Minimum cruising cat-size & cost

Discussion in 'Multihulls' started by Alex.A, Feb 24, 2010.

  1. Manie B
    Joined: Sep 2006
    Posts: 2,043
    Likes: 120, Points: 63, Legacy Rep: 1818
    Location: Cape Town South Africa

    Manie B Senior Member

    In calm water (like a dam) calculated motor should give at least 10 knots

    you need 3x that for the actual boat at least

    so if calculations show 5hp buy a 15hp
    fourstroke 30% lighter on fuel what i found personally
     
  2. Richard Woods
    Joined: Jun 2006
    Posts: 2,209
    Likes: 175, Points: 63, Legacy Rep: 1244
    Location: Back full time in the UK

    Richard Woods Woods Designs

    Thank you for having my designs high on your list.

    You cannot go wrong with a high thrust 9.9hp Yamaha on a 9m catamaran. We even had one on our 34ft Romany and could cruise at 5.5knots under power. But that boat was at the top end of size for a single engine. However I also used one on my 28ft Gypsy and my 30ft Sagitta. It worked great on those smaller designs.

    You want a minimum cruising cat, so you will have to accept that sometimes you cannot sail or motor as fast as you'd like.

    I think you will regret not having standing headroom in at least the hulls. If nothing else it means the freeboard is low so the boat is wet to sail, and there is also a greater risk of bridgedeck slamming. Both of these lead to discomfort at best. I assume you want to enjoy your cruising??

    I think it unlikely that you will find any professional designer willing to "check over" your own design. I wouldn't do it. For two reasons: 1) it makes me liable for any of your design faults. 2) It would take me so long it would be cheaper for you to buy one of my stock designs.

    You do have to think about insurance, certification (if needed) and resale value when designing your own boat.

    Hope that helps

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  3. marshmat
    Joined: Apr 2005
    Posts: 4,127
    Likes: 149, Points: 63, Legacy Rep: 2043
    Location: Ontario

    marshmat Senior Member

    I keep hearing good things about these small Yamahas. My only concern would be that if you're in an area where Yamaha dealers are hard to find (admittedly, there aren't many such places), spare parts and warranty coverage may be sporadic.
    Agreed.... at least a small area of standing headroom in the hulls would be quite desirable. Low, slim racing hulls don't seem appropriate for something you'll be living aboard for months at a time.

    The way I see it: if you have the engineering knowledge to design a small boat (and I only deal with small boats- smaller than Richard's, at least), you don't have much need for a designer's help, and if you don't have the engineering knowledge, the designer essentially has to treat it as starting a custom design from scratch. I can't take responsibility for work that isn't mine.

    Both well known designers; you've certainly realized by now that Woods boats are a bit more spacious and modern, Wharrams tend towards the rustic, simple and time-tested. Choosing a boat is really a matter of personal taste and preference, more than anything else: it's an emotional decision, so go with what fits your style and makes you happy.
    Designing can be a lot of fun, if you like thick books full of equations and long essays on design tradeoffs. (As an engineering physicist, I find this sort of stuff relaxing.... small craft design is something I do just because I like it, but I doubt I'll ever make a full time job out of it.) If the idea of spending thousands of hours to learn how it all works isn't appealing, it's probably better to find a designer whose philosophy and approach match yours. A good one should be able to take whatever sketches and preliminary drawings you have, combine them with his/her engineering knowledge, and come out of it with a custom design that looks and performs the way you want it to.
     
  4. Alex.A
    Joined: Feb 2010
    Posts: 348
    Likes: 9, Points: 0, Legacy Rep: 108
    Location: South Africa

    Alex.A Senior Member

    Thanks guys - designing is a fascinating process and is teaching me exactly how much does go into creating a finished boat!!!
    Even if i dont design one - i like learning the how and why of things and while complex math isn't really my thing, it is teaching me a lot about boats, which will allow me to make informed decisions in the future.
    And all you people out there giving time and info on this (and other) forums - thank you very much!!!

    Speed not so much the issue as saftey and being able to get out of trouble if needed.
    Freeboard at 1m to 1m10 / deck 1m up and beams 90cm - more than 10% of length! Freeboard is low.... but can be upped along with headroom.
    Hulls are narrow - hull beam 70cm at wl =12.85 and flared going up to 1.2m.
    9m loa - 7.5m at wl. Beam 5.4m = 60%.
    I like double enders...... and rounded - quarter circle.
    Headroom idea is that in ok weather or anchoured i will have full headroom.
    But am at the beginning of this all and no doubt it will develop and change lots as i go.......
    And simplicity/low cost are more complex than i would have thought....
     
  5. Richard Woods
    Joined: Jun 2006
    Posts: 2,209
    Likes: 175, Points: 63, Legacy Rep: 1244
    Location: Back full time in the UK

    Richard Woods Woods Designs

    I have never had any problems with the Yamaha outboards except the time I was hit by lightning. I have had 5 of them, starting in 1985. So no need to worry unduly about spares

    A good starting point when designing anything is "use your eyes and plagiarize"

    Based on you initial requirements, from months ago, a boat that would suit you would be my 28ft Gypsy. That is a hugely successful boat with a couple of Pacific crossings to its credit, plus many offshore trips.

