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Max prop on a saildrive

10K views 16 replies 5 participants last post by  SailNet Archive 
#1 ·
I just ordered a new boat and opted for the saildrive instead of the standard shaft and prop. I did so because in this particular boat, with the standard propellor and shaft configuration, there is a hard pull to port due to location of the prop and rudder. The saildrive puts the prop that much further forward of the rudder and reduces prop wash. My question is, does the max prop work as well with this system as it does with the standard configuration? Would it be a worthwhile option over the folding prop that comes standard with the saildrive system on this boat? My main concern is straight tracking in reverse as I have a tight slip to back out of. (into) Larry
 
#2 ·
Oddly enough saildrive systems generally have more prop walk than conventional systems. I would not expect better performance under power or sail with a max prop over a well designed folding prop except in that situation where you need stop the boat quickly by putting the boat in reverse. That said a max prop would have slightly worse performance when sailing.

Jeff
 
#3 ·
The people I know with sail drives all talk about the LACK of propwalk, and how the boats back straight and true. In fact, they all give the sail drive very high marks for close maneuvering.
 
#4 ·
I had a saildrive on my Laser 28 and thought there was a lot of prop walk for the size of the engine and prop. I had also experienced the same on a boat that I raced as well. Discussions that I have had seems to suggest that there is a bit more prop walk because if the vertical prop position but like other things in boating I can only assume that it is heavily dependent on the installation.

Jeff
 
#5 ·
I had a saildrive on my Laser 28 and thought there was a lot of prop walk for the size of the engine and prop. I had also experienced the same on a boat that I raced as well. Discussions that I have had seems to suggest that there is a bit more prop walk because if the vertical prop position but like other things in boating I can only assume that it is heavily dependent on the installation.

Jeff
 
#7 ·
Actually, in forward the MaxProp provides about 96% of the efficiency of a fixed prop. The difference in drag under sail between the Max and folders is virtually inconsequential. In reverse the MaxProp provides much higher directional stability and efficiency than any folding propeller and approximately 80% of what a fixed prop would provide. If maximizing performance under sail and preserving backing power is your concern, the MaxProp is probably your best choice.
 
#9 ·
sailmc,

Your MaxProp, for that matter almost any 3 blade feathering or folding prop, will deliver much better than 75% efficiency in forward (compared to an equivalent sized 3 blade fixed prop). The advantage of the Max is that it rotates its blades in reverse to turn its blade leading edges the most effective orientation for reverse. This actually increases its backing efficiency as much as 80% over that of a fixed prop. See this URL for the particulars.
http://www.max-prop.com/max-prop-in-pictures.html
 
#11 ·
L:

Let''s try to get back to your original issues.

Selecting a feathering prop will provide less drag when sailing (over a conventional fixed prop of the same # of blades and diameter). Unlike a folding prop, a feathering prop should provide stronger backing power. For a given hull, a saildrive should provide less prop wash than conventional running gear because the turning moment of the prop is closer to the CLR of the hull/keel (even tho'' a conventional shaft does incline the thrust a bit, as Jeff mentions). So...so far that seems to justify your engine choice and interest in a feathering prop.

However, I''m not convinced the MaxProp product (which I now use and like very much) is the optimum choice for a saildrive installation. I''d talk with your builder, your boat''s designer and/or the prop manufacturers, trying to distill out which feathering props were initially designed for saildrive systems, which after all can present some very different issues. Look at how close that bevel gearing is to the prop: which props will impose the least off-balance loading should one blade heavily foul or get nicked, e.g. Which prop most easily permits anode replacement while in the water, given that otherwise your sail leg serves as the anode? I can see some variables in here that would weigh heavily on my choice of prop product.

One (unsolicited) comment: you''ve chosen an engine installation that brings some significant compromises, just to avoid a bit of prop walk. If it isn''t too late to order the boat with the conventional engine choice, I''d encourage you to rethink the choice...

Jack
 
#12 ·
We just got our first boat with a Saildrive. I was reluctant (for the reasons Jack states) but have seen few problems with them on boats I know. One friend has had a Farr 1020 with Saildrive for almost 20 years, no problems and the technology has surely advanced. Granted we sail in cold, less corrosive waters. There is virtually no propwalk on our boat, due to the factors listed above. Backing out of a slip is a pleasure, its like a car, just turn the wheel. The horizontal drive is very efficient - the prop is pushing back, not partially down. The freedom from vibration is very good - no shaft alignment issues.

I agree Max-props have low drag under sail, as do folding props, and they are unsurpassed in reverse. The problem with Max-props is low efficiency in forward, due to the flat blades without twist or cup. Remember we use forward 99%+ of the time. So how much much power do you need to back out of a slip or set a hook? I used a Martec 2 blade folder for years, famous for low power in reverse; maybe I needed a couple hundred more RPM in reverse but so what? We have several friends with Max-props unhappy with fuel efficiency, due in part I suspect to the low efficiency of the flat blades. They do offer the advantage of messing with pitch till it''s right and that may account for the people who swear by them - they finally got the right pitch prop.

We got a 3 blade Flex-0-fold. With a clean bottom our 41'' boat with 55 hp gets 9.5 knots at full throttle. The three blade gives you more margin for balance issues as Jack mentions, and 55 hp is marginal to absorb with a 2 blade. At 2200 RPM we get 8 knots even. We give up some power to a Max-prop in reverse but there is so much surplus it''s never missed. I suspect you''ll like the Saildrive. Keep those zincs up.

jon k
 
#14 ·
Larry

I for one (there are not to many of us) like saildrive. There are several reasons. 1. It is always on the very bottom of the boat near the keel. Not near the stern like standard inboard, not hanging off the transom like an outboard. 2. It take up ALOT less space. No drive shaft, the area aft of the power head is open for storage. 3. The vibration is alot lower than on most inboard mounted auxs. 4. The boat is usually easier to control under power.


Now the drawbacks as I see them. 1. Maintanance is a must. The tail (transmission) must be serveried seasonally (if you don''t you wish you''ll had). If you don''t use a folding prop your preformance is effected. And the Biggest of all drawbacks ... OMC ... :)

Saildrive is an old idea now being used more and more in new boats it really isn''t a bad way to go
 
#16 ·
I have heard nothing but good things about the Tanmar saildrive. Because of the location on the tail through the hull you will get more power to the prop than with conventional drives. As long as you are strick about keeping up the maintance on your drive tail you will be very happy you went with saildrive.
 
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