Which outboard motor for 22' Tri?

Discussion in 'Multihulls' started by aussiebushman, Jan 1, 2014.

  1. aussiebushman
    Joined: Oct 2009
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    Location: Taralga NSW

    aussiebushman Innovator

    G'Day all.

    My old (mid 70's) 8M Tohatsu finally got beyond the point where more repair work was sensible, so I'm scraping the money together for a replacement.

    Where the tri is moored there are furious wind problems and difficult access to the fore & aft mooring, so I need a combination of absolute reliability, easy starting, light weight and the ability to push the boat along safely in strong wind conditions.

    The research suggests 2 stroke would be more suitable for these criteria than 4 stroke and although the current motor is an 8 Hp, I'd like advice on whether a modern 6 might be as good. I do favour the Tohatsu, Yamaha or Merc brands and although they are cheap, I will not touch the Chinese stuff after numerous problems with Chinese generators on the farm.

    Please feel free to comment or criticise my thinking and any advice of suitable motors would be very welcome.

    Another question here - I'm thinking of changing the standard mounting bracket for a vertical slide like the one posted on one of the forums - picture attached. That would be a lot simpler to raise and lower than having to balance over the stern to raise/lower and tilt the engine while the wind is pushing the boat all over the place. Has anyone tried this system on a tri?

    Thanks

    Alan
     

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  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Get the engine that has the biggest diameter propellor for the hp, they usually have greater reduction in the gearbox ratio. That way you have a motor that can deliver maximum thrust at relatively low boat speed. You have then to select a propellor pitch, likely toward the lower end of the available range. You are probably better with an ultra-long 25" leg too, that way you can have the prop in the water better, with less leg drag. Check manufacturer's specs.
     
  3. Richard Woods
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    Richard Woods Woods Designs

    I used the 6hp extraLS Tohatsu for several years and wasn't that impressed. Its basically an uprated single cyl 4hp so was noisy and didn't have much power

    My choice would be the high thrust Yamaha 8 or 9.9, both are excellent engines

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  4. aussiebushman
    Joined: Oct 2009
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    aussiebushman Innovator

    Good advice, Gentlemen

    I have heard good things about the Yamaha too and the 8 sounds about right. I'll definitely find out about the available props because you are absolutely correct about needing the thrust when moving slowly into that ***** of a mooring.

    What is your reason for suggesting the LS advice though? Where the motor is currently mounted, the prop gets plently deep enough. Even with the bracket in the "up" position, the prop is still in the water so the motor has to be tilted. I don't have a picture from the correct angle of view, but this one shows how little clearance there is - both from the transom to the motor and from the waterline to the prop. This has meant mounting the motor further back from the transom on an extension to give it room to tilt.

    It also means hanging over the stern to start, release and raise it - precisely what I'm trying to avoid doing. Too easy to fall out of the cockpit, quite apart from having to leave the helm. (I have wheel steering connected to a rudder on each ama). Maybe an electric start (if available on the 8 HP) would solve part of the problem, especially if the vertical slide system mentioned earlier allows enough travel. The throttle control is OK with a tiller extension and I have made up an extension so I can engage gears from the helm.

    What thoughts?

    Alan
     

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  5. Mr Efficiency
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    Mr Efficiency Senior Member

    If you are happy with the shaft length, well and good. I was just thinking that if the boat is pitching up and down, and there is nothing much ahead of the outboard leg, a longer leg with a more streamlined shape may help, but you know your boat better than I do.
     
