Which would have the best range A boat fitted with a single outboard which is on the marginal size for it and will have to run at higher revs to cruise or The same boat fitted with twins of the same motors that will be right down in the rev range to achieve the same cruise speed
bigger is better, the thing that scares me about twins is the cost of servicing.
butt I am a tight bugger.
take a feed & leave the rest to breed
I recon that's a hard call to make !
twin engines will require more fuel, ( another tank or a larger one) which equals, more weight in the donks hanging off the back and probably double the weight in fuel and drag !.......so im thinking there probably wouldn't be much difference in range at all !
interesting question ! could be wrong ! im sure there are those here with fuel usage with the same hull or there abouts to get an idea, but I wouldn't have thought range would be considerably different ! ive not owned a twin, so I would be interested in others responses.
bonneville
Why would there be double the fuel? No one said anything about increasing fuel capacity!
To be somewhat scientific about it, to propel a certain boat at a set speed, requires X HP, now whether that HP is produced by 1 engine or two makes little difference, it still takes X HP, and to produce that said HP takes the same amount of fuel.
Provided efficiencies are the same. Two transmissions, two skegs, but more prop area. A single will have the best range, twins are probably safer if you running long distances.
then the answer to the question is the single will have more range !Originally Posted by Noelm
two motors, will not burn less fuel because of required H/P
HP comparisons to working less harder with two, is sort of right, BUT, there's a thing called extra weight/ drag/ and as already said, more fuel !!
The single would have the biggest range
on an apples for apples situation.
but lots of other advantages in a twin set up.
bonneville
is this a generic question or
do we specifically have a mono or a cat in mind ?
Transire vinus forticulus
I totally agree with bonneville's statement. May I ask, why not just get a more powerful outboard so that it provides more HP than one that is just "marginal"?
Cheers
Bob
At a guess he has, in his opinion, an underpowered boat and was simply going to purchase a motor the same as he already has. Like I say though - just a guess
I know absolutely nothing about engines but I would have thought that any engine fitted that is basically struggling to cruise is not an option at all and you would be thoroughly disappointed in the outcome, I am sure if you did a search on this forum the same question and answer will be found in various guises. I would settle for a higher HP engine and surely it would be cheaper than buying 2 smaller units as well as servicing and maintenance costs. Once again is this question related to a purchase of possibly 2 similar boats already set up with what your asking or just a pub debate.
Mmmmm. What if I chose to run a 90hp on my boat instead of the 115 it has on it? I reckon it would still be able to cruise at 20 knots but the 90 would probably be working harder and using more fuel than the 115 at the same speed. Kinda flaws your theory a little.
It's not that simple. If the 90 has passed the point in it's torque curve where efficency starts to drop to get your 20 Knots, but the 115 hasn't, then yes. If the 90 is at it's peak efficency at the 20 knot mark and the 115 hasn't reached it's optimum then it may go the other way. Chances are though that unless the 90 is running close to WOT to achieve the required speed, the difference would be very minimal unless the 115 is a heavier, larger capacity engine.
Yes, what he says is correct, there is a thousand variables of course, "IF" we are considering a certain speed, on the same boat, then the HP to achieve that speed is a constant value, that constant value equates to fuel used whether that be a 150 working at half throttle, a 90 running at ideal RPM, or anything in between (in a way) as I said, there is a lot of variables. People often up the HP, thinking they will save fuel (and sometimes they do) but a well powered boat, running at optimum RPM, will be every bit as efficient as a big HP motor running outside it optimum power band for the same cruise speed.
More HP = Less Fuel, that's what I used to tell my old man 50 years ago.
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