Twin/Triple Outboard configuration

[Adis]

Sorry if this have been discussed somewhere in an older post

Can anyone tell me roughly how much (as a percentage value maybe) we are losing by adopting a twin or triple configuration outboard to a planning boat?

As an example, let's assume the Mercury 300HP Verado.

In single configuration, the net power is 300HP

In twin configuration, the power is roughly what? I would think that it will not be like having a single engine 600HP output, since there is interaction between the two submerged drives and props. According to some people, there will be a "power loss" which is "estimated" to be about 30% of the total power, i.e. in our example, about 180HP "loss", thus a net power of about 420HP.

Similarly there supposed to be a power "loss" from a triple configuration, i.e. not really a total of 900HP.

Does anyone can clarify this, and provide me with a rule of thumb in order to have a rough estimate?

I appreciate any help on the above. Thanks in advance!

[Adis]

So, there is no one who can provide me with a hint?

HpT={Hp1+Hp2+Hp3}/3

[Adis]

So, you mean that there is actually no power loss in the outcome?

I.e. if I install two outboards of 100HP each, I will have EXACTLY the same power output and therefore results (same top speed) as if I install one of 200HP??? Is this correct?

Of course you dont lose any power. I has to go somewhere. Maybe just Knot where you want it to go.


Speed on the otherhand is not a direct dependant upon power. you need to factor in water and wind resistance on your variable planning surface if your planning or on your variable submerged hull surface with its variable wave resonances at diffent frequencies. then yourve got boundry layers and reflections and all kinds of other stuff.

Remember those 600p pound Mules can only run just so fast no matter how many you have.

[alan white]

Why not attempt to answer the question? Power could very well be lost in interaction between two props.
The question isn't relative to anything but a single outboard. Not sea state, water viscosity, thermal efficiency etc.
I personally don't know the answer, but someone here will.

[kenJ]

Engines don't lose power, 300 hp is still 300hp no matter how many engines are side by side. I think what he is asking is will he loose maximum thrust when he uses multiple engines. I was looking at a center cockpit ocean fisher in the 60' range the other day on a trailer. The center engine was the only one that had the cavitation plate in the correct place. The two outer engines had the props much further below the hull. There has got to be some loss of efficiency, but I don't know how to calculate it.

[powerabout]

You will always go faster with one big engine as you only have one gearbox in the water.
Assuming a production conventional boat, the outboard has been designed to do a specific job so gear ratio and prop diameters are all but fixed.
BUT if you have some workboat installation where you need all the prop you can get..that is a different story.

A few examples re fast boats, back in my day 28 foot v bottoms were raced with 2 v6 outboards and did about 70mph with a 3rd engine they went 5 mph faster if you were lucky. ( just an example of HP and drag)
There is no interaction between props once you are on the plane.
Racing sterndrives have the blade tips between 1 to 2inches apart.
So do you want to;
go fast
go reliable
go fuel efficant ( that will depend on many factors and at whay speed)
easy to handle
better weight distibution
remove torque, both hull and steering( using counter rotation gearboxes )
My experience, 2 is good and 3 is a pain in the ar*e
twins versus a V8 yammi? The Yami is designed to push a heavy boat not a fast one faster just like the old V8 OMC's.