Conference vicki::boats

    
    
    A "SURFACE DRIVE" is  an Inboard engine that  is set up with a direct
    drive unit of this description. The proppeller is attatched to the
    drive shaft extending from the transom at the waterline. The shaft is
    enclosed in a housing that is connected in both X & Y axis by hydrolic
    cylinders to control boat manuvering and trim. This is in lue of a
    rudder. The propeller is of a surface cavitional design made to produce
    maximum effecenticy when only one blade is submersed.
    
    The concept behind the design is that by extending the point of thrust
    aft, The effective waterline of the hull is increased. As is well known
    in boat design the relationship of speed is goverened by the length X
    breath X displacement. Other implications are the increased tooth the
    prop has due to the turbulance of hull design being further from the
    point of thrust. ie: The  prop gets a better bite on the water.
    
    Also with the prop being 50% out of water at maximum trim, the
    resistance felt by the engine is lessened. Hence more efficent.
    Only one blade of the propeller is working at any given time.
    
    Cavitational resistance due to running gear is greatly reduced. The
    bottom line is much more speed, better control at speed & less fuel
    consumption.
    
    So WHY dosn't every boat use them?? Basicly for  the reason that
    manuvering at headway speed is terrible. They are vunerable to damage
    when Trailering, Docking or in close quarters. Low RPM trust is not
    efficent and they don't back down worth a dam.
    
    If your objective is to go fast, use less fuel, have less moving
    parts?? Then this is the one for YOU.
    
    If you want a little less speed, minimum moving parts and economical
    running go for a straight INBOARD.
    
    If you have a design space problem and nothing else will fit? Go V
    drive. Higher cost in purchace, Maintaince & fuel consumption.
    
    If you need better manuveability  at slow speed and backing down with
    more parts higher maintaince and more fuel cost? Go Inboard/Outboard.
    
    Or close up that transom hole and install an Outboard motor on a
    Bracket. Advantages are longer waterline, self contained unit. Which
    gives you more space in the boat & Easy maintaince or replacement.
    
    In short, Evaluate what you will use the boat for? Fish?, Ski?, Dive?
    Cruise? Race? and add all the good points/Bad points and then pick 
    the one that works for you.
    
                                    Walt
    
                                (An outboard lover & an Inboard Owner)
    
    

    
    Walt pretty well summed it up in reply .1, so I'll just add
    one other comment.  You didn't mention what type of boat
    you're looking at, but it will have to a big expensive boat
    when finished to be worth the expense of installing a suface 
    drive.   Otherwise, the cost of the drive could far outweigh
    the value of the boat.
    
    Rick

    The boat I had in mind is a twenty foot Chris Craft I can get for
    a song (popular or otherwise).  The dealer pulled the motor and
    drive for a warranty job with $$$ dispensation from the manufacturer.
    
    The description of the surface drive was excellent.  Who sells
    something like this?  I have a dozen catalogs showing an occassional
    replacement part, no assemblies.  As this would be my second boat
    it would be a toy for me to play with.
    
    I have seen pictures of surface drives with a rudder out behind
    the prop, was this what you were descibing?  This type of drive
    seems to be very popular with racers.  Chuck Norris and Walter Payton
    just tried to make a record run between Chicago and Detroit with
    a Scarab running two CAT diesels and surface drives.  They had more
    problems with electronics and parts falling off the boat in ten
    to fifteen foot than the drive system (they did loose one blade
    on one prop.  Replaced in fifteen minutes in fifty degree water;
    no that's Cajones).

RE: Note 566.3  

>>    The boat I had in mind is a twenty foot Chris Craft I can get for
>>  a song (popular or otherwise).  The dealer pulled the motor and
>>  drive for a warranty job with $$$ dispensation from the manufacturer.


This sounds an awful lot like it may be one of the Chris Craft
Scorpions with a defective hull.  If it is, check the hull very
closely before you buy.  It seems they reduced the number of
stringers to cut manufacturing costs.  Unfortunately they weakened
the hull to the point that in many cases they cracked or actually
broke apart and sank.  Many of the boats were unrepairable or had 
such extensive damage that they required expensive repairs.  In 
most cases Chris Craft left the owners holding the bag, and the 
case has been investigated by the Coast Guard and had quite a bit 
of coverage in the BOAT/US newsletter. 

The failure to even acknowledge that they had aproblem, let alone
do anything to correct the effected boats is one of the reasons
for the bankrupcy of Murray Chris Craft.  There are enough well
made boats available that it had an effect on the sales of their 
entire product line.  No one wants to buy a boat from a manufacturer 
who has proven he will not back up his product.  I believe this
would make a good case study of how *not* to do business for any
business student.

