft shrouds further forward than in most current rigs. Due to the backstays it has only moderate roach, Since the mast is stepped at the companionway bulkhead, all lines are led to the cockpit without the need for turning blocks, etc.

As an offshore rig I believe it has significant advantages:

Firstly, the dedicated furling staysail is a suitable storm sail and is cut with a high foot and made out of heavy weight (9.5 oz.) dacron. In storm conditions I can simply furl up the headsail and proceed without worries about going to the foredeck to set a galerider, or equivalent over the furled, lighter weight genoa. As the wind picks up, I can reef it even more if necessary and the sheeting angles, already appropriate for a relatively small staysail, can be readily adjusted to accomodate an even smaller sail.

Furthermore, the storm sail is mounted further inboard, as it should be and the sheets are pre-rigged (unlike a galerider). Yes, you can attempt to reef your headsail for use as a storm sail, but the lighter weight material that is suitable for such a sail makes it much more likely to blow out, or at least stretch out of shape. Furthermore, in doing that it is almost impossible to get the appropriate sheeting angles to flatten a small triangle at the very front of the boat.

The smaller roach on the main and the fact that the aft shrouds are mounted further forward than is possible without backstays creates two advantages: firstly, the main can be let out further without interfering with the shrouds (good for durability, sail trim off the wind and in reducing the risk of accidental gybes); secondly, sails with smaller roaches tend to have a better shape when reefed.

The disadvantages? Upwind performance is compromised to some extent by this lower aspect ratio rig and, nothing can beat a flat top for reaching. In my boat's current environment (Lake Ontario) I must say that I would prefer the performance advantages of current-style rig. However, for offshore (or even for sailing in strong trades/Christmas winds), I believe that the catamaran cutter rig still has much to offer.

Other aspects of the design/construction of an older design like mine versus the current trends are also a mixed bag. I prefer the lower freeboard on my boat for ease of boarding as well as reduced windage (and she tacks very easily); on the other hand, I despise the tiered 'xmas tree' appearance that it results in, even though it makes climbing to the top of the coachouse easy. I love the tempered glass fixed portlights (strong and permanent), but I wish I had louvers or a brow to produce shade on the forward fixed ports/hatches.

I love the fact that I have watertight collision compartments fore and aft and that I can perform maintenance on the diesels in a dry environment (below decks), without risk of losing tools/parts/fasteners and while seated comfortably on in the inside curvature of the hull. On the other hand, I hate the increased interior noise and the need to remove a berth cushion in order to get access.

I have my own opinion about plumb bows and floating furniture, but I'll leave that for another time.

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Old 02-10-2010, 00:45   #6
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What I am seeing in Australia, Brisbane in particular which is very popular for multihull builders is a trend to larger motors and higher speeds which properly designed multihulls can deliver.
A friend of mine has a 42 ft Grainger Cat with 2 x 170 hp Steyer diesels which cruises at 15 knots.
Also a number of cataramans are coming out with no sails just efficient motors on essentially sailing designs see "cat man do"
Myself i have built a motor sailor which will sail downwind but is essentially a motor trimaran.
Plus with better weather forecasting and availability ( ) and "no cruising if you don't have a schedule" ( avoid the bad weather when possible )
I really think this changes the overall view of what cruising used to be. Steve Dashew said in one of his books that if you can achieve 200 miles in a day you can avoid most bad weather patterns, including Cyclones.
Speed and forecasting, changes the rules.??
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Old 02-10-2010, 21:37   #7
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Good Day,

I am very pleased that I have found people with similar thoughts about cruising cats. Thank you very much for your great thoughts.
I have a different thought in that I don't like the large mains as with the loads involved, they do seem to create a degree of handling grief for two up cruisers, not to mention the cost.
Therefore I will have the cutter rig with no main and the mast stepped well aft. Slippery hulls, light weight and a large barber-hauled genoa will still give us good up wind performance. The genoa will have two sails on the same furler to be separated when down wind as a double poled out head sail.
On the previous suggestions of diesel sails I will have two 30hp engines that will give us 8.5knots cruising as the boat is slippery, long and light (5.5 tonne), to be used with the rig if good averages are a must.

Thank you for providing the great discussions

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Old 18-11-2010, 11:41   #8
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Tom, thanks for your comments although, obviously, not many others found the discussion great, or even interesting. Was your boat designed by Bob Oram with the rig you describe, or is it something which you specified? Instead of twin, individually poled-out headsails, have you thought about fitting a 'twistle'. or 'thistle' rig, as I think it is called: two headsails with a hinged pole that is attached to the clew of each sail and held aloft by a guy? Apparently it assists greatly in self-steering downwind and makes trim much easier.

Is there anyone here who has had experience with both a cutter (or perhaps Prout) rig on a cat and with the more current designs featuring fractional rigs, no backstays and flat-top mains? How did you find them to compare in a variety of wind conditions?

