outboard power on larger cruising cats

Discussion in 'Multihulls' started by Steve W, Aug 14, 2016.

  1. Steve W
    Joined: Jul 2004
    Posts: 1,806
    Likes: 57, Points: 48, Legacy Rep: 608
    Location: Duluth, Minnesota

    Steve W Senior Member

    Looking for informed opinions on appropriate outboard size to replace diesels on a 44ft 14000lb cruising cat. The boat currently has a pair of diesels of around 30hp with saildrives. I know that a lot of Australian cats of this size such as the orams 44c use outboards but have only found one for sale that has 25s but would like to find out if that size is adequate. High thrust would seem to be desirable but Yamaha for example only shows a 20" leg in the 25. Any opinions particularly from those with actual experience on the subject would be very much appreciated.

    Steve.
     
  2. catsketcher
    Joined: Mar 2006
    Posts: 1,197
    Likes: 87, Points: 48, Legacy Rep: 790
    Location: Australia

    catsketcher Senior Member

    I use a single Hi Thrust 25 on my 4000kg 38ft cat. It is easily powerful enough for my boat - gets it to almost 10 knots under power (light ship no water or extra people on board) cruise at 7 knots all day.

    Great motor - only had one problem when I gave it dirty fuel. Cleaned out the carby and it was great again.

    The Seawind 1160 light uses twin Yammies as well. Search for pics.

    The leg is not really long enough for me so my nacelle pivots up and down as well which is not really good. If I was to do a new install I would do what Seawind do with their 9.9s on the 1000. On this the outboard is locked onto a pivoting mount inside the nacelle. Gets the outboard down when required and nice and high when not used. You can try and extend the leg. I looked into doing this myself but haven't. In Australia there is a bloke who can extend the legs but I would just do what Seawind do. (One friend had a problem with their extended leg rattling out the end of the crankshaft due to the longer shaft wobbling)

    The reverse on the 25 is fabulous.

    I know people like diesels but having had outboards I would do all I could to stay away from expensive diesels, extra drag, expensive folding props, and surprisingly less reliable than a modern 4 stroke.

    cheers

    Phil
     
  3. brian eiland
    Joined: Jun 2002
    Posts: 4,788
    Likes: 157, Points: 73, Legacy Rep: 1903
    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

    Is that Hi Thrust 25 different than their other 25's? Does it turn a larger prop to get the extra thrust?

    I recall have a 9.9 hp Yamaha 4-stroke outboard that had a big gear reduction in the output shaft, and then turned a larger prop than normal. That outboard truly was hi-torque. But I didn't think they were building anything similar nowadays??
     
  4. Steve W
    Joined: Jul 2004
    Posts: 1,806
    Likes: 57, Points: 48, Legacy Rep: 608
    Location: Duluth, Minnesota

    Steve W Senior Member

    Yes, the 9.9 is in a class of its own with a 2 .92 : 1 reduction. As far as I know no other high thrust outboard has such a low reduction, not even any of Yamaha's other high thrust models which is a shame. There has to be a point where the HP of a regular thrust motor equals the thrust of the 9.9 but I don't know what HP that would be.
    Phil, do you think a pair of 25s would be enough for a 14000 lb cat?
     
  5. catsketcher
    Joined: Mar 2006
    Posts: 1,197
    Likes: 87, Points: 48, Legacy Rep: 790
    Location: Australia

    catsketcher Senior Member

    What type of boat?

    The Seawind 1160 Lite weighs 6500kg and uses 2 outboards - 2 x 20s or 2 x 25s.

    Kankama weighs 4000kg and can do almost 10 knots under power when light. She can cruise at 7 knots all day - well we could do more but then I am putting money into making waves.

    http://www.seawindcats.com/models/seawind-1160-lite/

    The reduction on the 25 is about 2.4:1. The leg is not really long enough so what Seawind does (on the 1000) is to mount the outboard on a pivoting mount. The mount pivots down to get the motor close to the water and then raises the mount well clear when under sail. The 1160 does not have this feature.

    http://www.oceannavigator.com/Ocean-Voyager-2015/Yacht-Review-Seawind-1160-Lite/

    You will need to do some pretty major work to install outboard nacelles but it may be better than replacing diesels.

    cheers

    Phil
     
  6. Steve W
    Joined: Jul 2004
    Posts: 1,806
    Likes: 57, Points: 48, Legacy Rep: 608
    Location: Duluth, Minnesota

    Steve W Senior Member

    Thanks Phil, this is exactly the info I was looking for. There is a company over here that makes extender block kits for many outboards in 5" increments but I don't remember their name offhand. I have seen motors with a couple of them stacked on Reynolds 33 cats. I believe Tohatsu also has a 25hp with 2.42 :1 reduction. Did you buy a remote model or a tiller model and add remotes? Over here I don't think the manufacturers allow the dealers to sell the remote models to the general public but rather require the dealer to rig it wheres you can add remotes to a tiller model yourself which is what I did with the T9.9 on my old Gemini. It would be nice if one mfg would make a 30hp 3 cyl with a reduction like the 9.9 swinging a huge prop and a 30" leg.
     
