aluminium "wharram" catamaran - Wharram Builders and Friends2024-03-29T13:13:55Zhttps://wharrambuilders.ning.com/forum/topics/aluminium-wharram-catamaran?commentId=2195841%3AComment%3A107783&feed=yes&xn_auth=noAll discussions run their cou…tag:wharrambuilders.ning.com,2013-10-13:2195841:Comment:1081172013-10-13T22:58:45.664ZGalway Bayhttps://wharrambuilders.ning.com/profile/GalwayBay
<p>All discussions run their course and at 30 replies this one must be near it's end ...</p>
<p>I do not like the role of "naysayer" please I hope you build a boat and I am trying only to be helpful by providing a sounding board for your ideas. I am from an older time of Wharram design my familiarity is more with the Pahi and Classic rather than Tiki.</p>
<p>Much of what follows is a re-cap of what I have already said.</p>
<p>As to material Alu. is obviously excellent especially at this [ large…</p>
<p>All discussions run their course and at 30 replies this one must be near it's end ...</p>
<p>I do not like the role of "naysayer" please I hope you build a boat and I am trying only to be helpful by providing a sounding board for your ideas. I am from an older time of Wharram design my familiarity is more with the Pahi and Classic rather than Tiki.</p>
<p>Much of what follows is a re-cap of what I have already said.</p>
<p>As to material Alu. is obviously excellent especially at this [ large ] size.</p>
<p>These waterlines look much less full forward than I would expect on a Wharram or other cruiser. My Pahi for comparison is practically parallel sided for 50% of it's length and quite blunt at bow and stern. This is a good catamaran shape there are very good reasons for it. It is very well suited to a boat with a moderate rig.</p>
<p>Again I have nowhere seen that you have previous experience. 50ft is I think just too big for an experiment which is what a first design must be. I know of no successful designer whose first boat was this big.</p>
<p>I would love to see you try first at maybe 25 ft. At 1/8 the cost.</p> at the end it comes up as wha…tag:wharrambuilders.ning.com,2013-10-13:2195841:Comment:1082092013-10-13T17:07:29.455ZChris Samoisyhttps://wharrambuilders.ning.com/profile/ChrisSamoisy
<p>at the end it comes up as what someone prefers on his boat. what qualities his boat should have and for what it should be used mostly later. It becomes even more difficult if you want to use it as a multipurpose vessel. in reality this ones first priority is a real cruising catamaran, fishing is just an idea like < why not not use it as a fishing boat aswell? So we made the calcs. and a possible setup of the cat as a fisher version. what material you use on a boat is your personal…</p>
<p>at the end it comes up as what someone prefers on his boat. what qualities his boat should have and for what it should be used mostly later. It becomes even more difficult if you want to use it as a multipurpose vessel. in reality this ones first priority is a real cruising catamaran, fishing is just an idea like < why not not use it as a fishing boat aswell? So we made the calcs. and a possible setup of the cat as a fisher version. what material you use on a boat is your personal choice aswell, as long the construction and design is made for it. the hullshape is reflecting of what seakeeping abilities you want on your boat. it is always a weighting up. in this point of view (hullshape) I m definetly sold to wharram shapes and wharram ideas of what means seaworthiness. but I m also sold to aluminium boatbuilding. OB motors i think are good because you just buy them and put them and that s it. if broken you change them. here 2 horizontal cuts to see the hullshapes (plane horizontal)<a href="http://storage.ning.com/topology/rest/1.0/file/get/1930096169?profile=original" target="_self"><img width="721" class="align-left" src="http://storage.ning.com/topology/rest/1.0/file/get/1930096169?profile=RESIZE_1024x1024" width="721"/></a>.<a href="http://storage.ning.com/topology/rest/1.0/file/get/1930098631?profile=original" target="_self"><img width="721" class="align-full" src="http://storage.ning.com/topology/rest/1.0/file/get/1930098631?profile=RESIZE_1024x1024" width="721"/></a>real canoeshape on waterline height at 9.2tons/at 90cm, 1/11ratio beam/ WL Lenght. more up you go more it becomes a normal wharram shape at the end closer and closer like the roofshape (last cut at 120cm from baseline). the last one is not draft! the max. draft is at 101cm/12 tons.</p> What Galway Bay says is easy…tag:wharrambuilders.ning.com,2013-10-12:2195841:Comment:1080992013-10-12T22:06:11.967ZJeremy Walkerhttps://wharrambuilders.ning.com/profile/JeremyWalker
<p>What Galway Bay says is easy to gree with and I connot help thinking that that the use of aluminium should have more influence on design.......for example the bottom plate could be made alot wider to create a shallower draught and lower wetted area shape. Welded ally plate would make addition of centre plate cases an easy thing to construct as well as low maintenance factors. Lateral resistance in addition to shallow draught is available as and when needed, with a thick bottom plate…</p>
