Dual Outboards on a Monohull

I have a 70 HP 4 stroke Suzuki I may sell, I keep wondering how it would be to get another and fit the two on my other boat, which has a 130 Hp 2stroke Yamaha. Just wondering what the general opinion of this concept is.


mako magic's picture

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Date Joined: 03/08/05

some boats are designed to

Wed, 2009-11-18 18:36

some boats are designed to run twin outboards, generally having a transom weight, you generally cant just bolt on twin motors, can cause more hassles ie balance and weight issues affecting trim etc

nackers's picture

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Date Joined: 23/10/09

twins

Wed, 2009-11-18 18:45

cant c the benifit of two motors apart from havin a good auxilary or your other boat is a cat             twice the servicing/ parts bill            personally i would go for a 150 fourstroke yamahahahahahaha laughn all the way home

 

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Date Joined: 21/02/08

Actually I was on a monohull

Wed, 2009-11-18 20:21

Actually I was on a monohull with twins fitted just yesterday, it was rad.

You do need the transom specced to suit but there are benefits. Two motors can trim the boat up, much like trim tabs, you have a ballsy aux in an emergency, you can run one fwd and the other back to turn the boat sharply, its fantastic in pens.

Interestingly the price is often just right too, it costs more than twice as much to buy the single big motor than the two equalling the same horses.

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Kawika's picture

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Date Joined: 01/12/06

I have a small boat (18')

Wed, 2009-11-18 23:09

I have a small boat (18') which I used to run with a single engine but have switched over to two engines.  I like the twins MUCH better than the single engine for all the reasons till mentions above.  Here's a link to my setup:

http://www.ukuleles.com/Fishing/My%20Boat/MyBoat.htm

  aloha,

Dave Hurd, Hilo, Hawaii 

Dean's picture

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Date Joined: 23/02/07

you loose some power however

Wed, 2009-11-18 23:17

you loose some power however with drag on two motors and more fuel compared to one engine.

Faulkner Family's picture

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Date Joined: 11/03/08

i would personally opt for a

Thu, 2009-11-19 04:57

i would personally opt for a larger single motor rather than 2 on the back. outboards cost a bit for a service so thats double , the fuel you will use will increase and running 2 motors doesnt mean you will get double the hp you will loose out on from memory around 30 % of total hp combined saying you are running twin 70's you wont get 140 hp you will get around the 100 hp output. on the plus side if one motor breaks down you still have 1 to get you home

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just dhu it's picture

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Date Joined: 14/05/09

Twin Motors

Thu, 2009-11-19 08:42

I had twin 115s on a 6.2mt Vagabond which i pulled of and put on a single 200, the twin where good but you as the other s have said your paying 2 x services , your transom must also be suited for the twins and the legs have to be shorter as they are positioned further up the vee of the transom,  my complaint on a slim mono hull with twins was in a cross swell one motor was would come out of the water to often and you had to be on the throttle controls to often to match the revs. i also found the single motors would not lift the bow on trimming as well as the single motor.

I had the twins and thought two motors are safer, second day out in the rig 28 miles from the ramp the power steering line blew of and hence no control over both motors  , two 115 s doesnt give 230 hp theres some loss due to the two props cutting the same moving water

kane's picture

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Date Joined: 07/12/08

id choose 2, till said it right on imo

Thu, 2009-11-19 08:51

but i service my own gear so doing 2 oil changes or 1 isnt a big deal as i buy the oil in bulk etc.

definately nice to have high horsepower redundency if you like going way out west.

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Gooooone Fishin!

Posts: 6

Date Joined: 30/11/09

TWINS

Wed, 2009-12-02 09:30

Got twins on mine but main reasons was for manouverability on a bigger boat and so when i want to go the montes or out for a few days wont have to travel with any one else

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early to bed early to rise fish like hell and make up lies

Posts: 92

Date Joined: 02/11/09

Twin OBs

Wed, 2009-12-02 10:10

I have had several boats (ali & frp) over the years all with single motors (ib & ob). The boat I currently have is a 26' keywest (frp), when I bought it it had a singe 250hp outboard and did 35 knots wot.

The motor blew and I fitted 2 x 140hp Johnson 4s (suzukis), now the boat does 38 knots and handling has improved by 60%. Fuel consumption has gone down considerably but the original single was a 2s so you would expect so.

The upshoot here is I will never ever buy another boat (over 20') that does not have twins fitted.

 

Mick

iana's picture

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Date Joined: 21/09/09

I think all of the replys are right.

Sat, 2009-12-05 18:09

For me two motors are a dream. But I was expecting a bit more action from those that have twins fitted.

I read an article where a test boat with a single was fitted with twins and the figures they got were quite un expected, the twins being better all round.

I think the main issue is increased weight (dissplacement) and trim, power from the motors used to correct imbalance rather than pushing the boat along.

The fact that there is twice the likleyhood of something going wrong is correct, which is countered by the fact that one still has (if your steering is OK) 50% power to get you home.

