In designing my 40ft motor/ sailor,
I found it very hard to justify buying
They are heavy, cost the earth, and do not have the longevity of diesels in trucks or tractors.
The reason that diesels have a high failure rate in cruising boats, is that diesels run best under a load. A lot of cruisers run their motor
to recharge batteries
or only use them for getting in/of the harbour.
The cylinders glaze over and life of the motor is significantly reduced.
The boat should be designed for Outboards.
( I would not recommend an Inboard petrol motor on a yacht)
It is also not a good idea to just hang them out the back.
Get the lower geared/ high trust/larger propellor model with a long or extra long shaft.
The only down side, in my mind, is you will need larger fuel
capacity for petrol motors.
The four strokes give better fuel
economy over a wider range of RPM
than a two stroke.
Two strokes are lighter, much easier to fix and much much cheaper.(half price
If your new model two stroke outboard motor is run at 3500-4500 rpm
, fuel consumption
will not be that much different from a four stroke.
I am in the process of putting 2 X 90 two stroke outboards on my 40ft aluminium fast displacement
One motor at 4,000rpm will give me a cruising speed of 10 knots.
The other motor is a spare. Or by running both motors together I will get 16 knots plus if I need it.?
We have sails
, when there is wind
, for sailing downwind or on a reach.
We can't Tack.
But hey, the sails
cost a total of $2,000.
I know lots of cruisers (particually mono's) will swear that Diesels are the only way? However modern outboards are much better than they used to be, they are light and cheap
More and more Multihulls are now going with two outboards, properly mounted. I would recommended buying
larger HP than generally recommended and run them at no more than 1/2 to 3/4 throttle giving more economical fuel consumption