Horstman scaled

Discussion in 'Multihulls' started by rberrey, Dec 8, 2012.

  1. rberrey
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    rberrey Senior Member

    Finished my punch work yesterday and my crew and myself were layed off. Time to find a new occupation,like boat building.It's also time to decide on wether to scale the Tristar 31 up by about %5. So to get my ducks in a row I need to make sure of how to go about scaling and the side effects. First off Ed said I wont have to beef up the scantlings, he also said he would'nt scale it up, which will answer the question ( why dont you ask Ed ?). First question is do I multiply my length x 0.05 and devide by number of stations or multiply 0.05 x distences between each station? I would scale overall beam of the boat and not scale up the frames, so about 32'10"/20', so how much would I need to scale up the mast and sail area by? Thanks , Rick
     
  2. cavalier mk2
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    cavalier mk2 Senior Member

    10% wouldn't hurt. So you are stretching and going for more overall beam but not increasing the hull widths. Faster. Doubling length gives 16 times the stability while heeling forces increase only by the cube. You need to check out into the Laws of Mechanical Similitude and William Froude.

    Multiply x 1.05 for station locations. If stations were 4' apart they are now 4.2' apart. Jeez Rick what a pain the 31 is pretty big as it is.

    I try to get people to ask Ed because I believe people bothering him makes him less grumpy and gives him interesting things to contemplate. Plus everybody should hear him say Mickey Mouse.
     
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  3. rberrey
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    rberrey Senior Member

    Ed answers your questions on the letter you send him , the answers are most of the time short , like "yes or no". It should'nt be much of a pain Cav ,I have to make a form for the foam , so no big deal, just the spacing of the frame molds. Many of my frames are already cut ,and I did,nt take any thickness out for the difference in foam build thickness -v- ply build. I also bought foam for all of the interior build, so will 1/2" to an inch here and there hurt me , I dont know. I have about %15 more foam and %20 more epoxy on hand than needed to build as per plans because I bought in bulk. Do I build a boat that may be a bit slower and a bit tight when I sit down to the table, or one that is a foot and half bigger with a little more payload and an extra layer of skin for punture resistance? Calling Ed is better than writting him, but if I strech the 31 I will wait untill the hull,s are done before I call. He'll either hang up on me or get involved ;). Rick
     
  4. cavalier mk2
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    cavalier mk2 Senior Member

    No it isn't really that much of a pain if you plan it. Lay out the drawings and plans and change EVERYTHING before you start . That way you reduce the risk of error when you're building and in a hurry. The 10% figure was for rig size increase because you will be able to carry more than 5% but I didn't work out the details. I'd contemplate a skeg for the beaching. Increasing the size 5% everywhere it would be something like 5% squared more surface area and 5% cubed for the interior volume increase so check and see if you have enough foam. Better to have some extra for construction waste than run out. I build mock ups of the hull shape and interior components using cardboard and cheap thin ply for the patterns. This lets me see if there is enough elbow room and use the ply patterns to mark out the real thing. Definitely worth the time when planning. We really like are new layout but i had to fine tune what I had drawn out. If you make a short hull section model you'll get an idea of the stock space and can go from there.
     
  5. rberrey
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    rberrey Senior Member

    I plan on doing a mock up after I complete the hull shell. The only thing I might change on Ed,s interior plan is putting a bench in like the 36, and lifting the dinette floor area up for added storage.. In the galley and dinette area %5 will give me 5 1/2" more length with ply, so only about 4 1/2" with foam. I might find me a big woman and need the extra inchs on one side of the dinette. I bought extra H80 and then bought some renicell to stiffen up keel area, so plenty of foam.
     
  6. cavalier mk2
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    cavalier mk2 Senior Member

    Maybe you should make the hull sections wider after all....I've found if you are non PC enough everybody stays off the boat and you can get there faster!
     
  7. catsketcher
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    catsketcher Senior Member

    I would increase mold frame spacing as you wish. In Oz John Hitch designed a 33ft cat. With longer frame spacing it became the Hitchiker 40. Two were designed with even greater spacing to be Hitchiker 50s. You will have to try very hard to make a boat worse off by making it longer.

    Increasing the hull beam is far more tricky. Longer boats are usually proportionally slimmer than short boats. If you increase beam as well you will not do this. Making the hull longer will give you extra payload and pitch resistance - I would not make the hulls wider too. If you want more space then go and buy plans for a 35 footer instead.

