SELECT
ENGINE
TRANSMISSION
PROPELLER
The Nav Station...
DISCUSSION FORUM
INSTALLATION
OPERATION
QUICKLINKS
SERVICING
SELECTION
Yanmar Pleasure Boat Marine Engine Help
Overview
For those of you who want to cut to the chase the links on the port side take you to specific information for each subject under this topic.
Correct selection is a very important part of the project and for everything to work properly it all starts here. You will find this the hardest part of all, how can you tell if the salesman is only trying to get rid of the stock he has instead of selling you the engine, transmission and propeller you need? In my experience the transmission ratio is generally the biggest problem with the salesman selling a propeller to suit the ratio, not the boat. On the big jobs this can cost thousands of dollars to fix. Definition of a Sailor: a person who prefers the process of getting there. Definition of a Seaman: a person who prefers being there. Which Engine? Rules of thumb: Which propeller? Sailboat or displacement launch: Fit as large a diameter propeller as possible. Which transmission ~ gearbox / clutch / reversing clutch ~? TRANSMISSIONS get a page of their own.
On the port side are links that can help give you piece of mind. If in doubt, visit the Discussion Forum or .
One of the many great things about boating is that you can do it at many levels, only the size of the toys are different.
I once met a sailor who sold his 'xyz' brand of engine after it broke down 3 times in 3 days while coming down the Mississipi River. He swung it out on the boom into someone elses boat , cleaned up the engine room and stowed a lengthy supply of food into his new pantry. Several years later he arrived in New Zealand, still with no engine! He was a happy sailor too.
"Dont need one of them new-fangled things Dick", he drawled, "ah got wind power!"
That wont help those of us who want to go places and do things. The trend today is for more and more horsepower, regardless of the type of boat. Gone are the days when a 20 tonne displacement sailboat had a Stewart Turner or Atomic 4 as an 'auxillary'. That boat will now have a Yanmar 4JH3-TE 75hp engine to punch into the swell and head wind when the skipper decides it's time to go somewhere. The term 'auxillary' would appear to be redundant.
Launch owners are no longer satisfied with a semi-displacement vessel that 'runs on the smell of an oily rag' and demand planning vessels with ever increasing horsepower that will beat their mates to their favourite fishing hole, or be first to the best anchorage in the bay.
Sailboat or displacement launch: one horsepower per 500 pounds ( plus/minus 50lbs ), one kilowatt per 170kg of fully loaded boat is enough to punch into an average seaway. (...ah... no! I can't define 'average seaway', use your imagination 
)
Planning hull: this depends on how fast you want to go, see HERE.
A planning hull with an all up weight of 10 tonnes wanting to cruise at 25 knots will need at least 530 horsepower, 395Kw. An 11 tonne boat wanting to cruise at 25 knots will need 580 horsepower or 432Kw.
Remember that more engines equal more weight and the extra drive train weight also needs to be taken into account.
You also need to factor in those extra girlfriends, dogs, beer and ice for the summer cruise.
The latest online engine brochures are HERE.
You need to take into account the available gearbox ratios. e.g. a 3GM30 with a 2.36:1 ratio gearbox will swing a 15 inch (380mm), a 2.61:1 ratio will swing a 16 inch (405mm) and a 3.2:1 ratio will swing an 18 inch (460mm) diameter propeller. If the shape is something like a Briski racing folder where the blade tapers toward the tip, add an inch to the above figures.
Planning Hulls and/or 'Z' drives: Check with the designer, there are more variables than I have the space or time for. e.g. The faster you go the smaller the propeller diameter.
Rotation: 'Lefthand' (LH) is anti-clockwise, 'Righthand' (RH) is clockwise. 
A table with engine models, gearbox ratios, optimum propeller diameters and direction of rotation is HERE.