Chris Craft is now owned by OMC, which is *not* liable for any 
warranty repairs or claims against CC's built by Murray.  According 
to the latest BOAT/US newsletter, Murray is trying to find someone 
with the facilities to repair the boats they built, since they no 
longer have any dealers or facilities of their own.  They said that 
OMC does not want to get involved in the whole mess, but that 
surprisingly Genmar (Wellcraft, Larson, etc.) is interested in 
handling the repairs.

At any rate, if the hull you're looking at has been scrapped on a 
warranty claim, it sounds like the manufacturer has already determined
it to be unrepairable.  Or at least unrepairable at a labor rate of
$30-40 per hour.  It may well be worth it for a backyard mechanic,
but check it over real closely first.

Rick

    
    Couple (actually more than a couple) of comments:
    
    Surface drives are faster and more efficient because they reduce drag
    by eliminating 'underwater appendages' like fixed rudders and shafts
    (of inboards) and below-the-surface gear housings (like I/Os); they are 
    not faster because they locate the point of thrust further aft,
    although that can be translated into speed if the hull is properly
    configured to take advantage of minimized turbulence to the prop.
    
    Surface drives handle IDENTICALLY to standard I/Os at slow speeds and
    in reverse - if you know how to do it. Surface drives handle radically
    differently at high speeds than I/Os. 
    
    The drives should ONLY be used in pairs: in a surfacing situation, the
    thrust is partially to the side - you do need a counter-rotating drive
    to cancel this out. This is magnified by the lack of underwater drag
    that would normally be there with an I/O or inboard...and really gets
    hairy at high speeds. Even been in a high speed spin out in a deep V?
    Very traumatic - to be avoided at all costs.
    
    The drives are extremely expensive - you will never recoup your
    investment in a 20' Chris.
    
    Props are also very expensive (no, your standard Quicksilver prop won't
    fit/do it). Expect to pay more than $1k for a prop (more like $1.5k).
    Also, you do NOT want a two or three bladed prop - remember you have be
    careful of destructive resonances (I've seen 2 and three bladed props
    lose blades (and chew the *&^%*&% out of surrounding structures this
    way)).
    
    An interesting side effect of surfaced props is that they make the
    entire hull vibrate - women giggle. (bet you think I'm kidding)
    
    The drives must be placed at precisely the correct 'X' location or they
    don't work very well. Mfrs get this location by repeated trails, a
    luxury you do not have.
    
    The hull/transom configuration is also critical - usually there are
    special notches which must be built into the hull in order to realize
    the benefits of surface drives. You need the notches in order to make
    sure that water gets to the props which are mounted higher than normal.
    
    Also, if the hull already has holes for a standard I/O, surface drives
    use different (and smaller) holes; you will also need to locate the
    motor differently in the hull (probably lower) - want to build custom
    motor mounts? Also, the entire steering and tilt mechanism is
    externally mounted - you must first buy all this stuff, then find room
    for it inside and outside, then locate the optimum position for the
    drive (oops, I need two, don't I) .... :-)
    
    Net: replace the drive/motor with similar stuff and you've got a boat
    which is ready to go with no experimentation needed.
    
    If you have the bucks for surface drives - buy a hull designed for
    them; else, save many headaches and go boating instead.
                                                                   
    Mitchell
    
    
    
    

    I can see what you mean about the expense of a surface drive.
    Although, a little giggling in the boat wouldn't do any harm.
    Rereading this note it seems an inboard has many advantages.  It
    seems simple with few moving parts, the technology is well understood
    and it appears efficient.  The only drawback is space.  If a VEE
    drive is used the cockpit could be designed like the Glastron Futura,
    a wide back seat with coolers on both sides of the engine.  Would
    this configuration be FAST and functional.
    
    I know, find a Mercruser motor and drive and fill the empty hole...
    There's no fun in doing this.  The family insists that's want I
    do with the other boat.
    
    Does anyone have a Mercruser motor and drive for sale?

    OOPS! One more question.  Where do people learn how to design and
    build boats.  I've never heard of any type of school.  Any good
    books on the subject?

    
    check the boston globe (sundays) in the classified section...also, look
    in POWERBOAT magazine for used motors and drives. russel marine (i
    think) in worcester sells these things cheaply (or used to). sometimes
    they're remanufactured items that are priced accordingly...also high
    performance marinas can sometimes dig up these items from people who
    are 'powering up'. check with tiger marine in newburyport, ma...they
    may be able to find something.
    
    building boats? most of the hulls today are hulls that were designed
    many moons ago, and the molds have been bought out from failed
    businesses. the new guys usually change the deck molds and relocate
    bulkheads to change cabin/cockpit layout.
    
    designing? have no real idea other than to work for a builder for a
    while and then do your own thing. i suppose that there are CAD programs
    around to do that, but i don't know where.
    
    have fun!
    
    (by the way, that model chris had some problems with deck/hull
    bonding...give it a real good look before laying out cash)
    
    mitchell