<p>What Galway Bay says is easy to gree with and I connot help thinking that that the use of aluminium should have more influence on design.......for example the bottom plate could be made alot wider to create a shallower draught and lower wetted area shape. Welded ally plate would make addition of centre plate cases an easy thing to construct as well as low maintenance factors. Lateral resistance in addition to shallow draught is available as and when needed, with a thick bottom plate taking to the ground without problem.</p>
<p>Since you have seen Wakataitea's craft, the use of a similar longtail engine is surely a better option than the OB motors as well? </p> Thanks for reply - you seem t…tag:wharrambuilders.ning.com,2013-10-11:2195841:Comment:1080222013-10-11T18:17:32.303ZGalway Bayhttps://wharrambuilders.ning.com/profile/GalwayBay
<p>Thanks for reply - you seem to have considered many of the alternatives available to you. </p>
<p>For what it is worth I live in a high wind area and it is my experience that for passable windward work the rig should not be much less in height than LOA. Much less and you will mostly be motoring to windward. My experience is with European traditional rig and a Wharram cutter.</p>
<p>The design point here is that there is no point building more windward ability into the hull than the rig can…</p>
<p>Thanks for reply - you seem to have considered many of the alternatives available to you. </p>
<p>For what it is worth I live in a high wind area and it is my experience that for passable windward work the rig should not be much less in height than LOA. Much less and you will mostly be motoring to windward. My experience is with European traditional rig and a Wharram cutter.</p>
<p>The design point here is that there is no point building more windward ability into the hull than the rig can deliver, as you will pay a price [ extra drag ]on all other points of sail - including motoring.</p>
<p>After 20 yrs. with my Wharram and some small experience of some others my opinion of deep "V" hulls is that the real drawback is not the often quoted windward ability but the poor steering. My Wharram is easily the most difficult boat in my harbour to berth. This is a drawback in a fishing boat which comes / goes daily. Boatsmith has previously posted that he eliminated the skeg on his 8M [ Tiki 26 ] used for day charter for this reason.</p>
<p>I still favour a shallower hull for the purposes you outline for instance in Wharram terms something based on the very shallow "V""Amatasi" rather than deep "V".</p>
<p>I hope the discussion has been helpful to you and that you go ahead and build your dream.</p> this one falls in the group o…tag:wharrambuilders.ning.com,2013-10-11:2195841:Comment:1079882013-10-11T15:43:31.446ZChris Samoisyhttps://wharrambuilders.ning.com/profile/ChrisSamoisy
<p>this one falls in the group of the Islander range 55 and 65ft of the wharram cats. in a way a smaller design of the islander 55. I would recommend the same rig (a wingsail schooner rig) as on the islander 55 (88ft/ton). just need to add a second mast and the mast support. the mast support is a channel with a bolt fore and after the mast, so you can change the position between the beams freely without taking the mast down. The lateen (or crab claw rig) on the picture is only on the first…</p>
<p>this one falls in the group of the Islander range 55 and 65ft of the wharram cats. in a way a smaller design of the islander 55. I would recommend the same rig (a wingsail schooner rig) as on the islander 55 (88ft/ton). just need to add a second mast and the mast support. the mast support is a channel with a bolt fore and after the mast, so you can change the position between the beams freely without taking the mast down. The lateen (or crab claw rig) on the picture is only on the first building because of the local weather conditions where this boat will be sailed and for the fishermen who are using a very similar rig on their small fishing boats. all year round south easterly passat winds, most of the time 15 , 20 knots or more. waves 2 to 4m are often here. the sails will be produced locally with locals and so the wooden mast. I would like to put light carbon spars one day later and increase the sailsize but only if realy needed. 2 outboarders 25 hp midship between the hulls, similar arrangement as tiki 46. I have just seen that the islander 55 has close weight caracteristiques, 7 tons empty and 12 tons laden.</p> Chris - you seem to be an exp…tag:wharrambuilders.ning.com,2013-10-10:2195841:Comment:1080112013-10-10T08:55:28.612ZGalway Bayhttps://wharrambuilders.ning.com/profile/GalwayBay
<p>Chris - you seem to be an experienced and competent alu. fabricator. I hope you go ahead and build this boat or some other.</p>
