I'm not going to argue with John about his numbers, but will say - my last 10,000 miles of real cruising numbers prove that our motor (Bruce Roberts designed sailboat hull) boat can save while keeping up with or actually passing John's MORGAN's CLOUD underway depending on the passage. HOW YOU PUT IT ALL TOGETHER AND OPERATE IT IS THE KEY TO GOOD ECONOMY.
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A Sailor’s Motorboat
Morgan’s Cloud as a Motorboat
- Low speed cruise at 6 knots burning just 1.1 US gallons (4.2 liters) an hour, yielding almost 6 miles to the US gallon.
- High speed cruise at 7.8 knots burning 2.4 gallons (9 liters) an hour, yielding 3.25 miles per gallon.
- All empty range of about 1700 miles at low speed cruise.
- All empty range of about 1000 miles at high speed cruise.
- Really good stabilization as long as there is even the tiniest amount of wind. Rolls her guts out with no wind, although we are quite used to that and it bothers us less than you might think.
- Sail assist that can halve the fuel burn in optimal conditions.
- Built-in get home power in case the main engine fails. For the motorboat people in the audience, we sailors call it a rig.
- Walk-in stand up engine room.
- Limit of positive stability of about 140 degrees, without taking deckhouses into account.
- Relatively long thin displacement hull that needs just 87 HP to reach 9.6 knots burning 4.6 gallons (17.5 liters) an hour (estimate from engine power curve).
- Low speed cruise around 6.5 knots burning about 3.5 gallons (13.2 liters) an hour, yielding 1.8 miles per gallon. (how about 2.3 gph)
- High speed cruise of around 7.8 knots burning about 6 gallons (22.7 liters) an hour or 1.3 miles per gallon—ouch! (how about 3.4 gph)
- All empty range of about 3000 miles at low speed cruise. (depends on tankage)
- All empty range of about 1900 miles at high speed cruise. (depends on tankage)
- Separate get-home wing engine. (other alternatives should be considered)
- Walk-in stand up engine room with even more room than Morgan’s Cloud.
- Substantially more accommodation space. Like about double, although not as usable as you might think because a lot of space gets wasted in short wide boats. (Plus a full sized washer and dryer, large shower and head - feels like home not RV camping.)
- Really nice wheelhouse for watch standing and watching the world go by in comfort. (Don't forget about standing outside on most sailboats taking your turn at the wheel - Arctic cold? Yabetcha!).
- Active stabilizers that work in all conditions (unless they fail) but increase fuel burn. (alternative 'fish' paravanes should be considered - no power required to use underway)
- Limit of positive stability of…well, the builder does not, at least that I can find, publish that, or, I suspect, wish to discuss it. I’m guessing between 70 and 90 degrees, and that assumes that the deck houses stay watertight. (Come on John - you said 'crossing oceans' quality)
- Needs 174 HP to reach 9.3 knots burning 9.5 gallons (36 liters) an hour (estimate from engine power curve).
A Real Cruise
A Better Idea
- Removed most of the keel, because you don’t need much of one if you don’t have a mast—that would be good, because the wetted surface goes way down.
- Got rid of most of the 18,000 pounds of lead, for the same reason.
- Squared off the stern and got rid of the aft overhang, because motorboats don’t heel, so you don’t need a pointy stern to match the pointy bow (as long as you get the prismatic coefficient and water plane balance right).
- Got rid of some of the bow overhang.
- Added a wheelhouse.
(THIS IS A MAJOR POINT - STUDY THIS UNTIL YOU "GET IT".)