  6. pogo
    Joined: Mar 2010
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    pogo ingenious dilletante

    I' ve had a 9.9 Yami fourstroke on my 10, 6 m Tri, indeed , high thrust, but heavy.
    My second outboard was a 15hp Mercury twostroke. The motor is much lighter.
    The main advantage is that one can shift withe the tiller. Turn the handle right--forward, turn left-backwards.
    In your case , stern mounted , you might lengthen the tiller with a simple vacuumcleaner tube . The handle/shifting acts in each tiller position , over vertical to about 160 degrees ( showing backwards).
    The motor consumed 3liters per hour on 3/4 throttle .
    Astonishing was it's thrust. With the standard prop ( !) for RIBs nearly equal to the 9.9 !
    For good thrust backwards i installed this "bell" on the prop shaft . With this equipment the prop moves backwards on it' s shaft, closing the exhaust at the end. the prop can't ventilate with this device---swallowing the exhaust gases, they are pushed forward.
    As i wrote the Thrust of the mercury is the same as with the Yami 9.9, but the acceleration/decceleration is slower --- no it is not as abrubt, cause of the smaller prop , whose rpm one can control with the tillerhandle much much better.
    The abrubt shifting with the abrubt high thrust has been the reason for selling my 9.9er , the gearbox slowly gave up. ( My tri is 35' , weighing 2 tons loaded, in a blow she needs sometimes "fast panicshiftings" . This is not the case with the 15hp twostroke , one shifts fast but smooth , accelerates under control , pushing up the rpm like a turbine. very fine , not so nervwrecking.)
    The 15 HP Mercury has enough torque, coming from about 260ccm --same as the 9. 9. That' s a key too ! The Motor is also avaible with 10 and 8 HP . Available als longshafts , or ultra- longshafts .
    Your Tri . Considering the weight , at least 46kg of the Yami 8, or 9.9, i would opt for 15hp Mercury--36Kg ultralong.
    Ask for the alternator ! I don't remember this device being standard, originally/normally these motors are for RIBs and other open boats without electrics . But, they are also available with other props , e- start and everything , up to remote shifting ( shifting box in cockptit) ---seldom ordered.
    In my view less is more , handstart is less vunerable, reliable , shifting in the tillerhandle is less vunerable , reliable ....
    I think for sporty, open multihulls up to 2 tons and/ or small multihulls , it' s a good motor .


    http://www.marinawassersport.de/index.php?option=com_content&view=article&id=319&Itemid=367

    http://www.marinawassersport.de/index.php?option=com_content&view=article&id=319&Itemid=367

    I see, my english isn' t as good as i want it to....
    But, it might also be the rum ....
    Cheers....


    pogo
     
  7. pogo
    Joined: Mar 2010
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    pogo ingenious dilletante

    That is much true, but it is common thinking and calculation out of monohull experience.
    For a light multihull , prop diameter , prop pitch and gearbox can be defined much more with action/reaction principle in mind ---- rocketdrive system , or principle. That must'nt result in poor acceleration /deccelaration !
    Calculating the Prop and gearbox for a light multihull with conventional methods also means that the boat never will run above it's hullspeed.

    No , i' ve no calculating method for light multihulls.

    I only have some experience with it. For example an 8 m 750kg Tri with a custommade 5 bladed high pitch prop on a standard 4 HP twostroke doing 9kn .

    Is the "rocketdrive theorie" for multihulls worth a discussion ?

    pogo
     
  8. aussiebushman
    Joined: Oct 2009
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    aussiebushman Innovator

    Thanks Pogo - good input

    The remote tiller and gearshifts are no problem as already noted because I have a propriety clamp-on extension for the former and a custom made rod that screws onto the shift lever and extends to the helm. It is the starting that I would like to change from rip to electric start.

    The alternator is not strictly necessary due to 2 X 40W solar panels on the stern arch servicing the house battery. Of course, if the motor had electric starting, that might change this situation.

    Although weight is an issue, the major need is for as much thrust as possible due to the wind conditions I described earlier. My current Tohatsu is sited on an extension to provide room to tilt to get it out of the water. I think I have solved part of that by making up the vertical slide system mentioned earlier. It allows much greater vertical movement than the standard spring loaded unit, also it moves the weight forward by 250 mm and will eliminate the hassle of leaning over to release the tilt lever. Lifting and lowering can be done within the safety of the cockpit.