<p>A couple of last suggestions on design and meant in a positive and helpful way -</p>
<p>I have fished from my cat [ who has not ?] and over the side is better than over the stern as from this position drift / fish pulling will easily result in lines getting caught in skegs / steering gear. So central cabin would leave the sides clear for fishing gear.</p>
<p>Work…</p>
<p>Chris - you seem to be an experienced and competent alu. fabricator. I hope you go ahead and build this boat or some other.</p>
<p>A couple of last suggestions on design and meant in a positive and helpful way -</p>
<p>I have fished from my cat [ who has not ?] and over the side is better than over the stern as from this position drift / fish pulling will easily result in lines getting caught in skegs / steering gear. So central cabin would leave the sides clear for fishing gear.</p>
<p>Work boats used typically 100 sq ft sail/ ton. They were not renowned for windward work until leisure sailors increased their sail areas. 51 ft Tehini sets 100 - 150 /ton. On my 31 ft I set 200 / ton. Now I only have your thumbnail sketch but it looks like about 50 / ton.</p>
<p>If this is true this is a motorboat with auxiliary sail. As such it will perform better with a wider shallower hull.</p> you are right, the skegs and…tag:wharrambuilders.ning.com,2013-10-09:2195841:Comment:1080092013-10-09T19:00:29.172ZChris Samoisyhttps://wharrambuilders.ning.com/profile/ChrisSamoisy
<p>you are right, the skegs and the hang on stern rudders like a tiki 46 are not visible on the pictures. This design will of course have them, pretty much the same as wharrams have. I find the setup of the rudder still the best and most simple one. calculations have be done plenty during the last 3 years of development on this design. These days there are many pc programms who calculate all kind of stuff. LCF, LCB, Cp,Cb, Cm, Cwp and many more of indicators which need to be understood well and…</p>
<p>you are right, the skegs and the hang on stern rudders like a tiki 46 are not visible on the pictures. This design will of course have them, pretty much the same as wharrams have. I find the setup of the rudder still the best and most simple one. calculations have be done plenty during the last 3 years of development on this design. These days there are many pc programms who calculate all kind of stuff. LCF, LCB, Cp,Cb, Cm, Cwp and many more of indicators which need to be understood well and changed well if needed to get a nice hull shape. especially LCF, LCB and CLR are very important that they are positioned on the right place and right relation to each other and not to forget the rig which plays also into it. thatfore good PC programms are a "must". A few years ago I was a kind saying that these people just sitting on a chair the whole day long are not able to design better than a many years long ecperinced sailor and boatbuilder. PC programms cannot do it better. During the planing stage (which has taken at least 3 years) it has shown me, and I did not like to agree with, that the " seat warmers" in the office are right with their calculations and much more precise. However, it does not mean that long known approved hull designs are not fullfilling these criterias. often the calculations are just showing that the design is seaworthy and always will be. the changes you make on newer designs are anyway just slightly different of existing approved designs. designing a good hull is always a compromise.</p> Skegs aren't there? The stern…tag:wharrambuilders.ning.com,2013-10-08:2195841:Comment:1078632013-10-08T22:32:12.083ZRafhttps://wharrambuilders.ning.com/profile/RaffaelePagliarini
<p>Skegs aren't there? The stern is higher and the bow goes in deeper, this is a recipe for a boat that will broach easily and will demand a lot of rudder work to keep in coarse. (broaching is the tendency of a boat to slide away from the wanted coarse and put it self across the waves. This is especially so when going downhill) The sailplane will have to be further ford which it means smaller main and bigger jib or adding a bowsprit. To change hull shape and boat weight might results in very…</p>
<p>Skegs aren't there? The stern is higher and the bow goes in deeper, this is a recipe for a boat that will broach easily and will demand a lot of rudder work to keep in coarse. (broaching is the tendency of a boat to slide away from the wanted coarse and put it self across the waves. This is especially so when going downhill) The sailplane will have to be further ford which it means smaller main and bigger jib or adding a bowsprit. To change hull shape and boat weight might results in very undesirable behaviours and possible disastrous losses of time and money. </p> I know nothing about scantlin…tag:wharrambuilders.ning.com,2013-10-08:2195841:Comment:1079702013-10-08T19:42:09.279ZGalway Bayhttps://wharrambuilders.ning.com/profile/GalwayBay