    So I would start with that as a baseline and modify it to suit your own needs

    Good luck

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  6. Alex.A
    Joined: Feb 2010
    Posts: 348
    Likes: 9, Points: 0, Legacy Rep: 108
    Location: South Africa

    Alex.A Senior Member

    I do like the gypsy.
    The wife wants to know what being hit by lightning was like?
     
  7. Fanie
    Joined: Oct 2007
    Posts: 4,604
    Likes: 177, Points: 63, Legacy Rep: 2484
    Location: Colonial "Sick Africa"

    Fanie Fanie

    Hits by lightning or Yamaha's :D

    If it's hits by lightning you should consider a different religion maybe.
    If outboards, give the poor things oil, they'll last longer :p

    Enlightning ? :rolleyes:
     
  8. Fanie
    Joined: Oct 2007
    Posts: 4,604
    Likes: 177, Points: 63, Legacy Rep: 2484
    Location: Colonial "Sick Africa"

    Fanie Fanie

    I was hit by lightning once. I was on the phone with a customer when I was hit. I just saw a flash and when I 'woke up' I was lying in the chair on my back with the phone on my chest. No clue how long I was out.

    That's why I suggested to Richard consider changing religion.
    I now believe when there's heavy weather, stay away from wired telephones :D
     
  9. Richard Woods
    Joined: Jun 2006
    Posts: 2,209
    Likes: 175, Points: 63, Legacy Rep: 1244
    Location: Back full time in the UK

    Richard Woods Woods Designs

    You can read about my lightning experience on the Articles pages of my website

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  10. catsketcher
    Joined: Mar 2006
    Posts: 1,315
    Likes: 165, Points: 63, Legacy Rep: 790
    Location: Australia

    catsketcher Senior Member

    Yammie

    Here is a good talk by a sailor from Australia who circumnavigated using Yamaha 9.9s. His boat is a 32 footer stretched a little. As for finding spares, Chris (the featured sailor) says it is much easier to find outboard spares and petrol than diesel spares and diesel.

    http://www.seawindcats.com/index.pl?page=584

    cheers

    Phil
     
  11. Richard Woods
    Joined: Jun 2006
    Posts: 2,209
    Likes: 175, Points: 63, Legacy Rep: 1244
    Location: Back full time in the UK

    Richard Woods Woods Designs

    Rush is another Australian circumnavigating catamaran (33ft Crowther) that used a single 9.9 Yamaha.

    You are right about the oil. The first high thrust models had a fail safe design flaw, later rectified. You had to change the oil every 50 hours, not because there was less of it, but because the viscosity changed

    That doesn't seem to be a problem now

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  12. cavalier mk2
    Joined: Mar 2010
    Posts: 2,201
    Likes: 104, Points: 63, Legacy Rep: 214
    Location: Pacific NW North America

    cavalier mk2 Senior Member

    I found the ultralight nylon/plastic prop to be good for a extra 1/2 knot on the Yamaha high thrust we use on my Vagabond mk2. We can go over 7 knots flat out when light but usually cruise at 5 1/2 to 6 for economy. I ran the formulas and with that prop there is almost no slip which was a new one for me. The best thing about them is they are easy to work on if you ever have to. It will still make good headway into a rising wind.
     
  13. cavalier mk2
    Joined: Mar 2010
    Posts: 2,201
    Likes: 104, Points: 63, Legacy Rep: 214
    Location: Pacific NW North America

    cavalier mk2 Senior Member

    I better send in this correction before the nitpickers come after me. The ultra light prop was on our first 9.9, We haven't gotten around to reinstalling it since installing a 25" shaft version which is a neat option to look for. We kept the same prop depth but raised the motor height to keep the power head out of the spray. I've run outboards without the Yamaha's reduction gear but the prop is always functioning with lots of slip and headwinds slow the boat down more. If you can't find a 9.9 high thrust you should look at bigger 4 strokes. The gas used in a 2 stroke will weigh the boat down !
     
  14. oldsailor7
    Joined: May 2008
    Posts: 2,097
    Likes: 44, Points: 48, Legacy Rep: 436
    Location: Sydney Australia

    oldsailor7 Senior Member

    Sounds like a Buccaneer 24 would suit you just fine.
    There is a great pic of Samnz B24 on a weekend cruise with two couples on board, on the B24 thread. We've done coastal cruising with three on board. The loo is best positioned under the head of the forward berth.

    And small is less expensive. :D
     

  15. rob denney
    Joined: Feb 2005
    Posts: 890
    Likes: 285, Points: 63, Legacy Rep: 436
    Location: Australia

    rob denney Senior Member

    Maybe for a cat, but Blind Date, the 15m near sister ship of the proa in the video has recently fitted a single 9.9 Yamaha. Does 8 knots.

    Rob
     
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.