    The locals here reckon Mercs favour high performance over reliability and consequently prefer Yamaha, Tohatsu or Evinrude as the all round best brands for performance and service , other than Honda which is far more expensive. I advertised and have sold the Tohatsu. Due to my meager budget, I'm having to look at some good second hand motors. There is an 8 HP Evinrude available at a good price because the elderly owner can't drag it up and down the beach to his tinny and wants a lighter motor. That seems a genuine reason for him to sell it, so I'll check it out. Has anyone had any problems with Evinrude?

    I appreciate your advice about the prop size and thrust and will see if I can get a dual thrust 9" X 5" that seems to offer the best solution for my conditions. What do you think of that choice?

    Thanks again

    Alan
     

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  9. DennisRB
    Joined: Sep 2004
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    DennisRB Senior Member

    IMO you already have the best engine. Just replace it with a newer version which has not done so many hours. I love my tohatsu 8hp. If you can, try and get the 9.8hp version. This 2 cyl engine comes in 6-8-9.8hp versions all weighing in at 23kg so you may aswell get the one with the highest power (the 9.8 having the best power to weight ratio of any outboard in this HP range). I believe you can still buy them new so they have been continuously updated but are more or less the same as they always were, if it aint broke dont fix it.
     
  10. aussiebushman
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    aussiebushman Innovator

    Good advice Dennis

    The only problem is availability on the second hand market. I just can't afford a new one at this time. There is a Tohatsu 9.9 available but that must be the 4-stroke and a lot heavier. For that reason, I might end up with the Evinrude 8 but I agree that a Tohatsu or Yamaha would be better
     
  11. DennisRB
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    DennisRB Senior Member

    Yeah its all about finding a bargain. I saw a 12" tinnie with trailer, bimini, new depth sounder GPS, and 2 year old tohatsu 9.8 for sale for $1500. It was too far from my house otherwise I would have got it just for the engine and sold the rest with a cheaper engine. I got my 8hp for $350 and it is in good condition.
     
  12. aussiebushman
    Joined: Oct 2009
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    aussiebushman Innovator

    Solution found - sort of!

    At the weekend I got a 6 HP Evinude for only $350. It had been virtually rebuilt and started first go. The guy really did not need the money - you should have seen the house right on the waterfront and the 2 Mercs parked in the triple garage.

    I would have preferred an 8 Hp or 9.8 but at that price, it can easily be resold if something bigger turns up. In the short term, it will do the job

    Thanks everyone for your help

    Alan
     
  13. Moggy
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    Moggy Senior Member

    Look at the Tohatsu 6hp 4 stroke, it looks to be a good compromise between thrust and weight. They run around $1900 though.
     
  14. aussiebushman
    Joined: Oct 2009
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    aussiebushman Innovator

    Yes thanks Moggy

    After a terrible 2013 when everything seemed to break down in rapid succession I can't afford a new motor at present. Having just got over the costs of replacing 2 generators, a car engine and a computer and printer that got fried by a lightning strike just before Christmas, I'll have to see how this 6 hp OMC performs. It was cheap enough that I can resell it at the same price I paid and get someting better in a few months time.

    $1900 isn't too bad but I'm still unsure about the benefits of a 4 stroke versus one of the more modern 2 stroke options like the Tohatsu or Yamaha 8s or even a 9.8 that someone on this forum suggested has the same weight as the 8 but more power.

    Cheers

    Alan
     

  15. DennisRB
    Joined: Sep 2004
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    DennisRB Senior Member

    For me the 9.8 Tohatsu 2 stroke is a no brainier for certain uses such as a tender or probably a light weight sailboat which sails well. Dont confuse the 9.8 (which comes in 6-8-9.8hp) for the 9.9 (which comes in 9.9-15 and a whopping 18hp!). Once again if you want to step up to this size motor you may as well go for the tohatsu 18hp. Which weighs as much as all other 9.9s besides the tohatsu 9.8.

    On a heavier boat which motors a lot a 4 stroke would probably be better. But the T18 would probably be interesting on your boat at full throttle!
     
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