  7. Steve W
    Joined: Jul 2004
    Posts: 1,806
    Likes: 57, Points: 48, Legacy Rep: 608
    Location: Duluth, Minnesota

    Steve W Senior Member

    Phil, I assume your single steers with the helm like mine on the Gemini, works amazingly well but I suspect we would want twins on a larger cat so I'm wondering if they steer or are fixed ahead on cats like the Seawind and just use the throttles like with diesels when docking.

    Steve.
     
  8. catsketcher
    Joined: Mar 2006
    Posts: 1,197
    Likes: 87, Points: 48, Legacy Rep: 790
    Location: Australia

    catsketcher Senior Member

    My single is locked straight ahead. I have the option to steer it but never have bothered. All the twins I know have remote control as does my 25.

    5 inches of extension would be very nice and all that I would want.

    cheers

    Phil
     
  9. Spiv
    Joined: Jun 2007
    Posts: 221
    Likes: 16, Points: 28, Legacy Rep: 207
    Location: The Big Wide Blue Brother

    Spiv Ancient Mariner

    Steve,

    I had twin Yamahas 25 XXL on my Schionning 12.5 cat. Weight around 7.5~8T.
    The XXL were mounted in pods (nacelles) on the side of the hulls, under the main bulkhead, so much more forward than any diesel can be mounted.
    Fixed steering, but could pivot on 'a dime'.
    Had 'Hi-trust' gear box, with Hi-trust props with external exhaust hubs: people would fall if I reversed hard!!!

    The original install on pods, left a gap between hulls and pods that would slam underway, so I subsequently faired that in and it was much better. (please ask if not clear).

    We could do 9.5kn, cruise at 6.5 easily, we then changed for 50HP XL Johnsons and it was the worst mistake ever. Lots of cavitation and no reverse power.
     

    Attached Files:

  10. brian eiland
    Joined: Jun 2002
    Posts: 4,788
    Likes: 157, Points: 73, Legacy Rep: 1903
    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

    Interesting, but I don't know that I fully understand 'gap between hulls and pods'?

    How did you fair it in better?
     
  11. jorgepease
    Joined: Feb 2012
    Posts: 1,614
    Likes: 46, Points: 48, Legacy Rep: 75
    Location: Florida

    jorgepease Senior Member

  12. Spiv
    Joined: Jun 2007
    Posts: 221
    Likes: 16, Points: 28, Legacy Rep: 207
    Location: The Big Wide Blue Brother

    Spiv Ancient Mariner

    The pics shows the pod as it was designed by Schionning.
    The rough hand sketch shows the modification I did to reduce slamming (sorry, no pic...)
     

    Attached Files:

  13. catsketcher
    Joined: Mar 2006
    Posts: 1,197
    Likes: 87, Points: 48, Legacy Rep: 790
    Location: Australia

    catsketcher Senior Member

    Thanks for that Stefano. I am thinking of going twins and building nacelles is on the cards. I can see how the waves could get squeezed on your initial build.

    Where did the bottom of the bracket sit on your 25? Was it 50mm above the water at rest or lower?

    Can I also ask - why the nacelles. Scionnings usually use the vertical mount in the aft sections of each hull. Why didn't yougo down this road?

    cheers

    Phil
     
  14. UpOnStands
    Joined: Nov 2015
    Posts: 681
    Likes: 14, Points: 18, Legacy Rep: 16
    Location: Sydney

    UpOnStands Senior Member

    quick question for the group
    is there any maximum angle at which a 4-stroke outboard should be carried?
    the usual tilt angle is 70 degrees. How much further can the motor, in this case a Suzuki DF25AL, be inclined?
     

  15. raf pali
    Joined: Mar 2012
    Posts: 71
    Likes: 1, Points: 8, Legacy Rep: 12
    Location: Australia

    raf pali Junior Member

    Slamming, vibration, drag, sprays, noise, dead weight and cavitation with loss of speed and over fuel consumption, were a nightmare on my 33f 4T cat. The motor a Yamaha 9.9 was mounted on a central pod that caused the all mess. I cut it out and build a ss A frame pivoted structure that can be lowered to the water when motoring and lifted flush to the deck when sailing. When in action, the motor surfs on a board following the up n down of the waves and that solved all the above and made cruising a better experience. This new A frame surfing system has been working for about 6 months now and although is still an experimental and development project, have had no problems so far.
    Works like a charm and can only recommend it to anyone wanting to power a sailing cat with outboards.
    Cheers.
     

    Attached Files:

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.