Expanding on my comment to John Marshall; there is always a danger of damage to the main running grear (rudder and prop), including entanglement in nets or lines. Having a rudder on the wing engine gives slightly more drag, but if you have to , or want to, use the wing engine, you have water flow over the wing rudder for a positive steering, vs poor flow over the main rudder when using the wing engine. This gets away from the 8 to 10 degrees (which is quite a bit) of rudder angle which John mentions. A true controlable pitch 3 bladed prop is a lot more effecient than any of the folding props. (I used folding props in racing sailboats for years, but would dive on the boat to change out the prop to a three blade for any serious powering)--the folding props could get the boat out of the slip, and back (most of the time)--occasionally the props would fail to open in reverse, or only partly open in foreward. A good controlable pitch prop is considerably more expensive, but also much more effecient--and will give a good turn of speed. If you are running a 20 KW genset, it is likely that you will have a 40 hp diesel engiene to power this. 40 hp on the shaft, will certainly give enough "get home" speed. On the other hand, the vast majority of work boats have a single screw--and no thrusters. They do fine over 99% of the time--but if they break down, there is usually another vessel near by to tow them home. As I have said before, I have never had a diesel engine fail at sea which I could not fix in a few minutes. But I have lost a transmission. Once the transmission is gone, there is thrust power from the main engine. Also the wing engine can eaisly be put to work driving a large DC alternator, and thus regulalry exercised, providing 110 volt power to the vessel through an Inverter. Bob Austin

The Gori prop that Nordhavn puts on the N55's is a three-blade folding prop with two pitches that can be selected by combinations of switching between forward and reverse gear. I generally use low pitch so that my engine can reach max RPM, but on a long run, I'd probably try the higher pitch to reduce RPM for a given speed. But without adding another rudder, there is no getting around that 8 to 10 degree deflection. John On Sep 16, 2009, at 1:02 PM, bob Austin wrote: > Expanding on my comment to John Marshall; there is always a danger > of damage > to the main running grear (rudder and prop), including entanglement > in nets or > lines. Having a rudder on the wing engine gives slightly more drag, > but if > you have to , or want to, use the wing engine, you have water flow > over the > wing rudder for a positive steering, vs poor flow over the main > rudder when > using the wing engine. This gets away from the 8 to 10 degrees > (which is > quite a bit) of rudder angle which John mentions. > > A true controlable pitch 3 bladed prop is a lot more effecient than > any of the > folding props. (I used folding props in racing sailboats for years, > but would > dive on the boat to change out the prop to a three blade for any > serious > powering)--the folding props could get the boat out of the slip, and > back > (most of the time)--occasionally the props would fail to open in > reverse, or > only partly open in foreward. A good controlable pitch prop is > considerably > more expensive, but also much more effecient--and will give a good > turn of > speed. > > If you are running a 20 KW genset, it is likely that you will have a > 40 hp > diesel engiene to power this. 40 hp on the shaft, will certainly > give enough > "get home" speed. > > On the other hand, the vast majority of work boats have a single > screw--and no > thrusters. They do fine over 99% of the time--but if they break > down, there > is usually another vessel near by to tow them home. As I have said > before, I > have never had a diesel engine fail at sea which I could not fix in > a few > minutes. But I have lost a transmission. Once the transmission is > gone, > there is thrust power from the main engine. Also the wing engine > can eaisly > be put to work driving a large DC alternator, and thus regulalry > exercised, > providing 110 volt power to the vessel through an Inverter. > > Bob Austin > _______________________________________________ > http://lists.samurai.com/mailman/listinfo/passagemaking-under-power > > To unsubscribe send email to > passagemaking-under-power-request@lists.samurai.com with the word > UNSUBSCRIBE and nothing else in the subject or body of the message. > > Passagemaking Under Power and PUP are trademarks of Water World > Productions, formerly known as Trawler World Productions.