    I have met quite a few people who wished they had built a larger boat instead of trying to fit everything in a small boat. I also have friends who have large cats which are faster and more commodious than they need. Be brutally honest now and pay extra for getting the correct design. If you are compromising now then you would be better off restarting with the design that will fill your needs. In every build I have done I have made some mistaking of my desires or expectations and have wished I could go back in time and give myself some advice. Usually it is to not save money by being clever - be honest with yourself and do a good job. You will make some mistakes but they should be minor if you have the right design in the first place.

    Going 5% longer is no worries. Many cats in Oz have an extra 1 metre on the stern. Making the rig larger and hulls wider means you don't like the design so get another one.

    cheers

    Phil
     
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  8. cavalier mk2
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    cavalier mk2 Senior Member

    I pretty much agree Phil. The wider hull comment was a feeble attempt at humor but I think Rick knows this. The over all beam spacing could be increased by the same amount keeping the hull sections but really doesn't pay off like length with a wing deck tri because of the increase in surface area and materials. I'd probably keep close to the stock rig height and add light air sails but then I'm sail conservatively, as we cruise instead of race. In a 5% stretch he doesn't have to change anything but I imagine those long Hitchhikers had frames of some kind added between the stations.
     
  9. cavalier mk2
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    cavalier mk2 Senior Member

    I've seen boats where the owner thought he was being crafty. 2 things you can't fool however are time and the sea. Those boats stood up to neither. It makes sense to use the best materials and do the best work you can. Size wise I think you'll get more use if you stay with a size you can handle and maintain yourself because there are times when you'll need to. When you buy a boat you can see how it does before you change things - then you know what is working and what needs help. Building it pays to try and get some experience on the type so you know what you are getting. I haven't ever heard people regret making their boat sail better and faster when the changes were kept within reason for the design.
     
  10. rberrey
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    rberrey Senior Member

    The 31 is the right design for me, my issues are fat hulls building with foam , and extra foam. Taking the overall beam the %5 should give me close to the same boat as designed just a little skinner hulls. We are not talking about that much more boat. I dont want to increase the mast hight any more than needed. My thought is I can keep close to the same sail plan but use a sq top main, it will be a cruising boat. I will not widen my hull frames other than what occurs from added material thickness, I will widen the overall beam to keep L/B ratio as per designed. My hulls are about 8.5 , so %5 should put me at around 8.8 to 8.9. I could go with a 35' or 36' design, but these are much more boat disp wise than the 31 even after its scaled. The L/B raito on the' 31 is greater than L/B ratio on the 35' and 36' for some reason , my 31+ may end up as wide as these boats, but nowhere near their disp range.
     
  11. cavalier mk2
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    cavalier mk2 Senior Member

    The smaller the boat the more beam you need for equivalent stability, so the longer ones don't need as much to be as stable. Have you checked out the 35XR? It is a lean Tristar out of the box.
     
  12. rberrey
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    rberrey Senior Member

    I looked at the 35s and 36, the 36 was the one I wanted, the 27'9" was all I needed and the 31 was what I let my nephew talk me into because of the payload . I dont see the 35' offered on Ed,s stock list any more ,only the 35XRC. One day you might talk Ed into explaining how his designs evolved. The 27'9" and 31' are close in size range, yet the 31' is much more conservative . The 31XR and 32XR are off his plan list, within the 31' plans there are pages with 4800 disp and some with different LOA . There was a post concerning an accident that I read years back about one of his designs ,it stated poor seamanship as the cause. I have wondered if it was a 32XR or boat in this size range. Your next jump is to the 35' with 3 within a foot in size . I dont think you can inprove on the 24' or 27'9" for their intended use. But you would think in the 31' size range there would be a 33' and the 32XR would be offered. It just seems to me that the 31' sets in a gap as far as design is concerned. I think if I built a 35XRC Cav you would fly down and test it out:). There is a 37XRC for sale but they put a dogger on it and made it a moter sailer. Rick
     
  13. cavalier mk2
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    cavalier mk2 Senior Member

    I saw the 37xrc and thought it could be saved with a smaller motor and work on the dodger. Test sails are always fun ;) There is a regular 35 in the NW but somebody said there were some problems here and there.
     
  14. Richard Woods
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    Richard Woods Woods Designs

    I suspect you mean Manitou. It had been ashore in Cowichan Bay, BC, Canada, for a couple of years for non boating reasons, but is now back in commission.

    I have been on it, and raced against it, but not actually sailed it myself

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     

  15. cavalier mk2
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    cavalier mk2 Senior Member

    No, Pleiades in Everett WA. I haven't looked recently bu it has been out of the water for years at Dagmar's, an interesting dry storage for boats off I5. Old Pivers go there to morph into even stranger water craft.
    How did they do ? A friend up there got his tri run into by Cat Sass this year so I know the racers are serious but some of the cruisers are just out for the fun.
     
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