Conference unifix::sailing

As to the speed increase: Very difficult to say. Practical Sailor did 
some tests that indicated that the drag from fixed-blade propellers is 
significant, especially in light winds. As I recall, the loss in speed 
was on the order of a half knot. You might consult "The Propeller 
Handbook" by Dave Gerr (which I have not read). 

Would a Maxprop be worth it? Depends on how you define "worth it". For 
me, no. Since I don't race, a little more or less speed when daysailing
is of no consequence. And we don't have any large, light air sails,
either. When coastal passage making we use the engine in very light
winds since we usually (unfortunately) have to get from here to there by
a certain time. Our rather narrow two-blade fixed propeller is good 
enough, especially since there are some other somewhat expensive things 
I'd like to get more than a feathering prop.

Alan

    
    	Why not try a 2 blade. I have a 78 T30 with Atomic 4 and I have a
    12" 2 blade and find performance under power just fine. Plus with a 2
    blade you can rotate it so it rests with blades verticle and "kind" of
    hide it behind the keel (good placement for this on the T30). Going
    with a vanilla 2 blade  could save lots of bucks.
    

    You ask if it's worth while to go with a feathering prop.  Depends on
    what you want to do with the boat, and maybe how long you're going to
    keep it.  If you sail in an area which has a lot of light air days,
    you'll likely derive greater benefit than if you usually sail in
    moderate or heavy air.
    
    A number of years ago, Alan B used a rather interesting bit of logic in
    regards to the fairness of PHRF ratings and allowances.  His hypothesis
    was if the allowances for things like folding/feathering props is fair, 
    half of the boats racing are going to have a fixed prop, and the other half
    will have folding/feathering.  In the Salem/Marblehead area of
    Massachusetts, most of the racers have a feathering (or more commonly)
    a folding prop.  Seems most of them are willing to take the six second
    per mile penalty a movable prop costs, in contrast to a two bladed
    fixed prop.  On the other hand, above decks roller furlers, which have
    an allowance of six seconds a mile, are used by few racers.  Factor in
    the fact that a movable prop will set a person back hundreds of
    dollars and a fixed prop is "free", and it seems there is a perception that
    a movable prop is worth much more than six seconds/mile.
    
    I bought a folding prop for my C+C 29-2 the year after I bought the
    boat.  I figure the average person looking to buy my boat when I put it
    on the market, will assign a very low dollar value to the folding prop.  
    
    Did most Tartan 30s come with two balde or three blade props?  Paul's
    suggestion about looking for a two blade prop, might be a good one. 
    (ouch. it hurts to say that!)  There may even be some used two blades
    around, making the cost of a two blade unit real low.
    
    The folding prop I use has a ton more thrust in reverse than the fixed two 
    blade prop that came on the boat, so I picked up a bit of a bonus in
    that regard.  A friend of mine used a Max prop on his boat and spent
    more than a bit of time fiddling with adjustments to get what he
    thought was maximum thrust.  Personally, I don't like having things
    under water which are supposed to move precise amounts in order to give
    me propulsion and/or brakes.
    
    djc
    
    
     
    
    
    
    

    Thanks for the responses. I value personal opinions more than marketing
    hipe. Practical Sailor tests reveal only 0.5 knot difference? I was
    hoping for at least 1 knot. Practical Sailor performs many of their
    tests under "controlled" conditions, and often draw rebukes from
    manufacturers due to PS's inaccurate conclusions. I will, however, try
    to get The Propeller Book. Thanks Alan.
    
    If I'm going to replace the prop, it will be either a feathering or a
    folding. I've heard stories about high vibration with folding props,
    both blades not opening completely, and having to "slam" the engine
    into reverse to get the blades to open. Not so with a feathering. There
    is no need to align the feathering prop. Once the pitch is correctly
    set, it will out perform a fixed prop........I think I'm selling
    myself.
    
    I just bought this boat 2 years ago, and plan to keep it
    .....forever??? Seriously, this is the boat I always wanted, and
    although it is old, it is in great shape. We day sail, occasional
    weekend cruise, and club race. The average winds here are 5-14 knots,
    usually more toward the 5 knot end. Performance has always been an
    issue with me. I'm the guy you're sailing next to who is constantly
    tweaking this and that, to try to beat you home. 
    
    Thanks again folks! 

    Older Martecs, and maybe some of the newer ones are the only folding
    props I've heard of which sometimes had one blade drop open while
    sailing, and also had frequent occasions in which one blade opened but
    not both.
    
    The Gori prop I bought seven or so years ago has big gears which
    open the two blades.  Absolutely no way for one blade to move
    independently of the other.  The model I have has been
    replaced/superceded by a more sleekly shaped unit, also made in
    Scandinavia someplace.  My blades fold parallel to one another with a
    gap of maybe an inch and a half between them.  The newer version folds
    with the blades (nearly) touching along their parallel faces, probably
    making the new one a bit more slippery.
    
    Times I've looked at the bottom of Paul's T30 it looked as though it
    would be easier to fit a feathering prop than most folding props I've
    seen.
    
    djc
    

    re: .2  Hey Paul, you old sea dog....How are you?  I didn't see you
    around this summer.
    
    re: .4  While I'm sure that everyone has an opinion, I have some 1st
            hand experience.  I owned a '73 T30 that came with a 2 bladed
            fixed prop (which I might still have somewhere...).  I decided
            to race the boat and changed the prop to a Martec folding.
    
            I wind ranges of 0-5 Kts APT, I saw a .8 to 1.5 knot difference
            in speed, depending on point of sail.  Interestingly, the 1.5
    	    KT increase was in downwind runs.  Paul, I hadn't been hiding
            the blades behind the keel as you suggested (good idea).
    
            With the Martec, I had NO problems with vibration, blades not
            opening, or reverse thrust.  The T30 has a nice skegged rudder
            which helps to provide directional control in reverse.  We 
            kept the boat in the Merrimac (which requires decent
            propulsion).  The boat was powered with an Atomic 4.
    
            If you want, I'll see if I have the 2 blade prop kicking
            around.  Cheers!

    remember to pop it in reverse, no matter what.  A spinning prop will
    triple the drag and even the folders spin at 6 or so knots boatspeed.
    when they spin, they open up.
    
    why reverse? transmission clutch lets it freewheel in forward.