outboard power on larger cruising cats

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

  1. Steve W
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    Steve W Senior Member

    Stefano, its early days but I expect we will stay inside as much as we can as the boat will be minimally equipped, its been out of the water for years and is bare and while we will add what we need it will be minimal. I expect we will do the Erie canal route which I have done before and,yes, we do need to take the mast down. We should be able to get the motors close behind the aft beam. The boat has long transoms with steps so there is quite a bit of boat behind the beam. As I said before, this has to be an easy install, not necessarily the final install but I suspect by the time we get it home we will know exactly what we need.
    Uos, the boat is not mine, it belongs to my son and his girlfriend. The entire aft cabins have been devoted to walk in engine rooms so going with outboards opens up a lot of real estate. We have only spent a couple of days with the boat so what to do with those spaces will evolve as time goes by.

    Steve.
     
  2. UpOnStands
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    UpOnStands Senior Member

    the long transoms explain the slight increase in overall length from the 13m of the original simpson plan. Should sail well.
    how is your time window for the Great Lakes passage?
     
  3. Zulu40
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    Zulu40 Junior Member

    I was reading about Evinrude 2 strokes having both EFI and oil injection, thats how it will go for modern 2 strokes I think. Pre-mix should be avoided

    another thing they have is a trolling mode for fishermen, where there are considerable savings in fuel to be had at low RPM

    I wonder if the gear ratios compare, what would be the difference between the thirsty but reliable Yamahas or new tech lightweight Evinrudes ?
     
  4. Zulu40
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    Zulu40 Junior Member

    All the best has been said already I think, but what I gather from previous threads is central pod fitments are best avoided as a correct depth is difficult if not impossible to achieve and props often leave the water.

    Also from power cat operators if props are not under the keel they are more prone to cavitate especially with bigger engines. The closer hulls are together the more interference drag there is between them, and much of that is aerated water best avoided.

    The ideal outboard isnt yet made, if it were it would be around 3:1 ratio, diesel, and 4 blade prop.

    One thing Im thinking for power cats, can they do without rudders entirely?
     
  5. UpOnStands
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    UpOnStands Senior Member

    For guys running outboards, how much fresh water do you use for flushing them? And do you flush them religiously?
    running the garden hose for 5 minutes means a lot of good stuff is lost.
     
  6. catsketcher
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    catsketcher Senior Member

    I have flushed my outboard about 4 times in 8 years - when it was out of the water. I worry a little about the salt in the galleries but some mechanics tell me not to worry - run them for a long time every now and then and I was told it would heat up the interior and help release the salt build up. There is a product called Saltaway or similar but I have never used it. Won't know about anything till I take the water jacket off and I won't do that unless I have to.

    cheers

    Phil
     
  7. Steve W
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    Steve W Senior Member

    We have just returned from a grueling4 day trip to florida to prepare the Simpson 13m cat my son and his girlfriend have just bought, 54 hours on the road, the rest preparing the boat for winter and lots of brainstorming, taking measurements and templates for the upcoming conversion to outboard power, I think we have a solid plan for twin Yamaha 25 high thrusts that should work well. We have a good location for fuel tanks on the bridge deck under the cockpit seats directly ahead of each motor so the search begins for an off the shelf poly tank that will fit the space. I am curious as to what fuel capacity others are using for cats with this setup.

    Steve.
     
  8. brian eiland
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    brian eiland Senior Member

    For curiosity sakes, what are those twin 25 hp outboards going to cost you? (I'm not up to speed on current outboard cost).

    Have you determined a 'likely' installation design at this point??

    Have you posted, or do you have a layout plan of your vessel??
     
  9. Zulu40
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    Zulu40 Junior Member

    Outboard cost? depends where you are, $5,000-$7,000 each, or around half an inboard install complete.

    Depending on capacity (weight) as large tankage can weigh a lot. The tanks are best located on the CG of the vessel so trim is unaffected by the % capacity. If thats not ideal then as close to as possible.
     
  10. brian eiland
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    brian eiland Senior Member

    I did see this in reading back thru the subject thread.

    So you may hook up a temp system, then plan a more permanent one after you get the boat back north??
     
  11. Zulu40
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    Zulu40 Junior Member

  12. brian eiland
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    brian eiland Senior Member

    Duo-prop, dual prop outboards

    Has anyone on this forum had any experience with these somewhat rare outboards that make use of dual counter-rotating props. Seems they got pretty got reviews on this discussion,
    http://www.thehulltruth.com/boating-forum/230846-duo-prop-outboard.html

    https://www.youtube.com/watch?v=chfDSJ2d_a4


    And I seem to remember seeing a VERY good video presentation of a duo-prop runabout challenge against an identical vessel with a single prop. I remember it took place in Venice Italy. And it may have been an IO type unit,...perhaps Volvo. But overall it really displayed the significant advantages of the dual prop arrangement.

    Wish I could find that video??
     
  13. jorgepease
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    jorgepease Senior Member

    The Yamaha TRP's are common in Texas where micro drafting boats jack motors high. They give great grip but it comes at a high cost and if they break expect a high repair bill.

    The smallest motor I've ever heard they make them for was the 150. These days most, including me, use cupped props. They hold where other props just spin and create foam. The difference is night and day and it only costs like $60 to get a prop cupped. Baumann Marine is one of the best. One thing to consider is that it does eat up rpm's, reduce pitch is necessary.


     
  14. brian eiland
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    brian eiland Senior Member

    I cupped the prop on my 9.9 Yamaha hi-thrust outboard, and gained effectively almost another half a knot (calm water) speed out of it,...on 37 foot Louisiane catamaran.

    Now that I recall it was also possible to remove that portion of the handle from the outboard engine that had the throttle twist control (and shifting lever if I remember correctly). I mounted that portion of the handle in a vertical fashion on the rear cockpit bulkhead close to where the helmsman would be standing during docking maneuvers. Just had to get some longer cables to make the connection between the now remote handle control and the engine itself.

    That was a pretty slick deal as I no longer had to reach down to the outboard engine itself to give it throttle, nor to shift it.
     

  15. brian eiland
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    brian eiland Senior Member

    Of course you could always go back to a more primitive method of dual propulsion....:D:D

    Cat Propulsion, rowing style.JPG
     
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