I have heard that some manufacturers of cats with the more current rigs specify that you cannot use headsails/screechers etc., without the mainsail also being up (presumably to make up for the lack of backstays) - what does your manufacturer recommend in that regard and how does it impact on downwind/heavy air sailing? I assume that the topping lift could serve the same function, but.... Does anyone have plans/recommendation for what to do if the mainsail blows out, or the topping lift fails?

Furthermore, while many if not most offshore monohulls are equipped with storm jibs and/or storm trysails, I have seen very few cats equipped with the same. I'd be interested in hearing from those who have (or don't have) them and the reason for their choice. Finally, for those who do have them, how are they rigged - ie, galerider-style storm jibs over the furled headsail, or a dedicated sail that requires the headsail to be unfurled, dropped and bagged before the storm jib is bent on, or a dedicated internal stay, either fixed or removable (as in a Solent rig).

Does anyone have a storm trysail with a dedicated track? For those who don't, how many reefs do you have in your main and what is the perecentage of the final reef?

I may be wrong, but it is my impression that most multihullers spend more money on and pay more attention to performance sails, than to storm sails. With the increased risks associated with a capsize in a mulithull, I wonder if we should be spending more time designing rigs, or at least equipping our boats with sails dedicated to these conditions. Alternatively, how many others take the approach of Dave of 'Maxing Out', who prefers to drop all sail and start the diesels when a squall approaches? Certainly a multi will tend to be much more stable/comfortable under power and without sail up than a mono.

In any event, I'd love to hear the thoughts/experiences of others with respect to multihull rigs for sailing offshore. If you would also like to opine about other aspects of the design of multihulls for those conditions, please do.

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Old 18-11-2010, 12:17   #9
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Just want you to know, I am enjoying this thread very much and hope others will join in with their opinions. I am a newbie, thus not much to add myself...
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Old 19-11-2010, 03:12   #10
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Good Day Brad,

When we first started the project,(we are self builders as are most Oram owners), our boat was conceived as a sloop rigged fast cruising cat. Fast and light goes hand in hand with Bob's designs and and the paradigm amongst fellow Oram builders was that only a sloop rig could do this. Therefore a large number of the Oram cruisers are set up as so and more than a few actually race regularly and successfully.

Amongst the feed back we have had from other long distance Oram cruisers and quite a few other fast designs, is that so many dislike struggling with a costly large full batten main and the associated huge loads generated. This is particularly important for two up older crews. In fact so many of them tend not to use their mains much and their engines a lot more.

Bobs latest rig designs have addressed this evolving concern. He also has very slippery hulls which mean that a 25% to 50% increase in engine power means being able to motor economically at good speed. So here has evolved the Oram motorsailer design. We therefore have been very lucky with our slow build to take advantage of an aft stepped mast with a large genoa around 40 sq metres and a little furled staysail/stormsail around 17 sq metres inside at the COE.

Your suggestion of a twistle or thistle rig is very similar to what we will do with our genoa downwind as the genoa will actually be two sails rolled on the same furler and laying together up when going to windward. Bob's design has the genoa, barberhauled, to assist the windward performance. Naturally when downwind the two sails become 80sq metres with no handling heartaches Especially now that the whole rig is 3 metres aft of the sloop design.

Thanks for the great discussion and I am sorry I did not reply in a timely manner, I spend a lot of my time building.

If you are interested in how our rig evolved there is more information on our website. Also the Bob Oram Design site has good coverage of his latest motorsailer concepts and his latest "axe" hulls.

Regards Tom
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Old 19-11-2010, 05:24   #11
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This is a great discussion. I'm a monohull guy, but I do like seeing mention of safety considerations, rather than pure performance considerations. I think most (if not all) monohull sailors are more than a little wary about overpowering a cat into a capsize situation.

With the improved performance, and obviously superior comfort/accommodations available on cruising cats, it would seem that the next 'big step' in cat design would deal with safety. That isn't to say that cats are unsafe by any stretch of the imagination, but there is most certainly that stigma out there, and one way to dispel a baseless or weak stigma is to present some reasonable improvements to the model which would suggest dramatically improved safety.

I've often wondered about different rigging concepts on cats. It would seem to present all kinds of different possibilities, but about the most aggressive/different rigging designs I've seen are main-less sloop rigs with the mast set far astern.
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Old 19-11-2010, 13:36   #12
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Regarding the safety, some cats are making great strides. A well built cat can have the same safety as a modern cruiseliner which is compliant with the "Safe Return to Port" standards of SOLAS. Specifically through the use of water tight engine rooms, water tight forward bow lockers, etc. an owner can potentially have a boat which can return to port under it's own power in the event of the loss of any single compartment. Chris White designs, African Cats, Antares, Gunboat all strive in that direction. There are many other factors in marine safety, but I believe that this design improvement is one of the most significant since Plimsoll lines. The obvious trade off is to accomodation space, as many other cats would seek to maximize interior accomodations to maximize the number of paying, charter guests.
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Old 19-11-2010, 16:42   #13
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Brad, thanks for starting this excellent thread. You've captured already most of what I would have mentioned. The only thing that jumps to my mind, and it doesn't affect performance off-shore per se, is balsa below the waterline. Too many stories and too big a risk for me when I make my purchase.
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