Originally Posted by Wibs
Twin Engine Advantages...
Peace of mind that you can easily get home without outside assistance
if one engine fails. Plus increased manoeuvrability.
And the disadvantages...
More expensive, increased maintenance costs, twice the drag in the water
and increased fuel consumption (typically a twin engine setup will use approx
1.5 times more fuel than a single installation of the same Horse Power).
I used to run 2 identical 7m RIBs, 1 with twin Honda 90s and the other with a single Honda 225hp, so feel like I know the advantages and disadvantages pretty well.
The single had far better acceleration and about 10 knots extra at the top end, although this probably had more to do with the extra 45hp than having less drag.
In terms of fuel, there was very little in it. We ran both from Plymouth to Salcombe and back on a few occasions and they would always use about the same. The twins were actually more economical if just pottering around, as used to only run one at a time.
Initial purchase and maintenance costs were both substantially higher on the twin.
The twin was far more manoeuvrable, especially in a cross wind/tide.
We never had a mechanical failure due to a fault on the actual engines. The only failures we had were due to fuel contamination and electrical issues linked to the battery/isolators. Twins wouldn't help with the fuel contamination and having twin batteries/isolators would make a single almost as good as a twin on the electrics.
I always preferred driving the twin, but economics unfortunately meant that when the time came to change them we went for 2 single engined RIBs.