So I'll still be selling my beautiful 4/s Suzuki and I'll have to put up with the spluttering Yamaha.

 

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Date Joined: 09/12/09

Twin OBS

Wed, 2009-12-16 23:20

I have had a few boats ranging from 12ft tinnies to 23ft huntsman fibreglass. Always had singles, big and small. Thought boats handled well. Few weeks ago I traded my 575f signature with 150, for a haines with twin 150! What a difference! U don't know how good twins really are til u drive in rough seas. They do handle different and u need to get use to different driving style. One big advantage I have seen so far is the ability to trim the boat in ways a single just can't do. The rougher it gets the more the twins come into there own. I will never go back to a single, unless it was a small tinny. Plus I don't need to push the 150s and on average only pur around 2800rpm! where as my old rig I would constantly push her over 5000rpm to get the same speed. Less revs mean less stress on motors. fuel cost so far I can see is only about 20% more cause I am cruising at a much lower rev range, unless I really open her up. But so far no need, cause she flies around the 2800mark.

Iceman's picture

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Date Joined: 17/03/09

Twin Outboards

Thu, 2009-12-17 09:00

At Whitfords Sea Rescue we have been running twin OB on our smaller vessles for about 10 years. The main reason is manoeuvering and safety of having a second engine. Things to consider include:

Weight on the transom and how it will affect the balance of the vessel.

Spacing between the engines.

Will you be able to lift one engine and leave the other in the water. You can get steering sytems that will allow this. That way if you do loose one engine you can lift it to reduce drag.

If you have hydraulic steering you made need to get power assist.

One of the engines will need to have counter rotating prop. This can increase cost as change in gear box is required with some models. If not counter rotating boat will pull to the port and be difficult to steer particularly at high speed. Yamaha have these model available.

 

We are are about to build an 11.3m Naiad with twin Yamaha 350Hp V8 on the back.

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Bodie's picture

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yammy 350 V8's waste of

Thu, 2009-12-17 09:51

yammy 350 V8's waste of money :)

Put the verardo 350's on :)

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Date Joined: 02/11/09

Counter rotating props

Thu, 2009-12-17 16:58

There is a bit of a fallacy about 2 x same direction props. With the first set of twins I had fitted, both were right hand rotating and they steered just fine; no pulling to port or any real effects. They were hit by a truck and I brought 2 new ones; this time counter rotating. I havent really noticed any great difference except a decrease in speed of a couple of knots with the counter rotaters; probably due to the couple of degrees kick out needed with counter rotating props.

 

Mick

iana's picture

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Kickout

Thu, 2009-12-17 17:19

Can you explain "kick out" a bit further.

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Date Joined: 02/11/09

For some reason

Mon, 2009-12-21 14:44

I beleive it is to make sure that the boat tracks straight. When the twin counter rotating o'boards are fitted,  they are not set up parallel; rather they are set up with a couple of degrees pointing away from each other. With the original set of same rotation motors I had, they were set up parallel. But with the new ones we were told  by the manufacturers to mount them with the kick out.

Once mounted, any deviation from tracking true was taken up with adjustment of the little fin at the back of the anticav plate.

Cheers  Mick

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Date Joined: 09/12/09

My new boat has twin

Fri, 2010-02-05 09:15

My new boat has twin 150etecs and they are counter rotating. They are also mounted parrallel. I have never had a problem with it. She always tracks straight. Slow or fast. Next time I am at the shop I will ask about this kick out. But have never heard of it til now. What boat and motors do you have Mick? As I really want to find out more about different twin set ups.

Thanks
Dr. Drift

Posts: 402

Date Joined: 04/11/09

2 motors

Wed, 2009-12-23 20:14

2 motors are very practical, gives ou peace of mind, i have heard if placed to close together they can "fight each other"

iana's picture

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Date Joined: 21/09/09

Kick out on dual outboards.

Wed, 2009-12-23 21:22

Been thinking about what Mick has written about kickout and his loss of top speed. And of course what David has written. Cant find any info on the net about kickout.

One of the problems effecting dual outboards is the doubling up of the wetted areas of the motors. This is causing resistance when cutting through the water. These items have been designed to be streamlined so that the resistance is at a minimum.

 Having each motor kicked out would mean that the streamlined shape of each leg is not traveling parrallel to the axis of the boat, and a larger wetted area is being exposed to the water flow. That is assuming that the water is flowing parrallel to the keel.

The resistance, or drag caused by any obstruction will increase (I think) by the square of the speed. So top end speed will be lost. This obstruction (drag) also is caused by the trim tab on the leg, being adjusted to counter the motor kick out.

And the fact that the two motors are kicked may mean they are fighting each other, trying to turn the boat, but in opposite directions instead of putting the power to full use.

Increased fuel consumption, loss of top speed.

I would like to see how the boat responds with both motors mounted parrallel.

These are just my thoughts.