<p>I know nothing about scantlings in alu. but I am happy to hear the beams are 380mm high not 200mm which is the sort of size I might expect on a 30 ft. boat.</p>
<p> Reading your posts again I get the idea this is maybe a commercial proposition for you ? You speak of "two versions being available ?" So what question really should we try to answer for you ? Yes you can build this boat and it will "work" i.e. it will float, sail somewhat, and proceed under power and be long lived and…</p>
<p>I know nothing about scantlings in alu. but I am happy to hear the beams are 380mm high not 200mm which is the sort of size I might expect on a 30 ft. boat.</p>
<p> Reading your posts again I get the idea this is maybe a commercial proposition for you ? You speak of "two versions being available ?" So what question really should we try to answer for you ? Yes you can build this boat and it will "work" i.e. it will float, sail somewhat, and proceed under power and be long lived and safe.</p>
<p>But could you build this on spec. as a cruiser in the hope of recovering your money +...well look at the sale offers on this site compared to build costs. Even a pro. builder would not launch a new build without the first deposit...</p>
<p>Fishing boats are even more difficult. Long lining is mostly done in small [cheap] boats. This boat is hugely more expensive. No one will buy it unless it guarantees them to catch a correspondingly huge catch.</p>
<p>50 ft is a very big platform to try out new ideas on, or for a first design. Unless you are seriously wealthy I would love to see you try the concept at perhaps 30 ft. Nobody gets it perfect first time.</p>
<p>J.W. tried this concept [ and won a design competition ] at 25? 27? ft. Interesting that he did not use the deep "V".</p>
<p>Personally I think that if he had developed this shape 30 yr. ago we would all be sailing better boats now.</p>
<p> </p> a chine can have a few reason…tag:wharrambuilders.ning.com,2013-10-08:2195841:Comment:1076802013-10-08T19:11:30.589ZChris Samoisyhttps://wharrambuilders.ning.com/profile/ChrisSamoisy
<p>a chine can have a few reasons. one uses a chine to have more space inside for example. in this alucat design we have put a chine because of having the possibility to give the underwater hull shape a better form and the aluminium construction needs it for stability. if you have one flat sheet on the side you are pretty much fixed with it. you can change the wide of the keel and the shape ofe the roof and that gives you the underwater shape. so that minimizes your design pretty much…</p>
<p>a chine can have a few reasons. one uses a chine to have more space inside for example. in this alucat design we have put a chine because of having the possibility to give the underwater hull shape a better form and the aluminium construction needs it for stability. if you have one flat sheet on the side you are pretty much fixed with it. you can change the wide of the keel and the shape ofe the roof and that gives you the underwater shape. so that minimizes your design pretty much (hobby-horsing and other minus). I was very surprised what is possible with a chine on the right height and with the variable distance you can give between the chines and the curveture on the sides. by keeping enough draft (important for lateral surface as keel which wharram cats need for windward ability) you can make a very nice aproachment to modern hullshapes underwater and still keep the seawaorthiness of the V hull shape. If you look at the Amatasi it is the best example for it. take a similar hull design on abig cat you will have nice hulls. There Wharram uses the advantage of a chine to give exactly these changes underwater. now another strong point of aluminium boatbuilding: if you look at the size of an entire side sheet it would be to big and not handy to put on place. so you are happy to have the entire side cut in two long sheets (one chine). all pieces are anyway cnc cut and will sit perfect on place. so the sides come together nicely where you put the chine welding, a kind of reference line. a chine is always a good line from where you cane work from. in aluminium a chine doesn t make a significant price difference, where in plywood i can imagine the hassle a chine brings with it. even the ringframes are two or three pieces which you weld togehter very quikly. the entire boat it s a big puzzle of pieces to weld together. this construction is meant to build upside down, put the roof down on a flat surface and than you tig the longitudinals and the ringframes on it a.s.o. don t compare plywood boatbuilding construction time with aluminium. aluminium boatbuilding with cnc cutting files are so much faster to built! you must have seen it that you can belive it. ask Nz and australian alu-boatbuilders. i like also that you can weld all kind of small pieces on the roof or wherever. no holes to drilling in the hull with aluminium. the pahi 52 comes in my mind also which is similar in size.</p>