Latest News: Forums Cruising Boat Speed with outboard

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  • #3850
    BluTak
    Participant

    Can anyone give me any idea of what boat speed they get with their motors in flat water when loaded with cruising gear. Do you get 6 knts with a 2.2hp engine or does it need to be 4 hp?
    Robert

    #7655
    Anonymous
    Inactive

    There’s a long history here on choosing an outboard. I can’t recall a direct answer to your question but on my family trips (heavily laden boat) I think 4 knots would sound more accurate. Speed seems the same whether using a 2.2 or a 3.5 and anyhting much bigger is going to get heavy…..its about how hard you push your engine, the harder you go can just increase fuel consumption not speed. Others will explain better but 6 knots sems a bit ambitious.

    #7656

    We use a Honda 2.3 and 3-4 knots is comfortable and economical. We have done a steady 5 knots but that uses quite a bit more fuel. Could have pushed it harder but would just have ended up using lots more fuel and not gaining a vast amount of boat speed.

    Jonathan
    W2312

    #7657
    Bob Harland
    Participant

    I cannot say much about outboards, but here is the theory on hull speed:

    the speed v for a displacement hull is
    v x approx 1.34 x square root of{LWL}
    where v is in knots and LWL is in feet

    that’s a bit over 5 knots for a Wayfarer
    So to exceed that speed the boat needs to plane. Which I guess needs a lot more power.

    More info here;
    http://en.wikipedia.org/wiki/Hull_speed

    hope that helps.

    #7658
    matoi
    Member

    On my last trip with Ralph, I took an outboard to see how it goes:

    1974 Johnson 2stroke, 2hp, 11kg = 3.5 kt cruising speed

    pushed it harder and speed increased very little, while fuel consumption drastically changed for worse – just as others say….

    I heard that newer machines consume less, are quiter and push the boat faster, but seem to be bigger and heavier than this one.

    #7662
    Anonymous
    Inactive

    I have a 2Hp Yamaha and that will push the boat at 3+knots and run for 2.5 hours on .9Ltr approx 35 mph

    #7670
    BluTak
    Participant

    Thanks a lot for the information. One more query. Where do you all keep your engines? Do they fit in the rear hatch, do you leave them on the outboard bracket permanently or on the bottom boards?
    Many Thanks
    Robert

    #7676
    Anonymous
    Inactive

    I leave my engine in place on the transom, but as I have transom sheeting there is a secondary sheeting position approximately 18inches in from the end of the boom to stop the sheet catching during gybes.

    #7679
    Anonymous
    Inactive

    All depends what sailing I am doing. If I anticipate I’m going to need the motor at some point then I mount it on the transom. If I’m in “aesthetic purist mode” and there’s a good breeze I like to hide it in the rear locker knowing it’s there for emergencies. It can be a hassle getting the motor mounted once you are out on the water though, eg needing to drop the anchor to stop you drifting backwards or worse trying to get out the way of some big boat…. oars are a quicker way to get you moving.

    As a slight deviation how have people here established their boat speed? Mine was a guestimate and obviously over a distance you could calculate your speed from time travelled and maps or charts. Or were most people reading off handheld GPS?
    cheers
    Dave

    #7682
    Anonymous
    Inactive

    Dave Mac wrote:
    As a slight deviation how have people here established their boat speed? Mine was a guestimate and obviously over a distance you could calculate your speed from time travelled and maps or charts. Or were most people reading off handheld GPS?
    I use a GPS to get SOG

    #7694
    BluTak
    Participant

    Thank you all for you help. It doesn’t look as if I’ll be left behind with my seagull! I had heard that people were getting 6knts which made me wonder if I was living in the dark ages and needed a bit more ooomph!
    Robert

    #7703
    Swiebertje
    Participant

    @Simon McE wrote:

    Dave Mac wrote:
    As a slight deviation how have people here established their boat speed? Mine was a guestimate and obviously over a distance you could calculate your speed from time travelled and maps or charts. Or were most people reading off handheld GPS?
    I use a GPS to get SOG

    I had a SOG of 5+ knots once while motoring, then I realized I had a 3 knot current running with me…..

    When talking about boat speed and engine power we should only consider speed through the water. An Engine does not help with or against current.

    I always tell other sailors that anything over 2 hp is for others (as in towing others). If you want to go in a plane with a boat like a Wayfarer you would probably need a 10 to 15 hp engine. The weight of these buggers is something you don’t want on your transom. Having said that, it is safe to assume we are, like many other sail boats, limited by our hull speed. A 2 hp Engine easily pushes a Wayfarer up to its hull speed and once there you can go back to almost half throttle. If you want to tow three or more other wayfarers a 4 hp may be a better choice but remember that a 2 hp weighs 11 to 12 kg and a 4 hp 20 to 24 kg. That weight is where you least want it, at the transom. That makes the choice easy I would say.

    #7989
    BluTak
    Participant

    For anybody who happens to be interested I did trial on flat lake, no mast, no cruising gear and got around 4 knots (SOG gps) with Seagull forty + with clutch and weedless prop (12:30 gearbox) and also forty + direct drive and hydrofan prop (10:35 gearbox). Both at around half throttle engine not straining – extra revs did not give much extra speed

    Tried hydrofan prop and also 5 blade century prop on clutch model and it didn’t have enough power

    Also tried seagull century and got around an extra 0.5 knot but it wasn’t running very well (I borrowed the engine and it was longshaft)

    So I’m sticking with forty + and clutch. I had a very interesting afternoon on my local pond!

    This may be of interest to impecunious cruisers

    Robert

    #8947
    keithw
    Member

    I have a mariner 3.3HP 2 Stroke mounted on a boat’s & bits removable bracket. The mean speed of 2 runs in opposite directions on the river Frome @ Wareham was 6.2 miles per hour,This was more than hull speed & the boat was obviously planing.The weight on the boat was my 14 stone + approx: 100 lbs.
    The MK2 came on to the plane very easily & I dont think another one or two persons placed sensibly would have much difference. I really would not want a motor that is any heavier. Really don’t like the motor this far back because of the weight leverage also difficult @ dangerous to control in certain conditions
    Have tried fitting motor directly on transom and found it much more controlable but could’nt get it deep enough in the water and on turning cavitation occured.I am still thinking what to do.The dry weight of motor is 28.5lbs

    #8950
    BluTak
    Participant

    The obvious answer is slow down or buy a speed boat! But how are you steering. You need to clamp the motor ahead and steer using the rudder or use an outboard tiller extension so that you can sit well in the boat.
    But you need to get to the throttle which means going back. At slow speeds this isn’t a big deal but… I put a bracket on for a friend who used a 10hp Mercury – it was terrifying!!
    Most people just use the outboard as “auxilliary” power ie below hull speed. I think if you’re planning on planing you need to have a serious think about the controls and trim

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